Author name code: sterling ADS astronomy entries on 2022-09-14 author:"Sterling, Alphonse" ------------------------------------------------------------------------ Title: Genesis and Coronal-jet-generating Eruption of a Solar Minifilament Captured by IRIS Slit-raster Spectra Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Moore, Ronald L.; Sterling, Alphonse C.; De Pontieu, Bart Bibcode: 2022arXiv220900059P Altcode: We present the first IRIS Mg II slit-raster spectra that fully capture the genesis and coronal-jet-generating eruption of a central-disk solar minifilament. The minifilament arose in a negative-magnetic-polarity coronal hole. The Mg II spectroheliograms verify that the minifilament plasma temperature is chromospheric. The Mg II spectra show that the erupting minifilament's plasma has blueshifted upflow in the jet spire's onset and simultaneous redshifted downflow at the location of the compact jet bright point (JBP). From the Mg II spectra together with AIA EUV images and HMI magnetograms, we find: (i) the minifilament forms above a flux cancelation neutral line at an edge of a negative-polarity network flux clump; (ii) during the minifilament's fast-eruption onset and jet-spire onset, the JBP begins brightening over the flux-cancelation neutral line. From IRIS2 inversion of the Mg II spectra, the JBP's Mg II bright plasma has electron density, temperature, and downward (red-shift) Doppler speed of 1012 cm^-3, 6000 K, and 10 kms, respectively, and the growing spire shows clockwise spin. We speculate: (i) during the slow rise of the erupting minifilament-carrying twisted flux rope, the top of the erupting flux-rope loop, by writhing, makes its field direction opposite that of encountered ambient far-reaching field; (ii) the erupting kink then can reconnect with the far-reaching field to make the spire and reconnect internally to make the JBP. We conclude that this coronal jet is normal in that magnetic flux cancelation builds a minifilament-carrying twisted flux rope and triggers the JBP-generating and jet-spire-generating eruption of the flux rope. Title: NuSTAR observations of a quiet Sun minifilament eruption Authors: Hannah, Iain; Sterling, Alphonse; Grefenstette, Brian; Glesener, Lindsay; White, Stephen; Smith, David; Cooper, Kristopher; Krucker, Sam; Paterson, Sarah; Hudson, Hugh Bibcode: 2022cosp...44.2538H Altcode: We present a unique set of observations of a confined minifilament eruption from the quiet-Sun during solar minimum. The Nuclear Spectroscopic Telescope Array (NuSTAR) spotted a tiny, compact hard X-ray (HXR) flare on 2019 April 26, peaking about 02:06UT for a few minutes, finding brief emission >5MK. Observations with SDO/AIA and Hinode/XRT show this HXR emission was due to a tiny flare arcade underneath a confined minifilament eruption - behaviour similar to those seen in both major active-region filament eruptions and minifilament eruptions that lead to coronal jets. Line-of-sight magnetograms from SDO/HMI show that this eruption is due to opposite polarity flux moving together and cancelling and not due to flux emergence. This eruption occurred near disk-centre, so the Earth orbiting observatories provide a top-down view of the event, but fortuitously a side-on view is obtained from STEREO-A/SECCHI, giving a clearer sense of eruption geometry. We also explore the possibility of non-thermal emission due to accelerated electrons in the NuSTAR HXR observations of this small-scale phenomena in the quiet Sun. Title: Bipolar Ephemeral Active Regions, Magnetic Flux Cancellation, and Solar Magnetic Explosions Authors: Moore, Ronald L.; Panesar, Navdeep K.; Sterling, Alphonse C.; Tiwari, Sanjiv K. Bibcode: 2022ApJ...933...12M Altcode: 2022arXiv220313287M We examine the cradle-to-grave magnetic evolution of 10 bipolar ephemeral active regions (BEARs) in solar coronal holes, especially aspects of the magnetic evolution leading to each of 43 obvious microflare events. The data are from the Solar Dynamics Observatory: 211 Å coronal EUV images and line-of-sight photospheric magnetograms. We find evidence that (1) each microflare event is a magnetic explosion that results in a miniature flare arcade astride the polarity inversion line (PIL) of the explosive lobe of the BEAR's anemone magnetic field; (2) relative to the BEAR's emerged flux-rope Ω loop, the anemone's explosive lobe can be an inside lobe, an outside lobe, or an inside-and-outside lobe; (3) 5 events are confined explosions, 20 events are mostly confined explosions, and 18 events are blowout explosions, which are miniatures of the magnetic explosions that make coronal mass ejections (CMEs); (4) contrary to the expectation of Moore et al., none of the 18 blowout events explode from inside the BEAR's Ω loop during the Ω loop's emergence; and (5) before and during each of the 43 microflare events, there is magnetic flux cancellation at the PIL of the anemone's explosive lobe. From finding evident flux cancellation at the underlying PIL before and during all 43 microflare events-together with BEARs evidently being miniatures of all larger solar bipolar active regions-we expect that in essentially the same way, flux cancellation in sunspot active regions prepares and triggers the magnetic explosions for many major flares and CMEs. Title: Homologous Compact Major Blowout-eruption Solar Flares and their Production of Broad CMEs Authors: Sahu, Suraj; Joshi, Bhuwan; Sterling, Alphonse C.; Mitra, Prabir K.; Moore, Ronald L. Bibcode: 2022ApJ...930...41S Altcode: 2022arXiv220303954S We analyze the formation mechanism of three homologous broad coronal mass ejections (CMEs) resulting from a series of solar blowout-eruption flares with successively increasing intensities (M2.0, M2.6, and X1.0). The flares originated from NOAA Active Region 12017 during 2014 March 28-29 within an interval of ≍24 hr. Coronal magnetic field modeling based on nonlinear force-free field extrapolation helps to identify low-lying closed bipolar loops within the flaring region enclosing magnetic flux ropes. We obtain a double flux rope system under closed bipolar fields for all the events. The sequential eruption of the flux ropes led to homologous flares, each followed by a CME. Each of the three CMEs formed from the eruptions gradually attained a large angular width, after expanding from the compact eruption-source site. We find these eruptions and CMEs to be consistent with the "magnetic-arch-blowout" scenario: each compact-flare blowout eruption was seated in one foot of a far-reaching magnetic arch, exploded up the encasing leg of the arch, and blew out the arch to make a broad CME. Title: Another Look at Erupting Minifilaments at the Base of Solar X-Ray Polar Coronal "Standard" and "Blowout" Jets Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep K. Bibcode: 2022ApJ...927..127S Altcode: 2022arXiv220112314S We examine 21 solar polar coronal jets that we identify in soft X-ray images obtained from the Hinode/X-ray telescope (XRT). We identify 11 of these as blowout jets and four as standard jets (with six uncertain), based on their X-ray-spire widths being respectively wide or narrow (compared to the jet's base) in the XRT images. From corresponding extreme ultraviolet (EUV) images from the Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA), essentially all (at least 20 of 21) of the jets are made by minifilament eruptions, consistent with other recent studies. Here, we examine the detailed nature of the erupting minifilaments (EMFs) in the jet bases. Wide-spire ("blowout") jets often have ejective EMFs, but sometimes they instead have an EMF that is mostly confined to the jet's base rather than ejected. We also demonstrate that narrow-spire ("standard") jets can have either a confined EMF, or a partially confined EMF where some of the cool minifilament leaks into the jet's spire. Regarding EMF visibility: we find that in some cases the minifilament is apparent in as few as one of the four EUV channels we examined, being essentially invisible in the other channels; thus, it is necessary to examine images from multiple EUV channels before concluding that a jet does not have an EMF at its base. The sizes of the EMFs, measured projected against the sky and early in their eruption, is 14″ ± 7″, which is within a factor of 2 of other measured sizes of coronal-jet EMFs. Title: Further Evidence for the Minifilament-eruption Scenario for Solar Polar Coronal Jets Authors: Baikie, Tomi K.; Sterling, Alphonse C.; Moore, Ronald L.; Alexander, Amanda M.; Falconer, David A.; Savcheva, Antonia; Savage, Sabrina L. Bibcode: 2022ApJ...927...79B Altcode: 2022arXiv220108882B We examine a sampling of 23 polar-coronal-hole jets. We first identified the jets in soft X-ray (SXR) images from the X-ray telescope (XRT) on the Hinode spacecraft, over 2014-2016. During this period, frequently the polar holes were small or largely obscured by foreground coronal haze, often making jets difficult to see. We selected 23 jets among those adequately visible during this period, and examined them further using Solar Dynamics Observatory's (SDO) Atmospheric Imaging Assembly (AIA) 171, 193, 211, and 304 Å images. In SXRs, we track the lateral drift of the jet spire relative to the jet base's jet bright point (JBP). In 22 of 23 jets, the spire either moves away from (18 cases) or is stationary relative to (4 cases) the JBP. The one exception where the spire moved toward the JBP may be a consequence of line-of-sight projection effects at the limb. From the AIA images, we clearly identify an erupting minifilament in 20 of the 23 jets, while the remainder are consistent with such an eruption having taken place. We also confirm that some jets can trigger the onset of nearby "sympathetic" jets, likely because eruption of the minifilament field of the first jet removes magnetic constraints on the base-field region of the second jet. The propensity for spire drift away from the JBP, the identification of the erupting minifilament in the majority of jets, and the magnetic-field topological changes that lead to sympathetic jets, all support or are consistent with the minifilament-eruption model for jets. Title: Birth and Evolution of a Jet-Base-Topology Solar Magnetic Field with Four Consecutive Major Flare Explosions Authors: Doran, Ilana; Panesar, Navdeep K.; Tiwari, Sanjiv; Moore, Ron; Bobra, Monica; Sterling, Alphonse Bibcode: 2021AGUFMSH35B2039D Altcode: During 2011 September 6-8, NOAA solar active region (AR) 11283 produced four consecutive major coronal mass ejections (CMEs) each with a co-produced major flare (GOES class M5.3, X2.1, X1.8, and M6.7). We examined the ARs magnetic field evolution leading to and following each of these major solar magnetic explosions. We follow flux emergence, flux cancellation and magnetic shear buildup leading to each explosion, and look for sudden flux changes and shear changes wrought by each explosion. We use AIA 193 A images and line-of-sight HMI vector magnetograms from Solar Dynamics Observatory (SDO), and SunPy, SHARPkeys, and IDL Solarsoft to prepare and analyze these data. The observed evolution of the vector field informs how magnetic field emergence and cancellation lead to and trigger the magnetic explosions, and thus informs how major CMEs and their flares are produced. We find that (1) all four flares are triggered by flux cancellation, (2) the third and fourth explosions (X1.8 and M6.7) begin with a filament eruption from the cancellation neutral line, (3) in the first and second explosions a filament erupts in the core of a secondary explosion that lags the main explosion and is probably triggered by Hudson-effect field implosion under the adjacent main exploding field, and (4) the transverse field suddenly strengthens along each main explosions underlying neutral line during the explosion, also likely due to Hudson-effect field implosion. Our observations are consistent with flux cancellation at the explosions underlying neutral line being essential in the buildup and triggering of each of the four explosions in the same way as in smaller-scale magnetic explosions that drive coronal jets. Title: Studying Solar Active-Region Magnetic Evolution Leading to a Confined Eruption Authors: Zigament, Benjamin; Sterling, Alphonse; Moore, Ronald; Falconer, David Bibcode: 2021AGUFMSH35B2037Z Altcode: Current research suggests that there exists a continuum of solar eruptions ranging from the comparatively small, such as coronal jets, to extremely large eruptions that produce coronal mass ejections (CMEs) and solar flares, with all sharing a common triggering mechanism: a filament/flux rope eruption triggered by magnetic flux cancellation. For coronal jets the erupting "minifilaments" are of length ~10,000 km (Sterling et al. 2015, Panesar et al. 2016), while the larger eruptions are accompanied by eruptions of typical filaments of size ~several x 10^4 --- ~3x10^5 km. Sterling et al. (2018) examined this idea for two small ARs (flux ~ 2x10^21 Mx) that erupted to make CMEs. They tracked the evolution of the ARs from emergence to eruption and found eruption to occur when some of the emerged flux drifted together and underwent cancellation along the main magnetic neutral line on the interior of the AR, with eruption occurring after about 30---50% of the total flux of the respective regions canceled. Here we perform a similar study, using Solar Dynamics Observatory (SDO) AIA EUV images and SDO/HMI magnetograms, of a smaller AR (total flux <~10^21 Mx) that emerged in isolation near the neutral line in a large overarching old weak-field magnetic arcade on 2014 September 8. It produced a confined eruption (i.e., one that did not make a CME) about three days later, on September 10 near 18:45 UT. The ARs flux reached maximum about 12 hr after emergence start, and then decreased continuously, with the decrease being partly from cancellation of small flux clumps in the interior of the AR. The eruption occurred when the flux had decreased by about 20%, and was centered on the neutral line of the emerged AR, but also involved filament-holding field along some of the old arcades neutral line. That filament underwent a confined eruption as part of the overall confined eruption. The emerged ARs being inside the larger arcade, its smaller size, and its smaller amount of cancellation may be reasons why the eruption was confined, instead of being ejective and producing a CME as in the two cases of Sterling et al (2018). This work was supported by funding from NASA's HGI Program. Title: Probing Upflowing Regions in the Quiet Sun and Coronal Holes Authors: Schwanitz, Conrad; Harra, Louise; Raouafi, Nour E.; Sterling, Alphonse C.; Moreno Vacas, Alejandro; del Toro Iniesta, Jose Carlos; Orozco Suárez, David; Hara, Hirohisa Bibcode: 2021SoPh..296..175S Altcode: 2021arXiv211012753S Recent observations from Parker Solar Probe have revealed that the solar wind has a highly variable structure. How this complex behaviour is formed in the solar corona is not yet known, since it requires omnipresent fluctuations, which constantly emit material to feed the wind. In this article we analyse 14 upflow regions in the solar corona to find potential sources for plasma flow. The upflow regions are derived from spectroscopic data from the EUV Imaging Spectrometer (EIS) on board Hinode determining their Doppler velocity and defining regions which have blueshifts stronger than −6 kms−1. To identify the sources of these blueshift data from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI), on board the Solar Dynamics Observatory (SDO), and the X-ray Telescope (XRT), on board Hinode, are used. The analysis reveals that only 5 out of 14 upflows are associated with frequent transients, like obvious jets or bright points. In contrast to that, seven events are associated with small-scale features, which show a large variety of dynamics. Some resemble small bright points, while others show an eruptive nature, all of which are faint and only live for a few minutes; we cannot rule out that several of these sources may be fainter and, hence, less obvious jets. Since the complex structure of the solar wind is known, this suggests that new sources have to be considered or better methods used to analyse the known sources. This work shows that small and frequent features, which were previously neglected, can cause strong upflows in the solar corona. These results emphasise the importance of the first observations from the Extreme-Ultraviolet Imager (EUI) on board Solar Orbiter, which revealed complex small-scale coronal structures. Title: Relation of Microstreams in the Polar Solar Wind to Switchbacks and Coronal X-Ray Jets Authors: Neugebauer, Marcia; Sterling, Alphonse C. Bibcode: 2021ApJ...920L..31N Altcode: 2021arXiv211000079N Ulysses data obtained at high solar latitudes during periods of minimum solar activity in 1994 and 2007 are examined to determine the relation between velocity structures called microstreams and folds in the magnetic field called switchbacks. A high correlation is found. The possibility of velocity peaks in microstreams originating from coronal X-ray jets is reexamined; we now suggest that microstreams are the consequence of the alternation of patches of switchbacks and quiet periods, where the switchbacks could be generated by minifilament/flux rope eruptions that cause coronal jets. Title: What Causes Faint Solar Coronal Jets From Emerging Flux Regions In Coronal Holes? Authors: Harden, A.; Panesar, N.; Moore, R.; Sterling, A.; Adams, M. Bibcode: 2021AAS...23821314H Altcode: Using EUV images and line-of-sight magnetograms from Solar Dynamics Observatory, we examine eight emerging bipolar magnetic regions (BMRs) in central-disk coronal holes for whether the emerging magnetic arch made any noticeable coronal jets directly, via reconnection with ambient open field as modeled by Yokoyama & Shibata (1995). During emergence, each BMR produced no obvious EUV coronal jet of normal brightness, but each produced one or more faint EUV coronal jets that are discernible in AIA 193 Å images. The spires of these jets are much fainter and usually narrower than for typical EUV jets that have been observed to be produced by minifilament eruptions in quiet regions and coronal holes. For each of 26 faint jets from the eight emerging BMRs, we examine whether the faint spire was evidently made a la Yokoyama & Shibata (1995). We find: (1) 16 of these faint spires evidently originate from sites of converging opposite-polarity magnetic flux and show base brightenings like those in minifilament-eruption-driven coronal jets, (2) the 10 other faint spires maybe were made by a burst of the external-magnetic-arcade-building reconnection of the emerging magnetic arch with the ambient open field, reconnection directly driven by the arch's emergence, but (3) none were unambiguously made by such emergence-driven reconnection. Thus, for these eight emerging BMRs, the observations indicate that emergence-driven external reconnection of the emerging magnetic arch with ambient open field at most produces a jet spire that is much fainter than in previously-reported, much more obvious coronal jets driven by minifilament eruptions. Title: Network Jets As The Driver Of Counter-streaming Flows In A Solar Filament Authors: Panesar, N. K.; Tiwari, S.; Moore, R.; Sterling, A. Bibcode: 2021AAS...23820506P Altcode: We investigate the driving mechanism of counter-streaming flows in a solar filament, using EUV images from SDO/AIA, line of sight magnetograms from SDO/HMI, IRIS SJ images, and H-alpha data from GONG. We find that: (i) persistent counter-streaming flows along adjacent threads of a small (100" long) solar filament is present; (ii) both ends of the solar filament are rooted at the edges of magnetic network flux lanes; (iii) recurrent small-scale jets (also known as network jets) occur at both ends of the filament; (iv) some of the network jets occur at the sites of flux cancelation between the majority-polarity flux and merging minority-polarity flux patches; (v) these multiple network jets clearly drive the counter-streaming flows along the adjacent threads of the solar filament for ~2 hours with an average speed of 70 km s-1; (vi) some the network jets show base brightenings, analogous to the base brightenings of coronal jets; and (vii) the filament appears wider (4") in EUV images than in H-alpha images (2.5"), consistent with previous studies. Thus, our observations show that counter-streaming flows in the filament are driven by network jets and possibly these driving network jet eruptions are prepared and triggered by flux cancelation. Title: The Missing Cool Corona In The Flat Magnetic Field Around Solar Active Regions Authors: Singh, T.; Sterling, A.; Moore, R. Bibcode: 2021AAS...23831321S Altcode: SDO/AIA images the full solar disk in several EUV bands that are each sensitive to coronal plasma emissions of one or more specific temperatures. We observe that when isolated active regions (ARs) are on the disk, full-disk images in some of the coronal EUV channels show the outskirts of the AR as a dark moat surrounding the AR. Here we present several specific examples, selected from time periods when there was only a single AR present on the disk. Visually, moats are observed to be most prominent in the AIA 171 Angstrom band, which has the most sensitivity to emission from plasma at log10 T = 5.8. By using the emission measure distribution with temperature, we find the intensity of the moat to be most depressed over the temperature range log10 T ~ 5.7-6.2 for all the cases. We argue that the dark moat exists because the pressure from the strong magnetic field that splays out from the AR presses down on underlying magnetic loops, flattening those loops — along with the lowest of the AR's own loops over the moat — to a low altitude. Those loops, which would normally emit the bulk of the 171 Angstrom emission, are restricted to heights above the surface that are too low to have 171 Angstrom emitting plasmas sustained in them, while hotter EUV-emitting plasmas are sustained in the overlying higher-altitude long AR-rooted coronal loops. This potentially explains the low-coronal-temperature dark moats surrounding the ARs. Title: On Making Magnetic-flux-rope Omega Loops For Solar Bipolar Magnetic Regions Of All Sizes By Convection Cells Authors: Moore, R.; Tiwari, S.; Panesar, N.; Sterling, A. Bibcode: 2021AAS...23831318M Altcode: This poster gives an overview of Moore, R. L., Tiwari, S. K., Panesar, N. K., & Sterling, A. C. 2020, ApJ Letters, 902:L35. We propose that the magnetic-flux-rope omega loop that emerges to become any bipolar magnetic region (BMR) is made by a convection cell of the omega-loop's size from initially horizontal magnetic field ingested through the cell's bottom. This idea is based on (1) observed characteristics of BMRs of all spans (~1000 to ~200,000 km), (2) a well-known simulation of the production of a BMR by a supergranule-sized convection cell from horizontal field placed at cell bottom, and (3) a well-known convection-zone simulation. From the observations and simulations, we (1) infer that the strength of the field ingested by the biggest convection cells (giant cells) to make the biggest BMR omega loops is ~103 G, (2) plausibly explain why the span and flux of the biggest observed BMRs are ~200,000 km and ~1022 Mx, (3) suggest how giant cells might also make "failed BMR" omega loops that populate the upper convection zone with horizontal field, from which smaller convection cells make BMR omega loops of their size, (4) suggest why sunspots observed in a sunspot cycle's declining phase tend to violate the hemispheric helicity rule, and (5) support a previously proposed amended Babcock scenario (Moore, R. L., Cirtain, J. W., & Sterling, A. C. 2016, arXiv:1606.05371) for the sunspot cycle's dynamo process. Because the proposed convection-based heuristic model for making a sunspot-BMR omega loop avoids having ~105 G field in the initial flux rope at the bottom of the convection zone, it is an appealing alternative to the present magnetic-buoyancy-based standard scenario and warrants testing by high-enough-resolution giant-cell magnetoconvection simulations. Title: Coronal-jet-producing Minifilament Eruptions As A Possible Source Of Parker Solar Probe (PSP) Switchbacks Authors: Sterling, A.; Moore, R. Bibcode: 2021AAS...23812306S Altcode: The Parker Solar Probe (PSP) has observed copious rapid magnetic field direction changes in the near-Sun solar wind. These features have been called "switchbacks," and their origin is a mystery. But their widespread nature suggests that they may be generated by a frequently occurring process in the Sun's atmosphere. We examine the possibility that the switchbacks originate from coronal jets. Recent work suggests that many coronal jets result when photospheric magnetic flux cancels, and forms a small-scale "minifilament" flux rope that erupts and reconnects with coronal field. We argue that the reconnected erupting minifilament flux rope can manifest as an outward propagating Alfvenic fluctuation that steepens into an increasingly compact disturbance as it moves through the solar wind. Using previous observed properties of coronal jets that connect to coronagraph-observed white-light jets (a.k.a. "narrow CMEs"), along with typical solar wind speed values, we expect the coronal-jet-produced disturbances to traverse near-perihelion PSP in less than or about 25 min, with a velocity of about 400 km/s. To consider further the plausibility of this idea, we show that a previously studied series of equatorial latitude coronal jets, originating from the periphery of an active region, generate white-light jets in the outer corona (seen in STEREO/COR2 coronagraph images; 2.5 — 15 solar radii), and into the inner heliosphere (seen in STEREO/Hi1 heliospheric imager images; 15 — 84 solar radii). Thus it is tenable that disturbances put onto open coronal magnetic field lines by coronal-jet-producing erupting minifilament flux ropes can propagate out to PSP space and appear as switchbacks. This work was supported by the NASA Heliophysics Division, and by the NASA/MSFC Hinode Project. For further details see Sterling & Moore (2020, ApJ, 896, L18). Title: What Causes Faint Solar Coronal Jets from Emerging Flux Regions in Coronal Holes? Authors: Harden, Abigail R.; Panesar, Navdeep K.; Moore, Ronald L.; Sterling, Alphonse C.; Adams, Mitzi L. Bibcode: 2021ApJ...912...97H Altcode: 2021arXiv210307813H Using EUV images and line-of-sight magnetograms from Solar Dynamics Observatory, we examine eight emerging bipolar magnetic regions (BMRs) in central-disk coronal holes for whether the emerging magnetic arch made any noticeable coronal jets directly, via reconnection with ambient open field as modeled by Yokoyama & Shibata. During emergence, each BMR produced no obvious EUV coronal jet of normal brightness, but each produced one or more faint EUV coronal jets that are discernible in AIA 193 &angst; images. The spires of these jets are much fainter and usually narrower than for typical EUV jets that have been observed to be produced by minifilament eruptions in quiet regions and coronal holes. For each of 26 faint jets from the eight emerging BMRs, we examine whether the faint spire was evidently made a la Yokoyama & Shibata. We find that (1) 16 of these faint spires evidently originate from sites of converging opposite-polarity magnetic flux and show base brightenings like those in minifilament-eruption-driven coronal jets, (2) the 10 other faint spires maybe were made by a burst of the external-magnetic-arcade-building reconnection of the emerging magnetic arch with the ambient open field, with reconnection directly driven by the arch's emergence, but (3) none were unambiguously made by such emergence-driven reconnection. Thus, for these eight emerging BMRs, the observations indicate that emergence-driven external reconnection of the emerging magnetic arch with ambient open field at most produces a jet spire that is much fainter than in previously reported, much more obvious coronal jets driven by minifilament eruptions. Title: Fine-Scale Features of the Sun's Atmosphere: Spicules and Jets Authors: Sterling, Alphonse C. Bibcode: 2021GMS...258..221S Altcode: No abstract at ADS Title: Critical Science Plan for the Daniel K. Inouye Solar Telescope (DKIST) Authors: Rast, Mark P.; Bello González, Nazaret; Bellot Rubio, Luis; Cao, Wenda; Cauzzi, Gianna; Deluca, Edward; de Pontieu, Bart; Fletcher, Lyndsay; Gibson, Sarah E.; Judge, Philip G.; Katsukawa, Yukio; Kazachenko, Maria D.; Khomenko, Elena; Landi, Enrico; Martínez Pillet, Valentín; Petrie, Gordon J. D.; Qiu, Jiong; Rachmeler, Laurel A.; Rempel, Matthias; Schmidt, Wolfgang; Scullion, Eamon; Sun, Xudong; Welsch, Brian T.; Andretta, Vincenzo; Antolin, Patrick; Ayres, Thomas R.; Balasubramaniam, K. S.; Ballai, Istvan; Berger, Thomas E.; Bradshaw, Stephen J.; Campbell, Ryan J.; Carlsson, Mats; Casini, Roberto; Centeno, Rebecca; Cranmer, Steven R.; Criscuoli, Serena; Deforest, Craig; Deng, Yuanyong; Erdélyi, Robertus; Fedun, Viktor; Fischer, Catherine E.; González Manrique, Sergio J.; Hahn, Michael; Harra, Louise; Henriques, Vasco M. J.; Hurlburt, Neal E.; Jaeggli, Sarah; Jafarzadeh, Shahin; Jain, Rekha; Jefferies, Stuart M.; Keys, Peter H.; Kowalski, Adam F.; Kuckein, Christoph; Kuhn, Jeffrey R.; Kuridze, David; Liu, Jiajia; Liu, Wei; Longcope, Dana; Mathioudakis, Mihalis; McAteer, R. T. James; McIntosh, Scott W.; McKenzie, David E.; Miralles, Mari Paz; Morton, Richard J.; Muglach, Karin; Nelson, Chris J.; Panesar, Navdeep K.; Parenti, Susanna; Parnell, Clare E.; Poduval, Bala; Reardon, Kevin P.; Reep, Jeffrey W.; Schad, Thomas A.; Schmit, Donald; Sharma, Rahul; Socas-Navarro, Hector; Srivastava, Abhishek K.; Sterling, Alphonse C.; Suematsu, Yoshinori; Tarr, Lucas A.; Tiwari, Sanjiv; Tritschler, Alexandra; Verth, Gary; Vourlidas, Angelos; Wang, Haimin; Wang, Yi-Ming; NSO and DKIST Project; DKIST Instrument Scientists; DKIST Science Working Group; DKIST Critical Science Plan Community Bibcode: 2021SoPh..296...70R Altcode: 2020arXiv200808203R The National Science Foundation's Daniel K. Inouye Solar Telescope (DKIST) will revolutionize our ability to measure, understand, and model the basic physical processes that control the structure and dynamics of the Sun and its atmosphere. The first-light DKIST images, released publicly on 29 January 2020, only hint at the extraordinary capabilities that will accompany full commissioning of the five facility instruments. With this Critical Science Plan (CSP) we attempt to anticipate some of what those capabilities will enable, providing a snapshot of some of the scientific pursuits that the DKIST hopes to engage as start-of-operations nears. The work builds on the combined contributions of the DKIST Science Working Group (SWG) and CSP Community members, who generously shared their experiences, plans, knowledge, and dreams. Discussion is primarily focused on those issues to which DKIST will uniquely contribute. Title: The Missing Cool Corona in the Flat Magnetic Field around Solar Active Regions Authors: Singh, Talwinder; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2021ApJ...909...57S Altcode: 2020arXiv201215406S Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) images the full solar disk in several extreme-ultraviolet (EUV) bands that are each sensitive to coronal plasma emissions of one or more specific temperatures. We observe that when isolated active regions (ARs) are on the disk, full-disk images in some of the coronal EUV channels show the outskirts of the AR as a dark moat surrounding the AR. Here we present seven specific examples, selected from time periods when there was only a single AR present on the disk. Visually, we observe the moat to be most prominent in the AIA 171 Å band, which has the most sensitivity to emission from plasma at log10 T = 5.8. By examining the 1D line-of-sight emission measure temperature distribution found from six AIA EUV channels, we find the intensity of the moat to be most depressed over the temperature range log10 T ≍ 5.7-6.2 for most of the cases. We argue that the dark moat exists because the pressure from the strong magnetic field that splays out from the AR presses down on underlying magnetic loops, flattening those loops—along with the lowest of the AR's own loops over the moat—to a low altitude. Those loops, which would normally emit the bulk of the 171 Å emission, are restricted to heights above the surface that are too low to have 171 Å emitting plasmas sustained in them, according to Antiochos & Noci, while hotter EUV-emitting plasmas are sustained in the overlying higher-altitude long AR-rooted coronal loops. This potentially explains the low-coronal-temperature dark moats surrounding the ARs. Title: Coronal Jets Observed at Sites of Magnetic Flux Cancelation Authors: Panesar, Navdeep Kaur; Sterling, Alphonse; Moore, Ronald; Tiwari, Sanjiv Kumar Bibcode: 2021cosp...43E1783P Altcode: Solar jets of all sizes are magnetically channeled narrow eruptive events; the larger ones are often observed in the solar corona in EUV and coronal X-ray images. Recent observations show that the buildup and triggering of the minifilament eruptions that drive coronal jets result from magnetic flux cancelation under the minifilament, at the neutral line between merging majority-polarity and minority-polarity magnetic flux patches. Here we investigate the magnetic setting of on-disk small-scale jets (also known as jetlets) by using high resolution 172A images from the High-resolution Coronal Imager (Hi-C2.1) and EUV images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), and UV images from the Interface Region Imaging Spectrograph (IRIS), and line-of-sight magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). We observe jetlets at edges of magnetic network lanes. From magnetograms co-aligned with the Hi-C, IRIS, and AIA images, we find that the jetlets stem from sites of flux cancelation between merging majority-polarity and minority-polarity flux patches, and some of the jetlets show faint brightenings at their bases reminiscent of the base brightenings in coronal jets. Based on these observations of jetlets and our previous observations of ∼90 coronal jets in quiet regions and coronal holes, we infer that flux cancelation is the essential process in the buildup and triggering of jetlets. Our observations suggest that network jetlet eruptions are small-scale analogs of both larger-scale coronal jet eruptions and the still-larger-scale eruptions that make major CMEs. Title: Network Jets as the Driver of Counter-streaming Flows in a Solar Filament Authors: Panesar, N. K.; Tiwari, S. K.; Moore, R. L.; Sterling, A. C. Bibcode: 2020AGUFMSH0240004P Altcode: We investigate the driving mechanism of counter-streaming flows in a solar filament, using EUV images from SDO/AIA, line of sight magnetograms from SDO/HMI, IRIS SJ images, and H-alpha data from GONG. We find that: (i) persistent counter-streaming flows along adjacent threads of a small (100" long) solar filament is present; (ii) both ends of the solar filament are rooted at the edges of magnetic network flux lanes; (iii) recurrent small-scale jets (also known as network jets) occur at both ends of the filament; (iv) some of the network jets occur at the sites of flux cancelation between the majority-polarity flux and merging minority-polarity flux patches; (v) these multiple network jets clearly drive the counter-streaming flows along the adjacent threads of the solar filament for ~2 hours with an average speed of 70 km s-1; (vi) some the network jets show base brightenings, analogous to the base brightenings of coronal jets; and (vii) the filament appears wider (4") in EUV images than in H-alpha images (2.5"), consistent with previous studies. Thus, our observations show that counter-streaming flows in the filament are driven by network jets and possibly these driving network jet eruptions are prepared and triggered by flux cancelation. Title: On Making Magnetic-flux-rope Ω Loops for Solar Bipolar Magnetic Regions of All Sizes by Convection Cells Authors: Moore, Ronald L.; Tiwari, Sanjiv K.; Panesar, Navdeep K.; Sterling, Alphonse C. Bibcode: 2020ApJ...902L..35M Altcode: 2020arXiv200913694M We propose that the flux-rope Ω loop that emerges to become any bipolar magnetic region (BMR) is made by a convection cell of the Ω-loop's size from initially horizontal magnetic field ingested through the cell's bottom. This idea is based on (1) observed characteristics of BMRs of all spans (∼1000 to ∼200,000 km), (2) a well-known simulation of the production of a BMR by a supergranule-sized convection cell from horizontal field placed at cell bottom, and (3) a well-known convection-zone simulation. From the observations and simulations, we (1) infer that the strength of the field ingested by the biggest convection cells (giant cells) to make the biggest BMR Ω loops is ∼103 G, (2) plausibly explain why the span and flux of the biggest observed BMRs are ∼200,000 km and ∼1022 Mx, (3) suggest how giant cells might also make "failed-BMR" Ω loops that populate the upper convection zone with horizontal field, from which smaller convection cells make BMR Ω loops of their size, (4) suggest why sunspots observed in a sunspot cycle's declining phase tend to violate the hemispheric helicity rule, and (5) support a previously proposed amended Babcock scenario for the sunspot cycle's dynamo process. Because the proposed convection-based heuristic model for making a sunspot-BMR Ω loop avoids having ∼105 G field in the initial flux rope at the bottom of the convection zone, it is an appealing alternative to the present magnetic-buoyancy-based standard scenario and warrants testing by high-enough-resolution giant-cell magnetoconvection simulations. Title: Possible Evolution of Minifilament-Eruption-Produced Solar Coronal Jets, Jetlets, and Spicules, into Magnetic-Twist-Wave “Switchbacks” Observed by the Parker Solar Probe (PSP) Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep K.; Samanta, Tanmoy Bibcode: 2020JPhCS1620a2020S Altcode: 2020arXiv201012991S Many solar coronal jets result from erupting miniature-filament (“minifilament”) magnetic flux ropes that reconnect with encountered surrounding far-reaching field. Many of those minifilament flux ropes are apparently built and triggered to erupt by magnetic flux cancelation. If that cancelation (or some other process) results in the flux rope’s field having twist, then the reconnection with the far-reaching field transfers much of that twist to that reconnected far-reaching field. In cases where that surrounding field is open, the twist can propagate to far distances from the Sun as a magnetic-twist Alfvénic pulse. We argue that such pulses from jets could be the kinked-magnetic-field structures known as “switchbacks,” detected in the solar wind during perihelion passages of the Parker Solar Probe (PSP). For typical coronal-jet-generated Alfvénic pulses, we expect that the switchbacks would flow past PSP with a duration of several tens of minutes; larger coronal jets might produce switchbacks with passage durations ∼1hr. Smaller-scale jet-like features on the Sun known as “jetlets” may be small-scale versions of coronal jets, produced in a similar manner as the coronal jets. We estimate that switchbacks from jetlets would flow past PSP with a duration of a few minutes. Chromospheric spicules are jet-like features that are even smaller than jetlets. If some portion of their population are indeed very-small-scale versions of coronal jets, then we speculate that the same processes could result in switchbacks that pass PSP with durations ranging from about ∼2 min down to tens of seconds. Title: Sequential Lid Removal in a Triple-decker Chain of CME-producing Solar Eruptions Authors: Joshi, Navin Chandra; Sterling, Alphonse C.; Moore, Ronald L.; Joshi, Bhuwan Bibcode: 2020ApJ...901...38J Altcode: 2020arXiv200804525J We investigate the onsets of three consecutive coronal mass ejection (CME) eruptions in 12 hr from a large bipolar active region (AR) observed by the Solar Dynamics Observatory (SDO), the Solar Terrestrial Relations Observatory (STEREO), the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI), and the Geostationary Operational Environmental Satellite (GOES). Evidently, the AR initially had a "triple-decker" configuration: three flux ropes in a vertical stack above the polarity inversion line (PIL). Upon being bumped by a confined eruption of the middle flux rope, the top flux rope erupts to make the first CME and its accompanying AR-spanning flare arcade rooted in a far apart pair of flare ribbons. The second CME is made by eruption of the previously arrested middle flux rope, which blows open the flare arcade of the first CME and produces a flare arcade rooted in a pair of flare ribbons closer to the PIL than those of the first CME. The third CME is made by blowout eruption of the bottom flux rope, which blows open the second flare arcade and makes its own flare arcade and pair of flare ribbons. Flux cancellation observed at the PIL likely triggers the initial confined eruption of the middle flux rope. That confined eruption evidently triggers the first CME eruption. The lid-removal mechanism instigated by the first CME eruption plausibly triggers the second CME eruption. Further lid removal by the second CME eruption plausibly triggers the final CME eruption. Title: Network Jets as the Driver of Counter-streaming Flows in a Solar Filament/Filament Channel Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Moore, Ronald L.; Sterling, Alphonse C. Bibcode: 2020ApJ...897L...2P Altcode: 2020arXiv200604249P Counter-streaming flows in a small (100″ long) solar filament/filament channel are directly observed in high-resolution Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) extreme-ultraviolet (EUV) images of a region of enhanced magnetic network. We combine images from SDO/AIA, SDO/Helioseismic and Magnetic Imager (HMI), and the Interface Region Imaging Spectrograph (IRIS) to investigate the driving mechanism of these flows. We find that: (I) counter-streaming flows are present along adjacent filament/filament channel threads for ∼2 hr, (II) both ends of the filament/filament channel are rooted at the edges of magnetic network flux lanes along which there are impinging fine-scale opposite-polarity flux patches, (III) recurrent small-scale jets (known as network jets) occur at the edges of the magnetic network flux lanes at the ends of the filament/filament channel, (IV) the recurrent network jet eruptions clearly drive the counter-streaming flows along threads of the filament/filament channel, (V) some of the network jets appear to stem from sites of flux cancelation, between network flux and merging opposite-polarity flux, and (VI) some show brightening at their bases, analogous to the base brightening in coronal jets. The average speed of the counter-streaming flows along the filament/filament channel threads is 70 km s-1. The average widths of the AIA filament/filament channel and the Hα filament are 4″ and 2"5, respectively, consistent with the earlier findings that filaments in EUV images are wider than in Hα images. Thus, our observations show that the continually repeated counter-streaming flows come from network jets, and these driving network jet eruptions are possibly prepared and triggered by magnetic flux cancelation. Title: Coronal-jet-producing Minifilament Eruptions as a Possible Source of Parker Solar Probe Switchbacks Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2020ApJ...896L..18S Altcode: 2020arXiv200604990S The Parker Solar Probe (PSP) has observed copious rapid magnetic field direction changes in the near-Sun solar wind. These features have been called "switchbacks," and their origin is a mystery. But their widespread nature suggests that they may be generated by a frequently occurring process in the Sun's atmosphere. We examine the possibility that the switchbacks originate from coronal jets. Recent work suggests that many coronal jets result when photospheric magnetic flux cancels, and forms a small-scale "minifilament" flux rope that erupts and reconnects with coronal field. We argue that the reconnected erupting-minifilament flux rope can manifest as an outward propagating Alfvénic fluctuation that steepens into an increasingly compact disturbance as it moves through the solar wind. Using previous observed properties of coronal jets that connect to coronagraph-observed white-light jets (a.k.a. "narrow CMEs"), along with typical solar wind speed values, we expect the coronal-jet-produced disturbances to traverse near-perihelion PSP in ≲25 minutes, with a velocity of ∼400 km s-1. To consider further the plausibility of this idea, we show that a previously studied series of equatorial latitude coronal jets, originating from the periphery of an active region, generate white-light jets in the outer corona (seen in STEREO/COR2 coronagraph images; 2.5-15 R⊙), and into the inner heliosphere (seen in Solar-Terrestrial Relations Observatory (STEREO)/Hi1 heliospheric imager images; 15-84 R⊙). Thus it is tenable that disturbances put onto open coronal magnetic field lines by coronal-jet-producing erupting-minifilament flux ropes can propagate out to PSP space and appear as switchbacks. Title: Onset of Magnetic Explosion in Solar Coronal Jets in Quiet Regions on the Central Disk Authors: Panesar, Navdeep K.; Moore, Ronald L.; Sterling, Alphonse C. Bibcode: 2020ApJ...894..104P Altcode: 2020arXiv200604253P We examine the initiation of 10 coronal jet eruptions in quiet regions on the central disk, thereby avoiding near-limb spicule-forest obscuration of the slow-rise onset of the minifilament eruption. From the Solar Dynamics Observatory/Atmospheric Imaging Assembly 171 Å 12 s cadence movie of each eruption, we (1) find and compare the start times of the minifilament's slow rise, the jet-base bright point, the jet-base-interior brightening, and the jet spire, and (2) measure the minifilament's speed at the start and end of its slow rise. From (a) these data, (b) prior observations showing that each eruption was triggered by magnetic flux cancelation under the minifilament, and (c) the breakout-reconnection current sheet observed in one eruption, we confirm that quiet-region jet-making minifilament eruptions are miniature versions of CME-making filament eruptions, and surmise that in most quiet-region jets: (1) the eruption starts before runaway reconnection starts, (2) runaway reconnection does not start until the slow-rise speed is at least ∼1 km s-1, and (3) at and before eruption onset, there is no current sheet of appreciable extent. We therefore expect that (I) many CME-making filament eruptions are triggered by flux cancelation under the filament, (II) emerging bipoles seldom, if ever, directly drive jet production because the emergence is seldom, if ever, fast enough, and (III) at a separatrix or quasi-separatrix in any astrophysical setting of a magnetic field in low-beta plasma, a current sheet of appreciable extent can be built only dynamically by a magnetohydrodynamic convulsion of the field, not by quasi-static gradual converging of the field. Title: Possible Production of Solar Spicules by Microfilament Eruptions Authors: Sterling, Alphonse C.; Moore, Ronald L.; Samanta, Tanmoy; Yurchyshyn, Vasyl Bibcode: 2020ApJ...893L..45S Altcode: 2020arXiv200404187S We examine Big Bear Solar Observatory (BBSO) Goode Solar Telescope (GST) high spatial resolution (0"06), high-cadence (3.45 s), Hα-0.8 Å images of central-disk solar spicules, using data of Samanta et al. We compare with coronal-jet chromospheric-component observations of Sterling et al. Morphologically, bursts of spicules, referred to as "enhanced spicular activities" by Samanta et al., appear as scaled-down versions of the jet's chromospheric component. Both the jet and the enhanced spicular activities appear as chromospheric-material strands, undergoing twisting-type motions of ∼20-50 km s-1 in the jet and ∼20-30 km s-1 in the enhanced spicular activities. Presumably, the jet resulted from a minifilament-carrying magnetic eruption. For two enhanced spicular activities that we examine in detail, we find tentative candidates for corresponding erupting microfilaments, but not the expected corresponding base brightenings. Nonetheless, the enhanced-spicular-activities' interacting mixed-polarity base fields, frequent-apparent-twisting motions, and morphological similarities to the coronal jet's chromospheric-temperature component, suggest that erupting microfilaments might drive the enhanced spicular activities but be hard to detect, perhaps due to Hα opacity. Degrading the BBSO/GST-image resolution with a 1"0-FWHM smoothing function yields enhanced spicular activities resembling the "classical spicules" described by, e.g., Beckers. Thus, a microfilament eruption might be the fundamental driver of many spicules, just as a minifilament eruption is the fundamental driver of many coronal jets. Similarly, a 0"5-FWHM smoothing renders some enhanced spicular activities to resemble previously reported "twinned" spicules, while the full-resolution features might account for spicules sometimes appearing as 2D-sheet-like structures. Title: Hi-C 2.1 Observations of Small-scale Miniature-filament-eruption-like Cool Ejections in an Active Region Plage Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep K.; Reardon, Kevin P.; Molnar, Momchil; Rachmeler, Laurel A.; Savage, Sabrina L.; Winebarger, Amy R. Bibcode: 2020ApJ...889..187S Altcode: 2019arXiv191202319S We examine 172 Å ultra-high-resolution images of a solar plage region from the High-Resolution Coronal Imager, version 2.1 (Hi-C 2.1, or Hi-C) rocket flight of 2018 May 29. Over its five minute flight, Hi-C resolved a plethora of small-scale dynamic features that appear near noise level in concurrent Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) 171 Å images. For 10 selected events, comparisons with AIA images at other wavelengths and with Interface Region Imaging Spectrograph (IRIS) images indicate that these features are cool (compared to the corona) ejections. Combining Hi-C 172 Å, AIA 171 Å, IRIS 1400 Å, and Hα, we see that these 10 cool ejections are similar to the Hα "dynamic fibrils" and Ca II "anemone jets" found in earlier studies. The front of some of our cool ejections are likely heated, showing emission in IRIS 1400 Å. On average, these cool ejections have approximate widths 3"2 ± 2"1, (projected) maximum heights and velocities 4"3 ± 2"5 and 23 ± 6 km s-1, and lifetimes 6.5 ± 2.4 min. We consider whether these Hi-C features might result from eruptions of sub-minifilaments (smaller than the minifilaments that erupt to produce coronal jets). Comparisons with SDO's Helioseismic and Magnetic Imager (HMI) magnetograms do not show magnetic mixed-polarity neutral lines at these events' bases, as would be expected for true scaled-down versions of solar filaments/minifilaments. But the features' bases are all close to single-polarity strong-flux-edge locations, suggesting possible local opposite-polarity flux unresolved by HMI. Or it may be that our Hi-C ejections instead operate via the shock-wave mechanism that is suggested to drive dynamic fibrils and the so-called type I spicules. Title: Early Results from the Solar-Minimum 2019 Total Solar Eclipse Authors: Pasachoff, J. M.; Lockwood, C. A.; Inoue, J. L.; Meadors, E. N.; Voulgaris, A.; Sliski, D.; Sliski, A.; Reardon, K. P.; Seaton, D. B.; Caplan, R. M.; Downs, C.; Linker, J. A.; Sterling, A. C. Bibcode: 2020AAS...23535903P Altcode: We report on first results from our observations in Chile on July 2, 2019, that revealed the extreme-solar-minimum corona, with only equatorial streamers and with visible polar plumes. We have observations in clear skies from our three observing sites: (1) The Cerro Tololo Inter-American Observatory, 7,240-foot altitude, 2 min 6 sec; (2) La Higuera, centerline, 2,500-foot altitude, 2 min 35 sec totality; (3) La Serena, sea level, 2 min 15 sec totality. Prominences on the limb provided orientation and coordination with spacecraft observations from NOAA's GOES-R Solar Ultraviolet Imager (SUVI) and the Atmospheric Imaging Assembly (AIA) on NASA's Solar Dynamics Observatory (SDO). The double-diamond ring at second contact will extend our determination of a new IAU-recommended value of the solar diameter through comparison with models taking into account the precise lunar profile. Our coronal spectra from slitless spectrographs, from CTIO, showed the Fe XIV 530.3 nm green line substantially weaker than the Fe X 637.4 nm red line, corresponding to the relatively low coronal temperature at this phase of the solar-activity cycle. On the spectra we also detected the weak coronal emission line of Ar X at 553.3 nm, as we also detected at the previous total solar eclipse of August 21, 2017, in the USA. We show a comparison of the eclipse observation with a prediction of the structure of the corona from an MHD model, carried out by Predictive Science Inc. (PSI). We consider the lines of sight to NASA's Parker Solar Probe at the times of total eclipses, when we can examine the coronal imaging in terms of electron density to compare with the in situ measurements.

We received major support from grant AGS-903500 from the Solar Terrestrial Program, Atmospheric and Geospace Sciences Division, U.S. National Science Foundation. The CTIO site was courtesy of Associated Universities for Research in Astronomy (AURA). We had additional student support from the Massachusetts NASA Space Grant Consortium; Sigma Xi; the Global Initiatives Fund at Williams College; and the University of Pennsylvania. PSI was supported by AFOSR, NASA, and NSF. ACS received support from the NASA/HGI program, and from the MSFC Hinode project. AV thanks the mathematician Christophoros Mouratidis for his help with the data reduction of the spectra. Title: Early results from the solar-minimum 2019 total solar eclipse Authors: Pasachoff, Jay M.; Lockwood, Christian A.; Inoue, John L.; Meadors, Erin N.; Voulgaris, Aristeidis; Sliski, David; Sliski, Alan; Reardon, Kevin P.; Seaton, Daniel B.; Caplan, Ronald M.; Downs, Cooper; Linker, Jon A.; Schneider, Glenn; Rojo, Patricio; Sterling, Alphonse C. Bibcode: 2020IAUS..354....3P Altcode: We observed the 2 July 2019 total solar eclipse with a variety of imaging and spectroscopic instruments recording from three sites in mainland Chile: on the centerline at La Higuera, from the Cerro Tololo Inter-American Observatory, and from La Serena, as well as from a chartered flight at peak totality in mid-Pacific. Our spectroscopy monitored Fe X, Fe XIV, and Ar X lines, and we imaged Ar X with a Lyot filter adjusted from its original H-alpha bandpass. Our composite imaging has been compared with predictions based on modeling using magnetic-field measurements from the pre-eclipse month. Our time-differenced sites will be used to measure motions in coronal streamers. Title: A Two-Sided-Loop X-Ray Solar Coronal Jet and a Sudden Photospheric Magnetic-field Change, Both Driven by a Minifilament Eruption Authors: Sterling, A. C.; Harra, L. K.; Moore, R. L.; Falconer, D. A. Bibcode: 2019AGUFMSH11D3382S Altcode: Most of the commonly discussed solar coronal jets are of the type consisting of a

single spire extending approximately vertically from near the solar surface into the

corona. Recent research shows that eruption of a miniature filament (minifilament)

drives at least many such single-spire jets, and concurrently generates a miniflare at the

eruption site. A different type of coronal jet, identified in X-ray images during the

Yohkoh era, are two-sided-loop jets, which extend from a central excitation location

in opposite directions, along two opposite low-lying coronal loops that are more-or-less

horizontal to the surface. We observe such a two-sided-loop jet from the edge of active

region (AR) 12473, using data from Hinode XRT and EIS, and SDO AIA and HMI. Similar

to single-spire jets, this two-sided-loop jet results from eruption of a minifilament, which

accelerates to over 140 km/s before abruptly stopping upon striking overlying

nearly-horizontal magnetic field at ∼ 30,000 km altitude and producing the two-sided-loop

jet via interchange reconnection. Analysis of EIS raster scans show that a hot

brightening, consistent with a small flare, develops in the aftermath of the eruption,

and that Doppler motions (∼ 40 km/s) occur near the jet-formation region. As with

many single-spire jets, the trigger of the eruption here is apparently magnetic

flux cancelation, which occurs at a rate of ∼ 4×10^18 Mx/hr, comparable to the rate

observed in some single-spire AR jets. An apparent increase in the (line-of-sight)

flux occurs within minutes of onset of the minifilament eruption, consistent with the

apparent increase being due to a rapid reconfiguration of low-lying magnetic field

during the minifilament eruption. Details appear in Sterling et al. (2019, ApJ, 871, 220). Title: Hi-C 2.1 Observations of Jetlet-like Events at Edges of Solar Magnetic Network Lanes Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.; Winebarger, Amy R.; Tiwari, Sanjiv K.; Savage, Sabrina L.; Golub, Leon E.; Rachmeler, Laurel A.; Kobayashi, Ken; Brooks, David H.; Cirtain, Jonathan W.; De Pontieu, Bart; McKenzie, David E.; Morton, Richard J.; Peter, Hardi; Testa, Paola; Walsh, Robert W.; Warren, Harry P. Bibcode: 2019ApJ...887L...8P Altcode: 2019arXiv191102331P We present high-resolution, high-cadence observations of six, fine-scale, on-disk jet-like events observed by the High-resolution Coronal Imager 2.1 (Hi-C 2.1) during its sounding-rocket flight. We combine the Hi-C 2.1 images with images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and the Interface Region Imaging Spectrograph (IRIS), and investigate each event’s magnetic setting with co-aligned line-of-sight magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). We find that (i) all six events are jetlet-like (having apparent properties of jetlets), (ii) all six are rooted at edges of magnetic network lanes, (iii) four of the jetlet-like events stem from sites of flux cancelation between majority-polarity network flux and merging minority-polarity flux, and (iv) four of the jetlet-like events show brightenings at their bases reminiscent of the base brightenings in coronal jets. The average spire length of the six jetlet-like events (9000 ± 3000 km) is three times shorter than that for IRIS jetlets (27,000 ± 8000 km). While not ruling out other generation mechanisms, the observations suggest that at least four of these events may be miniature versions of both larger-scale coronal jets that are driven by minifilament eruptions and still-larger-scale solar eruptions that are driven by filament eruptions. Therefore, we propose that our Hi-C events are driven by the eruption of a tiny sheared-field flux rope, and that the flux rope field is built and triggered to erupt by flux cancelation. Title: Cradle-to-Grave Evolution and Explosiveness of the Magnetic Field from Bipolar Ephemeral Active Regions (BEARs) in Solar Coronal Holes Authors: Panesar, N. K.; Nagib, C.; Moore, R. L.; Sterling, A. C. Bibcode: 2019AGUFMSH11D3386P Altcode: We report on the entire magnetic evolution and history of magnetic-explosion eruption production of each of 7 bipolar ephemeral active regions (BEARs) observed in on-disk coronal holes in line-of-sight magnetograms and in coronal EUV images. One of these BEARs made no eruptions. The other 6 BEARs together display three kinds of magnetic-explosion eruptions: (1) blowout eruptions (eruptions that make a wide-spire blowout jet), (2) partially-confined eruptions (eruptions that make a narrow-spire standard jet), (3) confined eruptions (eruptions that make no jet, i.e., make only a spireless EUV microflare). The 7 BEARs are a subset of a set of 60 random coronal-hole BEARs that were observed from the advent to the final dissolution of the BEAR's minority-polarity magnetic flux. The emergence phase (time interval from advent to maximum minority flux) for the 60 BEARs had been previously visually estimated using the magnetograms, to find if magnetic-explosion eruption events commonly occur inside a BEAR's emerging magnetic field (as had been assumed by Moore et al 2010, ApJ 720:757). That inspection found no inside eruption during the estimated emergence phase of any of the 60 BEARs. In this new work, for each of the 7 BEARs, we obtain a more reliable determination of when the emergence phase ended by finding the time of the BEAR's maximum minority flux from a time plot of the BEAR's minority flux measured from the magnetograms. These plots show: (1) none of the 7 BEARs had an inside eruption while the BEAR was emerging, and (2) for these 7 BEARs, the visually-estimated emergence end time was never more than 6 hours before the measured time of maximum minority flux. Of the 60 BEARs, in only 6 was there an inside eruption within 6 hours after the visually-estimated end of emergence. The above two results for the 7 BEARs, together with the previous visual inspection of the 60 BEARs, support that a great majority (at least 90%) of the explosive magnetic fields from BEARs in coronal holes are prepared and triggered to explode by magnetic flux cancellation, and that such flux cancellation seldom occurs inside an emerging BEAR. The visual inspection of the magnetograms of the 60 BEARs showed that the pre-eruption flux cancellation was either on the outside of the BEAR during or after the BEAR's emergence or on the inside of the BEAR after the BEAR's emergence. Title: Onset of the Magnetic Explosion in On-disk Solar Coronal Jets Authors: Panesar, N. K.; Moore, R. L.; Sterling, A. C. Bibcode: 2019AGUFMSH11D3384P Altcode: In our recent studies of ~10 quiet region and ~13 coronal hole coronal, we found that flux cancelation is the fundamental process in the buildup and triggering of the minifilament eruption that drives the production of the jet. Here, we investigate the onset and growth of the ten on-disk quiet region jets, using EUV images from SDO/AIA and magnetograms from SDO/HMI. We find that: (i) in all ten events the minifilament starts to rise at or before the onset of the signature of internal or external reconnection; (ii) in two out of ten jets brightening from the external reconnection starts at the same time as the slow rise of the minifilament and (iii) in six out of ten jets brightening from the internal reconnection starts before the start of the brightening from external reconnection. These observations show that the magnetic explosion in coronal jets begins in the same way as the magnetic explosion in filament eruptions that make solar flares and coronal mass ejections (CMEs). Our results indicate (1) that coronal jets are miniature versions of CME-producing eruptions and flux cancelation is the fundamental process that builds and triggers both the small-scale and the large-scale eruptions, and (2) that, contrary to the view of Moore et al (2018), the current sheet at which the external reconnection occurs in coronal jets usually starts to form at or after the onset of (and as a result of) the slow rise of the minifilament flux-rope eruption, and so is seldom of appreciable size before the onset of the slow rise of the minifilament flux-rope eruption. Title: Further Evidence for Magnetic Flux Cancelation as the Build-up and Trigger Mechanism for Eruptions in Isolated Solar Active Regions Authors: Sterling, A. C.; Buell, A.; Moore, R. L.; Falconer, D. A. Bibcode: 2019AGUFMSH11D3388S Altcode: We examine the magnetic evolution of three eruption-producing solar active regions (ARs), one each from 2013, 2014, and 2017, using data from SDO HMI and AIA. Each of the ARs is relatively small, so that we can follow its entire development during a single disk passage, from birth by emergence through the time of the respective eruptions; the first-, second-, and third-born respectively lived 3, 6.5, and 3 days before eruption. Each AR was relatively isolated, with minimal interaction with surrounding ARs, allowing us to study each AR as an approximately isolated system. CMEs resulted from eruptions in the first two ARs, while the third AR's eruption was smaller and appeared confined. In each AR, the eruption was seated on an interval of the AR's magnetic polarity inversion line (neutral line) where opposite-polarity flux was merging together and undergoing apparent cancelation. Our results, together with an earlier pilot study of two ARs by Sterling et al. (2018), and along with recent studies of solar coronal jets, support the view that the magnetic field that explodes to produce solar eruptions of size scales ranging from jets to CMEs are usually built and triggered by flux cancelation along a sharp neutral line. Title: Generation of solar spicules and subsequent atmospheric heating Authors: Samanta, Tanmoy; Tian, Hui; Yurchyshyn, Vasyl; Peter, Hardi; Cao, Wenda; Sterling, Alphonse; Erdélyi, Robertus; Ahn, Kwangsu; Feng, Song; Utz, Dominik; Banerjee, Dipankar; Chen, Yajie Bibcode: 2019Sci...366..890S Altcode: 2020arXiv200602571S Spicules are rapidly evolving fine-scale jets of magnetized plasma in the solar chromosphere. It remains unclear how these prevalent jets originate from the solar surface and what role they play in heating the solar atmosphere. Using the Goode Solar Telescope at the Big Bear Solar Observatory, we observed spicules emerging within minutes of the appearance of opposite-polarity magnetic flux around dominant-polarity magnetic field concentrations. Data from the Solar Dynamics Observatory showed subsequent heating of the adjacent corona. The dynamic interaction of magnetic fields (likely due to magnetic reconnection) in the partially ionized lower solar atmosphere appears to generate these spicules and heat the upper solar atmosphere. Title: Achievements of Hinode in the first eleven years Authors: Hinode Review Team; Al-Janabi, Khalid; Antolin, Patrick; Baker, Deborah; Bellot Rubio, Luis R.; Bradley, Louisa; Brooks, David H.; Centeno, Rebecca; Culhane, J. Leonard; Del Zanna, Giulio; Doschek, George A.; Fletcher, Lyndsay; Hara, Hirohisa; Harra, Louise K.; Hillier, Andrew S.; Imada, Shinsuke; Klimchuk, James A.; Mariska, John T.; Pereira, Tiago M. D.; Reeves, Katharine K.; Sakao, Taro; Sakurai, Takashi; Shimizu, Toshifumi; Shimojo, Masumi; Shiota, Daikou; Solanki, Sami K.; Sterling, Alphonse C.; Su, Yingna; Suematsu, Yoshinori; Tarbell, Theodore D.; Tiwari, Sanjiv K.; Toriumi, Shin; Ugarte-Urra, Ignacio; Warren, Harry P.; Watanabe, Tetsuya; Young, Peter R. Bibcode: 2019PASJ...71R...1H Altcode: Hinode is Japan's third solar mission following Hinotori (1981-1982) and Yohkoh (1991-2001): it was launched on 2006 September 22 and is in operation currently. Hinode carries three instruments: the Solar Optical Telescope, the X-Ray Telescope, and the EUV Imaging Spectrometer. These instruments were built under international collaboration with the National Aeronautics and Space Administration and the UK Science and Technology Facilities Council, and its operation has been contributed to by the European Space Agency and the Norwegian Space Center. After describing the satellite operations and giving a performance evaluation of the three instruments, reviews are presented on major scientific discoveries by Hinode in the first eleven years (one solar cycle long) of its operation. This review article concludes with future prospects for solar physics research based on the achievements of Hinode. Title: Magnetic Flux Cancellation as the Trigger Mechanism of Solar Coronal Jets Authors: McGlasson, Riley A.; Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2019ApJ...882...16M Altcode: 2019arXiv190606452M Coronal jets are transient narrow features in the solar corona that originate from all regions of the solar disk: active regions, quiet Sun, and coronal holes. Recent studies indicate that at least some coronal jets in quiet regions and coronal holes are driven by the eruption of a minifilament following flux cancellation at a magnetic neutral line. We have tested the veracity of that view by examining 60 random jets in quiet regions and coronal holes using multithermal (304, 171, 193, and 211 Å) extreme ultraviolet images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly and line-of-sight magnetograms from the SDO/Helioseismic and Magnetic Imager. By examining the structure and changes in the magnetic field before, during, and after jet onset, we found that 85% of these jets resulted from a minifilament eruption triggered by flux cancellation at the neutral line. The 60 jets have a mean base diameter of 8800 ± 3100 km and a mean duration of 9 ± 3.6 minutes. These observations confirm that minifilament eruption is the driver and magnetic flux cancellation is the primary trigger mechanism for most coronal hole and quiet region coronal jets. Title: Hi-C2.1 Observations of Solar Jetlets at Sites of Flux Cancelation Authors: Panesar, Navdeep; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2019AAS...23411701P Altcode: Solar jets of all sizes are magnetically channeled narrow eruptive events; the larger ones are often observed in the solar corona in EUV and coronal X-ray images. Recent observations show that the buildup and triggering of the minifilament eruptions that drive coronal jets result from magnetic flux cancelation under the minifilament, at the neutral line between merging majority-polarity and minority-polarity magnetic flux patches. Here we investigate the magnetic setting of six on-disk small-scale jet-like/spicule-like eruptions (also known as jetlets) by using high resolution 172A images from the High-resolution Coronal Imager (Hi-C2.1) and EUV images from Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and line-of-sight magnetograms from SDO/Helioseismic and Magnetic Imager (HMI). From magnetograms co-aligned with the Hi-C and AIA images, we find that (i) these jetlets are rooted at edges of magnetic network lanes (ii) some jetlets stem from sites of flux cancelation between merging majority-polarity and minority-polarity flux patches (iii) some jetlets show faint brightenings at their bases reminiscent of the base brightenings in coronal jets. Based on the 6 Hi-C jetlets that we have examined in detail and our previous observations of 30 coronal jets in quiet regions and coronal holes, we infer that flux cancelation is the essential process in the buildup and triggering of jetlets. Our observations suggest that network jetlets result from small-scale eruptions that are analogs of both larger-scale coronal jet minifilament eruptions and the still-larger-scale eruptions that make major CMEs. This work was supported by the NASA/MSFC NPP program and the NASA HGI Program. Title: A Two-Sided-Loop X-Ray Solar Coronal Jet and a Sudden Photospheric Magnetic-field Change, Both Driven by a Minifilament Eruption Authors: Sterling, Alphonse C.; Harra, Louise; Moore, Ronald L.; Falconer, David Bibcode: 2019AAS...23431701S Altcode: Most of the commonly discussed solar coronal jets are of the type consisting of a single spire extending approximately vertically from near the solar surface into the corona. Recent research shows that eruption of a miniature filament (minifilament) drives at least many such single-spire jets, and concurrently generates a miniflare at the eruption site. A different type of coronal jet, identified in X-ray images during the Yohkoh era, are two-sided-loop jets, which extend from a central excitation location in opposite directions, along two opposite low-lying coronal loops that are more-or-less horizontal to the surface. We observe such a two-sided-loop jet from the edge of active region (AR) 12473, using data from Hinode XRT and EIS, and SDO AIA and HMI. Similar to single-spire jets, this two-sided-loop jet results from eruption of a minifilament, which accelerates to over 140 km/s before abruptly stopping upon striking overlying nearly-horizontal magnetic field at ∼30,000 km altitude and producing the two-sided-loop jet via interchange reconnection. Analysis of EIS raster scans show that a hot brightening, consistent with a small flare, develops in the aftermath of the eruption, and that Doppler motions (∼40 km/s) occur near the jet-formation region. As with many single-spire jets, the trigger of the eruption here is apparently magnetic flux cancelation, which occurs at a rate of ∼4×1018 Mx/hr, comparable to the rate observed in some single-spire AR jets. An apparent increase in the (line-of-sight) flux occurs within minutes of onset of the minifilament eruption, consistent with the apparent increase being due to a rapid reconfiguration of low-lying magnetic field during the minifilament eruption. Details appear in Sterling et al. (2019, ApJ, 871, 220). Title: A Two-sided Loop X-Ray Solar Coronal Jet Driven by a Minifilament Eruption Authors: Sterling, Alphonse C.; Harra, Louise K.; Moore, Ronald L.; Falconer, David A. Bibcode: 2019ApJ...871..220S Altcode: 2018arXiv181105557S Most of the commonly discussed solar coronal jets are the type that consist of a single spire extending approximately vertically from near the solar surface into the corona. Recent research supports that eruption of a miniature filament (minifilament) drives many such single-spire jets and concurrently generates a miniflare at the eruption site. A different type of coronal jet, identified in X-ray images during the Yohkoh era, are two-sided loop jets, which extend from a central excitation location in opposite directions, along low-lying coronal loops that are more-or-less horizontal to the surface. We observe such a two-sided loop jet from the edge of active region (AR) 12473, using data from Hinode X-Ray Telescope (XRT) and Extreme Ultraviolet Imaging Spectrometer (EIS), and from Solar Dynamics Observatory’s (SDO) Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI). Similar to single-spire jets, this two-sided loop jet results from eruption of a minifilament, which accelerates to over 140 km s-1 before abruptly stopping after striking an overlying nearly horizontal-loop field at ∼30,000 km in altitude and producing the two-sided loop jet. An analysis of EIS raster scans shows that a hot brightening, consistent with a small flare, develops in the aftermath of the eruption, and that Doppler motions (∼40 km s-1) occur near the jet formation region. As with many single-spire jets, the magnetic trigger here is apparently flux cancelation, which occurs at a rate of ∼4 × 1018 Mx hr-1, broadly similar to the rates observed in some single-spire quiet-Sun and AR jets. An apparent increase in the (line-of-sight) flux occurs within minutes of the onset of the minifilament eruption, consistent with the apparent increase being due to a rapid reconfiguration of low-lying fields during and soon after the minifilament-eruption onset. Title: Evidence of Twisting and Mixed-polarity Solar Photospheric Magnetic Field in Large Penumbral Jets: IRIS and Hinode Observations Authors: Tiwari, Sanjiv K.; Moore, Ronald L.; De Pontieu, Bart; Tarbell, Theodore D.; Panesar, Navdeep K.; Winebarger, Amy R.; Sterling, Alphonse C. Bibcode: 2018ApJ...869..147T Altcode: 2018arXiv181109554T A recent study using Hinode (Solar Optical Telescope/Filtergraph [SOT/FG]) data of a sunspot revealed some unusually large penumbral jets that often repeatedly occurred at the same locations in the penumbra, namely, at the tail of a penumbral filament or where the tails of multiple penumbral filaments converged. These locations had obvious photospheric mixed-polarity magnetic flux in Na I 5896 Stokes-V images obtained with SOT/FG. Several other recent investigations have found that extreme-ultraviolet (EUV)/X-ray coronal jets in quiet-Sun regions (QRs), in coronal holes (CHs), and near active regions (ARs) have obvious mixed-polarity fluxes at their base, and that magnetic flux cancellation prepares and triggers a minifilament flux-rope eruption that drives the jet. Typical QR, CH, and AR coronal jets are up to 100 times bigger than large penumbral jets, and in EUV/X-ray images they show a clear twisting motion in their spires. Here, using Interface Region Imaging Spectrograph (IRIS) Mg II k λ2796 SJ images and spectra in the penumbrae of two sunspots, we characterize large penumbral jets. We find redshift and blueshift next to each other across several large penumbral jets, and we interpret these as untwisting of the magnetic field in the jet spire. Using Hinode/SOT (FG and SP) data, we also find mixed-polarity magnetic flux at the base of these jets. Because large penumbral jets have a mixed-polarity field at their base and have a twisting motion in their spires, they might be driven the same way as QR, CH, and AR coronal jets. Title: IRIS and SDO Observations of Solar Jetlets Resulting from Network-edge Flux Cancelation Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.; Tiwari, Sanjiv K.; De Pontieu, Bart; Norton, Aimee A. Bibcode: 2018ApJ...868L..27P Altcode: 2018arXiv181104314P Recent observations show that the buildup and triggering of minifilament eruptions that drive coronal jets result from magnetic flux cancelation at the neutral line between merging majority- and minority-polarity magnetic flux patches. We investigate the magnetic setting of 10 on-disk small-scale UV/EUV jets (jetlets, smaller than coronal X-ray jets but larger than chromospheric spicules) in a coronal hole by using IRIS UV images and SDO/AIA EUV images and line-of-sight magnetograms from SDO/HMI. We observe recurring jetlets at the edges of magnetic network flux lanes in the coronal hole. From magnetograms coaligned with the IRIS and AIA images, we find, clearly visible in nine cases, that the jetlets stem from sites of flux cancelation proceeding at an average rate of ∼1.5 × 1018 Mx hr-1, and show brightenings at their bases reminiscent of the base brightenings in larger-scale coronal jets. We find that jetlets happen at many locations along the edges of network lanes (not limited to the base of plumes) with average lifetimes of 3 minutes and speeds of 70 km s-1. The average jetlet-base width (4000 km) is three to four times smaller than for coronal jets (∼18,000 km). Based on these observations of 10 obvious jetlets, and our previous observations of larger-scale coronal jets in quiet regions and coronal holes, we infer that flux cancelation is an essential process in the buildup and triggering of jetlets. Our observations suggest that network jetlet eruptions might be small-scale analogs of both larger-scale coronal jets and the still-larger-scale eruptions producing CMEs. Title: Coronal Jets, and the Jet-CME Connection Authors: Sterling, Alphonse C. Bibcode: 2018JPhCS1100a2024S Altcode: 2019arXiv191202808S Solar coronal jets have been observed in detail since the early 1990s. While it is clear that these jets are magnetically driven, the details of the driving process has recently been updated. Previously it was suspected that the jets were a consequence of magnetic flux emergence interacting with ambient coronal field. New evidence however indicates that often the direct driver of the jets is erupting field, often carrying cool material (a “minifilament”), that undergoes interchange magnetic reconnection with preexisting field ([1]). More recent work indicates that the trigger for eruption of the minifilament is frequently cancelation of photospheric magnetic fields at the base of the minifilament. These erupting minifilaments are analogous to the better-known larger-scale filament eruptions that produce solar flares and, frequently, coronal mass ejections (CMEs). A subset of coronal jets drive narrow “white-light jets,” which are very narrow CME-like features, and apparently a few jets can drive wider, although relatively weak, “streamer-puff” CMEs. Here we summarize these recent findings. Title: Magnetic Flux Cancelation as the Buildup and Trigger Mechanism for CME-producing Eruptions in Two Small Active Regions Authors: Sterling, Alphonse C.; Moore, Ronald L.; Panesar, Navdeep K. Bibcode: 2018ApJ...864...68S Altcode: 2018arXiv180703237S We follow two small, magnetically isolated coronal mass ejection (CME)-producing solar active regions (ARs) from the time of their emergence until several days later, when their core regions erupt to produce the CMEs. In both cases, magnetograms show: (a) following an initial period where the poles of the emerging regions separate from each other, the poles then reverse direction and start to retract inward; (b) during the retraction period, flux cancelation occurs along the main neutral line of the regions; (c) this cancelation builds the sheared core field/flux rope that eventually erupts to make the CME. In the two cases, respectively 30% and 50% of the maximum flux of the region cancels prior to the eruption. Recent studies indicate that solar coronal jets frequently result from small-scale filament eruptions, with those “minifilament” eruptions also being built up and triggered by cancelation of magnetic flux. Together, the small-AR eruptions here and the coronal jet results suggest that isolated bipolar regions tend to erupt when some threshold fraction, perhaps in the range of 50%, of the region's maximum flux has canceled. Our observed erupting filaments/flux ropes form at sites of flux cancelation, in agreement with previous observations. Thus, the recent finding that minifilaments that erupt to form jets also form via flux cancelation is further evidence that minifilaments are small-scale versions of the long-studied full-sized filaments. Title: Flux Cancelation as the Trigger of Coronal Hole Jet Eruptions Authors: Panesar, Navdeep Kaur; Sterling, Alphonse C.; Moore, Ronald Lee Bibcode: 2018tess.conf40806P Altcode: Coronal jets are magnetically channeled narrow eruptions often observed in the solar corona. Recent observations show that coronal jets are driven by the eruption of a small-scale filament (minifilament). Here we investigate the triggering mechanism of jet-driving minifilament eruptions in coronal holes, by using X-ray images from Hinode, EUV images from SDO/AIA, and line of sight magnetograms from SDO/HMI. We study 13 on-disk randomly selected coronal hole jets, and track the evolution of the jet-base. In each case we find that there is a minifilament present in the jet-base region prior to jet eruption. The minifilaments reside above a neutral line between majority-polarity and minority-polarity magnetic flux patches. HMI magnetograms show continuous flux cancelation at the neutral line between the opposite polarity flux patches. Persistent flux cancelation eventually destabilizes the field that holds the minifilament plasma. The erupting field reconnects with the neighboring far-reaching field and produces the jet spire. From our study, we conclude that flux cancelation is the fundamental process for triggering coronal hole jets. Other recent studies show that jets in quiet regions and active regions also are accompanied by flux cancelation at minifilament neutral lines (Panesar et al. 2016b, Sterling et al. 2017); therefore the same fundamental process - namely, magnetic flux cancelation - triggers at least many coronal jets in all regions of the Sun. Title: Solar Explosions Imager (SEIM): A Next-Generation High-Resolution and High-Cadence EUV Telescope for Unraveling Eruptive Solar Features Authors: Sterling, Alphonse C.; Moore, Ronald Lee; Winebarger, Amy R. Bibcode: 2018tess.conf11002S Altcode: We present a skeletal proposal for a space-based EUV telescope to fly on the Next Generation Solar Physics Mission (NGSPM). A primary motivation is to unravel physical processes leading to small-scale solar features, such as solar coronal jets, and the processes leading to larger eruptions as well. Recent evidence suggests that jets result from eruptions of small-scale filaments (size scale: ~1—a few arcsec), analogous to larger filament eruptions that drive CMEs, and it is plausible that the even-smaller-scale spicules (∼0′′.1) operate in a similar fashion. Therefore an instrument planned around the concept of observing jet features, but with the highest practical resolution and cadence, would be valuable for observing various erupting solar features on many size and time scales. Resolution and cadence should be comparable to or better than that of Hi-C, i.e. ≤0''.1 pixels and ≤10 s cadence. While no single instrument could span the entire needed data-set space needed to address fully these questions, the proposed instrument would complement first-rate instrumentation (namely, DKIST) expected to be in operation around the time of expected deployment. If resources permit, the proposed EUV instrument could be supplemented with additional instrumentation, or such additional instrumentation could be proposed as (a) separate effort(s). Especially complementary would be a photospheric magnetograph having ≤0''.1 pixels, ≤1-minute cadence, line-of-sight-field sensitivity of ≤10 G, and few-arc-minute FOV. (The SEIM concept has been presented as a WhitePaper with the same title to the NGSPM planning committee.) Title: Onset of the Magnetic Explosion in Solar Polar X-Ray Jets Authors: Moore, Ronald Lee; Sterling, Alphonse C.; Panesar, Navdeep Kaur Bibcode: 2018tess.conf30598M Altcode: We follow up on the Sterling et al (2015, Nature, 523, 437) discovery that nearly all solar polar X-ray jets are made by an explosive eruption of closed magnetic field carrying a miniature cool-plasma filament in its core. In the same X-ray and EUV movies used by Sterling et al (2015), we examine the onset and growth of the driving magnetic explosion in 15 of the 20 jets that they studied. We find evidence that: (1) in a large majority of polar X-ray jets, the runaway internal tether-cutting reconnection under the erupting minifilament flux rope starts after both the minifilament's rise and the spire-producing breakout reconnection have started; and (2) in a large minority, (a) before the eruption starts there is a current sheet between the explosive closed field and the ambient open field, and (b) the eruption starts with breakout reconnection at that current sheet. The observed sequence of events as the eruptions start and grow support the idea that the magnetic explosions that make polar X-ray jets work the same way as the much larger magnetic explosions that make a flare and coronal mass ejection (CME). That idea, and recent observations indicating that magnetic flux cancelation is the fundamental process that builds the field in and around the pre-jet minifilament and triggers that field's jet-driving explosion, together suggest that flux cancelation inside the magnetic arcade that explodes in a flare/CME eruption is usually the fundamental process that builds the explosive field in the core of the arcade and triggers that field's explosion.

This work was funded by the Heliophysics Division of NASA's Science Mission Directorate through the Living With a Star Science Program and the Heliophysics Guest Investigators Program. Title: Observations of Large Penumbral Jets from IRIS and Hinode Authors: Tiwari, Sanjiv K.; Moore, Ronald Lee; De Pontieu, Bart; Tarbell, Theodore D.; Panesar, Navdeep Kaur; Winebarger, Amy R.; Sterling, Alphonse C. Bibcode: 2018tess.conf40807T Altcode: Recent observations from Hinode (SOT/FG) revealed the presence of large penumbral jets (widths ≥ 500 km, larger than normal penumbral microjets, which have widths < 400 km) repeatedly occurring at the same locations in a sunspot penumbra, at the tail of a penumbral filament or where the tails of several penumbral filaments apparently converge (Tiwari et al. 2016, ApJ). These locations were observed to have mixed-polarity flux in Stokes-V images from SOT/FG. Large penumbral jets displayed direct signatures in AIA 1600, 304, 171, and 193 channels; thus they were heated to at least transition region temperatures. Because large jets could not be detected in AIA 94 Å, whether they had any coronal-temperature plasma remains unclear. In the present work, for another sunspot, we use IRIS Mg II k 2796 slit jaw images and spectra and magnetograms from Hinode SOT/FG and SOT/SP to examine: whether penumbral jets spin, similar to spicules and coronal jets in the quiet Sun and coronal holes; whether they stem from mixed-polarity flux; and whether they produce discernible coronal emission, especially in AIA 94 Å images. Title: Onset of the Magnetic Explosion in Solar Polar Coronal X-Ray Jets Authors: Moore, Ronald L.; Sterling, Alphonse C.; Panesar, Navdeep K. Bibcode: 2018ApJ...859....3M Altcode: 2018arXiv180512182M We follow up on the Sterling et al. discovery that nearly all polar coronal X-ray jets are made by an explosive eruption of a closed magnetic field carrying a miniature filament in its core. In the same X-ray and EUV movies used by Sterling et al., we examine the onset and growth of the driving magnetic explosion in 15 of the 20 jets that they studied. We find evidence that (1) in a large majority of polar X-ray jets, the runaway internal/tether-cutting reconnection under the erupting minifilament flux rope starts after both the minifilament’s rise and the spire-producing external/breakout reconnection have started; and (2) in a large minority, (a) before the eruption starts, there is a current sheet between the explosive closed field and the ambient open field, and (b) the eruption starts with breakout reconnection at that current sheet. The variety of event sequences in the eruptions supports the idea that the magnetic explosions that make polar X-ray jets work the same way as the much larger magnetic explosions that make a flare and coronal mass ejection (CME). That idea and recent observations indicating that magnetic flux cancellation is the fundamental process that builds the field in and around the pre-jet minifilament and triggers that field’s jet-driving explosion together suggest that flux cancellation inside the magnetic arcade that explodes in a flare/CME eruption is usually the fundamental process that builds the explosive field in the core of the arcade and triggers that field’s explosion. Title: Magnetic Flux Cancelation as the Trigger of Solar Coronal Jets in Coronal Holes Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2018ApJ...853..189P Altcode: 2018arXiv180105344P We investigate in detail the magnetic cause of minifilament eruptions that drive coronal-hole jets. We study 13 random on-disk coronal-hole jet eruptions, using high-resolution X-ray images from the Hinode/X-ray telescope(XRT), EUV images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), and magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). For all 13 events, we track the evolution of the jet-base region and find that a minifilament of cool (transition-region-temperature) plasma is present prior to each jet eruption. HMI magnetograms show that the minifilaments reside along a magnetic neutral line between majority-polarity and minority-polarity magnetic flux patches. These patches converge and cancel with each other, with an average cancelation rate of ∼0.6 × 1018 Mx hr-1 for all 13 jets. Persistent flux cancelation at the neutral line eventually destabilizes the minifilament field, which erupts outward and produces the jet spire. Thus, we find that all 13 coronal-hole-jet-driving minifilament eruptions are triggered by flux cancelation at the neutral line. These results are in agreement with our recent findings for quiet-region jets, where flux cancelation at the underlying neutral line triggers the minifilament eruption that drives each jet. Thus, from that study of quiet-Sun jets and this study of coronal-hole jets, we conclude that flux cancelation is the main candidate for triggering quiet-region and coronal-hole jets. Title: A Microfilament-Eruption Mechanism for Solar Spicules Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2017AGUFMSH43A2791S Altcode: Recent studies indicate that solar coronal jets result from eruption of small-scale filaments, or "minifilaments" (Sterling et al. 2015, Nature, 523, 437; Panesar et al. ApJL, 832L, 7). In many aspects, these coronal jets appear to be small-scale versions of long-recognized large-scale solar eruptions that are often accompanied by eruption of a large-scale filament and that produce solar flares and coronal mass ejections (CMEs). In coronal jets, a jet-base bright point (JBP) that is often observed to accompany the jet and that sits on the magnetic neutral line from which the minifilament erupts, corresponds to the solar flare of larger-scale eruptions that occurs at the neutral line from which the large-scale filament erupts. Large-scale eruptions are relatively uncommon ( 1/day) and occur with relatively large-scale erupting filaments ( 10^5 km long). Coronal jets are more common (> 100s/day), but occur from erupting minifilaments of smaller size ( 10^4 km long). It is known that solar spicules are much more frequent (many millions/day) than coronal jets. Just as coronal jets are small-scale versions of large-scale eruptions, here we suggest that solar spicules might in turn be small-scale versions of coronal jets; we postulate that the spicules are produced by eruptions of ``microfilaments'' of length comparable to the width of observed spicules ( 300 km). A plot of the estimated number of the three respective phenomena (flares/CMEs, coronal jets, and spicules) occurring on the Sun at a given time, against the average sizes of erupting filaments, minifilaments, and the putative microfilaments, results in a size distribution that can be fit with a power-law within the estimated uncertainties. The counterparts of the flares of large-scale eruptions and the JBPs of jets might be weak, pervasive, transient brightenings observed in Hinode/CaII images, and the production of spicules by microfilament eruptions might explain why spicules spin, as do coronal jets. The expected small-scale neutral lines from which the microfilaments would be expected to erupt would be difficult to detect reliably with current instrumentation, but might be apparent with instrumentation of the near future. A summary of this work appears in Sterling and Moore 2016, ApJL, 829, L9. Title: Dynamic Solar Coronal Jets occurring in a Near-Limb Active Region Authors: Velasquez, J.; Sterling, A. C.; Falconer, D. A.; Moore, R. L.; Panesar, N. K. Bibcode: 2017AGUFMSH43A2792V Altcode: Coronal Jets are long, narrow columns of plasma ejected from the lower solar atmosphere into the corona and observed at coronal wavelengths. In this study, we observe a series of coronal jets occurring in NOAA active region (AR) 12473 on 2015 December 30. At that time the AR was approaching the Sun's west limb, allowing for observation of the jets in profile, contrasting with our recent studies of on-disk active region jets (Sterling et al. 2016, ApJ, 821, 100; and 2017, ApJ, 844, 28). We observe the jets using X-ray images from Hinode's X-Ray Telescope (XRT) and EUV images from the Solar Dynamic Observatory's (SDO) Atmospheric Imaging Assembly (AIA). Here, we investigate the dynamic trajectories of about 9 jets, by measuring the distance between the jet base and the leading edge of the erupting jet (i.e., the jet length) as a function of time, when observed in 304 Angstrom AIA images. All of the selected jets are concurrently visible in X-rays, and thus we are measuring properties of the chromospheric-transition region "cool component" of X-ray jets; in most cases, the appearance of the jets, such as the length of their spire, differs substantially between the X-ray and EUV 304 Angstrom images. For our selection of jets, we find that in the 304 Angstrom images many of them spin as they extend. Most of those in our selection do not make coronal mass ejections (CMEs); on average our jets have outward velocities of about 126 km/s, average maximum lengths of 84,000 km, and average lifetimes of 38 min. These values fall in the range of outward velocities and lifetimes found by Panesar et al. (2016, ApJ, 822, L23) for active-region 304 Angstrom jets that did not make CMEs. These values are also comparable to those found by Moschou et al. (2013, Solar Phys, 284, 427) for a selection of quiet Sun and coronal hole 304 Angstrom jets. One of our selected jets did make a CME, and it has outward velocity of about 240 km/s, consistent with the Panesar et al. (2016) results for CME-producing jets. Title: Magnetic Flux Cancellation as the Trigger of Solar Coronal Jets Authors: McGlasson, R.; Panesar, N. K.; Sterling, A. C.; Moore, R. L. Bibcode: 2017AGUFMSH43A2796M Altcode: Coronal jets are narrow eruptions in the solar corona, and are often observed in extreme ultraviolet (EUV) and X-ray images. They occur everywhere on the solar disk: in active regions, quiet regions, and coronal holes (Raouafi et al. 2016). Recent studies indicate that most coronal jets in quiet regions and coronal holes are driven by the eruption of a minifilament (Sterling et al. 2015), and that this eruption follows flux cancellation at the magnetic neutral line under the pre-eruption minifilament (Panesar et al. 2016). We confirm this picture for a large sample of jets in quiet regions and coronal holes using multithermal (304 Å 171 Å, 193 Å, and 211 Å) extreme ultraviolet (EUV) images from the Solar Dynamics Observatory (SDO) /Atmospheric Imaging Assembly (AIA) and line-of-sight magnetograms from the SDO /Helioseismic and Magnetic Imager (HMI). We report observations of 60 randomly selected jet eruptions. We have analyzed the magnetic cause of these eruptions and measured the base size and the duration of each jet using routines in SolarSoft IDL. By examining the evolutionary changes in the magnetic field before, during, and after jet eruption, we found that each of these jets resulted from minifilament eruption triggered by flux cancellation at the neutral line. In agreement with the above studies, we found our jets to have an average base diameter of 7600 ± 2700 km and an average duration of 9.0 ± 3.6 minutes. These observations confirm that minifilament eruption is the driver and magnetic flux cancellation is the primary trigger mechanism for nearly all coronal hole and quiet region coronal jet eruptions. Title: Origin of Pre-Coronal-Jet Minifilaments: Flux Cancellation Authors: Panesar, N. K.; Sterling, A. C.; Moore, R. L. Bibcode: 2017AGUFMSH41C..03P Altcode: We recently investigated the triggering mechanism of ten quiet-region coronal jet eruptions and found that magnetic flux cancellation at the neutral line of minifilaments is the main cause of quiet-region jet eruptions (Panesar et al 2016). However, what leads to the formation of the pre-jet minifilaments remained unknown. In the present work, we study the longer-term evolution of the magnetic field that leads to the formation of pre-jet minifilaments by using SDO/AIA intensity images and concurrent line of sight SDO/HMI magnetograms. We find that each of the ten pre-jet minifilaments formed due to progressive flux cancellation between the minority-polarity and majority-polarity flux patches (with a minority-polarity flux loss of 10% - 40% prior to minifilament birth). Apparently, the flux cancellation between the opposite polarity flux patches builds a highly-sheared field at the magnetic neutral line, and that field holds the cool transition region minifilament plasma. Even after the formation of minifilaments, the flux continues to cancel, making the minifilament body more thick and prominent. Further flux cancellation between the opposite-flux patches leads to the minifilament eruption and a resulting jet. From these observations, we infer that flux cancellation is usually the process that builds up the sheared and twisted field in pre-jet minifilaments, and that triggers it to erupt and drive a jet. Title: Onset of a Large Ejective Solar Eruption from a Typical Coronal-jet-base Field Configuration Authors: Joshi, Navin Chandra; Sterling, Alphonse C.; Moore, Ronald L.; Magara, Tetsuya; Moon, Yong-Jae Bibcode: 2017ApJ...845...26J Altcode: 2017arXiv170609176J Utilizing multiwavelength observations and magnetic field data from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), SDO/Helioseismic and Magnetic Imager (HMI), the Geostationary Operational Environmental Satellite (GOES), and RHESSI, we investigate a large-scale ejective solar eruption of 2014 December 18 from active region NOAA 12241. This event produced a distinctive “three-ribbon” flare, having two parallel ribbons corresponding to the ribbons of a standard two-ribbon flare, and a larger-scale third quasi-circular ribbon offset from the other two. There are two components to this eruptive event. First, a flux rope forms above a strong-field polarity inversion line and erupts and grows as the parallel ribbons turn on, grow, and spread apart from that polarity inversion line; this evolution is consistent with the mechanism of tether-cutting reconnection for eruptions. Second, the eruption of the arcade that has the erupting flux rope in its core undergoes magnetic reconnection at the null point of a fan dome that envelops the erupting arcade, resulting in formation of the quasi-circular ribbon; this is consistent with the breakout reconnection mechanism for eruptions. We find that the parallel ribbons begin well before (∼12 minutes) the onset of the circular ribbon, indicating that tether-cutting reconnection (or a non-ideal MHD instability) initiated this event, rather than breakout reconnection. The overall setup for this large-scale eruption (diameter of the circular ribbon ∼105 km) is analogous to that of coronal jets (base size ∼104 km), many of which, according to recent findings, result from eruptions of small-scale “minifilaments.” Thus these findings confirm that eruptions of sheared-core magnetic arcades seated in fan-spine null-point magnetic topology happen on a wide range of size scales on the Sun. Title: Onset of the Magnetic Explosion in Solar Polar Coronal X-Ray Jets Authors: Moore, Ronald L.; Sterling, Alphonse C.; Panesar, Navdeep Bibcode: 2017SPD....4820006M Altcode: We examine the onset of the driving magnetic explosion in 15 random polar coronal X-ray jets. Each eruption is observed in a coronal X-ray movie from Hinode and in a coronal EUV movie from Solar Dynamics Observatory. Contrary to the Sterling et al (2015, Nature, 523, 437) scenario for minifilament eruptions that drive polar coronal jets, these observations indicate: (1) in most polar coronal jets (a) the runaway internal tether-cutting reconnection under the erupting minifilament flux rope starts after the spire-producing breakout reconnection starts, not before it, and (b) aleady at eruption onset, there is a current sheet between the explosive closed magnetic field and ambient open field; and (2) the minifilament-eruption magnetic explosion often starts with the breakout reconnection of the outside of the magnetic arcade that carries the minifilament in its core. On the other hand, the diversity of the observed sequences of occurrence of events in the jet eruptions gives further credence to the Sterlling et al (2015, Nature, 523, 437) idea that the magnetic explosions that make a polar X-ray jet work the same way as the much larger magnetic explosions that make and flare and CME. We point out that this idea, and recent observations indicating that magnetic flux cancelation is the fundamental process that builds the field in and around pre-jet minifilaments and triggers the jet-driving magnetic explosion, together imply that usually flux cancelation inside the arcade that explodes in a flare/CME eruption is the fundamental process that builds the explosive field and triggers the explosion.This work was funded by the Heliophysics Division of NASA's Science Mission Directorate through its Living With a Star Targeted Research and Technology Program, its Heliophsyics Guest Investigators Program, and the Hinode Project. Title: Active Region Jets II: Triggering and Evolution of Violent Jets Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David; Panesar, Navdeep K.; Martinez, Francisco Bibcode: 2017SPD....4830403S Altcode: We study a series of X-ray-bright, rapidly evolving active-region coronal jets outside the leading sunspot of AR 12259, using Hinode/XRT, SDO/AIA and HMI, and IRIS/SJ data. The detailed evolution of such rapidly evolving “violent” jets remained a mystery after our previous investigation of active region jets (Sterling et al. 2016, ApJ, 821, 100). The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness ∼<2‧‧) miniature-filament (minifilament) “strands” from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2015, Nature, 523, 437). For some jets strands are difficult/ impossible to detect, perhaps due to their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ~1.5×10^19 Mx/hr. An average flux of ~5×10^18 Mx canceled prior to each episode, arguably building up ~10^28—10^29 ergs of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption buildup and triggering of at least many jets in active regions, quiet regions, and coronal holes. Title: Flux Cancelation as the trigger of quiet-region coronal jet eruptions Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2017SPD....4830402P Altcode: Coronal jets are frequent transient features on the Sun, observed in EUV and X-ray emissions. They occur in active regions, quiet Sun and coronal holes, and appear as a bright spire with base brightenings. Recent studies show that many coronal jets are driven by the eruption of a minifilament. Here we investigate the magnetic cause of jet-driving minifilament eruptions. We study ten randomly-found on-disk quiet-region coronal jets using SDO/AIA intensity images and SDO/HMI magnetograms. For all ten events, we track the evolution of the jet-base region and find that (a) a cool (transition-region temperature) minifilament is present prior to each jet eruption; (b) the pre-eruption minifilament resides above the polarity-inversion line between majority-polarity and minority-polarity magnetic flux patches; (c) the opposite-polarity flux patches converge and cancel with each other; (d) the ongoing cancelation between the majority-polarity and minority-polarity flux patches eventually destabilizes the field holding the minifilament to erupt outwards; (e) the envelope of the erupting field barges into ambient oppositely-directed far-reaching field and undergoes external reconnection (interchange reconnection); (f) the external reconnection opens the envelope field and the minifilament field inside, allowing reconnection-heated hot material and cool minifilament material to escape along the reconnected far-reaching field, producing the jet spire. In summary, we found that each of our ten jets resulted from a minifilament eruption during flux cancelation at the magnetic neutral line under the pre-eruption minifilament. These observations show that flux cancelation is usually the trigger of quiet-region coronal jet eruptions. Title: Magnetic Flux Cancellation as the Origin of Solar Quiet-region Pre-jet Minifilaments Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2017ApJ...844..131P Altcode: 2017arXiv170609079P We investigate the origin of 10 solar quiet-region pre-jet minifilaments, using EUV images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and magnetograms from the SDO Helioseismic and Magnetic Imager (HMI). We recently found that quiet-region coronal jets are driven by minifilament eruptions, where those eruptions result from flux cancellation at the magnetic neutral line under the minifilament. Here, we study the longer-term origin of the pre-jet minifilaments themselves. We find that they result from flux cancellation between minority-polarity and majority-polarity flux patches. In each of 10 pre-jet regions, we find that opposite-polarity patches of magnetic flux converge and cancel, with a flux reduction of 10%-40% from before to after the minifilament appears. For our 10 events, the minifilaments exist for periods ranging from 1.5 hr to 2 days before erupting to make a jet. Apparently, the flux cancellation builds a highly sheared field that runs above and traces the neutral line, and the cool transition region plasma minifilament forms in this field and is suspended in it. We infer that the convergence of the opposite-polarity patches results in reconnection in the low corona that builds a magnetic arcade enveloping the minifilament in its core, and that the continuing flux cancellation at the neutral line finally destabilizes the minifilament field so that it erupts and drives the production of a coronal jet. Thus, our observations strongly support that quiet-region magnetic flux cancellation results in both the formation of the pre-jet minifilament and its jet-driving eruption. Title: Evidence from IRIS that Sunspot Large Penumbral Jets Spin Authors: Tiwari, Sanjiv K.; Moore, Ronald L.; De Pontieu, Bart; Tarbell, Theodore D.; Panesar, Navdeep K.; Winebarger, Amy; Sterling, Alphonse C. Bibcode: 2017SPD....4810506T Altcode: Recent observations from {\it Hinode} (SOT/FG) revealed the presence of large penumbral jets (widths $\ge$500 km, larger than normal penumbral microjets, which have widths $<$ 400 km) repeatedly occurring at the same locations in a sunspot penumbra, at the tail of a filament or where the tails of several penumbral filaments apparently converge (Tiwari et al. 2016, ApJ). These locations were observed to have mixed-polarity flux in Stokes-V images from SOT/FG. Large penumbral jets displayed direct signatures in AIA 1600, 304, 171, and 193 channels; thus they were heated to at least transition region temperatures. Because large jets could not be detected in AIA 94 \AA, whether they had any coronal-temperature plasma remains unclear. In the present work, for another sunspot, we use IRIS Mg II k 2796 Å slit jaw images and spectra and magnetograms from Hinode SOT/FG and SOT/SP to examine: whether penumbral jets spin, similar to spicules and coronal jets in the quiet Sun and coronal holes; whether they stem from mixed-polarity flux; and whether they produce discernible coronal emission, especially in AIA 94 Å images. The few large penumbral jets for which we have IRIS spectra show evidence of spin. If these have mixed-polarity at their base, then they might be driven the same way as coronal jets and CMEs. Title: Babcock Redux: An Amendment of Babcock's Schematic of the Sun's Magnetic Cycle Authors: Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C. Bibcode: 2017SPD....4811103M Altcode: We amend Babcock's original scenario for the global dynamo process that sustains the Sun's 22-year magnetic cycle. The amended scenario fits post-Babcock observed features of the magnetic activity cycle and convection zone, and is based on ideas of Spruit & Roberts (1983, Nature, 304, 401) about magnetic flux tubes in the convection zone. A sequence of four schematic cartoons lays out the proposed evolution of the global configuration of the magnetic field above, in, and at the bottom of the convection zone through sunspot Cycle 23 and into Cycle 24. Three key elements of the amended scenario are: (1) as the net following-polarity magnetic field from the sunspot-region Ω-loop fields of an ongoing sunspot cycle is swept poleward to cancel and replace the opposite-polarity polar-cap field from the previous sunspot cycle, it remains connected to the ongoing sunspot cycle's toroidal source-field band at the bottom of the convection zone; (2) topological pumping by the convection zone's free convection keeps the horizontal extent of the poleward-migrating following-polarity field pushed to the bottom, forcing it to gradually cancel and replace old horizontal field below it that connects the ongoing-cycle source-field band to the previous-cycle polar-cap field; (3) in each polar hemisphere, by continually shearing the poloidal component of the settling new horizontal field, the latitudinal differential rotation low in the convection zone generates the next-cycle source-field band poleward of the ongoing-cycle band. The amended scenario is a more-plausible version of Babcock's scenario, and its viability can be explored by appropriate kinematic flux-transport solar-dynamo simulations. A paper giving a full description of our dynamo scenario is posted on arXiv (http://arxiv.org/abs/1606.05371).This work was funded by the Heliophysics Division of NASA's Science Mission Directorate through the Living With a Star Targeted Research and Technology Program and the Hinode Project. Title: Solar Active Region Coronal Jets. II. Triggering and Evolution of Violent Jets Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Panesar, Navdeep K.; Martinez, Francisco Bibcode: 2017ApJ...844...28S Altcode: 2017arXiv170503040S We study a series of X-ray-bright, rapidly evolving active region coronal jets outside the leading sunspot of AR 12259, using Hinode/X-ray telescope, Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) and Helioseismic and Magnetic Imager (HMI), and Interface Region Imaging Spectrograph (IRIS) data. The detailed evolution of such rapidly evolving “violent” jets remained a mystery after our previous investigation of active region jets. The jets we investigate here erupt from three localized subregions, each containing a rapidly evolving (positive) minority-polarity magnetic-flux patch bathed in a (majority) negative-polarity magnetic-flux background. At least several of the jets begin with eruptions of what appear to be thin (thickness ≲ 2\prime\prime ) miniature-filament (minifilament) “strands” from a magnetic neutral line where magnetic flux cancelation is ongoing, consistent with the magnetic configuration presented for coronal-hole jets in Sterling et al. (2016). Some jets strands are difficult/impossible to detect, perhaps due to, e.g., their thinness, obscuration by surrounding bright or dark features, or the absence of erupting cool-material minifilaments in those jets. Tracing in detail the flux evolution in one of the subregions, we find bursts of strong jetting occurring only during times of strong flux cancelation. Averaged over seven jetting episodes, the cancelation rate was ∼ 1.5× {10}19 Mx hr-1. An average flux of ∼ 5× {10}18 Mx canceled prior to each episode, arguably building up ∼1028-1029 erg of free magnetic energy per jet. From these and previous observations, we infer that flux cancelation is the fundamental process responsible for the pre-eruption build up and triggering of at least many jets in active regions, quiet regions, and coronal holes. Title: The Triggering Mechanism of Coronal Jets and CMEs: Flux Cancelation Authors: Panesar, Navdeep K.; Sterling, Alphonse; Moore, Ronald Bibcode: 2017shin.confE..27P Altcode: Recent investigations (e.g. Sterling et al 2015, Panesar et al 2016) show that coronal jets are driven by the eruption of a small-scale filament (10,000 - 20,000 km long, called a minifilament) following magnetic flux cancelation at the neutral line underneath the minifilament. Minifilament eruptions appear to be analogous to larger-scale solar filament eruptions: they both reside, before the eruption, in the highly sheared field between the adjacent opposite-polarity magnetic flux patches (neutral line); jet-producing minifilament and larger-scale solar filament first show a slow-rise, followed by a fast-rise as they erupt; during the jet-producing minifilament eruption a jet bright point (JBP) appears at the location where the minifilament was rooted before the eruption, analogous to the situation with CME-producing larger-scale filament eruptions where a solar flare arcade forms during the filament eruption along the neutral line along which the filament resided prior to its eruption. In the present study we investigate the triggering mechanism of CME-producing large solar filament eruptions, and find that enduring flux cancelation at the neutral line of the filaments often triggers their eruptions. This corresponds to the finding that persistent flux cancelation at the neutral is the cause of jet-producing minifilament eruptions. Thus our observations support coronal jets being miniature version of CMEs. Title: Evaluation of the Minifilament-Eruption Scenario for Solar Coronal Jets in Polar Coronal Holes Authors: Sterling, A. C.; Baikie, T. K.; Falconer, D. A.; Moore, R. L.; Savage, S. L. Bibcode: 2016AGUFMSH31B2574S Altcode: Solar coronal jets are suspected to result from magnetic reconnection low in the Sun's atmosphere. Sterling et al. (2015) looked at 20 jets in polar coronal holes, using X-ray images from the Hinode/X-Ray Telescope (XRT) and EUV images from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA). They suggested that each jet was driven by the eruption of twisted closed magnetic field carrying a small-scale filament, which they call a "minifilament", and that the jet was produced by reconnection of the erupting field with surrounding open field. In this study, we carry out a more extensive examination of polar coronal jets. From 280 hours of XRT polar coronal hole observations spread over two years (2014-2016), we identified 117 clearly-identifiable X-ray jet events. From the broader set, we selected 25 of the largest and brightest events for further study in AIA 171, 193, 211, and 304 Angstrom images. We find that at least the majority of the jets follow the minifilament-eruption scenario, although for some cases the evolution of the minifilament in the onset of its eruption is more complex then presented in the simplified schematic of Sterling et al. (2015). For all cases in which we could make a clear determination, the spire of the X-ray jet drifted laterally away from the jet-base-edge bright point; this spire drift away from the bright point is consistent with expectations of the minifilament-eruption scenario for coronal-jet production. This work was supported with funding from the NASA/MSFC Hinode Project Office, and from the NASA HGI program. Title: Solar Coronal Jets in Active Regions Authors: Sterling, A. C.; Moore, R. L.; Martinez, F.; Falconer, D. A. Bibcode: 2016AGUFMSH43E..06S Altcode: Solar coronal jets are common in both coronal holes and in active regions. Recently, Sterling et al. (2015, Nature 523, 437), using data from Hinode/XRT and SDO/AIA, found that coronal jets originating in polar coronal holes result from the eruption of small-scale filaments (minifilaments). The jet bright point (JBP) seen in X-rays and hotter EUV channels off to one side of the base of the jet's spire develops at the location where the minifilament erupts, consistent with the JBPs being miniature versions of typical solar flares that occur in the wake of large-scale filament eruptions. Here we consider whether active region coronal jets also result from the same minifilament-eruption mechanism, or whether they instead result from a different process, such as emerging flux. Here we present observations of NOAA active region 12259, over 13-20 Jan 2015, using observations from Hinode/XRT, and from SDO/AIA and HMI. We focused on 13 standout jets that we identified from an initial survey of the XRT X-ray images, and we found many more jets in the AIA data set, which have higher cadence and more continuous coverage than our XRT data. All 13 jets originated from identifiable magnetic neutral lines; we further found magnetic flux cancelation to be occurring at essentially all of these neutral lines. At least 6 of those 13 jets were homologous, developing with similar morphology from nearly the same location, and in fact there were many more jets in the homologous sequence apparent in the higher-fidelity AIA data. Each of these homologous jets was consistent with minifilament-like ejections at the start of the jets. Other jets displayed a variety of morphologies, at least some of which were consistent with minifilament eruptions. For other jets however we have not yet clearly deciphered the driving mechanism. Our overall conclusions are similar to those of our earlier study of active region jets (Sterling et al. 2016, ApJ, 821, 100), where we found: some jets clearly to result from mini-filament eruptions; it was difficult to disentangle the mechanism of some other jets; and all of the jets originated from magnetic neutral lines, most of which were undergoing flux cancelation. This work was supported by funding from NASA/HGI, from the Hinode project, and (for FM) from the NASA/MSFC Research Experience for Undergraduates (REU) program. Title: Flux Cancellation Leading to Solar Filament Eruptions Authors: Popescu, R. M.; Panesar, N. K.; Sterling, A. C.; Moore, R. L. Bibcode: 2016AGUFMSH31B2572P Altcode: Solar filaments are strands of relatively cool, dense plasma magnetically suspended in the lower density hotter solar corona. They trace magnetic polarity inversion lines (PILs) in the photosphere below, and are supported against gravity at heights of up to 100 Mm above the chromosphere by the magnetic field in and around them. This field erupts when it is rendered unstable by either magnetic flux cancellation or emergence at or near the PIL. We have studied the evolution of photospheric magnetic flux leading to ten observed filament eruptions. Specifically, we look for gradual magnetic changes in the neighborhood of the PIL prior to and during eruption. We use Extreme Ultraviolet (EUV) images from the Atmospheric Imaging Assembly (AIA), and magnetograms from the Helioseismic and Magnetic Imager (HMI), both onboard the Solar Dynamics Observatory (SDO), to study filament eruptions and their photospheric magnetic fields. We examine whether flux cancellation or/and emergence leads to filament eruptions and find that continuous flux cancellation was present at the PIL for many hours prior to each eruption. We present two events in detail and find the following: (a) the pre-eruption filament-holding core field is highly sheared and appears in the shape of a sigmoid above the PIL; (b) at the start of the eruption the opposite arms of the sigmoid reconnect in the middle above the site of (tether-cutting) flux cancellation at the PIL; (c) the filaments first show a slow-rise, followed by a fast-rise as they erupt. We conclude that these two filament eruptions result from flux cancellation in the middle of the sheared field and are in agreement with the standard model for a CME/flare filament eruption from a closed bipolar magnetic field [flux cancellation (van Ballegooijen and Martens 1989 and Moore and Roumelrotis 1992) and runaway tether-cutting (Moore et. al 2001)]. Title: Coronal Jets from Minifilament Eruptions in Active Regions Authors: Sterling, A. C.; Martinez, F.; Falconer, D. A.; Moore, R. L. Bibcode: 2016AGUFMSH31B2567S Altcode: Solar coronal jets are transient (frequently of lifetime 10 min) features that shoot out from near the solar surface, become much longer than their width, and occur in all solar regions, including coronal holes, quiet Sun, and active regions (e.g., Shimojo et al. 1996, Certain et al. 2007). Sterling et al. (2015) and other studies found that in coronal holes and in quiet Sun the jets result when small-scale filaments, called ``minifilaments,'' erupt onto nearby open or high-reaching field lines. Additional studies found that coronal-jet-onset locations (and hence presumably the minifilament-eruption-onset locations) coincided with locations of magnetic-flux cancellation. For active region (AR) jets however the situation is less clear. Sterling et al. (2016) studied jets in one active region over a 24-hour period; they found that some AR jets indeed resulted from minifilament eruptions, usually originating from locations of episodes of magnetic-flux cancelation. In some cases however they could not determine whether flux was emerging or canceling at the polarity inversion line from which the minifilament erupted; and for other jets of that region minifilaments were not conclusively apparent prior to jet occurrence. Here we further study AR jets, by observing them in a single AR over a one-week period, using X-ray images from Hinode/XRT and EUV/UV images from SDO/AIA, and line-of-sight magnetograms and white-light intensity-grams from SDO/HMI. We initially identified 13 prominent jets in the XRT data, and examined corresponding AIA and HMI data. For at least several of the jets, our findings are consistent with the jets resulting from minifilament eruptions, and originating from sights of magnetic-field cancelation. Thus our findings support that, at least in many cases, AR coronal jets result from the same physical processes that produce coronal jets in quiet-Sun and coronal-hole regions. FM was supportedby the Research Experience for Undergraduates (REU) program at NASA/MSFC and the University of Alabama, Huntsville. Additional support was from the NASA HGI program and the Hinode project. Title: Solar Coronal Jets: Observations, Theory, and Modeling Authors: Raouafi, N. E.; Patsourakos, S.; Pariat, E.; Young, P. R.; Sterling, A. C.; Savcheva, A.; Shimojo, M.; Moreno-Insertis, F.; DeVore, C. R.; Archontis, V.; Török, T.; Mason, H.; Curdt, W.; Meyer, K.; Dalmasse, K.; Matsui, Y. Bibcode: 2016SSRv..201....1R Altcode: 2016arXiv160702108R; 2016SSRv..tmp...31R Coronal jets represent important manifestations of ubiquitous solar transients, which may be the source of significant mass and energy input to the upper solar atmosphere and the solar wind. While the energy involved in a jet-like event is smaller than that of "nominal" solar flares and coronal mass ejections (CMEs), jets share many common properties with these phenomena, in particular, the explosive magnetically driven dynamics. Studies of jets could, therefore, provide critical insight for understanding the larger, more complex drivers of the solar activity. On the other side of the size-spectrum, the study of jets could also supply important clues on the physics of transients close or at the limit of the current spatial resolution such as spicules. Furthermore, jet phenomena may hint to basic process for heating the corona and accelerating the solar wind; consequently their study gives us the opportunity to attack a broad range of solar-heliospheric problems. Title: Magnetic Flux Cancelation as the Trigger of Solar Quiet-region Coronal Jets Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L.; Chakrapani, Prithi Bibcode: 2016ApJ...832L...7P Altcode: 2016arXiv161008540P We report observations of 10 random on-disk solar quiet-region coronal jets found in high-resolution extreme ultraviolet (EUV) images from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly and having good coverage in magnetograms from the SDO/Helioseismic and Magnetic Imager (HMI). Recent studies show that coronal jets are driven by the eruption of a small-scale filament (called a minifilament). However, the trigger of these eruptions is still unknown. In the present study, we address the question: what leads to the jet-driving minifilament eruptions? The EUV observations show that there is a cool-transition-region-plasma minifilament present prior to each jet event and the minifilament eruption drives the jet. By examining pre-jet evolutionary changes in the line of sight photospheric magnetic field, we observe that each pre-jet minifilament resides over the neutral line between majority-polarity and minority-polarity patches of magnetic flux. In each of the 10 cases, the opposite-polarity patches approach and merge with each other (flux reduction between 21% and 57%). After several hours, continuous flux cancelation at the neutral line apparently destabilizes the field holding the cool-plasma minifilament to erupt and undergo internal reconnection, and external reconnection with the surrounding coronal field. The external reconnection opens the minifilament field allowing the minifilament material to escape outward, forming part of the jet spire. Thus, we found that each of the 10 jets resulted from eruption of a minifilament following flux cancelation at the neutral line under the minifilament. These observations establish that magnetic flux cancelation is usually the trigger of quiet-region coronal jet eruptions. Title: The 2016 Transit of Mercury Observed from Major Solar Telescopes and Satellites Authors: Pasachoff, Jay M.; Schneider, Glenn; Gary, Dale; Chen, Bin; Sterling, Alphonse C.; Reardon, Kevin P.; Dantowitz, Ronald; Kopp, Greg A. Bibcode: 2016DPS....4811705P Altcode: We report observations from the ground and space of the 9 May 2016 transit of Mercury. We build on our explanation of the black-drop effect in transits of Venus based on spacecraft observations of the 1999 transit of Mercury (Schneider, Pasachoff, and Golub, Icarus 168, 249, 2004). In 2016, we used the 1.6-m New Solar Telescope at the Big Bear Solar Observatory with active optics to observe Mercury's transit at high spatial resolution. We again saw a small black-drop effect as 3rd contact neared, confirming the data that led to our earlier explanation as a confluence of the point-spread function and the extreme solar limb darkening (Pasachoff, Schneider, and Golub, in IAU Colloq. 196, 2004). We again used IBIS on the Dunn Solar Telescope of the Sacramento Peak Observatory, as A. Potter continued his observations, previously made at the 2006 transit of Mercury, at both telescopes of the sodium exosphere of Mercury (Potter, Killen, Reardon, and Bida, Icarus 226, 172, 2013). We imaged the transit with IBIS as well as with two RED Epic IMAX-quality cameras alongside it, one with a narrow passband. We show animations of our high-resolution ground-based observations along with observations from XRT on JAXA's Hinode and from NASA's Solar Dynamics Observatory. Further, we report on the limit of the transit change in the Total Solar Irradiance, continuing our interest from the transit of Venus TSI (Schneider, Pasachoff, and Willson, ApJ 641, 565, 2006; Pasachoff, Schneider, and Willson, AAS 2005), using NASA's SORCE/TIM and the Air Force's TCTE/TIM. See http://transitofvenus.info and http://nicmosis.as.arizona.edu.Acknowledgments: We were glad for the collaboration at Big Bear of Claude Plymate and his colleagues of the staff of the Big Bear Solar Observatory. We also appreciate the collaboration on the transit studies of Robert Lucas (Sydney, Australia) and Evan Zucker (San Diego, California). JMP appreciates the sabbatical hospitality of the Division of Geosciences and Planetary Sciences of the California Institute of Technology, and of Prof. Andrew Ingersoll there. The solar observations lead into the 2017 eclipse studies, for which JMP is supported by grants from the NSF AGS and National Geographic CRE. Title: Babcock Redux: An Amendment of Babcock's Schematic of the Sun's Magnetic Cycle Authors: Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C. Bibcode: 2016usc..confE...5M Altcode: 2016arXiv160605371M We amend Babcock's original scenario for the global dynamo process that sustains the Sun's 22-year magnetic cycle. The amended scenario fits post-Babcock observed features of the magnetic activity cycle and convection zone, and is based on ideas of Spruit & Roberts (1983) about magnetic flux tubes in the convection zone. A sequence of four schematic cartoons lays out the proposed evolution of the global configuration of the magnetic field above, in, and at the bottom of the convection zone through sunspot Cycle 23 and into Cycle 24. Three key elements of the amended scenario are: (1) as the net following-polarity magnetic field from the sunspot-region -loop fields of an ongoing sunspot cycle is swept poleward to cancel and replace the opposite-polarity polar-cap field from the previous sunspot cycle, it remains connected to the ongoing sunspot cycle's toroidal source-field band at the bottom of the convection zone; (2) topological pumping by the convection zone's free convection keeps the horizontal extent of the poleward-migrating following-polarity field pushed to the bottom, forcing it to gradually cancel and replace old horizontal field below it that connects the ongoing-cycle source-field band to the previous-cycle polar-cap field; (3) in each polar hemisphere, by continually shearing the poloidal component of the settling new horizontal field, the latitudinal differential rotation low in the convection zone generates the next-cycle source-field band poleward of the ongoing-cycle band. The amended scenario is a more-plausible version of Babcock's scenario, and its viability can be explored by appropriate kinematic flux-transport solar-dynamo simulations. A paper of the above title and authors, giving a full description of the solar dynamo scenario of this abstract, is available at http://arxiv.org/abs/1606.05371. This work was funded by the Heliophysics Division of NASA's Science Mission Directorate through the Living With a Star Targeted Research and Technology Program and the Hinode Project. Title: A Microfilament-eruption Mechanism for Solar Spicules Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2016ApJ...828L...9S Altcode: 2016arXiv161200430S Recent investigations indicate that solar coronal jets result from eruptions of small-scale chromospheric filaments, called minifilaments; that is, the jets are produced by scaled-down versions of typical-sized filament eruptions. We consider whether solar spicules might in turn be scaled-down versions of coronal jets, being driven by eruptions of microfilaments. Assuming a microfilament's size is about a spicule's width (∼300 km), the estimated occurrence number plotted against the estimated size of erupting filaments, minifilaments, and microfilaments approximately follows a power-law distribution (based on counts of coronal mass ejections, coronal jets, and spicules), suggesting that many or most spicules could result from microfilament eruptions. Observed spicule-base Ca II brightenings plausibly result from such microfilament eruptions. By analogy with coronal jets, microfilament eruptions might produce spicules with many of their observed characteristics, including smooth rise profiles, twisting motions, and EUV counterparts. The postulated microfilament eruptions are presumably eruptions of twisted-core micro-magnetic bipoles that are ∼1.″0 wide. These explosive bipoles might be built and destabilized by merging and cancelation of approximately a few to 100 G magnetic-flux elements of size ≲ 0\buildrel{\prime\prime}\over{.} 5{--}1\buildrel{\prime\prime}\over{.} 0. If, however, spicules are relatively more numerous than indicated by our extrapolated distribution, then only a fraction of spicules might result from this proposed mechanism. Title: Homologous Jet-driven Coronal Mass Ejections from Solar Active Region 12192 Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2016ApJ...822L..23P Altcode: 2016arXiv160405770P We report observations of homologous coronal jets and their coronal mass ejections (CMEs) observed by instruments onboard the Solar Dynamics Observatory (SDO) and the Solar and Heliospheric Observatory (SOHO) spacecraft. The homologous jets originated from a location with emerging and canceling magnetic field at the southeastern edge of the giant active region (AR) of 2014 October, NOAA 12192. This AR produced in its interior many non-jet major flare eruptions (X- and M- class) that made no CME. During October 20 to 27, in contrast to the major flare eruptions in the interior, six of the homologous jets from the edge resulted in CMEs. Each jet-driven CME (∼200-300 km s-1) was slower-moving than most CMEs, with angular widths (20°-50°) comparable to that of the base of a coronal streamer straddling the AR and were of the “streamer-puff” variety, whereby the preexisting streamer was transiently inflated but not destroyed by the passage of the CME. Much of the transition-region-temperature plasma in the CME-producing jets escaped from the Sun, whereas relatively more of the transition-region plasma in non-CME-producing jets fell back to the solar surface. Also, the CME-producing jets tended to be faster and longer-lasting than the non-CME-producing jets. Our observations imply that each jet and CME resulted from reconnection opening of twisted field that erupted from the jet base and that the erupting field did not become a plasmoid as previously envisioned for streamer-puff CMEs, but instead the jet-guiding streamer-base loop was blown out by the loop’s twist from the reconnection. Title: A Series of Streamer-Puff CMEs Driven by Solar Homologous Jets from Active Region 12192 Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2016SPD....47.0622P Altcode: We investigate characteristics of solar coronal jets that originated from active region NOAA 12192 and produced coronal mass ejections (CMEs). This active region produced many non-jet major flare eruptions (X and M class) that made no CME. A multitude of jets occurred from the southeast edge of the active region, and in contrast to the major-flare eruptions in the core, six of these jets resulted in CMEs. Our jet observations are from multiple SDO/AIA EUV channels, including 304, 171 and 193Å, and CME observations are taken from SOHO/LASCO C2 coronograph. Each jet-driven CME was relatively slow-moving (~200 - 300 km s-1) compared to most CMEs; had angular width (20° - 50°) comparable to that of the streamer base; and was of the “streamer-puff” variety, whereby a preexisting streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric-temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non-CME-producing jets fell back to the solar surface. We also found that the CME-producing jets tended to be faster in speed and longer in duration than the non-CME-producing jets. We expect that the jets result from eruptions of minifilaments (Sterling et al. 2015). We further propose that the CMEs are driven by magnetic twist injected into streamer-base coronal loops when erupting-twisted-minifilament field reconnects with the ambient field at the foot of those loops. This research was supported by funding from NASA's LWS program. Title: Analysis of an Anemone-Type Eruption in an On-Disk Coronal Hole Authors: Adams, Mitzi; Tennant, Allyn F.; Alexander, Caroline E.; Sterling, Alphonse C.; Moore, Ronald L.; Woolley, Robert Bibcode: 2016SPD....4740701A Altcode: We report on an eruption seen in a very small coronal hole (about 120'' across), beginning at approximately 19:00 UT on March 3, 2016. The event was initially observed by an amateur astronomer (RW) in an H-alpha movie from the Global Oscillation Network Group (GONG); the eruption attracted the attention of the observer because there was no nearby active region. To examine the region in detail, we use data from the Solar Dynamics Observatory (SDO), provided by the Atmospheric Imaging Assembly (AIA) in wavelengths 193 Å, 304 Å, and 94 Å, and the Helioseismic and Magnetic Imager (HMI). Data analysis and calibration activities such as scaling, rotation so that north is up, and removal of solar rotation are accomplished with SunPy. The eruption in low-cadence HMI data begins with the appearance of a bipole in the location of the coronal hole, followed by (apparent) expansion outwards when the intensity of the AIA wavelengths brighten; as the event proceeds, the coronal hole disappears. From high-cadence data, we will present results on the magnetic evolution of this structure, how it is related to intensity brightenings seen in the various SDO/AIA wavelengths, and how this event compares with the standard-anemone picture. Title: Minifilament Eruptions that Drive Coronal Jets in a Solar Active Region Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David; Panesar, Navdeep; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat Bibcode: 2016SPD....47.0334S Altcode: Solar coronal jets are common in both coronal holes and in active regions. Recently, Sterling et al. (2015), using data from Hinode/XRT and SDO/AIA, found that coronal jets originating in polar coronal holes result from the eruption of small-scale filaments (minifilaments). The jet bright point (JBP) seen in X-rays and hotter EUV channels off to one side of the base of the jet's spire develops at the location where the minifilament erupts, consistent with the JBPs being miniature versions of typical solar flares that occur in the wake of large-scale filament eruptions. Here we consider whether active region coronal jets also result from the same minifilament-eruption mechanism, or whether they instead result from a different mechanism, such as the hitherto popular ``emerging flux'' model for jets. We present observations of an on-disk active region that produced numerous jets on 2012 June 30, using data from SDO/AIA and HMI, and from GOES/SXI. We find that several of these active region jets also originate with eruptions of miniature filaments (size scale ~20'') emanating from small-scale magnetic neutral lines of the region. This demonstrates that active region coronal jets are indeed frequently driven by minifilament eruptions. Other jets from the active region were also consistent with their drivers being minifilament eruptions, but we could not confirm this because the onsets of those jets were hidden from our view. This work was supported by funding from NASA/LWS, NASA/HGI, and Hinode. Title: Early Evaluation of the Corona at the 2016 March 9 Total Solar Eclipse Authors: Pasachoff, Jay M.; Seaton, Daniel B.; Sterling, Alphonse C. Bibcode: 2016SPD....47.0326P Altcode: We observed the corona on 2016 March 9 with a variety of assets on the ground and in space. The umbra of the total eclipse swept across Indonesia and into the Pacific, with totality at our Indonesian observation sites lasting 2 min 45 s at Ternate in the Spice Islands (Malukus) and 2 min 10 at Belitung. We compare our ground-based results with the coronal configurations observed with PROBA2/SWAP and Hinode XRT. One of our scientific goals is to follow the coronal configuration over the solar-activity cycle, with the sunspot number now half its maximum of either its 2012 or 2014 peak. We are evaluating temporal changes by comparing eclipse observations made at several ground-based sites along the path, with the longest span being 75 min from Belitung to the Woleia atoll in mid-Pacific, 1:25 UTC to 2:40 UTC; we are evaluating whether the airborne observations made at 3:35 UTC on March 8 (across the International Dateline) are of suitable quality to provide further comparison at high spatial resolution. We also compare our images with the near-simultaneous coronal observations made with SOHO/LASCO, SDO/AIA, STEREO-A/SECCHI, and the Mauna Loa Solar Observatory's K-cor coronagraph. ACS received support for image analysis from the Hinode project. Title: Minifilament Eruptions that Drive Coronal Jets in a Solar Active Region Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Panesar, Navdeep K.; Akiyama, Sachiko; Yashiro, Seiji; Gopalswamy, Nat Bibcode: 2016ApJ...821..100S Altcode: We present observations of eruptive events in an active region adjacent to an on-disk coronal hole on 2012 June 30, primarily using data from the Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), SDO/Helioseismic and Magnetic Imager (HMI), and STEREO-B. One eruption is of a large-scale (∼100″) filament that is typical of other eruptions, showing slow-rise onset followed by a faster-rise motion starting as flare emissions begin. It also shows an “EUV crinkle” emission pattern, resulting from magnetic reconnections between the exploding filament-carrying field and surrounding field. Many EUV jets, some of which are surges, sprays and/or X-ray jets, also occur in localized areas of the active region. We examine in detail two relatively energetic ones, accompanied by GOES M1 and C1 flares, and a weaker one without a GOES signature. All three jets resulted from small-scale (∼20″) filament eruptions consistent with a slow rise followed by a fast rise occurring with flare-like jet-bright-point brightenings. The two more-energetic jets showed crinkle patters, but the third jet did not, perhaps due to its weakness. Thus all three jets were consistent with formation via erupting minifilaments, analogous to large-scale filament eruptions and to X-ray jets in polar coronal holes. Several other energetic jets occurred in a nearby portion of the active region; while their behavior was also consistent with their source being minifilament eruptions, we could not confirm this because their onsets were hidden from our view. Magnetic flux cancelation and emergence are candidates for having triggered the minifilament eruptions. Title: Probing Solar Eruption by Tracking Magnetic Cavities and Filaments Authors: Sterling, A. C.; Johnson, J. R.; Moore, R. L.; Gibson, S. E. Bibcode: 2015AGUFMSH53B2489S Altcode: A solar eruption is a tremendous explosion on the Sun that happens when energy stored in twisted (or distorted) magnetic fields is suddenly released. When this field is viewed along the axis of the twist in projection at the limb, e.g. in EUV or white-light coronal images, the outer portions of the pre-eruption magnetic structure sometimes appears as a region of weaker emission, called a "coronal cavity," surrounded by a brighter envelope. Often a chromospheric filament resides near the base of the cavity and parallel to the cavity's central axis. Typically, both the cavity and filament move outward from the Sun at the start of an eruption of the magnetic field in which the cavity and filament reside. Studying properties the cavities and filaments just prior to and during eruption can help constrain models that attempt to explain why and how the eruptions occur. In this study, we examined six different at-limb solar eruptions using images from the Extreme Ultraviolet Imaging Telescope (EIT) aboard the Solar and Heliospheric Observatory (SOHO). For four of these eruptions we observed both cavities and filaments, while for the remaining two eruptions, one had only a cavity and the other only a filament visible in EIT images. All six eruptions were in comparatively-quiet solar regions, with one in the neighborhood of the polar crown. We measured the height and velocities of the cavities and filaments just prior to and during the start of their fast-eruption onsets. Our results support that the filament and cavity are integral parts of a single large-scale erupting magnetic-field system. We examined whether the eruption-onset heights were correlated with the expected magnetic field strengths of the eruption-source regions, but no clear correlation was found. We discuss possible reasons for this lack of correlation, and we also discuss future research directions. The research performed was supported by the National Science Foundation under Grant No. AGS-1460767; J.J. participated in the Research Experience for Undergraduates (REU) program, at NASA/MSFC. Additional support was from a grant from the NASA LWS program. Title: Revised View of Solar X-Ray Jets Authors: Sterling, A. C.; Moore, R. L.; Falconer, D. A.; Adams, M. Bibcode: 2015AGUFMSH23D..04S Altcode: We investigate the onset of ~20 random X-ray jets observed by Hinode/XRT. Each jetwas near the limb in a polar coronal hole, and showed a ''bright point'' in anedge of the base of the jet, as is typical for previously-observed X-ray jets. Weexamined SDO/AIA EUV images of each of the jets over multiple AIA channels,including 304 Ang, which detects chromospheric emissions, and 171, 193, and 211 Ang,which detect cooler-coronal emissions. We find the jets to result from eruptionsof miniature (size <~10 arcsec) filaments from the bases of the jets. In manycases, much of the erupting-filament material forms a chromospheric-temperaturejet. In the cool-coronal channels, often the filament appears in absorption andthe hotter EUV component of the jet appears in emission. The jet bright point formsat the location from which the miniature filament erupts, analogous to theformation of a standard solar flare arcade via flare (``internal'') reconnection in the wake of the eruption of a typical larger-scale chromospheric filament. Thespire of the jet forms on open field lines that presumably have undergoneinterchange (''external'') reconnection with the erupting field that envelops andcarries the miniature filament. This is consistent with what we found for theonset of an on-disk coronal jet we examined in Adams et al. (2014), and theobservations of other workers. It is however not consistent with the basicversion of the ''emerging-flux model'' for X-ray jets. This work was supported byfunding from NASA/LWS, Hinode, and ISSI. Title: Exploring the properties of Solar Prominence Tornados Authors: Ahmad, E.; Panesar, N. K.; Sterling, A. C.; Moore, R. L. Bibcode: 2015AGUFMSH53B2485A Altcode: Solar prominences consist of relatively cool and dense plasma embedded in the hotter solar corona above the solar limb. They form along magnetic polarity inversion lines, and are magnetically supported against gravity at heights of up to ~100 Mm above the chromosphere. Often, parts of prominences visually resemble Earth-based tornados, with inverted-cone-shaped structures and internal motions suggestive of rotation. These "prominence tornados" clearly possess complex magnetic structure, but it is still not certain whether they actually rotate around a ''rotation'' axis, or instead just appear to do so because of composite internal material motions such as counter-streaming flows or lateral (i.e. transverse to the field) oscillations. Here we study the structure and dynamics of five randomly selected prominences, using extreme ultraviolet (EUV) 171 Å images obtained with high spatial and temporal resolution by the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamics Observatory (SDO) spacecraft. All of the prominences resided in non-active-region locations, and displayed what appeared to be tornado-like rotational motions. Our set includes examples oriented both broadside and end-on to our line-of-sight. We created time-distance plots of horizontal slices at several different heights of each prominence, to study the horizontal plasma motions. We observed patterns of oscillations at various heights in each prominence, and we measured parameters of these oscillations. We find the oscillation time periods to range over ~50 - 90 min, with average amplitudes of ~6,000 km, and with average velocities of ~7 kms-1. We found similar values for prominences viewed either broadside or end-on; this observed isotropy of the lateral oscillatory motion suggests that the apparent oscillations result from actual rotational plasma motions and/or lateral oscillations of the magnetic field, rather than to counter-streaming flows. This research was supported by the National Science Foundation under Grant No. AGS-1460767; EA participated in the Research Experience for Undergraduates (REU) program, at NASA/MSFC. Additional support was from a grant from the NASA LWS program. Title: A Series of Streamer-Puff CMEs Driven by Solar Homologous Jets Authors: Panesar, N. K.; Sterling, A. C.; Moore, R. L. Bibcode: 2015AGUFMSH54B..07P Altcode: Solar coronal jets are magnetically channeled narrow eruptions often observed in the solar atmosphere, typically in EUV and X-ray emission, and occurring in various solar environments including active regions and coronal holes. Their driving mechanism is still under discussion, but facts that we know about jets include: (a) they are ejected from or near sites of compact magnetic explosions (compact ejective solar flares), (b) they sometimes carry chromospheric material high into the corona along with coronal-temperature plasma, (c) the cool-material jet velocities can reach 100 km s-1 or more, and (d) some active-region jets produce coronal mass ejections (CMEs). Here we investigate characteristics of EUV jets that originated from active region NOAA 12192 and produced CMEs. This active region produced many non-jet major flare eruptions (X and M class) that made no CME. A multitude of jets also occurred in the region, and in contrast to the major-flare eruptions, seven of these jets resulted in CMEs. Our jet observations are from multiple SDO/AIA EUV channels, including 304, 171, 193 and 94 Å, and our CME observations are from SOHO/LASCO C2 images. Each jet-driven CME was relatively slow-moving; had angular width (30° - 70°) comparable to that of the streamer base; and was of the "streamer-puff" variety, whereby a preexisting streamer was transiently inflated but not removed (blown out) by the passage of the CME. Much of the chromospheric-temperature plasma of the jets producing the CMEs escaped from the Sun, whereas relatively more of the chromospheric plasma in the non-CME-producing jets fell back to the solar surface. We also found that the CME-producing jets tended to be faster in speed and longer in duration than the non-CME-producing jets. This research was supported by funding from NASA's LWS program. Title: Visibility of Hinode/XRT X-Ray Jets at AIA/EUV Wavelengths, a Temperature Indicator Authors: Sterling, A. C.; Bakucz Canario, D.; Moore, R. L.; Falconer, D. A. Bibcode: 2015AGUFMSH31B2415S Altcode: X-ray jets have been observed for years using data from the X-Ray Telescope (XRT) on the Hinode Satellite. Recently with the launch of the Solar Dynamics Observatory (SDO) it has been possible to observe solar jets over a range of EUV of wavelengths using the Atmospheric Imaging Assembly (AIA). In this study, we investigated the appearance of X-ray jets in AIA images at wavelengths of 304, 171, 193, 211, 131, 94, and 335 Å. We selected 20 random X-ray jets from XRT movies of the polar coronal holes and then examined AIA EUV images from the same locations and times to determine the visibility of the jets at the different EUV wavelengths. We found that the jets were almost always visible in the 193 and 211 Å channel images. In the "hottest" EUV channels (94 Å, 335 Å), usually the spire of the jet was not visible, although sometimes a base brightening could be discerned. At other wavelengths (171, 131, and 335), the results were mixed. Based on the response characteristics of AIA (Lemen et al, 2011) to the temperature of the observed radiating solar plasma, our finding that most jets are visible in the 193 and 211 Å channels is consistent with other recent studies that measured jet temperatures of 1.5~2.0 MK (Pucci et al, 2012 & Paraschiv et al, 2015). This work was supported by the NASA LWS and HGI programs. Title: Destabilization of a Solar Prominence/Filament Field System by a Series of Eight Homologous Eruptive Flares Leading to a CME Authors: Panesar, Navdeep K.; Sterling, Alphonse C.; Innes, Davina E.; Moore, Ronald L. Bibcode: 2015ApJ...811....5P Altcode: 2015arXiv150801952P Homologous flares are flares that occur repetitively in the same active region, with similar structure and morphology. A series of at least eight homologous flares occurred in active region NOAA 11237 over 2011 June 16-17. A nearby prominence/filament was rooted in the active region, and situated near the bottom of a coronal cavity. The active region was on the southeast solar limb as seen from the Solar Dynamics Observatory/Atmospheric Imaging Assembly, and on the disk as viewed from the Solar TErrestrial RElations Observatory/EUVI-B. The dual perspective allows us to study in detail behavior of the prominence/filament material entrained in the magnetic field of the repeatedly erupting system. Each of the eruptions were mainly confined, but expelled hot material into the prominence/filament cavity system (PFCS). The field carrying and containing the ejected hot material interacted with the PFCS and caused it to inflate, resulting in a step-wise rise of the PFCS approximately in step with the homologous eruptions. The eighth eruption triggered the PFCS to move outward slowly, accompanied by a weak coronal dimming. As this slow PFCS eruption was underway, a final “ejective” flare occurred in the core of the active region, resulting in strong dimming in the EUVI-B images and expulsion of a coronal mass ejection (CME). A plausible scenario is that the repeated homologous flares could have gradually destabilized the PFCS, and its subsequent eruption removed field above the acitive region and in turn led to the ejective flare, strong dimming, and CME. Title: Small-scale filament eruptions as the driver of X-ray jets in solar coronal holes Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Adams, Mitzi Bibcode: 2015Natur.523..437S Altcode: 2017arXiv170503373S Solar X-ray jets are thought to be made by a burst of reconnection of closed magnetic field at the base of a jet with ambient open field. In the accepted version of the `emerging-flux' model, such a reconnection occurs at a plasma current sheet between the open field and the emerging closed field, and also forms a localized X-ray brightening that is usually observed at the edge of the jet's base. Here we report high-resolution X-ray and extreme-ultraviolet observations of 20 randomly selected X-ray jets that form in coronal holes at the Sun's poles. In each jet, contrary to the emerging-flux model, a miniature version of the filament eruptions that initiate coronal mass ejections drives the jet-producing reconnection. The X-ray bright point occurs by reconnection of the `legs' of the minifilament-carrying erupting closed field, analogous to the formation of solar flares in larger-scale eruptions. Previous observations have found that some jets are driven by base-field eruptions, but only one such study, of only one jet, provisionally questioned the emerging-flux model. Our observations support the view that solar filament eruptions are formed by a fundamental explosive magnetic process that occurs on a vast range of scales, from the biggest mass ejections and flare eruptions down to X-ray jets, and perhaps even down to smaller jets that may power coronal heating. A similar scenario has previously been suggested, but was inferred from different observations and based on a different origin of the erupting minifilament. Title: Physical properties of solar polar jets. A statistical study with Hinode XRT data Authors: Paraschiv, A. R.; Bemporad, A.; Sterling, A. C. Bibcode: 2015A&A...579A..96P Altcode: 2015arXiv150507191P
Aims: The target of this work is to investigate the physical nature of polar jets in the solar corona and their possible contribution to coronal heating and solar wind flow based on the analysis of X-ray images acquired by the Hinode XRT telescope. We estimate the different forms of energy associated with many of these small-scale eruptions, in particular the kinetic energy and enthalpy.
Methods: Two Hinode XRT campaign datasets focusing on the two polar coronal holes were selected to analyze the physical properties of coronal jets; the analyzed data were acquired using a series of three XRT filters. Typical kinematical properties (e.g., length, thickness, lifetime, ejection rate, and velocity) of 18 jets are evaluated from the observed sequences, thus providing information on their possible contribution to the fast solar wind flux escaping from coronal holes. Electron temperatures and densities of polar-jet plasmas are also estimated using ratios of the intensities observed in different filters.
Results: We find that the largest amount of energy eventually provided to the corona is thermal. The energy due to waves may also be significant, but its value is comparatively uncertain. The kinetic energy is lower than thermal energy, while other forms of energy are comparatively low. Lesser and fainter events seem to be hotter, thus the total contribution by polar jets to the coronal heating could have been underestimated so far. The kinetic energy flux is usually around three times smaller than the enthalpy counterpart, implying that this energy is converted into plasma heating more than in plasma acceleration. This result suggests that the majority of polar jets are most likely not escaping from the Sun and that only cooler ejections could possibly have enough kinetic energy to contribute to the total solar wind flow. Title: Magnetic Untwisting in Solar Jets that Go into the Outer Corona in Polar Coronal Holes Authors: Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David A. Bibcode: 2015ApJ...806...11M Altcode: 2015arXiv150403700M We study 14 large solar jets observed in polar coronal holes. In EUV movies from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA), each jet appears similar to most X-ray jets and EUV jets that erupt in coronal holes; but each is exceptional in that it goes higher than most, so high that it is observed in the outer corona beyond 2.2 R Sun in images from the Solar and Heliospheric Observatory/Large Angle Spectroscopic Coronagraph (LASCO)/C2 coronagraph. From AIA He ii 304 Å movies and LASCO/C2 running-difference images of these high-reaching jets, we find: (1) the front of the jet transits the corona below 2.2 R Sun at a speed typically several times the sound speed; (2) each jet displays an exceptionally large amount of spin as it erupts; (3) in the outer corona, most of the jets display measureable swaying and bending of a few degrees in amplitude; in three jets the swaying is discernibly oscillatory with a period of order 1 hr. These characteristics suggest that the driver in these jets is a magnetic-untwisting wave that is basically a large-amplitude (i.e., nonlinear) torsional Alfvén wave that is put into the reconnected open field in the jet by interchange reconnection as the jet erupts. From the measured spinning and swaying, we estimate that the magnetic-untwisting wave loses most of its energy in the inner corona below 2.2 R Sun. We point out that the torsional waves observed in Type-II spicules might dissipate in the corona in the same way as the magnetic-untwisting waves in our big jets, and thereby power much of the coronal heating in coronal holes. Title: Small-Scale Filament Eruptions Leading to Solar X-Ray Jets Authors: Sterling, Alphonse; Moore, Ronald; Falconer, David Bibcode: 2015TESS....140701S Altcode: We investigate the onset of ~10 random X-ray jets observed by Hinode/XRT. Each jet was near the limb in a polar coronal hole, and showed a ``bright point'' in an edge of the base of the jet, as is typical for previously-observed X-ray jets. We examined SDO/AIA EUV images of each of the jets over multiple AIA channels, including 304 Å, which detects chromospheric emissions, and 171, 193, and 211 Å, which detect cooler-coronal emissions. We find the jets to result from eruptions of miniature (size <~10 arcsec) filaments from the bases of the jets. Much of the erupting-filament material forms a chromospheric-temperature jet. In the cool-coronal channels, often the filament appears in absorption and the hotter EUV component of the jet appears in emission. The jet bright point forms at the location from which the miniature filament erupts, analogous to the formation of a standard solar flare arcade in the wake of the eruption of a typical larger-scalechromospheric filament. The spire of the jet forms on open field lines that presumably have undergone interchange reconnection with the erupting field that envelops and carries the miniature filament. Thus these X-ray jets and their bright points are made by miniature filament eruptions via ``internal'' and ``external'' reconnection of the erupting field. This is consistent with what we found for the onset of an on-disk coronal jet we examined in Adams et al. (2014). This work was supported by funding from NASA/LWS, Hinode, and ISSI. Title: A Prominence/filament eruption triggered by eight homologous flares Authors: Panesar, Navdeep K.; Sterling, Alphonse; Innes, Davina; Moore, Ronald Bibcode: 2015TESS....140805P Altcode: Eight homologous flares occurred in active region NOAA 11237 over 16 - 17 June 2011. A prominence system with a surrounding coronal cavity was adjacent to, but still magnetically connected to the active region. The eight eruptions expelled hot material from the active region into the prominence/filament cavity system (PFCS) where the ejecta became confined. We mainly aim to diagnose the 3D dynamics of the PFCS during the series of eight homologous eruptions by using data from two instruments: SDO/AIA and STEREO/EUVI-B, covering the Sun from two directions. The field containing the ejected hot material interacts with the PFCS and causes it to inflate, resulting in a discontinuous rise of the prominence/filament approximately in steps with the homologous eruptions. The eighth eruption triggers the PFCS to move outward slowly, accompanied by a weak coronal dimming. Subsequently the prominence/filament material drains to the solar surface. This PFCS eruption evidently slowly opens field overlying the active region, which results in a final ‘ejective’ eruption from the core of the active region. A strong dimming appears adjacent to the final eruption’s flare loops in the EUVI-B images, followed by a CME. We propose that the eight homologous flares gradually disrupted the PFCS and removed the overlying field above the active region, leading to the CME via the ‘lid removal’ mechanism. Title: More Macrospicule Jets in On-Disk Coronal Holes Authors: Adams, Mitzi; Sterling, Alphonse; Moore, Ronald Bibcode: 2015TESS....120301A Altcode: We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or at disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of about ten jets in an equatorial coronal hole spanning 2011 February 27 and 28. We show the evolution of these jets in AIA 193 Å, examine the magnetic field configuration and flux changes in the jet area, and discuss the probable trigger mechanism of these events. We reported on another jet in this same coronal hole on 2011 February 27, ~13:04 UT (Adams et al 2014, ApJ, 783: 11). That jet is a previously unrecognized variety of blowout jet, in which the base-edge bright point is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field. In contrast, in the presently-accepted "standard" picture for blowout jets, the base-edge bright point is made by interchange reconnection of initially-closed erupting jet-base field with ambient open field. This poster presents further evidence of the production of the base-edge bright point in blowout jets by internal reconnection. Our observations suggest that most of the bigger and brighter EUV jets in coronal holes are blowout jets of the new-found variety. Title: Reconnection and Spire Drift in Coronal Jets Authors: Moore, Ronald; Sterling, Alphonse; Falconer, David Bibcode: 2015TESS....140702M Altcode: It is observed that there are two morphologically-different kinds of X-ray/EUV jets in coronal holes: standard jets and blowout jets. In both kinds: (1) in the base of the jet there is closed magnetic field that has one foot in flux of polarity opposite that of the ambient open field of the coronal hole, and (2) in coronal X-ray/EUV images of the jet there is typically a bright nodule at the edge of the base. In the conventional scenario for jets of either kind, the bright nodule is a compact flare arcade, the downward product of interchange reconnection of closed field in the base with impacted ambient open field, and the upper product of this reconnection is the jet-outflow spire. It is also observed that in most jets of either kind the spire drifts sideways away from the bright nodule. We present the observed bright nodule and spire drift in an example standard jet and in two example blowout jets. With cartoons of the magnetic field and its reconnection in jets, we point out: (1) if the bright nodule is a compact flare arcade made by interchange reconnection, then the spire should drift toward the bright nodule, and (2) if the bright nodule is instead a compact flare arcade made, as in a filament-eruption flare, by internal reconnection of the legs of the erupting sheared-field core of a lobe of the closed field in the base, then the spire, made by the interchange reconnection that is driven on the outside of that lobe by the lobe’s internal convulsion, should drift away from the bright nodule. Therefore, from the observation that the spire usually drifts away from the bright nodule, we infer: (1) in X-ray/EUV jets of either kind in coronal holes the interchange reconnection that generates the jet-outflow spire usually does not make the bright nodule; instead, the bright nodule is made by reconnection inside erupting closed field in the base, as in a filament eruption, the eruption being either a confined eruption for a standard jet or a blowout eruption (as in a CME) for a blowout jet, and (2) in this respect, the conventional reconnection picture for the bright nodule in coronal jets is usually wrong for observed coronal jets of either kind. Title: Exploring Euv Spicules Using 304 Ang He II Data from SDO/AIA Authors: Snyder, I. R.; Sterling, A. C.; Falconer, D. A.; Moore, R. L. Bibcode: 2014AGUFMSH51C4179S Altcode: We present results from an exploratory study of He II 304 ŠEUV spicules at the limb of the Sun. We also measured properties of one macrospicule; macrospicules are longer than most spicules, and much broader in width than spicules. We use high-cadence (12 sec) and high-resolution (0.6 arcsec pixels) data from the Atmospheric Imaging Array (AIA) instrument on the Solar Dynamic Observatory (SDO). All of the observed events occurred near the solar north pole, in quiet-Sun or coronal-hole environments. We examined the maximum lengths, maximum rise velocities, and lifetimes of about 30 EUV spicules and the macrospicule. For the bulk of the EUV spicules the ranges of these quantities are respectively ~10,000----40,000 km, 20---100 km/s, and ~100--- ~600 sec. For the macrospicule the corresponding quantities are respectively ~60,000 km, ~130 km/s, and ~1800 sec, which is typical of macrospicules measured by other workers. Therefore macrospicules are taller, longer-lived, and faster than most EUV spicules. The rise profiles of both the spicules and the macrospicules fit well to a second-order ("parabolic'') trajectory, although the acceleration was often weaker than that of solar gravity in the profiles fitted to the trajectories. Our macrospicule also had an obvious brightening at its base at birth, whereas such brightenings were not apparent for the EUV spicules. Most of the EUV spicules remained visible during their decent back to the solar surface, although a small percentage of the spicules and the macrospicule faded out before falling back to the surface. Our sample of macrospicules is not yet large enough to address whether they are scaled-up versions of EUV spicules, or independent phenomena. A.C.S. and R.L.M. were supported by funding from the Heliophysics Division of NASA's Science Mission Directorate through the Living With a Star Targeted Research and Technology Program, and the Hinode Project. I.R.S. was supported by NSF's Research Experience for Undergraduates Program. Title: Macrospicule Jets in On-Disk Coronal Holes Authors: Adams, M.; Sterling, A. C.; Moore, R. L. Bibcode: 2014AGUFMSH51C4178A Altcode: We examine the magnetic structure and dynamics of multiple jets found in coronal holes close to or on disk center. All data are from the Atmospheric Imaging Assembly (AIA) and the Helioseismic and Magnetic Imager (HMI) of the Solar Dynamics Observatory (SDO). We report on observations of ten jets in an equatorial coronal hole from 2011 February 27 and multiple jets found in equatorial coronal holes on these dates: 2010-June-4, 2012-March-13, 2013-May 29-2013, and 2014-February-24. We will show in detail the evolution of the jets and will compare the magnetic field arrangement and probable trigger mechanism of these events to those of a specific macrospicule jet observed on 2011 February 27. We recently discovered that this jet is a previously-unrecognized variety of blowout jet (Adams et al 2014, ApJ, 783: 11). In this variety, the reconnection bright point is not made by interchange reconnection of initially-closed erupting field in the base of the jet with ambient open field but is a miniature filament-eruption flare arcade made by internal reconnection of the legs of the erupting field. Title: Exploring He II 304 Å Spicules and Macrospicules at the Solar Limb Authors: Sterling, A. C.; Snyder, I. R.; Falconer, D. A.; Moore, R. L. Bibcode: 2014AGUFMSH53D..04S Altcode: We present results from a study of He II 304 Ang spicules and macrospiculesobserved at the limb of the Sun in 304 Ang channel image sequences from theAtmospheric Imaging Assembly (AIA) on the Solar Dynamics Observatory (SDO). Thesedata have both high spatial (0.6 arcsec pixels) and temporal (12 s) resolution. All of the observed events occurred in quiet or coronal hole regions near the solarpole. He II 304 Ang spicules and macrospicules are both transient jet-likefeatures, with the macrospicules being wider and having taller maximum heights thanthe spicules. We looked for characteristics of the populations of these twophenomena that might indicate whether they have the same initiation mechanisms. Weexamine the maximum heights, time-averaged rise velocities, and lifetimes of about30 spicules and about five macrospicules. For the spicules, these quantities are,respectively, ~10,000----40,000 km, 20---100 km/s, and a few 100--- ~600 sec. Forthe macrospicules the corresponding properties are >~60,000 km, >~55 km/s, andlifetimes of >~1800 sec. Therefore the macrospicules have velocities comparable tothose of the fastest spicules and live longer than the spicules. The leading-edgetrajectories of both the spicules and the macrospicules match well a second-order(``parabolic'') profile, although the acceleration in the fitted profiles is generally weaker than that of solar gravity. The macrospicules also have obviousbrightenings at their bases at their birth, while such brightenings are notapparent for most of the spicules. Our findings are suggestive of the twophenomena possibly having different initiation mechanisms, but this is not yetconclusive. A.C.S. and R.L.M. were supported by funding from the HeliophysicsDivision of NASA's Science Mission Directorate through the Living With a StarTargeted Research and Technology Program, and the Hinode Project. I.R.S. wassupported by NSF's Research Experience for Undergraduates Program. Title: Birth, Life, and Death of a Solar Coronal Plume Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.; Romoli, Marco Bibcode: 2014ApJ...793...86P Altcode: We analyze a solar polar-coronal-hole (CH) plume over its entire ≈40 hr lifetime, using high-resolution Solar Dynamic Observatory Atmospheric Imaging Assembly (AIA) data. We examine (1) the plume's relationship to a bright point (BP) that persists at its base, (2) plume outflows and their possible contribution to the solar wind mass supply, and (3) the physical properties of the plume. We find that the plume started ≈2 hr after the BP first appeared and became undetectable ≈1 hr after the BP disappeared. We detected radially moving radiance variations from both the plume and from interplume regions, corresponding to apparent outflow speeds ranging over ≈(30-300) km s-1 with outflow velocities being higher in the "cooler" AIA 171 Å channel than in the "hotter" 193 Å and 211 Å channels, which is inconsistent with wave motions; therefore, we conclude that the observed radiance variations represent material outflows. If they persist into the heliosphere and plumes cover ≈10% of a typical CH area, these flows could account for ≈50% of the solar wind mass. From a differential emission measure analysis of the AIA images, we find that the average electron temperature of the plume remained approximately constant over its lifetime, at T e ≈ 8.5 × 105 K. Its density, however, decreased with the age of the plume, being about a factor of three lower when the plume faded compared to when it was born. We conclude that the plume died due to a density reduction rather than to a temperature decrease. Title: New Aspects of a Lid-removal Mechanism in the Onset of an Eruption Sequence that Produced a Large Solar Energetic Particle (SEP) Event Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David A.; Knox, Javon M. Bibcode: 2014ApJ...788L..20S Altcode: We examine a sequence of two ejective eruptions from a single active region on 2012 January 23, using magnetograms and EUV images from the Solar Dynamics Observatory's (SDO) Helioseismic and Magnetic Imager (HMI) and Atmospheric and Imaging Assembly (AIA), and EUV images from STEREO/EUVI. This sequence produced two coronal mass ejections (CMEs) and a strong solar energetic particle event (SEP); here we focus on the magnetic onset of this important space weather episode. Cheng et al. showed that the first eruption's ("Eruption 1") flux rope was apparent only in "hotter" AIA channels, and that it removed overlying field that allowed the second eruption ("Eruption 2") to begin via ideal MHD instability; here we say that Eruption 2 began via a "lid removal" mechanism. We show that during Eruption 1's onset, its flux rope underwent a "tether weakening" (TW) reconnection with field that arched from the eruption-source active region to an adjacent active region. Standard flare loops from Eruption 1 developed over Eruption 2's flux rope and enclosed filament, but these overarching new loops were unable to confine that flux rope/filament. Eruption 1's flare loops, from both TW reconnection and standard-flare-model internal reconnection, were much cooler than Eruption 2's flare loops (GOES thermal temperatures of ~7.5 MK and 9 MK, compared to ~14 MK). The corresponding three sequential GOES flares were, respectively, due to TW reconnection plus earlier phase Eruption 1 tether-cutting reconnection, Eruption 1 later-phase tether-cutting reconnection, and Eruption 2 tether-cutting reconnection. Title: New Aspects of a Lid-Removal Mechanism in the Onset of a SEP-Producing Eruption Sequence Authors: Sterling, Alphonse C.; Moore, Ronald L.; Falconer, David; Knox, Javon M Bibcode: 2014AAS...22421202S Altcode: We examine a sequence of two ejective eruptions from a single active region on 2012 January 23, using magnetograms and EUV images from SDO/HMI and SDO/AIA, and EUV images from STEREO. Cheng et al. (2013) showed that the first eruption's (``Eruption 1'') flux rope was apparent only in ``hotter'' AIA channels, and that it removed overlying field that allowed the second eruption (``Eruption 2'') to begin via ideal MHD instability; here we say Eruption 2 began via a ``lid removal'' mechanism. We show that during Eruption-1's onset, its flux rope underwent ``tether weakening'' (TW) reconnection with the field of an adjacent active region. Standard flare loops from Eruption 1 developed over Eruption-2's flux rope and enclosed filament, but these overarching new loops were unable to confine that flux rope/filament. Eruption-1's flare loops, from both TW reconnection and standard-flare-model internal reconnection, were much cooler than Eruption-2's flare loops (GOES thermal temperatures of ~9 MK compared to ~14 MK). This eruption sequence produced a strong solar energetic particle (SEP) event (10 MeV protons, >10^3 pfu for 43 hrs), apparently starting when Eruption-2's CME blasted through Eruption-1's CME at 5---10 R_s. This occurred because the two CMEs originated in close proximity and in close time sequence: Eruption-1's fast rise started soon after the TW reconnection; the lid removal by Eruption-1's ejection triggered the slow onset of Eruption 2; and Eruption-2's CME, which started ~1 hr later, was three times faster than Eruption-1's CME. Title: Magnetic Untwisting in Jets that Go into the Outer Solar Corona in Polar Coronal Holes Authors: Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David Bibcode: 2014AAS...22440803M Altcode: We present results from a study of 14 jets that were observed in SDO/AIA EUV movies to erupt in the Sun’s polar coronal holes. These jets were similar to the many other jets that erupt in coronal holes, but reached higher than the vast majority, high enough to be observed in the outer corona beyond 2 solar radii from Sun center by the SOHO/LASCO/C2 coronagraph. We illustrate the characteristic structure and motion of these high-reaching jets by showing observations of two representative jets. We find that (1) the speed of the jet front from the base of the corona out to 2-3 solar radii is typically several times the sound speed in jets in coronal holes, (2) each high-reaching jet displays unusually large rotation about its axis (spin) as it erupts, and (3) in the outer corona, many jets display lateral swaying and bending of the jet axis with an amplitude of a few degrees and a period of order 1 hour. From these observations we infer that these jets are magnetically driven, propose that the driver is a magnetic-untwisting wave that is basically a large-amplitude (non-linear) torsional Alfven wave that is put into the open magnetic field in the jet by interchange reconnection as the jet erupts, and estimate that the magnetic-untwisting wave loses most of its energy before reaching the outer corona. These observations of high-reaching coronal jets suggest that the torsional magnetic waves observed in Type-II spicules can similarly dissipate in the corona and thereby power much of the coronal heating in coronal holes and quiet regions. This work is funded by the NASA/SMD Heliophysics Division’s Living With a Star Targeted Research & Technology Program. Title: A Small-scale Eruption Leading to a Blowout Macrospicule Jet in an On-disk Coronal Hole Authors: Adams, Mitzi; Sterling, Alphonse C.; Moore, Ronald L.; Gary, G. Allen Bibcode: 2014ApJ...783...11A Altcode: We examine the three-dimensional magnetic structure and dynamics of a solar EUV-macrospicule jet that occurred on 2011 February 27 in an on-disk coronal hole. The observations are from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA) and the SDO Helioseismic and Magnetic Imager (HMI). The observations reveal that in this event, closed-field-carrying cool absorbing plasma, as in an erupting mini-filament, erupted and opened, forming a blowout jet. Contrary to some jet models, there was no substantial recently emerged, closed, bipolar-magnetic field in the base of the jet. Instead, over several hours, flux convergence and cancellation at the polarity inversion line inside an evolved arcade in the base apparently destabilized the entire arcade, including its cool-plasma-carrying core field, to undergo a blowout eruption in the manner of many standard-sized, arcade-blowout eruptions that produce a flare and coronal mass ejection. Internal reconnection made bright "flare" loops over the polarity inversion line inside the blowing-out arcade field, and external reconnection of the blowing-out arcade field with an ambient open field made longer and dimmer EUV loops on the outside of the blowing-out arcade. That the loops made by the external reconnection were much larger than the loops made by the internal reconnection makes this event a new variety of blowout jet, a variety not recognized in previous observations and models of blowout jets. Title: The contribution of X-ray polar blowout jets to the solar wind mass and energy Authors: Poletto, Giannina; Sterling, Alphonse C.; Pucci, Stefano; Romoli, Marco Bibcode: 2014IAUS..300..239P Altcode: Blowout jets constitute about 50% of the total number of X-ray jets observed in polar coronal holes. In these events, the base magnetic loop is supposed to blow open in what is a scaled-down representation of two-ribbon flares that accompany major coronal mass ejections (CMEs): indeed, miniature CMEs resulting from blowout jets have been observed. This raises the question of the possible contribution of this class of events to the solar wind mass and energy flux. Here we make a first crude evaluation of the mass contributed to the wind and of the energy budget of the jets and related miniature CMEs, under the assumption that small-scale events behave as their large-scale analogs. This hypothesis allows us to adopt the same relationship between jets and miniature-CME parameters that have been shown to hold in the larger-scale events, thus inferring the values of the mass and kinetic energy of the miniature CMEs, currently not available from observations. We conclude our work estimating the mass flux and the energy budget of a blowout jet, and giving a crude evaluation of the role possibly played by these events in supplying the mass and energy that feeds the solar wind. Title: Physical Parameters of Standard and Blowout Jets Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.; Romoli, Marco Bibcode: 2013ApJ...776...16P Altcode: The X-ray Telescope on board the Hinode mission revealed the occurrence, in polar coronal holes, of much more numerous jets than previously indicated by the Yohkoh/Soft X-ray Telescope. These plasma ejections can be of two types, depending on whether they fit the standard reconnection scenario for coronal jets or if they include a blowout-like eruption. In this work, we analyze two jets, one standard and one blowout, that have been observed by the Hinode and STEREO experiments. We aim to infer differences in the physical parameters that correspond to the different morphologies of the events. To this end, we adopt spectroscopic techniques and determine the profiles of the plasma temperature, density, and outflow speed versus time and position along the jets. The blowout jet has a higher outflow speed, a marginally higher temperature, and is rooted in a stronger magnetic field region than the standard event. Our data provide evidence for recursively occurring reconnection episodes within both the standard and the blowout jet, pointing either to bursty reconnection or to reconnection occurring at different locations over the jet lifetimes. We make a crude estimate of the energy budget of the two jets and show how energy is partitioned among different forms. Also, we show that the magnetic energy that feeds the blowout jet is a factor of 10 higher than the magnetic energy that fuels the standard event. Title: Magnetic Untwisting in Most Solar X-Ray Jets Authors: Moore, Ronald L.; Sterling, A. C.; Falconer, D.; Robe, D. M. Bibcode: 2013SPD....4410304M Altcode: From 54 X-ray jets observed in the polar coronal holes by Hinode’s X-Ray Telescope (XRT) during coverage in movies from Solar Dynamic Observatory’s Atmospheric Imaging Assembly (AIA) taken in its He II 304 Å band at a cadence of 12 s, we have established a basic characteristic of solar X-ray jets: untwisting motion in the spire. In this presentation, we show the progression of few of these X-ray jets in XRT images and track their untwisting in AIA He II images. From their structure displayed in their XRT movies, 19 jets were evidently standard jets made by interchange reconnection of the magnetic-arcade base with ambient open field, 32 were evidently blowout jets made by blowout eruption of the base arcade, and 3 were of ambiguous form. As was anticipated from the >10,000 km span of the base arcade in most polar X-ray jets and from the disparity of standard jets and blowout jets in their magnetic production, few of the standard X-ray jets (3 of 19) but nearly all of the blowout X-ray jets (29 of 32) carried enough cool (T ~ 10^5 K) plasma to be seen in their He II movies. In the 32 X-ray jets that showed a cool component, the He II movies show 10-100 km/s untwisting motions about the axis of the spire in all 3 standard jets and in 26 of the 29 blowout jets. Evidently, the open magnetic field in nearly all blowout X-ray jets and probably in most standard X-ray jets carries transient twist. This twist apparently relaxes by propagating out along the open field as a torsional wave. High-resolution spectrograms and Dopplergrams have shown that most Type-II spicules have torsional motions of 10-30 km/s. Our observation of similar torsional motion in X-ray jets (1) strengthens the case for Type-II spicules being made in the same way as X-ray jets, by blowout eruption of a twisted magnetic arcade in the spicule base and/or by interchange reconnection of the twisted base arcade with the ambient open field, and hence (2) strengthens the case made by Moore et al (2011, ApJ, 731: L18) that the Sun's granule-size emerging magnetic bipoles, by making Type-II spicules, power the global corona and solar wind. This work was funded by NASA’s LWS TRT Program, NASA's Hinode Project, and NSF's REU Program. Title: An Automatic Detection Technique for Prominence Eruptions and Surges using SDO/AIA Images Authors: Yashiro, Seiji; Gopalswamy, N.; Makela, P.; Akiyama, S.; Sterling, A. C. Bibcode: 2013SPD....44...99Y Altcode: We present an automatic technique to detect and characterize eruptive events (EEs), e.g. prominence eruptions and surges, using SDO/AIA 304 Å images. The technique works as follows. 1) The SDO 304 Å images are polar-transformed for easy handling of the outward motion of EEs and for saving computer resources. 2) The transformed images are divided by a background map, which is determined as the minimum intensity of each pixel during 24 hours. 3) The EEs are defined as a region in the ratio maps with pixels having a ratio >2. Because a stationary prominence has relatively high background, the prominence is detected only when it moves. 4) Pattern recognition is performed to separate different EEs at different locations. 5) In successive images, two EEs with more than 50% of pixels overlapping are considered to be the same EE. 6) If the height of an EE increases monotonically in 5 successive images, we consider it as a reliable eruption. The technique detects 1428 prominence eruptions and 1921 surges from 2010 May to 2012 December. The locations of PEs identified by this technique clearly indicated decayed onset of the maximum phase in the south with respect to the north. This work was supported by NASA Living with a Star TR&T programAbstract (2,250 Maximum Characters): We present an automatic technique to detect and characterize eruptive events (EEs), e.g. prominence eruptions and surges, using SDO/AIA 304 Å images. The technique works as follows. 1) The SDO 304 Å images are polar-transformed for easy handling of the outward motion of EEs and for saving computer resources. 2) The transformed images are divided by a background map, which is determined as the minimum intensity of each pixel during 24 hours. 3) The EEs are defined as a region in the ratio maps with pixels having a ratio >2. Because a stationary prominence has relatively high background, the prominence is detected only when it moves. 4) Pattern recognition is performed to separate different EEs at different locations. 5) In successive images, two EEs with more than 50% of pixels overlapping are considered to be the same EE. 6) If the height of an EE increases monotonically in 5 successive images, we consider it as a reliable eruption. The technique detects 1428 prominence eruptions and 1921 surges from 2010 May to 2012 December. The locations of PEs identified by this technique clearly indicated decayed onset of the maximum phase in the south with respect to the north. This work was supported by NASA Living with a Star TR&T program Title: A Small-Scale Filament Eruption Leading to a Blowout Macrospicule Jet in an On-Disk Coronal Hole Authors: Sterling, Alphonse C.; Adams, M.; Moore, R. L.; Tennant, A. F.; Gary, G. A. Bibcode: 2013SPD....44...17S Altcode: We observe an eruptive jet that occurred in an on-disk solar coronal hole, using EUV images from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Assembly (AIA), supplemented by magnetic data from the SDO Helioseismic and Magnetic Imager (HMI). This jet is similar to features variously called macrospicules or erupting minifilaments. After an initial pre-eruptive phase, a concentration of absorbing, cool material in the AIA images moves with a substantially-horizontal motion toward a region of open magnetic field, and subsequently jets out along that vertical field. Prior to and during the jet's ~20 min lifetime, the magnetic flux integrated over the local region shows flux changes of &lt 20% of the background flux levels, with a time-averaged emergence rate of no more than <3 × 10^15 Mx/s in the neighborhood of the jet. Contrary to some jet models, there was no substantial recently-emerged bipolar field in the base of the jet. Instead, there was an established evolving magnetic arcade that held mini-filament-like cool plasma in its core field. We propose that subtle evolution of the magnetic flux in and around this arcade destabilized its core field, as in some standard-sized arcade blowout eruptions that produce a flare and CME following the slow rise of a standard-sized filament in the core of the arcade. Closed field carrying the cool plasma erupted into the open field and formed the blowout jet, evidently at least partly by interchange reconnection with the open field. Internal reconnection made compact bright "flare" loops inside the blowing-out arcade, while, on the outside, interchange reconnection made longer and dimmer EUV "crinkle" loops. That the loops made by the external reconnection were considerably larger than the loops made by the internal reconnection makes this event a new variety of blowout jet, a variety not recognized in previous observations and models of blowout jets. Title: The 2012 Total Eclipse Expeditions in Queensland Authors: Pasachoff, Jay M.; Babcock, B. A.; Lu, M.; Dantowitz, R.; Lucas, R.; Seiradakis, J. H.; Voulgaris, A.; Gaintatzis, P.; Steele, A.; Sterling, A. C.; Rusin, V.; Saniga, M. Bibcode: 2013SPD....44...51P Altcode: A total eclipse swept across Queensland and other sites in northeastern Australia on the early morning of 14 November 2012, local time. We mounted equipment to observe coronal images and spectra during the approximately 2 minutes of totality, the former for comparison with spacecraft images and to fill in the doughnut of imaging not well covered with space coronagraphs. Matching weather statistics, viewing was spotty, and our best observations were from a last-minute inland site on the Tablelands, with some observations from a helicopter at 9000 feet altitude over our original viewing site at Miallo. Only glimpses of the corona were visible at our Port Douglas and Trinity Beach, Cairns, locations, with totality obscured from our sites at Newell and Miallo, though some holes in the clouds provided coronal views from Palm Cove and elsewhere along the coast. Preliminary analysis of the spectra again shows Fe XIV stronger than Fe X, as in 2010 but not earlier, a sign of solar maximum, as was the coronal shape. An intriguing CME is discernible in the SE. Acknowledgments: We thank Terry Cuttle, Aram Friedman, Michael Kentrianakis, and Nicholas Weber for assistance and collaboration in Australia and Wendy Carlos for image processing. Our expedition was supported in part by NSF grant AGS-1047726 from Solar Terrestrial Research of the Atmospheric and Geospace Sciences Division, and by the Rob Spring Fund and Science Center funds at Williams College. ML was also supported in part by a Grant-In-Aid of Research from the National Academy of Sciences, administered by Sigma Xi, The Scientific Research Society (Grant ID: G20120315159311). VR and MS acknowledge support from projects VEGA 2/0003/13 and NGS-3139-12 of the National Geographic Society. We are grateful to K. Shiota (Japan) for kindly providing us with some of his 2012 eclipse coronal images. Title: The Cool Component and the Dichotomy, Lateral Expansion, and Axial Rotation of Solar X-Ray Jets Authors: Moore, Ronald L.; Sterling, Alphonse C.; Falconer, David A.; Robe, Dominic Bibcode: 2013ApJ...769..134M Altcode: We present results from a study of 54 polar X-ray jets that were observed in coronal X-ray movies from the X-ray Telescope on Hinode and had simultaneous coverage in movies of the cooler transition region (T ~ 105 K) taken in the He II 304 Å band of the Atmospheric Imaging Assembly (AIA) on Solar Dynamics Observatory. These dual observations verify the standard-jet/blowout-jet dichotomy of polar X-ray jets previously found primarily from XRT movies alone. In accord with models of blowout jets and standard jets, the AIA 304 Å movies show a cool (T ~ 105 K) component in nearly all blowout X-ray jets and in a small minority of standard X-ray jets, obvious lateral expansion in blowout X-ray jets but none in standard X-ray jets, and obvious axial rotation in both blowout X-ray jets and standard X-ray jets. In our sample, the number of turns of axial rotation in the cool-component standard X-ray jets is typical of that in the blowout X-ray jets, suggesting that the closed bipolar magnetic field in the jet base has substantial twist not only in all blowout X-ray jets but also in many standard X-ray jets. We point out that our results for the dichotomy, lateral expansion, and axial rotation of X-ray jets add credence to published speculation that type-II spicules are miniature analogs of X-ray jets, are generated by granule-size emerging bipoles, and thereby carry enough energy to power the corona and solar wind. Title: An upper limit to the solar wind mass loading by X-ray polar jets Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.; Romoli, Marco Bibcode: 2013AIPC.1539...62P Altcode: Hinode observations of polar coronal holes revealed a larger population of X-ray jets than previously reported. Some of these comply with the standard reconnection model suggested by Shibata et al. (1992), others, likely analogous to CME eruptions and referred to as blow-out jets (e.g. Moore et al., 2010), show a more structured morphology. We present here two events, representative of the two jet categories, that have been observed by HINODE and STEREO in polar coronal holes. Their outward speed has been evaluated from high resolution images; also, because the jets have been observed in multiple filters, we have been able to derive, via spectroscopic techniques, their temperature and density evolution, both along the jets and in time. Knowledge of these parameters allows us to estimate the mass flux that jets of the two types transport to the solar wind and, assuming a given frequency of events, to infer a value for the wind mass loading contributed by polar jets. Because there are insufficient data to establish the percentage of ejections which eventually fall back to the Sun and because the jets we analyzed are probably among the more energetic within their respective class of events, the estimate we give is an upper limit to the jet wind mass loading. Title: Three 2012 Transits of Venus: From Earth, Jupiter, and Saturn Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.; Edelman, E.; Reardon, K.; Widemann, T.; Tanga, P.; Dantowitz, R.; Silverstone, M. D.; Ehrenreich, D.; Vidal-Madjar, A.; Nicholson, P. D.; Willson, R. C.; Kopp, G. A.; Yurchyshyn, V. B.; Sterling, A. C.; Scherrer, P. H.; Schou, J.; Golub, L.; McCauley, P.; Reeves, K. Bibcode: 2013AAS...22131506P Altcode: We observed the 2012 June 6/5 transit seen from Earth (E/ToV), simultaneously with Venus Express and several other spacecraft not only to study the Cytherean atmosphere but also to provide an exoplanet-transit analog. From Haleakala, the whole transit was visible in coronal skies; among our instruments was one of the world-wide Venus Twilight Experiment's nine coronagraphs. Venus's atmosphere became visible before first contact. SacPeak/IBIS provided high-resolution images at Hα/carbon-dioxide. Big Bear's NST also provided high-resolution observations of the Cytherean atmosphere and black-drop evolution. Our liaison with UH's Mees Solar Observatory scientists provided magneto-optical imaging at calcium and potassium. Solar Dynamics Observatory's AIA and HMI, and the Solar Optical Telescope (SOT) and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance measurements with ACRIMSAT and SORCE/TIM, were used to observe the event as an exoplanet-transit analog. On September 20, we imaged Jupiter for 14 Hubble Space Telescope orbits, centered on a 10-hour ToV visible from Jupiter (J/ToV), as an exoplanet-transit analog in our own solar system, using Jupiter as an integrating sphere. Imaging was good, although much work remains to determine if we can detect the expected 0.01% solar irradiance decrease at Jupiter and the even slighter differential effect between our violet and near-infrared filters caused by Venus's atmosphere. We also give a first report on our currently planned December 21 Cassini UVIS observations of a transit of Venus from Saturn (S/ToV). Our E/ToV expedition was sponsored by the Committee for Research and Exploration/National Geographic Society; supplemented: NASA/AAS's Small Research Grant Program. We thank Rob Ratkowski, Stan Truitt, Rob Lucas, Aram Friedman, and Eric Pilger '82 at Haleakala, and Joseph Gangestad '06 at Big Bear for assistance, and Lockheed Martin Solar and Astrophysics Lab and Hinode science and operations teams for support for coordinated observations with NASA satellites. Our J/ToV observations were based on observations made with HST, operated by AURA, Inc., under NASA contract NAS 5-26555; these observations are associated with program #13067. Title: Observations from SDO, Hinode, and STEREO of a Twisting and Writhing Start to a Solar-filament-eruption Cascade Authors: Sterling, Alphonse C.; Moore, Ronald L.; Hara, Hirohisa Bibcode: 2012ApJ...761...69S Altcode: We analyze data from SDO (AIA, HMI), Hinode (SOT, XRT, EIS), and STEREO (EUVI) of a solar eruption sequence of 2011 June 1 near 16:00 UT, with an emphasis on the early evolution toward eruption. Ultimately, the sequence consisted of three emission bursts and two filament ejections. SDO/AIA 304 Å images show absorbing-material strands initially in close proximity which over ~20 minutes form a twisted structure, presumably a flux rope with ~1029 erg of free energy that triggers the resulting evolution. A jump in the filament/flux rope's displacement (average velocity ~20 km s-1) and the first burst of emission accompanies the flux-rope formation. After ~20 more minutes, the flux rope/filament kinks and writhes, followed by a semi-steady state where the flux rope/filament rises at (~5 km s-1) for ~10 minutes. Then the writhed flux rope/filament again becomes MHD unstable and violently erupts, along with rapid (50 km s-1) ejection of the filament and the second burst of emission. That ejection removed a field that had been restraining a second filament, which subsequently erupts as the second filament ejection accompanied by the third (final) burst of emission. Magnetograms from SDO/HMI and Hinode/SOT, and other data, reveal several possible causes for initiating the flux-rope-building reconnection, but we are not able to say which is dominant. Our observations are consistent with magnetic reconnection initiating the first burst and the flux-rope formation, with MHD processes initiating the further dynamics. Both filament ejections are consistent with the standard model for solar eruptions. Title: Production of High-Temperature Plasmas During the Early Phases of a C9.7 Flare. II. Bi-directional Flows Suggestive of Reconnection in a Pre-flare Brightening Region Authors: Watanabe, T.; Hara, H.; Sterling, A. C.; Harra, L. K. Bibcode: 2012SoPh..281...87W Altcode: 2012SoPh..tmp..185W The 6 June 2007 16:55 UT flare was well observed with high time-cadence sparse raster scans by the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. The observation covers an active region area of 240 arcsec × 240 arcsec with the 1 arcsec slit in about 160 seconds. Title: The 2012 Transit of Venus for Cytherean Atmospheric Studies and as an Exoplanet Analog Authors: Pasachoff, Jay M.; Schneider, G.; Babcock, B. A.; Lu, M.; Reardon, K. P.; Widemann, T.; Tanga, P.; Dantowitz, R.; Willson, R.; Kopp, G.; Yurchyshyn, V.; Sterling, A.; Scherrer, P.; Schou, J.; Golub, L.; Reeves, K. Bibcode: 2012DPS....4450806P Altcode: We worked to assemble as complete a dataset as possible for the Cytherean atmosphere in collaboration with Venus Express in situ and to provide an analog of spectral and total irradiance exoplanet measurements. From Haleakala, the whole transit was visible in coronal skies; our B images showed the evolution of the visibility of Venus's atmosphere and of the black-drop effect, as part of the Venus Twilight Experiment's 9 coronagraphs distributed worldwide with BVRI. We imaged the Cytherean atmosphere over two minutes before first contact, with subarcsecond resolution, with the coronagraph and a separate refractor. The IBIS imaging spectrometer at Sacramento Peak Observatory at H-alpha and carbon-dioxide also provided us high-resolution imaging. The NST of Big Bear Solar Observatory also provided high-resolution vacuum observations of the Cytherean atmosphere and black drop evolution. Our liaison with UH's Mees Solar Observatory scientists provided magneto-optical imaging at calcium and potassium. Spaceborne observations included the Solar Dynamics Observatory's AIA and HMI, and the Solar Optical Telescope (SOT) and X-ray Telescope (XRT) on Hinode, and total-solar-irradiance measurements with ACRIMSAT and SORCE/TIM, to characterize the event as an exoplanet-transit analog. Our expedition was sponsored by the Committee for Research and Exploration/National Geographic Society. Some of the funds for the carbon-dioxide filter for IBIS were provided by NASA through AAS's Small Research Grant Program. We thank Rob Lucas, Aram Friedman, and Eric Pilger '82 for assistance with Haleakala observing, Rob Ratkowski of Haleakala Amateur Astronomers for assistance with equipment and with the site, Stan Truitt for the loan of his Paramount ME, and Steve Bisque/Software Bisque for TheSky X controller. We thank Joseph Gangestad '06 of Aerospace Corp., a veteran of our 2004 expedition, for assistance at Big Bear. We thank the Lockheed Martin Solar and Astrophysics Laboratory and Hinode science and operations teams for planning and support. Title: Solar Spicules near and at the Limb, Observed from Hinode Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2012ASPC..454...87S Altcode: Solar spicules appear as narrow jets emanating from the chromosphere and extending into the corona. They have been observed for over a hundred years, mainly in chromospheric spectral lines such as H-alpha. Because they are at the limit of visibility of ground-based instruments, their nature has long been a puzzle. In recent years however, vast progress has been made in understanding them both theoretically and observationally, as spicule studies have undergone a revolution because of the superior resolution and time cadence of ground-based and space-based instruments. Even more rapid progress is currently underway, due to the Solar Optical Telescope (SOT) instrument on the Hinode spacecraft. Here we give a synopsis of our recent findings from a movie of sharpened images from the Hinode SOT Ca II filtergraph of spicules at and near the limb in a polar coronal hole. Title: Observational Evidence for Interaction Between X-ray Jets and Multiple Bright Points Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M. Bibcode: 2012ASPC..456..217P Altcode: The Hinode X-ray telescope (XRT) observed in November 2007 the Northen polar Coronal Hole (CH) over extended time periods. Among these we selected two 20 hours long time intervals and carried out a photometric analysis of several X-ray Bright Points (BPs), within a selected area, aiming at ascertaining whether there is any correlation between the BPs intensity fluctuations and the occurrence of jets originating within this area. Our results indicate that jets result from magnetic connectivity changes that also produced BP variability: the interaction between BPs and jets may be interpreted as the small scale version of the Active Regions phenomena where flares and eruptions are initiated by interacting bipoles. Title: Physical Parameters of a Blowout Jet Observed by HINODE and STEREO/EUVI Authors: Pucci, S.; Poletto, G.; Sterling, A.; Romoli, M. Bibcode: 2012ASPC..456..219P Altcode: The present work aims at identifying a typical blowout jet and inferring its physical parameters. To this end, we present a preliminary multi-instrument analysis of the bright X-ray jet that occurred in the north polar coronal hole on Nov. 3, 2007, at 11:50 UT. The jet shows the typical characteristics of “blowout jets'' (Moore et al. 2010), and was observed by Hinode/X-Ray Telescope (XRT) and by Stereo/Extreme UltraViolett Imager (EUVI) and COR1. Temperatures and Emission Measures (EMs) of the jet have been derived from the EUVI A data via the filter ratio technique in the pre-event, near maximum and in the post-maximum phases. Temperatures and EMs inferred from EUVI data are then used to calculate the predicted XRT Al-poly intensity: predicted values are compared with observed values and found to be consistent. Title: The Limit of Magnetic-Shear Energy in Solar Active Regions Authors: Moore, Ronald L.; Falconer, D. A.; Sterling, A. C. Bibcode: 2012AAS...22020438M Altcode: It has been found previously, by measuring from active-region magnetograms a proxy of the free energy in the active region’s magnetic field, (1) that there is a sharp upper limit to the free energy the field can hold that increases with the amount of magnetic field in the active region, the active region’s magnetic flux content, and (2) that most active regions are near this limit when their field explodes in a CME/flare eruption. That is, explosive active regions are concentrated in a main-sequence path bordering the free-energy-limit line in (flux content, free-energy proxy) phase space. Here we present evidence that specifies the underlying magnetic condition that gives rise to the free-energy limit and the accompanying main sequence of explosive active regions. Using a suitable free energy proxy measured from vector magnetograms of 44 active regions, we find evidence that (1) in active regions at and near their free-energy limit, the ratio of magnetic-shear free energy to the non-free magnetic energy the potential field would have is of order 1 in the core field, the field rooted along the neutral line, and (2) this ratio is progressively less in active regions progressively farther below their free-energy limit. Evidently, most active regions in which this core-field energy ratio is much less than 1 cannot be triggered to explode; as this ratio approaches 1, most active regions become capable of exploding; and when this ratio is 1, most active regions are compelled to explode.

This work was funded by NASA’s Science Mission Directorate through the Heliophysics Guest Investigators Program, the Hinode Project, and the Living With a Star Targeted Research & Technology Program. Title: Observations from SDO and Hinode of a Twisting and Writhing Start to a Solar-filament-eruption Cascade Authors: Sterling, Alphonse C.; Moore, R. L. Bibcode: 2012AAS...22050802S Altcode: We analyze data from SDO and hinode of a solar eruption sequence of 1 June 2011 near 16:00 UT, with emphasis on the early evolution toward eruption. Ultimately, the sequence consisted of three emission bursts and two filament ejections. SDO/AIA 304 Ang images show absorbing-material strands initially in close proximity that over 20 min form a twisted structure, presumably a flux rope with 1029 ergs of free energy that triggers the resulting evolution. A jump in the filament/flux rope's height (average velocity 20 km s-1) and the first burst of emission accompanies the flux-rope formation. After 20 min more, the flux rope/filament kinks and writhes, followed by a semi-steady state where the flux rope/filament rises at ( 5 km s-1) for 10 min. Then the writhed flux rope/filament again becomes MHD unstable and violently erupts, along with rapid (> 50 km s-1) ejection of the filament and the second burst of emission. That ejection removed field that had been restraining a second filament, which subsequently erupts as the second filament ejection accompanied by the third (final) burst of emission. Magnetograms from SDO/HMI and hinode/SOT, and other data, reveal several possible causes for initiating the flux-rope-building reconnection, but we are not able to say which is dominant. Our observations are consistent with tether-cutting reconnection initiating the first burst and the flux-rope formation, with MHD processes initiating the further dynamics. Both filament ejections are consistent with the standard model for solar eruptions. NASA supported this work through its Heliophysics program. Title: The Limit of Magnetic-shear Energy in Solar Active Regions Authors: Moore, Ronald L.; Falconer, David A.; Sterling, Alphonse C. Bibcode: 2012ApJ...750...24M Altcode: It has been found previously, by measuring from active-region magnetograms a proxy of the free energy in the active region's magnetic field, (1) that there is a sharp upper limit to the free energy the field can hold that increases with the amount of magnetic field in the active region, the active region's magnetic flux content, and (2) that most active regions are near this limit when their field explodes in a coronal mass ejection/flare eruption. That is, explosive active regions are concentrated in a main-sequence path bordering the free-energy-limit line in (flux content, free-energy proxy) phase space. Here, we present evidence that specifies the underlying magnetic condition that gives rise to the free-energy limit and the accompanying main sequence of explosive active regions. Using a suitable free-energy proxy measured from vector magnetograms of 44 active regions, we find evidence that (1) in active regions at and near their free-energy limit, the ratio of magnetic-shear free energy to the non-free magnetic energy the potential field would have is of the order of one in the core field, the field rooted along the neutral line, and (2) this ratio is progressively less in active regions progressively farther below their free-energy limit. Evidently, most active regions in which this core-field energy ratio is much less than one cannot be triggered to explode; as this ratio approaches one, most active regions become capable of exploding; and when this ratio is one, most active regions are compelled to explode. Title: Solar Polar X-Ray Jets and Multiple Bright Points: Evidence for Sympathetic Activity Authors: Pucci, Stefano; Poletto, Giannina; Sterling, Alphonse C.; Romoli, Marco Bibcode: 2012ApJ...745L..31P Altcode: We present an analysis of X-ray bright points (BPs) and X-ray jets observed by Hinode/X-Ray Telescope on 2007 November 2-4, within the solar northern polar coronal hole. After selecting small subregions that include several BPs, we followed their brightness evolution over a time interval of a few hours, when several jets were observed. We find that most of the jets occurred in close temporal association with brightness maxima in multiple BPs: more precisely, most jets are closely correlated with the brightening of at least two BPs. We suggest that the jets result from magnetic connectivity changes that also induce the BP variability. We surmise that the jets and implied magnetic connectivity we describe are small-scale versions of the active-region-scale phenomenon, whereby flares and eruptions are triggered by interacting bipoles. Title: The Global Context of Solar Activity During the Whole Heliosphere Interval Campaign Authors: Webb, D. F.; Cremades, H.; Sterling, A. C.; Mandrini, C. H.; Dasso, S.; Gibson, S. E.; Haber, D. A.; Komm, R. W.; Petrie, G. J. D.; McIntosh, P. S.; Welsch, B. T.; Plunkett, S. P. Bibcode: 2011SoPh..274...57W Altcode: The Whole Heliosphere Interval (WHI) was an international observing and modeling effort to characterize the 3-D interconnected "heliophysical" system during this solar minimum, centered on Carrington Rotation 2068, March 20 - April 16, 2008. During the latter half of the WHI period, the Sun presented a sunspot-free, deep solar minimum type face. But during the first half of CR 2068 three solar active regions flanked by two opposite-polarity, low-latitude coronal holes were present. These departures from the quiet Sun led to both eruptive activity and solar wind structure. Most of the eruptive activity, i.e., flares, filament eruptions and coronal mass ejections (CMEs), occurred during this first, active half of the interval. We determined the source locations of the CMEs and the type of associated region, such as active region, or quiet sun or active region prominence. To analyze the evolution of the events in the context of the global solar magnetic field and its evolution during the three rotations centered on CR 2068, we plotted the CME source locations onto synoptic maps of the photospheric magnetic field, of the magnetic and chromospheric structure, of the white light corona, and of helioseismological subsurface flows. Most of the CME sources were associated with the three dominant active regions on CR 2068, particularly AR 10989. Most of the other sources on all three CRs appear to have been associated with either isolated filaments or filaments in the north polar crown filament channel. Although calculations of the flux balance and helicity of the surface magnetic features did not clearly identify a dominance of one region over the others, helioseismological subsurface flows beneath these active regions did reveal a pronounced difference among them. These preliminary results suggest that the "twistedness" (i.e., vorticity and helicity) of subsurface flows and its temporal variation might be related to the CME productivity of active regions, similar to the relationship between flares and subsurface flows. Title: Lateral Offset of the Coronal Mass Ejections from the X-flare of 2006 December 13 and Its Two Precursor Eruptions Authors: Sterling, Alphonse C.; Moore, Ronald L.; Harra, Louise K. Bibcode: 2011ApJ...743...63S Altcode: Two GOES sub-C-class precursor eruptions occurred within ~10 hr prior to and from the same active region as the 2006 December 13 X4.3-class flare. Each eruption generated a coronal mass ejection (CME) with center laterally far offset (gsim 45°) from the co-produced bright flare. Explaining such CME-to-flare lateral offsets in terms of the standard model for solar eruptions has been controversial. Using Hinode/X-Ray Telescope (XRT) and EUV Imaging Spectrometer (EIS) data, and Solar and Heliospheric Observatory (SOHO)/Large Angle and Spectrometric Coronagraph (LASCO) and Michelson Doppler Imager (MDI) data, we find or infer the following. (1) The first precursor was a "magnetic-arch-blowout" event, where an initial standard-model eruption of the active region's core field blew out a lobe on one side of the active region's field. (2) The second precursor began similarly, but the core-field eruption stalled in the side-lobe field, with the side-lobe field erupting ~1 hr later to make the CME either by finally being blown out or by destabilizing and undergoing a standard-model eruption. (3) The third eruption, the X-flare event, blew out side lobes on both sides of the active region and clearly displayed characteristics of the standard model. (4) The two precursors were offset due in part to the CME originating from a side-lobe coronal arcade that was offset from the active region's core. The main eruption (and to some extent probably the precursor eruptions) was offset primarily because it pushed against the field of the large sunspot as it escaped outward. (5) All three CMEs were plausibly produced by a suitable version of the standard model. Title: Observed Aspects of Reconnection in Solar Eruptions Authors: Moore, Ronald L.; Sterling, Alphonse C.; Gary, G. Allen; Cirtain, Jonathan W.; Falconer, David A. Bibcode: 2011SSRv..160...73M Altcode: 2011SSRv..tmp..113M; 2011SSRv..tmp..189M; 2011SSRv..tmp...30M The observed magnetic field configuration and signatures of reconnection in the large solar magnetic eruptions that make major flares and coronal mass ejections and in the much smaller magnetic eruptions that make X-ray jets are illustrated with cartoons and representative observed eruptions. The main reconnection signatures considered are the imaged bright emission from the heated plasma on reconnected field lines. In any of these eruptions, large or small, the magnetic field that drives the eruption and/or that drives the buildup to the eruption is initially a closed bipolar arcade. From the form and configuration of the magnetic field in and around the driving arcade and from the development of the reconnection signatures in coordination with the eruption, we infer that (1) at the onset of reconnection the reconnection current sheet is small compared to the driving arcade, and (2) the current sheet can grow to the size of the driving arcade only after reconnection starts and the unleashed erupting field dynamically forces the current sheet to grow much larger, building it up faster than the reconnection can tear it down. We conjecture that the fundamental reason the quasi-static pre-eruption field is prohibited from having a large current sheet is that the magnetic pressure is much greater than the plasma pressure in the chromosphere and low corona in eruptive solar magnetic fields. Title: Spectroscopic Observations of a Coronal Moreton Wave Authors: Harra, Louise K.; Sterling, Alphonse C.; Gömöry, Peter; Veronig, Astrid Bibcode: 2011ApJ...737L...4H Altcode: We observed a coronal wave (EIT wave) on 2011 February 16, using EUV imaging data from the Solar Dynamics Observatory/Atmospheric Imaging Assembly (AIA) and EUV spectral data from the Hinode/EUV Imaging Spectrometer (EIS). The wave accompanied an M1.6 flare that produced a surge and a coronal mass ejection (CME). EIS data of the wave show a prominent redshifted signature indicating line-of-sight velocities of ~20 km s-1 or greater. Following the main redshifted wave front, there is a low-velocity period (and perhaps slightly blueshifted), followed by a second redshift somewhat weaker than the first; this progression may be due to oscillations of the EUV atmosphere set in motion by the initial wave front, although alternative explanations may be possible. Along the direction of the EIS slit the wave front's velocity was ~500 km s-1, consistent with its apparent propagation velocity projected against the solar disk as measured in the AIA images, and the second redshifted feature had propagation velocities between ~200 and 500 km s-1. These findings are consistent with the observed wave being generated by the outgoing CME, as in the scenario for the classic Moreton wave. This type of detailed spectral study of coronal waves has hitherto been a challenge, but is now possible due to the availability of concurrent AIA and EIS data. Title: Insights into Filament Eruption Onset from Solar Dynamics Observatory Observations Authors: Sterling, Alphonse C.; Moore, R. L.; Freeland, S. L. Bibcode: 2011SPD....42.0904S Altcode: 2011BAAS..43S.0904S We examine the buildup to and onset of an active region filament confined eruption of 2010 May 12, using EUV imaging data from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Array and line-of-sight magnetic data from the SDO Helioseismic and Magnetic Imager. Over the hour preceding eruption the filament undergoes a slow rise averaging 3 km/s, with a step-like trajectory. Accompanying a final rise step 20 minutes prior to eruption is a transient preflare brightening, occurring on loops rooted near the site where magnetic field had canceled over the previous 20 hr. Flow-type motions of the filament are relatively smooth with speeds 50 km/s prior to the preflare brightening and appear more helical, with speeds 50-100 km/s, after that brightening. After a final plateau in the filament's rise, its rapid eruption begins, and concurrently an outer shell "cocoon" of the filament material increases in emission in hot EUV lines, consistent with heating in a newly formed magnetic flux rope. The main flare brightenings start 5 minutes after eruption onset. The main flare arcade begins between the legs of an envelope-arcade loop that is nearly orthogonal to the filament, suggesting that the flare results from reconnection among the legs of that loop. This progress of events is broadly consistent with flux cancellation leading to formation of a helical flux rope that subsequently erupts due to onset of a magnetic instability and/or runaway tether cutting. A full description of this work appears in ApJ Letters 2011, 731, L3. NASA supported this work through its Solar Physics Supporting Research and Technology, Sun-Earth Connection Guest Investigator, and Living With a Star Targeted Research & Technology programs. Title: Insights into Filament Eruption Onset from Solar Dynamics Observatory Observations Authors: Sterling, Alphonse C.; Moore, Ronald L.; Freeland, Samuel L. Bibcode: 2011ApJ...731L...3S Altcode: We examine the buildup to and onset of an active region filament confined eruption of 2010 May 12, using EUV imaging data from the Solar Dynamics Observatory (SDO) Atmospheric Imaging Array and line-of-sight magnetic data from the SDO Helioseismic and Magnetic Imager. Over the hour preceding eruption the filament undergoes a slow rise averaging ~3 km s-1, with a step-like trajectory. Accompanying a final rise step ~20 minutes prior to eruption is a transient preflare brightening, occurring on loops rooted near the site where magnetic field had canceled over the previous 20 hr. Flow-type motions of the filament are relatively smooth with speeds ~50 km s-1 prior to the preflare brightening and appear more helical, with speeds ~50-100 km s-1, after that brightening. After a final plateau in the filament's rise, its rapid eruption begins, and concurrently an outer shell "cocoon" of the filament material increases in emission in hot EUV lines, consistent with heating in a newly formed magnetic flux rope. The main flare brightenings start ~5 minutes after eruption onset. The main flare arcade begins between the legs of an envelope-arcade loop that is nearly orthogonal to the filament, suggesting that the flare results from reconnection among the legs of that loop. This progress of events is broadly consistent with flux cancellation leading to formation of a helical flux rope that subsequently erupts due to onset of a magnetic instability and/or runaway tether cutting. Title: Solar X-ray Jets, Type-II Spicules, Granule-size Emerging Bipoles, and the Genesis of the Heliosphere Authors: Moore, Ronald L.; Sterling, Alphonse C.; Cirtain, Jonathan W.; Falconer, David A. Bibcode: 2011ApJ...731L..18M Altcode: From Hinode observations of solar X-ray jets, Type-II spicules, and granule-size emerging bipolar magnetic fields in quiet regions and coronal holes, we advocate a scenario for powering coronal heating and the solar wind. In this scenario, Type-II spicules and Alfvén waves are generated by the granule-size emerging bipoles (EBs) in the manner of the generation of X-ray jets by larger magnetic bipoles. From observations and this scenario, we estimate that Type-II spicules and their co-generated Alfvén waves carry into the corona an area-average flux of mechanical energy of ~7 × 105 erg cm-2 s-1. This is enough to power the corona and solar wind in quiet regions and coronal holes, and therefore indicates that the granule-size EBs are the main engines that generate and sustain the entire heliosphere. Title: Simultaneous Observations of the Chromosphere with TRACE and SUMER Authors: Pasachoff, Jay M.; Tingle, Evan D.; Dammasch, Ingolf E.; Sterling, Alphonse C. Bibcode: 2011SoPh..268..151P Altcode: 2010SoPh..tmp..209P; 2010SoPh..tmp..233P; 2010arXiv1010.4814P Using mainly the 1600 Å continuum channel and also the 1216 Å Lyman-α channel (which includes some UV continuum and C IV emission) aboard the TRACE satellite, we observed the complete lifetime of a transient, bright chromospheric loop. Simultaneous observations with the SUMER instrument aboard the SOHO spacecraft revealed interesting material velocities through the Doppler effect existing above the chromospheric loop imaged with TRACE, possibly corresponding to extended nonvisible loops, or the base of an X-ray jet. Title: Hinode extreme-ultraviolet imaging spectrometer observations of a limb active region Authors: O'Dwyer, B.; Del Zanna, G.; Mason, H. E.; Sterling, A. C.; Tripathi, D.; Young, P. R. Bibcode: 2011A&A...525A.137O Altcode:
Aims: We investigate the electron density and temperature structure of a limb active region.
Methods: We have carried out a study of an active region close to the solar limb using observations from the Extreme-ultraviolet Imaging Spectrometer (EIS) and the X-ray telescope (XRT) on board Hinode. The electron density and temperature distributions of the coronal emission have been determined using emission line intensity ratios. Differential emission measure (DEM) analysis and the emission measure (EM) loci technique were used to examine the thermal structure of the emitting plasma as a function of distance from the limb.
Results: The highest temperature and electron density values are found to be located in the core of the active region, with a peak electron number density value of 1.9 × 1010 cm-3 measured using the Fe XII 186.887 Å to 192.394 Å line intensity ratio. The plasma along the line of sight in the active region was found to be multi-thermal at different distances from the limb. The EIS and XRT DEM analyses appear to be in agreement in the temperature interval from log T = 6.5-6.7.
Conclusions: Our results provide new constraints for models of coronal heating in active regions. Title: Three-dimensional morphology of a coronal prominence cavity Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de Toma, G.; Hao, J.; Hill, S. M.; Hudson, H. S.; Marque, C.; McIntosh, P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.; Sterling, A.; Tripathi, D.; Williams, D. R.; Zhang, M. Bibcode: 2010AGUFMSH51A1667G Altcode: We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space- and ground-based observatories, spanning wavelengths from radio to soft-X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally-extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step towards quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager (EUVI) observations from the two Solar Terrestrial Relations Observatory (STEREO) spacecraft. This defines the morphological parameters of our model, from which we reproduce forward-modeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explains the observed variation in cavity visibility for the east vs. west limbs. Title: Three-dimensional Morphology of a Coronal Prominence Cavity Authors: Gibson, S. E.; Kucera, T. A.; Rastawicki, D.; Dove, J.; de Toma, G.; Hao, J.; Hill, S.; Hudson, H. S.; Marqué, C.; McIntosh, P. S.; Rachmeler, L.; Reeves, K. K.; Schmieder, B.; Schmit, D. J.; Seaton, D. B.; Sterling, A. C.; Tripathi, D.; Williams, D. R.; Zhang, M. Bibcode: 2010ApJ...724.1133G Altcode: We present a three-dimensional density model of coronal prominence cavities, and a morphological fit that has been tightly constrained by a uniquely well-observed cavity. Observations were obtained as part of an International Heliophysical Year campaign by instruments from a variety of space- and ground-based observatories, spanning wavelengths from radio to soft X-ray to integrated white light. From these data it is clear that the prominence cavity is the limb manifestation of a longitudinally extended polar-crown filament channel, and that the cavity is a region of low density relative to the surrounding corona. As a first step toward quantifying density and temperature from campaign spectroscopic data, we establish the three-dimensional morphology of the cavity. This is critical for taking line-of-sight projection effects into account, since cavities are not localized in the plane of the sky and the corona is optically thin. We have augmented a global coronal streamer model to include a tunnel-like cavity with elliptical cross-section and a Gaussian variation of height along the tunnel length. We have developed a semi-automated routine that fits ellipses to cross-sections of the cavity as it rotates past the solar limb, and have applied it to Extreme Ultraviolet Imager observations from the two Solar Terrestrial Relations Observatory spacecraft. This defines the morphological parameters of our model, from which we reproduce forward-modeled cavity observables. We find that cavity morphology and orientation, in combination with the viewpoints of the observing spacecraft, explain the observed variation in cavity visibility for the east versus west limbs. Title: Eruptive Signatures in the Solar Atmosphere During the WHI Campaign (20 March-16 April 2008) Authors: Sterling, Alphonse C. Bibcode: 2010HiA....15..498S Altcode: We examined EUV movies of the Sun during the period of the Whole Heliospheric Interval (WHI) campaign of 20 March-16 April 2008, searching for indications of eruptive events. Our data set was obtained from EIT on SOHO, using its 195 Å filter, and from EUVI on the two STEREO satellites, using their 171 Å, 195 Å, 284 Å, and 304 Å filters. Here we present a table showing results from our preliminary search. Title: Fibrillar Chromospheric Spicule-like Counterparts to an Extreme-ultraviolet and Soft X-ray Blowout Coronal Jet Authors: Sterling, Alphonse C.; Harra, Louise K.; Moore, Ronald L. Bibcode: 2010ApJ...722.1644S Altcode: We observe an erupting jet feature in a solar polar coronal hole, using data from Hinode/Solar Optical Telescope (SOT), Extreme Ultraviolet Imaging Spectrometer (EIS), and X-Ray Telescope (XRT), with supplemental data from STEREO/EUVI. From extreme-ultraviolet (EUV) and soft X-ray (SXR) images we identify the erupting feature as a blowout coronal jet: in SXRs it is a jet with a bright base, and in EUV it appears as an eruption of relatively cool (~50,000 K) material of horizontal size scale ~30'' originating from the base of the SXR jet. In SOT Ca II H images, the most pronounced analog is a pair of thin (~1'') ejections at the locations of either of the two legs of the erupting EUV jet. These Ca II features eventually rise beyond 45'', leaving the SOT field of view, and have an appearance similar to standard spicules except that they are much taller. They have velocities similar to that of "type II" spicules, ~100 km s-1, and they appear to have spicule-like substructures splitting off from them with horizontal velocity ~50 km s-1, similar to the velocities of splitting spicules measured by Sterling et al. Motions of splitting features and of other substructures suggest that the macroscopic EUV jet is spinning or unwinding as it is ejected. This and earlier work suggest that a subpopulation of Ca II type II spicules are the Ca II manifestation of portions of larger scale erupting magnetic jets. A different subpopulation of type II spicules could be blowout jets occurring on a much smaller horizontal size scale than the event we observe here. Title: Evidence for magnetic flux cancelation leading to an ejective solar eruption observed by Hinode, TRACE, STEREO, and SoHO/MDI Authors: Sterling, A. C.; Chifor, C.; Mason, H. E.; Moore, R. L.; Young, P. R. Bibcode: 2010A&A...521A..49S Altcode:
Aims: We study the onset of a solar eruption involving a filament ejection on 2007 May 20.
Methods: We observe the filament in Hα images from Hinode/SOT and in EUV with TRACE and STEREO/SECCHI/EUVI. Hinode/XRT images are used to study the eruption in soft X-rays. From spectroscopic data taken with Hinode/EIS we obtain bulk-flow velocities, line profiles, and plasma densities in the onset region. The magnetic field evolution was observed in SoHO/MDI magnetograms.
Results: We observed a converging motion between two opposite polarity sunspots that form the primary magnetic polarity inversion line (PIL), along which resides filament material before eruption. Positive-flux magnetic elements, perhaps moving magnetic features (MMFs) flowing from the spot region, appear north of the spots, and the eruption onset occurs where these features cancel repeatedly in a negative-polarity region north of the sunspots. An ejection of material observed in Hα and EUV marks the start of the filament eruption (its “fast-rise”). The start of the ejection is accompanied by a sudden brightening across the PIL at the jet's base, observed in both broad-band images and in EIS. Small-scale transient brightenings covering a wide temperature range (Log Te = 4.8-6.3) are also observed in the onset region prior to eruption. The preflare transient brightenings are characterized by sudden, localized density enhancements (to above Log ne [ cm-3] = 9.75, in Fe XIII) that appear along the PIL during a time when pre-flare brightenings were occurring. The measured densities in the eruption onset region outside the times of those enhancements decrease with temperature. Persistent downflows (red-shifts) and line-broadening (Fe XII) are present along the PIL.
Conclusions: The array of observations is consistent with the pre-eruption sheared-core magnetic field being gradually destabilized by evolutionary tether-cutting flux cancelation that was driven by converging photospheric flows, and the main filament ejection being triggered by flux cancelation between the positive flux elements and the surrounding negative field. A definitive statement however on the eruption's ultimate cause would require comparison with simulations, or additional detailed observations of other eruptions occurring in similar magnetic circumstances.

The video that accompanies Fig. 3 is only available in electronic form at http://www.aanda.org Title: Dichotomy of Solar Coronal Jets: Standard Jets and Blowout Jets Authors: Moore, Ronald L.; Cirtain, Jonathan W.; Sterling, Alphonse C.; Falconer, David A. Bibcode: 2010ApJ...720..757M Altcode: By examining many X-ray jets in Hinode/X-Ray Telescope coronal X-ray movies of the polar coronal holes, we found that there is a dichotomy of polar X-ray jets. About two thirds fit the standard reconnection picture for coronal jets, and about one third are another type. We present observations indicating that the non-standard jets are counterparts of erupting-loop Hα macrospicules, jets in which the jet-base magnetic arch undergoes a miniature version of the blowout eruptions that produce major coronal mass ejections. From the coronal X-ray movies we present in detail two typical standard X-ray jets and two typical blowout X-ray jets that were also caught in He II 304 Å snapshots from STEREO/EUVI. The distinguishing features of blowout X-ray jets are (1) X-ray brightening inside the base arch in addition to the outside bright point that standard jets have, (2) blowout eruption of the base arch's core field, often carrying a filament of cool (T ~ 104 - 105 K) plasma, and (3) an extra jet-spire strand rooted close to the bright point. We present cartoons showing how reconnection during blowout eruption of the base arch could produce the observed features of blowout X-ray jets. We infer that (1) the standard-jet/blowout-jet dichotomy of coronal jets results from the dichotomy of base arches that do not have and base arches that do have enough shear and twist to erupt open, and (2) there is a large class of spicules that are standard jets and a comparably large class of spicules that are blowout jets. Title: Production of High-temperature Plasmas During the Early Phases of a C9.7 Flare Authors: Watanabe, Tetsuya; Hara, Hirohisa; Sterling, Alphonse C.; Harra, Louise K. Bibcode: 2010ApJ...719..213W Altcode: Explosive chromospheric evaporation is predicted from some current solar flare models. In this paper, we analyze a flare with high time cadence raster scans with the EUV Imaging Spectrometer (EIS) on board the Hinode spacecraft. This observation covers an area of 240'' × 240'', with the 1'' slit in about 160 s. The early phases of a C9.7 flare that occurred on 2007 June 6 were well observed. The purpose of our analysis is to study for the first time the spatially resolved spectra of high-temperature plasma, especially from Fe XXIII and Fe XXIV, allowing us to explore the explosive chromospheric evaporation scenario further. Sections of raster images obtained between 17:20:09 and 17:20:29 (UT) show a few bright patches of emission from Fe XXIII/Fe XXIV lines at the footpoints of the flaring loops; these footpoints were not clearly seen in the images taken earlier, between 17:17:30 and 17:17:49 (UT). Fe XXIII spectra at these footpoints show dominating blueshifted components of -(300 to 400) km s-1, while Fe XV/XIV lines are nearly stationary; Fe XII lines and/or lower temperature lines show slightly redshifted features, and Fe VIII and Si VII to He II lines show ~+50 km s-1 redshifted components. The density of the 1.5-2 MK plasma at these footpoints is estimated to be 3 × 1010 cm-3 by the Fe XIII/XIV line pairs around the maximum of the flare. High-temperature loops connecting the footpoints appear in the Fe XXIII/XXIV images taken over 17:22:49-17:23:08 (UT) which is near the flare peak. Line profiles of these high-temperature lines at this flare peak time show only slowly moving components. The concurrent cooler Fe XVII line at 254.8 Å is relatively weak, indicating the predominance of high-temperature plasma (>107 K) in these loops. The characteristics observed during the early phases of this flare are consistent with the scenario of explosive chromospheric evaporation. Title: Hinode Solar Optical Telescope Observations of the Source Regions and Evolution of "Type II" Spicules at the Solar Polar Limb Authors: Sterling, Alphonse C.; Moore, Ronald L.; DeForest, Craig E. Bibcode: 2010ApJ...714L...1S Altcode: We examine solar spicules using high-cadence Ca II data of the north pole coronal hole region, using the Solar Optical Telescope (SOT) on the Hinode spacecraft. The features we observe are referred to as "Type II" spicules by De Pontieu et al. in 2007. By convolving the images with the inverse-point-spread function for the SOT Ca II filter, we are able to investigate the roots of some spicules on the solar disk, and the evolution of some spicules after they are ejected from the solar surface. We find that the source regions of at least some of the spicules correspond to locations of apparent-fast-moving (~few × 10 km s-1), transient (few 100 s), Ca II brightenings on the disk. Frequently the spicules occur when these brightenings appear to collide and disappear. After ejection, when seen above the limb, many of the spicules fade by expanding laterally (i.e., roughly transverse to their motion away from the solar surface), splitting into two or more spicule "strands," and the spicules then fade without showing any downward motion. Photospheric/chromospheric acoustic shocks alone likely cannot explain the high velocities (~100 km s-1) of the spicules. If the Ca II brightenings represent magnetic elements, then reconnection among those elements may be a candidate to explain the spicules. Alternatively, many of the spicules could be small-scale magnetic eruptions, analogous to coronal mass ejections, and the apparent fast motions of the Ca II brightenings could be analogs of flare loops heated by magnetic reconnection in these eruptions. Title: Blowout Jets: Hinode X-Ray Jets that Don't Fit the Standard Model Authors: Moore, Ronald L.; Cirtain, J. W.; Sterling, A. C. Bibcode: 2010AAS...21640620M Altcode: 2010BAAS...41..883M Nearly half of all H-alpha macrospicules in polar coronal holes appear to be miniature filament eruptions (Yamauchi et al 2004, ApJ, 605, 511). This suggests that there is a large class of X-ray jets in which the jet-base magnetic arcade undergoes a blowout eruption as in a CME, instead of remaining static as in most solar X-ray jets, the standard jets that fit the model advocated by Shibata (e.g., Shibata et al 1992, PASJ, 44, L173). Along with a cartoon depicting the standard model, we present a cartoon depicting the signatures expected of blowout jets in coronal X-ray images. From Hinode/XRT movies and STEREO/EUVI snapshots in polar coronal holes, we present examples of (1) X-ray jets that fit the standard model, and (2) X-ray jets that do not fit the standard model but do have features appropriate for blowout jets. These features are (1) a flare arcade inside the jet-base arcade in addition to the small flare arcade (bright point) outside that standard jets have, (2) a filament of cool (T 80,000 K) plasma that erupts from the core of the jet-base arcade, and (3) an extra jet strand that should not be made by the reconnection for standard jets but could be made by reconnection between the ambient unipolar open field and the opposite-polarity leg of the filament-carrying flux-rope core field of the erupting jet-base arcade. We therefore infer that these non-standard jets are blowout jets, jets made by miniature versions of the sheared-core-arcade eruptions that make CMEs.

This work was funded by NASA's Science Mission Directorate through the Heliophysics Guest Investigators Program, the Hinode Project, and the Living With a Star Targeted Research and Technology Program. Title: Solar Polar Spicules Observed with Hinode Authors: Sterling, Alphonse C.; Moore, R. L.; DeForest, C. E. Bibcode: 2010AAS...21640303S Altcode: 2010BAAS...41Q.878S We examine solar polar region spicules using high-cadence Ca II data from the Solar Optical Telescope (SOT) on the Hinode spacecraft. We sharpened the images by convolving them with the inverse-point-spread function of the SOT Ca II filter, and we are able to see some of the spicules originating on the disk just inside the limb. Bright points are frequently at the root of the disk spicules. These ``Ca II brightenings'' scuttle around at few x 10 km/s, live for 100 sec, and may be what are variously known as ``H2V grains,'' ``K2V grains,'' or "K2V bright points.'' When viewed extending over the limb, some of the spicules appear to expand horizontally or spit into two or more components, with the horizontal expansion or splitting velocities reaching 50 km/s. This work was funded by NASA's Science Mission Directorate through the Living With a Star Targeted Research and Technology Program, the Supporting Research and Program, the Heliospheric Guest Investigator Program, and the Hinode project. Title: Geometric Model of a Coronal Cavity Authors: Kucera, Therese A.; Gibson, S. E.; Rastawicki, D.; Dove, J.; de Toma, G.; Hao, J.; Hudson, H. S.; Marque, C.; McIntosh, P. S.; Reeves, K. K.; Schmidt, D. J.; Sterling, A. C.; Tripathi, D. K.; Williams, D. R.; Zhang, M. Bibcode: 2010AAS...21640510K Altcode: 2010BAAS...41..890K We observed a coronal cavity from August 8-18 2007 during a multi-instrument observing campaign organized under the auspices of the International Heliophysical Year (IHY). Here we present initial efforts to model the cavity with a geometrical streamer-cavity model. The model is based the white-light streamer model of Gibson et al. (2003), which has been enhanced by the addition of a cavity and the capability to model EUV and X-ray emission. The cavity is modeled with an elliptical cross-section and Gaussian fall-off in length and width inside the streamer. Density and temperature can be varied in the streamer and cavity and constrained via comparison with data. Although this model is purely morphological, it allows for three-dimensional, multi-temperature analysis and characterization of the data, which can then provide constraints for future physical modeling. Initial comparisons to STEREO/EUVI images of the cavity and streamer show that the model can provide a good fit to the data. This work is part of the effort of the International Space Science Institute International Team on Prominence Cavities. Title: Triggering of solar magnetic eruptions on various size scales Authors: Sterling, Alphonse Bibcode: 2010cosp...38.2839S Altcode: 2010cosp.meet.2839S A solar eruption that produces a coronal mass ejection (CME) together with a flare is driven by the eruption of a closed-loop magnetic arcade that has a sheared-field core. Before eruption, the sheared core envelops a polarity inversion line along which cool filament material may reside. The sheared-core arcade erupts when there is a breakdown in the balance between the confining downward-directed magnetic tension of the overall arcade field and the upward-directed force of the pent-up magnetic pressure of the sheared field in the core of the arcade. What triggers the breakdown in this balance in favor of the upward-directed force is still an unsettled question. We consider several eruption examples, using imaging data from the SoHO, TRACE and Hinode satellites, and other sources, along with information about the magnetic field of the erupting regions. In several cases, observations of large-scale eruptions, where the magnetic neutral line spans ∼ few ×10,000 km, are consistent with magnetic flux cancelation being the trigger to the eruption's onset, even though the amount of flux canceled is only ∼ few percent of the total magnetic flux of the erupting region. In several other cases, an initial compact (small size-scale) eruption occurs embedded inside of a larger closed magnetic loop system, so that the smaller eruption destabilizes and causes the eruption of the much larger system. In this way, small-scale eruptive events can result in eruption of much larger-scale systems. This work was funded by NASA's Science Mission Directorate thought the Living With a Star Targeted Research and Technology Program, the Supporting Research and Program, and the Hinode project. Title: Two types of magnetic flux cancelation in the solar eruption of 2007 May 20 Authors: Sterling, Alphonse; Moore, Ronald; Mason, Helen Bibcode: 2010cosp...38.1946S Altcode: 2010cosp.meet.1946S We study a solar eruption on 2007 May 20, in an effort to understand the cWe study a solar eruption of 2007 May 20, in an effort to understand the cause of the eruption's onset. The event produced a GOES class B6.7 flare peaking at 05:56 UT, while ejecting a surge/filament and producing a coronal mass ejection (CME). We examine several data sets, including Hα images from the Solar Optical Telescope (SOT) on Hinode, EUV images from TRACE, and line-of-sight magnetograms from SoHO/MDI. Flux cancelation occurs among two different sets of flux elements inside of the erupting active region: First, for several days prior to eruption, opposite-polarity sunspot groups inside the region move toward each other, leading to the cancelation of ∼ 1021 Mx of flux over three days. Second, within hours prior to the eruption, positive-polarity moving magnetic features (MMFs) flowing out of the positive-flux spots at ∼ 1 km/s repeatedly cancel with field inside a patch of negative-polarity flux located north of the sunspots. The filament erupts as a surge whose base is rooted in the location where the MMF cancelation occurs, while during the eruption that filament flows out along the polarity inversion line between the converging spot groups. We conclude that a plausible scenario is that the converging spot fields brought the magnetic region to the brink of instability, and the MMF cancelation pushed the system "over the edge," triggering the eruption. This work was funded by NASA's Science Mission Directorate thought the Living With a Star Targeted Research and Technology Program, the Supporting Research and Program, and the Hinode project. Title: Limb Spicules from the Ground and from Space Authors: Pasachoff, Jay M.; Jacobson, William A.; Sterling, Alphonse C. Bibcode: 2009SoPh..260...59P Altcode: 2009arXiv0909.0027P We amassed statistics for quiet-sun chromosphere spicules at the limb using ground-based observations from the Swedish 1-m Solar Telescope on La Palma and simultaneously from NASA's Transition Region and Coronal Explorer (TRACE) spacecraft. The observations were obtained in July 2006. With the 0.2 arcsecond resolution obtained after maximizing the ground-based resolution with the Multi-Object Multi-Frame Blind Deconvolution (MOMFBD) program, we obtained specific statistics for sizes and motions of over two dozen individual spicules, based on movies compiled at 50-second cadence for the series of five wavelengths observed in a very narrow band at Hα, on-band and at ± 0.035 nm and ± 0.070 nm (10 s at each wavelength) using the SOUP filter, and had simultaneous observations in the 160 nm EUV continuum from TRACE. The MOMFBD restoration also automatically aligned the images, facilitating the making of Dopplergrams at each off-band pair. We studied 40 Hα spicules, and 14 EUV spicules that overlapped Hα spicules; we found that their dynamical and morphological properties fit into the framework of several previous studies. From a preliminary comparison with spicule theories, our observations are consistent with a reconnection mechanism for spicule generation, and with UV spicules being a sheath region surrounding the Hα spicules. Title: Large-Scale Flows in Prominence Cavities Authors: Schmit, D. J.; Gibson, S. E.; Tomczyk, S.; Reeves, K. K.; Sterling, Alphonse C.; Brooks, D. H.; Williams, D. R.; Tripathi, D. Bibcode: 2009ApJ...700L..96S Altcode: Regions of rarefied density often form cavities above quiescent prominences. We observed two different cavities with the Coronal Multichannel Polarimeter on 2005 April 21 and with Hinode/EIS on 2008 November 8. Inside both of these cavities, we find coherent velocity structures based on spectral Doppler shifts. These flows have speeds of 5-10 km s-1, occur over length scales of tens of megameters, and persist for at least 1 hr. Flows in cavities are an example of the nonstatic nature of quiescent structures in the solar atmosphere. Title: Flows and Plasma Properties in Quiescent Cavities Authors: Schmit, Donald; Gibson, S.; Reeves, K.; Sterling, A.; Tomczyk, S. Bibcode: 2009SPD....40.1015S Altcode: Regions of rarefied density often form cavities above quiescent prominences. In an attempt to constrain the plasma properties of "equilibrium" cavities we conduct several diagnostics using Hinode/EIS, STEREO/EUVI, and CoMP. One novel observation is of large scale flows in cavities. Using different instruments to observe two distinct cavities off the solar limb in coronal emission lines, we find that spectral doppler shifts imply LOS velocities within cavities on the order of 1-10 km/s. These flows occur over length scales of several hundred Mm and persist for hours. Title: Solar Spicules Near and at the Limb, Observed from Hinode Authors: Sterling, Alphonse C. Bibcode: 2009SPD....40.1006S Altcode: Solar spicules appear as narrow jets emanating from the chromosphere and extending into the corona. They have been observed for over a hundred years, mainly in chromospheric spectral lines such as Hα. Because they are at the limit of visibility of ground-based instruments, their nature has long been a puzzle. In recent years however, vast progress has been made in understanding them both theoretically and observationally. Most recently, spicule studies have undergone a revolution because of the superior resolution, time cadence, and atmosphere-free observations from the Solar Optical Telescope (SOT) instrument on the Hinode spacecraft. Here we present observations of spicules from Hinode SOT, and consider how the observations from Hinode compare with historical observations. We include data taken in the blue and red wings of Hα, where the spicules have widths of a few 100 kms, and the longest ones reach 104 km in extent, similar to sizes long reported from ground-based instruments. Their dynamics are not easy to generalize, with many showing the upward movement followed by falling or fading, as traditionally reported, but with others showing more dynamic or even ejective aspects. There is a strong transverse component to their motion, as extensively reported previously from the Hinode data as evidence for Alfven waves.

NASA supported this work through its Living with a Star program. Title: Coronal Nonthermal Velocity Following Helicity Injection Before an X-Class Flare Authors: Harra, L. K.; Williams, D. R.; Wallace, A. J.; Magara, T.; Hara, H.; Tsuneta, S.; Sterling, A. C.; Doschek, G. A. Bibcode: 2009ApJ...691L..99H Altcode: We explore the "pre-flare" behavior of the corona in a three-day period building up to an X-class flare on 2006 December 13 by analyzing EUV spectral profiles from the Hinode EUV Imaging Spectrometer (EIS) instrument. We found an increase in the coronal spectral line widths, beginning after the time of saturation of the injected helicity as measured by Magara & Tsuneta. In addition, this increase in line widths (indicating nonthermal motions) starts before any eruptive activity occurs. The Hinode EIS has the sensitivity to measure changes in the buildup to a flare many hours before the flare begins. Title: New Evidence that CMEs are Self-Propelled Magnetic Bubbles Authors: Moore, R. L.; Sterling, A. C.; Suess, S. T. Bibcode: 2008ASPC..397...98M Altcode: We briefly describe the ``standard model'' for the production of coronal mass ejections (CMEs), and our view of how it works. We then summarize pertinent recent results that we have found from SOHO observations of CMEs and the flares at the sources of these magnetic explosions. These results support our interpretation of the standard model: a CME is basically a self-propelled magnetic bubble, a low-beta plasmoid, that (1) is built and unleashed by the tether-cutting reconnection that builds and heats the coronal flare arcade, (2) can explode from a flare site that is far from centered under the full-blown CME in the outer corona, and (3) drives itself out into the solar wind by pushing on the surrounding coronal magnetic field. Title: Early Hinode Observations of a Solar Filament Eruption Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2008ASPC..397..115S Altcode: We use Hinode X-Ray Telescope (XRT) and Solar Optical Telescope (SOT) filtergraph (FG) Stokes-V magnetogram observations to study the early onset of a solar eruption that includes an erupting filament that we observe in TRACE EUV images; this is one of the first filament eruptions seen with Hinode. The filament undergoes a slow rise for at least 30 min prior to its fast eruption and strong soft X-ray flaring, and the new Hinode data elucidate the physical processes occurring during the slow-rise period. During the slow-rise phase, a soft X-ray (SXR) sigmoid forms from apparent reconnection low in the sheared core field traced by the filament, and there is a low-level intensity peak in both EUV and SXRs during the slow rise. The SOT data show that magnetic flux cancelation occurs along the neutral line of the filament in the hours before eruption, and this likely caused the low-lying reconnection that produced the microflaring and the slow rise leading up to the eruption. Title: Magnetic Flux Cancelation Leading to the Eruption of a Coronal Mass Ejection: Observations from Hinode, SOHO, TRACE, and STEREO Authors: Sterling, A. C.; Chifor, C.; Mason, H.; Moore, R. L. Bibcode: 2008AGUSMSP23B..05S Altcode: We study a solar eruption involving ejection of a filament on 2007 May 20, using instruments on Hinode, STEREO, TRACE, and SOHO. We observe the filament in EUV from TRACE and STEREO, and in H-alpha from SOT on Hinode. We also see the eruption in soft X-rays with XRT on Hinode, and in several EUV lines from EIS on Hinode. SOHO/MDI magnetograms show that converging motion between opposite-polarity sunspots in the region result in expansion of large-scale loops overlying the region's primary magnetic neutral line, along which sits filament material prior to its eruption. The source location of an EUV filament's surge-like ejection is a negative-polarity magnetic region that is north of the interacting spots, and patches of magnetic field flow at ~ 0.5 km/s from the positive converging spots into the negative region in the north. Apparently, repeated episodes of flux cancelation occur where the flowing positive flux collides with the northern negative flux, and the source of the EUV filament's ejection is near this cancelation site. Spectroscopic data from EIS are available for a portion of the active region that includes the northern cancelation site, and from these data we obtain bulk-flow velocities, line-broadening turbulent velocities, and densities of plasma in the region. The array of observations is consistent with the pre-eruption sheared-core magnetic arcade being gradually destabilized by evolutionary tether-cutting flux cancelation that was driven by converging photospheric flows. Title: Initiation of Solar Eruptions Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2008ASPC..383..163S Altcode: We consider processes occurring just prior to and at the start of the onset of flare- and CME-producing solar eruptions. Our recent work uses observations of filament motions around the time of eruption onset as a proxy for the evolution of the fields involved in the eruption. Frequently the filaments show a slow rise prior to fast eruption, indicative of a slow expansion of the field that is about to explode. Work by us and others suggests that reconnection involving emerging or canceling flux results in a lengthening of fields restraining the filament-carrying field, and the consequent upward expansion of the field in and around the filament produces the filament's slow rise; that is, the reconnection weakens the magnetic ``tethers'' (``tether-weakening'' reconnection), and results in the slow rise of the filament. It is still inconclusive, however, what mechanism is responsible for the switch from the slow rise to the fast eruption. Title: Hinode Observations of the Onset Stage of a Solar Filament Eruption Authors: Sterling, Alphonse C.; Moore, Ronald L.; Berger, Thomas E.; Bobra, Monica; Davis, John M.; Jibben, Patricia; Kano, Ryohei; Lundquist, Loraine L.; Myers, D.; Narukage, Noriyuki; Sakao, Taro; Shibasaki, Kiyoto; Shine, Richard A.; Tarbell, Theodore D.; Weber, Mark Bibcode: 2007PASJ...59S.823S Altcode: We used Hinode X-Ray Telescope (XRT) and Solar Optical Telescope (SOT) filtergraph (FG) Stokes-V magnetogram observations, to study the early onset of a solar eruption that includes an erupting filament that we observe in TRACE EUV images. The filament undergoes a slow rise for at least 20min prior to its fast eruption and strong soft X-ray (SXR) flaring; such slow rises have been previously reported, and the new Hinode data elucidate the physical processes occurring during this period. XRT images show that during the slow-rise phase, an SXR sigmoid forms from apparent reconnection low in the sheared core field traced by the filament, and there is a low-level intensity peak in both EUV and SXRs during the slow rise. MDI and SOT FG Stokes-V magnetograms show that the pre-eruption filament is along a neutral line between opposing-polarity enhanced network cells, and the SOT magnetograms show that these opposing fields are flowing together and canceling for at least six hours prior to eruption. From the MDI data we measured the canceling network fields to be ∼ 40G, and we estimated that ∼ 1019 Mx of flux canceled during the five hours prior to eruption; this is only ∼ 5% of the total flux spanned by the eruption and flare, but apparently its tether-cutting cancellation was enough to destabilize the sigmoid field holding the filament and resulted in that field's eruption. Title: Coronal Dimming Observed with Hinode: Outflows Related to a Coronal Mass Ejection Authors: Harra, Louise K.; Hara, Hirohisa; Imada, Shinsuke; Young, Peter R.; Williams, David R.; Sterling, Alphonse C.; Korendyke, Clarence; Attrill, Gemma D. R. Bibcode: 2007PASJ...59S.801H Altcode: Coronal dimming has been a signature used to determine the source of plasma that forms part of a coronal mass ejection (CME) for many years. Generally dimming is detected through imaging instruments such as SOHO EIT by taking difference images. Hinode tracked active region 10930 from which there were a series of flares. We combined dimming observations from EIT with Hinode data to show the impact of flares and coronal mass ejections on the region surrounding the flaring active region, and we discuss evidence that the eruption resulted in a prolonged steady outflow of material from the corona. The dimming region shows clear structure with extended loops whose footpoints are the source of the strongest outflow (≈ 40 kms-1). This confirms that the loops that are disrupted during the event do lose plasma and hence are likely to form part of the CME. This is the first time the velocity of the coronal plasma has been measured in an extended dimming region away from the flare core. In addition there was a weaker steady outflow from extended, faint loops outside the active region before the eruption, which is also long lasting. These were disturbed and the velocity increased following the flare. Such outflows could be the source of the slow solar wind. Title: New Evidence for the Role of Emerging Flux in a Solar Filament's Slow Rise Preceding Its CME-producing Fast Eruption Authors: Sterling, Alphonse C.; Harra, Louise K.; Moore, Ronald L. Bibcode: 2007ApJ...669.1359S Altcode: We observe the eruption of a large-scale (~300,000 km) quiet-region solar filament leading to an Earth-directed ``halo'' coronal mass ejection (CME), using data from EIT, CDS, MDI, and LASCO on SOHO and from SXT on Yohkoh. Initially the filament shows a slow (~1 km s-1 projected against the solar disk) and approximately constant velocity rise for about 6 hr, before erupting rapidly, reaching a velocity of ~8 km s-1 over the next ~25 minutes. CDS Doppler data show Earth-directed filament velocities ranging from <20 km s-1 (the noise limit) during the slow-rise phase, to ~100 km s-1 early in the eruption. Beginning within 10 hr prior to the start of the slow rise, localized new magnetic flux emerged near one end of the filament. Near the start of and during the slow-rise phase, soft X-ray (SXR) microflaring occurred repeatedly at the flux-emergence site, and the magnetic arcade over the filament progressively brightened in a fan of illumination in SXRs. These observations are consistent with ``tether-weakening'' reconnection occurring between the newly emerging flux and the overlying arcade field containing the filament, and apparently this reconnection is the cause of the filament's slow rise. We cannot, however, discern whether the transition from slow rise to fast eruption was caused by a final episode of tether-weakening reconnection, or by one or some combination of other possible mechanisms allowed by the observations. Intensity ``dimmings'' and ``brightenings'' occurring both near to and relatively far from the location of the filament are possible signatures of the expansion (``opening'') of the erupting field and its reconnection with overarching field during the eruption. Title: Origin of the Sheared Magnetic Fields that Explode in Flares and Coronal Mass Ejections Authors: Moore, R. L.; Sterling, A. C. Bibcode: 2007ASPC..369..539M Altcode: From observations of 37 flare-arcade events, their magnetic settings, their sheared core fields, and the coronal mass ejections from these events, we find evidence that the sheared core fields in mature magnetic arcades are not formed by bodily emergence of a twisted flux rope along the neutral line. This implies that these sigmoidal sheared fields are instead formed by reconnection and flows above and in the photosphere. A high priority of Solar-B should be to discover the evolutionary processes that build the sigmoidal sheared fields along mature neutral lines. Title: The Width of a Solar Coronal Mass Ejection and the Source of the Driving Magnetic Explosion: A Test of the Standard Scenario for CME Production Authors: Moore, Ronald L.; Sterling, Alphonse C.; Suess, Steven T. Bibcode: 2007ApJ...668.1221M Altcode: We show that the strength (BFlare) of the magnetic field in the area covered by the flare arcade following a CME-producing ejective solar eruption can be estimated from the final angular width (Final θCME) of the CME in the outer corona and the final angular width (θFlare) of the flare arcade: BFlare~1.4[(Final θCME)/θFlare2 G. We assume (1) the flux-rope plasmoid ejected from the flare site becomes the interior of the CME plasmoid; (2) in the outer corona (R>2 Rsolar) the CME is roughly a ``spherical plasmoid with legs'' shaped like a lightbulb; and (3) beyond some height in or below the outer corona the CME plasmoid is in lateral pressure balance with the surrounding magnetic field. The strength of the nearly radial magnetic field in the outer corona is estimated from the radial component of the interplanetary magnetic field measured by Ulysses. We apply this model to three well-observed CMEs that exploded from flare regions of extremely different size and magnetic setting. One of these CMEs was an over-and-out CME, that is, in the outer corona the CME was laterally far offset from the flare-marked source of the driving magnetic explosion. In each event, the estimated source-region field strength is appropriate for the magnetic setting of the flare. This agreement (1) indicates that CMEs are propelled by the magnetic field of the CME plasmoid pushing against the surrounding magnetic field; (2) supports the magnetic-arch-blowout scenario for over-and-out CMEs; and (3) shows that a CME's final angular width in the outer corona can be estimated from the amount of magnetic flux covered by the source-region flare arcade. Title: Analysis of Erupting Solar Prominences in Terms of an Underlying Flux-Rope Configuration Authors: Krall, Jonathan; Sterling, Alphonse C. Bibcode: 2007ApJ...663.1354K Altcode: Data from four solar prominence eruptions are analyzed so as to examine the flux-rope configuration at the onset of eruption and to test specific aspects of an analytic flux-rope model of solar eruptions. The model encompasses both prominence eruptions and coronal mass ejections (CMEs) as generic elements of a typical erupting flux-rope structure. The hypothesized relationship between prominence footpoint separation and prominence acceleration profile is examined, as is the hypothesized geometrical relationship between the prominence and the CME leading edge (LE). While the simple model does not account for some observed features, the prominence and ``loop'' (LE) data are shown to be consistent with both the geometrical model and the theoretical acceleration profile. This analysis further suggests that the onset of eruption is associated with a situation in which the underlying flux-rope geometry maximizes the outward magnetic ``hoop'' force. Title: Coronal dimming observed with Hinode Authors: Harra, Louise; Hara, H.; Young, P.; Williams, D.; Sterling, A.; Attrill, G. Bibcode: 2007AAS...210.6305H Altcode: 2007BAAS...39..172H Coronal dimming has been a technique used to determine the source of plasma that forms part of a coronal mass ejection. Generally dimming is detected through imaging instruments such as SOHO EIT by taking difference images. In a few cases the SOHO-CDS has been used to determine outflowing material, and a decrease in density. Hinode tracked active region 10930 from which there were a series of flares. We combine dimming observations from EIT with Hinode data to show the impact of flares and coronal mass ejections on the region surrounding the flaring active region, and we discuss evidence that the eruption resulted in a prolonged steady outflow of material from the corona. Title: The Coronal-dimming Footprint of a Streamer-Puff Coronal Mass Ejection: Confirmation of the Magnetic-Arch-Blowout Scenario Authors: Moore, Ronald L.; Sterling, Alphonse C. Bibcode: 2007ApJ...661..543M Altcode: A streamer puff is a recently identified variety of coronal mass ejection (CME) of narrow to moderate width. It (1) travels out along a streamer, transiently inflating the streamer but leaving it largely intact, and (2) occurs in step with a compact ejective flare in an outer flank of the base of the streamer. These aspects suggest the following magnetic-arch-blowout scenario for the production of these CMEs: the magnetic explosion that produces the flare also produces a plasmoid that explodes up the leg of an outer loop of the arcade base of the streamer, blows out the top of this loop, and becomes the core of the CME. In this paper, we present a streamer-puff CME that produced a coronal dimming footprint. The coronal dimming, its magnetic setting, and the timing and magnetic setting of a strong compact ejective flare within the dimming footprint nicely confirm the magnetic-arch-blowout scenario. From these observations, together with several published cases of a transequatorial CME produced in tandem with an ejective flare or filament eruption that was far offset from directly under the CME, we propose the following. Streamer-puff CMEs are a subclass (one variety) of a broader class of ``over-and-out'' CMEs that are often much larger than streamer puffs but are similar to them in that they are produced by the blowout of a large quasi-potential magnetic arch by a magnetic explosion that erupts from one foot of the large arch, where it is marked by a filament eruption and/or an ejective flare. Title: Analysis of Polar Plumes Observed During March 29, 2006 Total Solar Eclipse Authors: Farid, Samaiyah; Winebarger, A.; Oluseyi, H.; Sterling, A.; Tan, A. Bibcode: 2007AAS...210.9508F Altcode: 2007BAAS...39..224F Polar plumes are long lived structures that occur in coronal holes and are thought to be the source region of the slow solar wind. In this poster, we present analysis of polar plumes observed during the March 29, 2006 solar eclipse from Cape Coast, Ghana. We have analyzed SOHO/EIT data of the same time and date of the eclipse to determine how the EUV intensity varies as a function of height. We have developed a steady-state one dimensional hydrodynamic model of plumes that includes a stratified heating rate, area expansion, and a non-zero velocity at the plume base. We have compared the intensity profiles from the model calculated for different heating rates and base velocities with the intensity profiles of the observed plumes. We present the results of our model and the analysis and make a conjecture about the mass contribution of plumes to the solar wind. Title: The Coronal-dimming Footprint Of A Streamer-puff Coronal Mass Ejection: Confirmation Of The Magnetic-arch-blowout Scenario Authors: Moore, Ronald L.; Sterling, A. C. Bibcode: 2007AAS...210.2907M Altcode: 2007BAAS...39..138M A streamer puff is a recently identified variety of coronal mass ejection (CME) of narrow to moderate width. It (1) travels out along a streamer, transiently inflating the streamer but leaving it largely intact, and (2) occurs in step with a compact ejective flare in an outer flank of the base of the streamer. These aspects suggest the following magnetic-arch-blowout scenario for the production of these CMEs: the magnetic explosion that produces the flare also produces a plasmoid that explodes up the leg of an outer loop of the arcade base of the streamer, blows out the top of this loop, and becomes the core of the CME. In this paper, we present a steamer-puff CME that produced a coronal dimming footprint. The coronal dimming, its magnetic setting, and the timing and magnetic setting of a strong compact ejective flare within the dimming footprint nicely confirm the magnetic-arch-blowout scenario. From these observations, together with several published cases of a trans-equatorial CME produced in tandem with an ejective flare or filament eruption that was far offset from directly under the CME, we propose the following. Streamer-puff CMEs are a subclass (one variety) of a broader class of “over-and-out” CMEs that are often much larger than steamer puffs but are similar to them in that they are produced by the blowout of a large quasi-potential magnetic arch by a magnetic explosion that erupts from one foot of the large arch, where it is marked by a filament eruption and/or an ejective flare.

This work was funded by the Heliophysics Division of NASA's Science Mission Directorate. Title: Combined Hinode, STEREO, And TRACE Observations of a Solar Filament Eruption: Evidence For Destabilization By Flux-Cancelation Tether Cutting Authors: Sterling, Alphonse C.; Moore, R. L.; Hinode Team Bibcode: 2007AAS...210.7207S Altcode: 2007BAAS...39R.179S We present observations from Hinode, STEREO, and TRACE of a solar filament eruption and flare that occurred on 2007 March 2. Data from the two new satellites, combined with the TRACE observations, give us fresh insights into the eruption onset process. HINODE/XRT shows soft X-ray (SXR) activity beginning approximately 30 minutes prior to ignition of bright flare loops. STEREO and TRACE images show that the filament underwent relatively slow motions coinciding with the pre-eruption SXR brightenings, and it underwent rapid eruptive motions beginning near the time of flare onset. Concurrent HINODE/SOT magnetograms showed substantial flux cancelation under the filament at the site of the pre-eruption SXR activity. From these observations we infer that progressive tether-cutting reconnection driven by photospheric convection caused the slow rise of the filament and led to its eruption.

NASA supported this work through a NASA Heliosphysics GI grant. Title: Cool-Plasma Jets that Escape into the Outer Corona Authors: Corti, Gianni; Poletto, Giannina; Suess, Steve T.; Moore, Ronald L.; Sterling, Alphonse C. Bibcode: 2007ApJ...659.1702C Altcode: We report on observations acquired in 2003 May during a SOHO-Ulysses quadrature campaign. The UVCS slit was set normal to the radial of the Sun along the direction to Ulysses at 1.7 Rsolar, at a northern latitude of 14.5°. From May 25 to May 28, UVCS acquired spectra of several short-lived ejections that represent the extension at higher altitudes of recursive EIT jets, imaged in He II λ304. The jets were visible also in LASCO images and seem to propagate along the radial to Ulysses. UVCS spectra showed an unusually high emission in cool lines, lasting for about 10-25 minutes, with no evidence of hot plasma. Analysis of the cool line emission allowed us to infer the physical parameters (temperature, density, and outward velocity) of jet plasma and the evolution of these quantities as the jet crossed the UVCS slit. From these quantities, we estimated the energy needed to produce the jet. We also looked for any evidence of the events in the in situ data. We conclude by comparing our results with those of previous works on similar events and propose a scenario that accounts for the observed magnetic setting of the source of the jets and allows the jets to be magnetically driven. Title: Initiation of Coronal Mass Ejections Authors: Moore, Ronald L.; Sterling, Alphonse C. Bibcode: 2006GMS...165...43M Altcode: This paper is a synopsis of the initiation of the strong-field magnetic explosions that produce large, fast coronal mass ejections. The presentation outlines our current view of the eruption onset, based on results from our own observational work and from the observational and modeling work of others. From these results and from physical reasoning, we and others have inferred the basic processes that trigger and drive the explosion. We describe and illustrate these processes using cartoons. The magnetic field that explodes is a sheared-core bipole that may or may not be embedded in surrounding strong magnetic field, and may or may not contain a flux rope before it starts to explode. We describe three different mechanisms that singly or in combination can trigger the explosion: (1) runaway internal tether-cutting reconnection, (2) runaway external tether-cutting reconnection, and (3) ideal MHD instability or loss or equilibrium. For most eruptions, high-resolution, high-cadence magnetograms and chromospheric and coronal movies (such as from TRACE or Solar-B) of the pre-eruption region and of the onset of the eruption and flare are needed to tell which one or which combination of these mechanisms is the trigger. Whatever the trigger, it leads to the production of an erupting flux rope. Using a simple model flux rope, we demonstrate that the explosion can be driven by the magnetic pressure of the expanding flux rope, provided the shape of the expansion is "fat" enough. Title: Wide and Narrow CMEs and their Source Explosions Observed at the Spring 2003 SOHO-Sun-Ulysses Quadrature Authors: Suess, S. T.; Corti, G.; Poletto, G.; Sterling, A.; Moore, R. Bibcode: 2006ESASP.617E.147S Altcode: 2006soho...17E.147S No abstract at ADS Title: Characteristics of EIT Dimmings in Solar Eruptions Authors: Adams, Mitzi; Sterling, A. C. Bibcode: 2006SPD....37.0114A Altcode: 2006BAAS...38..217A Intensity "dimmings" in coronal images are a key feature of solar eruptions. Such dimmings are likely the source locations for much of the material expelled in coronal mass ejections (CMEs). Characteristics such as the timing of the dimmings with respect to the onset of other eruption signatures, and the location of the dimmings in the context of the magnetic field environment of the erupting region, are indicative of the mechanism leading to the eruption. We examine dimmings of six eruptions in images from the EUV Imaging Telescope (EIT) on SOHO, along with supplementary soft X-ray (SXR) data from GOES and the SXR Telescope (SXT) on Yohkoh. We examine the timing of the dimming onset and compare with the time of EUV and SXR brightening and determine the timescale for the recovery from dimming for each event. With line-of-sight photospheric magnetograms from the MDI instrument on SOHO, we determine the magnetic structure of the erupting regions and the locations of the dimmings in those regions. >From our analysis we consider which mechanism likely triggered each eruption: internal tether cutting, external tether cutting ("breakout"), loss of equilibrium, or some other mechanism. Title: Initiation of the Slow-Rise and Fast-Rise Phases of an Erupting Solar Filamentby Localized Emerging Magnetic Field via Microflaring Authors: Sterling, Alphonse C.; Moore, R. L.; Harra, L. K. Bibcode: 2006SPD....37.0823S Altcode: 2006BAAS...38..234S EUV data from EIT show that a filament of 2001 February 28 underwent aslow-rise phase lasting about 6 hrs, before rapidly erupting in a fast-risephase. Concurrent images in soft X-rays (SXRs) from Yohkoh/SXT show that aseries of three microflares, prominent in SXT images but weak in EIT 195 AngEUV images, occurred near one end of the filament. The first and lastmicroflares occurred respectively in conjunction with the start of theslow-rise phase and the start of the fast-rise phase, and the second microflarecorresponded to a kink in the filament trajectory. Beginning within 10 hoursof the start of the slow rise, new magnetic flux emerged at the location of themicroflaring. This localized new flux emergence and the resulting microflares,consistent with reconnection between the emerging field and the sheared sigmoidcore magnetic field holding the filament, apparently caused the slow rise ofthis field and the transition to explosive eruption. For the first time insuch detail, the observations show this direct action of localized emergingflux in the progressive destabilization of a sheared core field in the onset ofa coronal mass ejection (CME). Similar processes may have occurred in otherrecently-studied events.NASA supported this work through NASA SR&T and SEC GI grants. Title: The Origin Of The Sheared Magnetic Fields That Erupt In Flares And Coronal Mass Ejections Authors: Moore, Ronald L.; Sterling, A. C. Bibcode: 2006SPD....37.2001M Altcode: 2006BAAS...38R.247M From a search of the Yohkoh/SXT whole-Sun movie in the years 2000 and 2001, we found 37 flare-arcade events for which there were full-disk magnetograms from SOHO/MDI, coronagraph movies from SOHO/LASCO, and before and after full-disk chromospheric images from SOHO/EIT and/or from ground-based observatories. For each event, the observations show or strongly imply that the flare arcade was produced in the usual way by the eruption of sheared core field (as a flux rope) from along the neutral line inside a mature bipolar magnetic arcade. Two-thirds (25) of these arcades had the normal leading-trailing magnetic polarity arrangement of the active regions in the hemisphere of the arcade, but the other third (12) had reversed polarity, their leading flux being the trailing-polarity remnant of one or more old active regions and their trailing flux being the leading-polarity remnant of one or more other old active regions. >From these observations, we conclude: (1) The sheared core field in a reversed-polarity arcade must be formed by processes in and above the photosphere, not by the emergence of a twisted flux rope bodily from below the photosphere. (2) The sheared core fields in the normal-polarity arcades were basically the same as those in the reversed-polarity arcades: both showed similar sigmoidal form and produced similar explosions (similar flares and CMEs). (3) Hence, the sheared core fields in normal-polarity mature arcades are likely formed mainly by the same processes as in reversed-polarity arcades. (4) These processes should be discernible in high-resolution magnetogram sequences and movies of the photosphere, chromosphere, and corona such those to come from Solar-B.This work was supported by NASA's Science Mission Directorate through its Solar and Heliospheric Physics Supporting Research & Technology program and its Heliophysics Guest Investigators program. Title: Recursive Narrowcmes Within a Coronal Streamer Authors: Bemporad, A.; Sterling, A. C.; Moore, R. L.; Poletto, G. Bibcode: 2005ESASP.600E.153B Altcode: 2005ESPM...11..153B; 2005dysu.confE.153B No abstract at ADS Title: A New Variety of Coronal Mass Ejection: Streamer Puffs from Compact Ejective Flares Authors: Bemporad, A.; Sterling, Alphonse C.; Moore, Ronald L.; Poletto, G. Bibcode: 2005ApJ...635L.189B Altcode: We report on SOHO UVCS, LASCO, EIT, and MDI observations of a series of narrow ejections that occurred at the solar limb. These ejections originated from homologous compact flares whose source was an island of included polarity located just inside the base of a coronal streamer. Some of these ejections result in narrow CMEs (``streamer puffs'') that move out along the streamer. These streamer puffs differ from ``streamer blowout'' CMEs in that (1) while the streamer is transiently inflated by the puff, it is not disrupted, and (2) each puff comes from a compact explosion in the outskirts of the streamer arcade, not from an extensive eruption along the main neutral line of the streamer arcade. From the observations, we infer that each streamer puff is produced by means of the inflation or blowing open of an outer loop of the arcade by ejecta from the compact-flare explosion in the foot of the loop. So, in terms of their production, our streamer puffs are a new variety of CME. Title: Slow-Rise and Fast-Rise Phases of an Erupting Solar Filament, and Flare Emission Onset Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2005ApJ...630.1148S Altcode: We observe the eruption of an active-region solar filament on 1998 July 11 using high time cadence and high spatial resolution EUV observations from the TRACE satellite, along with soft X-ray images from the soft X-ray telescope (SXT) on the Yohkoh satellite, hard X-ray fluxes from the BATSE instrument on the CGRO satellite and from the hard X-ray telescope (HXT) on Yohkoh, and ground-based magnetograms. We concentrate on the initiation of the eruption in an effort to understand the eruption mechanism. Prior to eruption the filament undergoes a slow upward movement in a slow-rise phase with an approximately constant velocity of ~15 km s-1 that lasts about 10 minutes. It then erupts in a fast-rise phase, accelerating to a velocity of ~200 km s-1 in about 5 minutes and then decelerating to ~150 km s-1 over the next 5 minutes. EUV brightenings begin about concurrently with the start of the filament's slow rise and remain immediately beneath the rising filament during the slow rise; initial soft X-ray brightenings occur at about the same time and location. Strong hard X-ray emission begins after the onset of the fast rise and does not peak until the filament has traveled to a substantial altitude (to a height about equal to the initial length of the erupting filament) beyond its initial location. Our observations are consistent with the slow-rise phase of the eruption resulting from the onset of ``tether cutting'' reconnection between magnetic fields beneath the filament, and the fast rise resulting from an explosive increase in the reconnection rate or by catastrophic destabilization of the overlying filament-carrying fields. About 2 days prior to the event, new flux emerged near the location of the initial brightenings, and this recently emerged flux could have been a catalyst for initiating the tether-cutting reconnection. With the exception of the sudden transition from the slow-rise phase to the fast-rise phase in our event, our filament's height-time profile is qualitatively similar to the plot of the erupting flux rope height as a function of time recently computed by Chen and Shibata for a model in which the eruption is triggered by reconnection between an emerging field and another field under the flux rope. Title: Shape and Reconnection of the Exploding Magnetic Field in the Onset of CMEs Authors: Moore, R. L.; Sterling, A. C.; Falconer, D. A.; Gary, G. A. Bibcode: 2005AGUSMSH54B..01M Altcode: From chromospheric and coronal images and line-of-sight and vector magnetograms of magnetic regions that produce CMEs, and from chromospheric and coronal movies of the onsets of CME eruptions, it appears that the magnetic field that explodes to drive the CME is initially the strongly sheared core of a magnetic arcade encasing a polarity dividing line in the magnetic flux. Before or during the onset of the explosion, the sheared core field becomes a flux rope, often carrying chromospheric material within it. For the erupting flux rope to drive the explosion, that is, for its magnetic energy content to decrease in the explosion, the flux rope's cross-sectional area must increase faster than its length. For instance, for isotropic expansion, the area increases as the square of the length, and the magnetic energy content of the flux rope decreases as the inverse of the length. The instability that initiates the eruption of the flux rope might be an ideal MHD kink instability, or might involve runaway tether-cutting reconnection. The reconnection begins below the flux rope (internal to the arcade) when the overall field configuration of the region is effectively that of a single bipole. When the flux rope resides in a multi-bipolar configuration having a magnetic null above the flux rope, the runaway tether-cutting reconnection might begin either below the flux rope or at the null above (external to) the arcade. We present examples of observed CME onsets that illustrate the above alternatives. In each example, reconnection below the flux rope begins early in the eruption. This indicates that internal tether cutting reconnection (classic tether-cutting reconnection) is important in unleashing the CME explosion in all cases, including those in which the explosion may be triggered by MHD kinking or by external reconnection (classic breakout reconnection). Title: Flare Emission Onset in the Slow-Rise and Fast-Rise Phases of an Erupting Solar Filament Observed with TRACE Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2005AGUSMSP44A..02S Altcode: We observe the eruption of an active-region solar filament of 1998 July~11 using high time cadence and high spatial resolution EUV observations from the TRACE satellite, along with soft X-ray images from the soft X-ray telescope (SXT) on the Yohkoh satellite, hard X-ray fluxes from the BATSE instrument on the ( CGRO) satellite and from the hard X-ray telescope (HXT) on Yohkoh, and ground-based magnetograms. We concentrate on the initiation of the eruption in an effort to understand the eruption mechanism. First the filament undergoes slow upward movement in a "slow rise" phase with an approximately constant velocity of ≍ 15~km~s-1 that lasts about 10~min, and then it erupts in a "fast-rise" phase, reaching a velocity of ≍ 200~km~s-1 in about 5~min, followed by a period of deceleration. EUV brightenings begin just before the start of the filament's slow rise, and remain immediately beneath the rising filament during the slow rise; initial soft X-ray brightenings occur at about the same time and location. Strong hard X-ray emission begins after the onset of the fast rise, and does not peak until the filament has traveled a substantial altitude (to a height about equal to the initial length of the erupting filament) beyond its initial location. Our observations are consistent with the slow-rise phase of the eruption resulting from the onset of "tether cutting" reconnection between magnetic fields beneath the filament, and the fast rise resulting from an explosive increase in the reconnection rate or by catastrophic destabilization of the overlying filament-carrying fields. About two days prior to the event new flux emerged near the location of the initial brightenings, and this recently-emerged flux could have been a catalyst for initiating the tether-cutting reconnection. With the exception of the initial slow rise, our findings qualitatively agree with the prediction for erupting-flux-rope height as a function of time in a model discussed by Chen & Shibata~(2000) based on reconnection between emerging flux and a flux rope. NASA supported this work through NASA SR&T and SEC GI grants. Title: X-Ray and EUV Observations of CME Eruption Onset Authors: Sterling, Alphonse C. Bibcode: 2005IAUS..226...27S Altcode: Why CMEs erupt is a major outstanding puzzle of solar physics. Signatures observable at the earliest stages of eruption onset may hold precious clues about the onset mechanism. We summarize and discuss observations from SOHO/EIT in EUV and from Yohkoh/SXT in soft X-rays of the pre-eruption and eruption phases of three CME expulsions, along with the eruptions' magnetic setting inferred from SOHO/MDI magnetograms. Our events involve clearly-observable filament eruptions and multiple neutral lines, and we use the magnetic settings and motions of the filaments to help infer the geometry and behavior of the associated erupting magnetic fields. Pre-eruption and early-eruption signatures include a relatively slow filament rise prior to eruption, and intensity dimmings and brightenings, both in the immediate neighborhood of the "core" (location of greatest magnetic shear) of the erupting fields and at locations remote from the core. These signatures and their relative timings place observational constraints on eruption mechanisms; our recent work has focused on implications for the so-called "tether cutting" and "breakout" models, but the same observational constraints are applicable to any model. Title: Tether-Cutting Energetics of a Solar Quiet Region Prominence Eruption Authors: Sterling, A. C. Bibcode: 2004ASPC..325..395S Altcode: We study the morphology and energetics of a slowly-evolving quiet region solar prominence eruption occurring on 1999 February 8-9 in the solar north polar crown region, using ion{Fe{xv}} EUV 284 AA data from the EUV Imaging Telescope (EIT) on SOHO and soft X-ray data from the soft X-ray telescope (SXT) on Yohkoh. After rising at approximately 1 kmps for about six hours, the prominence accelerates to a velocity of approximately 10 kmps leaving behind EUV and soft X-ray loop arcades of a weak flare in its source region. These flare brightenings are consistent with ``tether-cutting'' reconnection occurring beneath the rising prominence, but they only become apparent about two hours after the prominence's acceleration. Nonetheless, via energetic arguments we show that tether cutting could have been occurring nearer the time of the start of the fast rise, but not yet discernible in SXT images. Therefore we are unable to assess whether tether cutting was responsible for the the prominence's acceleration from these data alone. Title: The Relationship between Prominence Eruptions and Global Coronal Waves Authors: Attrill, G. D. R.; Harra, L. K.; Matthews, S. A.; Foley, C. R.; Sterling, A. C. Bibcode: 2004ASPC..325..409A Altcode: There has been much debate over the physical mechanism for producing global coronal waves (`EIT waves'). In this work, we investigate whether filament eruptions are directly associated with coronal waves. We analyse 45 coronal waves and search for evidence of filament eruptions. We used SOHO-EIT data, and EIT data along with any available ground-based Hα data to search for filament eruptions, and found that more than 50 % of coronal waves are clearly associated with eruptions. The speeds of the coronal waves, and the filament eruptions are similar. We discuss the implications of these results. Title: External and Internal Reconnection in Two Filament-Carrying Magnetic Cavity Solar Eruptions Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2004ApJ...613.1221S Altcode: We observe two near-limb solar filament eruptions, one of 2000 February 26 and the other of 2002 January 4. For both we use 195 Å Fe XII images from the Extreme-Ultraviolet Imaging Telescope (EIT) and magnetograms from the Michelson Doppler Imager (MDI), both of which are on the Solar and Heliospheric Observatory (SOHO). For the earlier event we also use soft X-ray telescope (SXT), hard X-ray telescope (HXT), and Bragg Crystal Spectrometer (BCS) data from the Yohkoh satellite, and hard X-ray data from the BATSE experiment on the Compton Gamma Ray Observatory (CGRO). Both events occur in quadrupolar magnetic regions, and both have coronal features that we infer belong to the same magnetic cavity structures as the filaments. In both cases, the cavity and filament first rise slowly at ~10 km s-1 prior to eruption and then accelerate to ~100 km s-1 during the eruption, although the slow-rise movement for the higher altitude cavity elements is clearer in the later event. We estimate that both filaments and both cavities contain masses of ~1014-1015 and ~1015-1016 g, respectively. We consider whether two specific magnetic reconnection-based models for eruption onset, the ``tether cutting'' and the ``breakout'' models, are consistent with our observations. In the earlier event, soft X-rays from SXT show an intensity increase during the 12 minute interval over which fast eruption begins, which is consistent with tether-cutting-model predictions. Substantial hard X-rays, however, do not occur until after fast eruption is underway, and so this is a constraint the tether-cutting model must satisfy. During the same 12 minute interval over which fast eruption begins, there are brightenings and topological changes in the corona indicative of high-altitude reconnection early in the eruption, and this is consistent with breakout predictions. In both eruptions, the state of the overlying loops at the time of onset of the fast-rise phase of the corresponding filament can be compared with expectations from the breakout model, thereby setting constraints that the breakout model must meet. Our findings are consistent with both runaway tether-cutting-type reconnection and fast breakout-type reconnection, occurring early in the fast phase of the February eruption and with both types of reconnection being important in unleashing the explosion, but we are not able to say which, if either, type of reconnection actually triggered the fast phase. In any case, we have found specific constraints that either model, or any other model, must satisfy if correct. Title: External and Internal Reconnection in Two Filament-Carrying Magnetic-Cavity Solar Eruptions Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2004AAS...204.1804S Altcode: 2004BAAS...36..683S We observe two near-limb solar filament eruptions, one of 2000 February 26 and the other of 2002 January 4, using 195 Å Fe xii\ images from SOHO/EIT and magnetograms from SOHO/MDI\@. For the earlier event we also use soft X-ray data from Yohkoh/SXT, and hard X-ray data from Yohkoh/HXT and CGRO/BATSE\@. Both events occur in quadrupolar magnetic regions, and both have coronal features belonging to the same magnetic-cavity-structures as the filaments. In both cases the cavity and filament have a slow-rise phase of ∼ 10 km s-1 prior to eruption, followed by a fast-rise phase of ∼ 100 km s-1 during eruption. We estimate both filaments and both cavities to contain masses of ∼ 1014-15 g and ∼ 1015-16 g, respectively. We consider two specific magnetic-reconnection-based models for eruption onset, the ``tether cutting'' and the ``breakout'' models. In the earlier event SXT images show an intensity increase during the 12-minute interval over which the fast phase begins, consistent with tether-cutting. Substantial hard X-rays, however, do not occur until after fast eruption is underway, which provides a constraint on the tether-cutting model. Also around the time fast eruption begins there are brightenings and topological changes in the corona indicative of high-altitude reconnection, consistent with breakout. In both eruptions, however, fast rise onset occurs while cavity-related coronal loops are still evolving from ``closed'' to ``open,'' providing constraints on the breakout model. Therefore our findings are consistent with aspects of both models, but we cannot say which, if either, mechanism triggered the fast phase. We have also found specific constraints that either model, or any other eruption-onset model, must satisfy if correct. NASA supported this work through SR&T and SEC GI grants. Title: Evidence for Gradual External Reconnection before Explosive Eruption of a Solar Filament Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2004ApJ...602.1024S Altcode: We observe a slowly evolving quiet-region solar eruption of 1999 April 18, using extreme-ultraviolet (EUV) images from the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) and soft X-ray images from the Soft X-ray Telescope (SXT) on Yohkoh. Using difference images, in which an early image is subtracted from later images, we examine dimmings and brightenings in the region for evidence of the eruption mechanism. A filament rose slowly at about 1 km s-1 for 6 hours before being rapidly ejected at about 16 km s-1, leaving flare brightenings and postflare loops in its wake. Magnetograms from the Michelson Doppler Imager (MDI) on SOHO show that the eruption occurred in a large quadrupolar magnetic region with the filament located on the neutral line of the quadrupole's central inner lobe between the inner two of the four polarity domains. In step with the slow rise, subtle EIT dimmings commence and gradually increase over the two polarity domains on one side of the filament, i.e., in some of the loops of one of the two sidelobes of the quadrupole. Concurrently, soft X-ray brightenings gradually increase in both sidelobes. Both of these effects suggest heating in the sidelobe magnetic arcades, which gradually increase over several hours before the fast eruption. Also, during the slow pre-eruption phase, SXT dimmings gradually increase in the feet and legs of the central lobe, indicating expansion of the central-lobe magnetic arcade enveloping the filament. During the rapid ejection, these dimmings rapidly grow in darkness and in area, especially in the ends of the sigmoid field that erupts with the filament, and flare brightenings begin underneath the fast-moving but still low-altitude filament. We consider two models for explaining the eruption: ``breakout,'' which says that reconnection occurs high above the filament prior to eruption, and ``tether cutting,'' which says that the eruption is unleashed by reconnection beneath the filament. The pre-eruption evolution is consistent with gradual breakout that led to (and perhaps caused) the fast eruption. Tether-cutting reconnection below the filament begins early in the rapid ejection, but our data are not complete enough to determine whether this reconnection began early enough to be the cause of the fast-phase onset. Thus, our observations are consistent with gradual breakout reconnection causing the long slow rise of the filament, but allow the cause of the sudden onset of the explosive fast phase to be either a jump in the breakout reconnection rate or the onset of runaway tether-cutting reconnection, or both. Title: Solar Spicules: Prospects for Breakthroughs in Understanding with Solar-B Authors: Sterling, A. Bibcode: 2004cosp...35.2435S Altcode: 2004cosp.meet.2435S Spicules densely populate the lower solar atmosphere; any image or movie of the chromosphere shows a plethora of them or their "cousins," such as mottles or fibrils. Yet despite several decades of effort we still do not know the mechanism that generates them, or how important their contribution is to the material and energy balance of the overall solar atmosphere. Solar-B will provide exciting new chromospheric observations at high time- and spatial-resolution, along with associated quality magnetic field data, that promise to open doors to revolutionary breakthroughs in spicule research. In this presentation we will review the current observational and theoretical status of spicule studies, and discuss prospects for advances in spicule understanding during the Solar-B era. Title: Solar 'EIT Waves' - What are They? Authors: Harra, L. K.; Sterling, A. C. Bibcode: 2004IAUS..219..498H Altcode: 2003IAUS..219E..65H Using spectral data from the Coronal Diagnostic Spectrometer (CDS) instrument on the Solar and Heliospheric Observatory (SOHO) spacecraft we observe a coronal wave feature which occurred in association with a solar eruption and flare on 1998 June~13. EUV images from the Transition Region and Coronal Explorer (TRACE) satellite show that the coronal wave consists of two aspects: (1) a ``bright wave'' which shows up prominently in the TRACE difference images moves with a velocity of approximately 200km/s and is followed by a strong dimming region behind it and (2) a ``weak wave'' which is faint in the TRACE images has a velocity of about 500km/s and appears to disperse out of the bright wave. A ``high-velocity'' CDS feature however occurs after the weak wave passes which appears to correspond to ejection of cool filament-like material in TRACE images. Our observations have similarities with a numerical simulation model of coronal waves presented by Chen etal (2002) who suggests that coronal waves consist of a faster-propagating piston-driven portion and a more slowly-propagating portion due to the opening of field lines associated with an erupting filament. Title: Tether-cutting Energetics of a Solar Quiet-Region Prominence Eruption Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2003ApJ...599.1418S Altcode: We study the morphology and energetics of a slowly evolving quiet-region solar prominence eruption occurring on 1999 February 8-9 in the solar north polar crown region, using soft X-ray data from the soft X-ray telescope (SXT) on Yohkoh and Fe XV EUV 284 Å data from the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO). After rising at ~1 km s-1 for about six hours, the prominence accelerates to a velocity of ~10 km s-1, leaving behind EUV and soft X-ray loop arcades of a weak flare in its source region. Intensity dimmings occur in the eruption region cospatially in EUV and soft X-rays, indicating that the dimmings result from a depletion of material. Over the first two hours of the prominence's rapid rise, flarelike brightenings occur beneath the rising prominence that might correspond to ``tether-cutting'' magnetic reconnection. These brightenings have heating requirements of up to ~1028-1029 ergs, and this is comparable to the mechanical energy required for the rising prominence over the same time period. If the ratio of mechanical energy to heating energy remains constant through the early phase of the eruption, then we infer that coronal signatures for the tether cutting may not be apparent at or shortly after the start of the fast phase in this or similar low-energy eruptions, since the plasma-heating energy levels would not exceed that of the background corona. Title: Tether-Cutting Energetics of a Solar Quiet Region Prominence Eruption Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2003AGUFMSH22A0182S Altcode: We study the morphology and energetics of a slowly-evolving quiet region solar prominence eruption occurring on 1999 February 8---9 in the solar north polar crown region, using Fe~xv EUV 284~Å data from the EUV Imaging Telescope (EIT) on SOHO and soft X-ray data from the soft X-ray telescope (SXT) on Yohkoh. After rising at ≈ 1~km~s-1 for about six hours, the prominence accelerates to a velocity of ≈ 10~km~s-1, leaving behind EUV and soft X-ray loop arcades of a weak flare in its source region. Intensity dimmings occur in the eruption region cospatially in EUV and soft X-rays, indicating that the dimmings result from a depletion of material. Over the first two hours of the prominence's rapid rise, flare-like brightenings occur beneath the rising prominence which may correspond to ``tether cutting'' magnetic reconnection. These brightenings have heating requirements of up to ∼ 1028---1029~ergs, and this is comparable to the mechanical energy required for the rising prominence over the same time period. If the ratio of mechanical energy to heating energy remains constant through the early phase of the eruption, then we infer that coronal signatures for the tether cutting may not be apparent at or shortly after the start of the faster-rise phase of the prominence in this or similar low-energy eruptions, since the plasma-heating energy levels would not exceed that of the background corona. Our findings have strong implications for the correct use of observations in testing theoretical ideas for the onset of solar eruptions. Title: A near-solar-cycle's worth of CME studied with Yohkoh Authors: Sterling, Alphonse C. Bibcode: 2003ESASP.535..415S Altcode: 2003iscs.symp..415S Yohkoh observed the Sun virtually continuously between August 1991 and December 2001, covering nearly a complete solar cycle. Among the instruments on board was the Soft X-ray Telescope (SXT), which gave us fresh perspectives on the dynamic nature of the solar corona. Data from Yohkoh, and from SXT in particular, are helping us undertstand the nature of Coronal Mass Ejections (CMEs). Although CMEs were a topic of interest from the start of the mission, major progress in relating Yohkoh observations to CMEs began in late 1996, following the start of observations of CMEs with the instruments on board the SOHO satellite. Since then we have learned much by combining the direct and indirect observations of CMEs from SOHO, with the coronal observations from SXT. We now have both an improved understanding of, and new questions about: the coronal source regions of CMEs, the nature of the material ejected in CMEs, the relation between CMEs and soft X-ray flares, and the underlying mechanism driving general solar eruptions. Title: Evidence for Gradual External Reconnection Leading to Explosive Eruption of a Solar Filament Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2003SPD....34.2301S Altcode: 2003BAAS...35..851S We observe a slowly-evolving quiet region solar eruption of 1999 April 18, using images in 195 Å Fe xii from EIT on SOHO, and in soft X-rays from SXT on Yohkoh. We examine dimmings and brightenings in difference images, where an early image is subtracted from later images, for evidence of the eruption mechanism. A filament rose slowly at about 1 km s-1 for six hours before being rapidly ejected at about 10 km s-1, leaving flare brightenings and post-flare loops in its wake. SOHO MDI data show that the eruption occurred in a quadrupolar region, with the filament location splitting the four magnetic sources. During the slow rise, subtle EIT dimmings occur between the filament and one of the remote magnetic regions. Concurrently, soft X-ray brightenings occur between the filament and either remote magnetic region. Both of these effects suggest temperature enhancements in magnetic loop systems on either side of the filament prior to eruption. Pre-eruption SXT dimmings occur on either side of and very close to the slowly rising filament, indicating expansion of enveloping magnetic loops. At the start of the rapid ejection, intense dimmings occur at the locations evacuated by the filament, and brightenings occur underneath the fast-moving but still low-altitude filament. We consider two models for explaining the eruption: ``breakout,'' which says that reconnection occurs high above the filament prior to eruption, and ``tether cutting,'' which says that the eruption is driven by reconnecting field lines beneath the filament. We find that pre-eruption evolution is consistent with breakout. Tether cutting-type reconnection occurs during the rapid ejection, but our data are not complete enough to determine whether that reconnection is the primary cause of the fast-phase onset. Title: Imaging and Spectroscopic Investigations of a Solar Coronal Wave: Properties of the Wave Front and Associated Erupting Material Authors: Harra, Louise K.; Sterling, Alphonse C. Bibcode: 2003ApJ...587..429H Altcode: Using spectral data from the Coronal Diagnostic Spectrometer (CDS) instrument on the Solar and Heliospheric Observatory spacecraft, we observe a coronal wave feature (often referred to as an EIT wave) that occurred in association with a solar eruption and flare on 1998 June 13. EUV images from the Transition Region and Coronal Explorer (TRACE) satellite show that the coronal wave consists of two aspects: (1) a ``bright wave,'' which shows up prominently in the TRACE difference images, moves with a velocity of approximately 200 km s-1, and is followed by a strong dimming region behind it and (2) a ``weak wave,'' which is faint in the TRACE images, has a velocity of about 500 km s-1, and appears to disperse out of the bright wave. The weak wave passes through the CDS field of view but shows little or no line-of-sight motions in CDS spectra (velocities less than about 10 km s-1). Only a small portion of the bright wave passes the CDS field of view, with the spectral lines showing insignificant shifts. A high-velocity CDS feature, however, occurs after the weak wave passes, which appears to correspond to ejection of cool, filament-like material in TRACE images. Our observations have similarities with a numerical simulation model of coronal waves presented by Chen et al., who suggest that coronal waves consist of a faster propagating, piston-driven portion and a more slowly propagating portion due to the opening of field lines associated with an erupting filament. Title: Doppler Detection of Material Outflows from Coronal Intensity ``Dimming Regions'' During Coronal Mass Ejection Onset Authors: Sterling, A.; Harra, Louise Bibcode: 2002AAS...200.3709S Altcode: 2002BAAS...34..696S ``Coronal dimmings,'' localized regions showing a precipitous drop in EUV or X-ray emission, are a key coronal signature of the sources of Coronal Mass Ejections (CMEs). Researchers often assume that dimmings result from a depletion of coronal material (i.e., a decrease in density along the line-of-sight), even when no obvious moving structure can be detected in images. Yet, this explanation has not been unambiguously established; in principle the dimmings could, for example, be due to a dramatic change in the temperature of the emitting material instead. Here we present the most direct evidence to-date that the dimmings result from mass loss, by observing Doppler motions of material leaving the regions as they dim. Using spectral data from the Coronal Diagnostic Spectrometer (CDS) on SOHO, we observe Doppler shifts in two different events. One of these, from 1998 March 31 near 9 UT, was near the solar limb and was associated with a CME traveling in the plane of the sky, while the other event, from 1999 July 19 near 1:50 UT, was on the solar disk and was associated with an Earth-directed ``halo'' CME\@. The limb event shows Doppler signatures of ≈ 30 km s-1 in coronal (Fe xvi and Mg ix) emission lines, where the enhanced velocities coincide with the locations of coronal dimming. An ``EIT wave'' accompanies the disk event, and a dimming region behind the wave shows strong blue-shifted Doppler signatures of ≈ 100 km s-1 in the O v transition region line. These results provide strong evidence that material from the dimming regions feeds into the CMEs. This work was supported by NASA's SR&T and GI Programs, and by PPARC. Title: SXT and EIT Observations of A Quiet Region Large-Scale Eruption: Implications for Eruption Theories Authors: Sterling, A. C.; Moore, R. L.; Thompson, B. J. Bibcode: 2002mwoc.conf..165S Altcode: We present Yohkoh/SXT and SOHO/EIT observations of a set of slow, large scale, quiet-region solar eruptions. In SXT data, these events seem to appear ``out of nothing,'' indicating that they are associated initially with weak magnetic fields and corresponding low heating rates. These events evolve relatively slowly, affording us an opportunity to examine in detail their development. We look for signatures of the start of the eruptions through intensity variations, physical motions, and dimming signatures in the SXT and EIT data. In particular, we look to see whether the earliest signatures are brightenings occurring in the ``core'' region (i.e., the location where the magnetic shear is strongest and the post-flare loops develop); such early brightenings in the core could be indicative of a ``tether-cutting'' process, whereby the eruption is instigated by magnetic reconnection among highly-sheared core fields. In our best-observed case, we find motions of the core fields beginning well before brightenings in the core. This is new evidence that tether-cutting is not the primary mechanism operating in solar eruptions. Rather, our observations are more consistent with the eruption process known as the ``breakout model'' (Antiochos et al. 1999), which holds that the eruption results from initial slow magnetic reconnections occurring high above (far from) the core region. Title: Contagious Coronal Heating from Recurring Emergence of Magnetic Flux Authors: Moore, R. L.; Falconer, D. A.; Sterling, A. C. Bibcode: 2002mwoc.conf...39M Altcode: For each of six old bipolar active regions, we present and interpret Yohkoh/SXT and SOHO/MDI observations of the development, over several days, of enhanced coronal heating in and around the old bipole in response to new magnetic flux emergence within the old bipole. The observations show: 1. In each active region, new flux emerges in the equatorward side of the old bipole, around a lone remaining leading sunspot and/or on the equatorward end of the neutral line of the old bipole. 2. The emerging field is marked by intense internal coronal heating, and enhanced coronal heating occurs in extended loops stemming from the emergence site. 3. In five of the six cases, a "rooster tail" of coronal loops in the poleward extent of the old bipole also brightens in response to the flux emergence. 4. There are episodes of enhanced coronal heating in surrounding magnetic fields that are contiguous with the old bipole but are not directly connected to the emerging field. From these observations, we suggest that the accommodation of localized newly emerged flux within an old active region entails far reaching adjustments in the 3D magnetic field throughout the active region and in surrounding fields in which the active region is embedded, and that these adjustments produce the extensive enhanced coronal heating. We Also Note That The Reason For The recurrence of flux emergence in old active regions may be that active-region flux tends to emerge in giant-cell convection downflows. If so, the poleward "rooster tail" is a coronal flag of a long-lasting downflow in the convection zone. This work was funded by NASA's Office of Space Science through the Solar Physics Supporting Research and Technology Program and the Sun-Earth Connection Guest Investigator Program. Title: Hα Proxies for EIT Crinkles: Further Evidence for Preflare ``Breakout''-Type Activity in an Ejective Solar Eruption Authors: Sterling, Alphonse C.; Moore, Ronald L.; Qiu, Jiong; Wang, Haimin Bibcode: 2001ApJ...561.1116S Altcode: We present Hα observations from Big Bear Solar Observatory of an eruptive flare in NOAA Active Region 8210, occurring near 22:30 UT on 1998 May 1. Previously, using the EUV Imaging Telescope (EIT) on the SOHO spacecraft, we found that a pattern of transient, localized brightenings, which we call ``EIT crinkles,'' appears in the neighborhood of the eruption near the time of flare onset. These EIT crinkles occur at a location in the active region well separated from the sheared core magnetic fields, which is where the most intense features of the eruption are concentrated. We also previously found that high-cadence images from the Soft X-ray Telescope (SXT) on Yohkoh indicate that soft X-ray intensity enhancements in the core begin after the start of the EIT crinkles. With the Hα data, we find remote flare brightening counterparts to the EIT crinkles. Light curves as functions of time of various areas of the active region show that several of the remote flare brightenings undergo intensity increases prior to the onset of principal brightenings in the core region, consistent with our earlier findings from EIT and SXT data. These timing relationships are consistent with the eruption onset mechanism known as the breakout model, introduced by Antiochos and colleagues, which proposes that eruptions begin with reconnection at a magnetic null high above the core region. Our observations are also consistent with other proposed mechanisms that do not involve early reconnection in the core region. As a corollary, our observations are not consistent with the so-called tether-cutting models, which say that the eruption begins with reconnection in the core. The Hα data further show that a filament in the core region becomes activated near the time of EIT crinkle onset, but little if any of the filament actually erupts, despite the presence of a halo coronal mass ejection (CME) associated with this event. Title: Material Outflows from Coronal Intensity ``Dimming Regions'' during Coronal Mass Ejection Onset Authors: Harra, Louise K.; Sterling, Alphonse C. Bibcode: 2001ApJ...561L.215H Altcode: One signature of expulsion of coronal mass ejections (CMEs) from the solar corona is the appearance of transient intensity dimmings in coronal images. These dimmings have generally been assumed to be due to discharge of CME material from the corona, and thus the ``dimming regions'' are thought of as an important signature of the sources of CMEs. We present spectral observations of two dimming regions at the time of expulsion of CMEs, using the Coronal Diagnostic Spectrometer (CDS) on the SOHO satellite. One of the dimming regions is at the solar limb and associated with a CME traveling in the plane of the sky, while the other region is on the solar disk and associated with an Earth-directed ``halo'' CME. From the limb event, we see Doppler signatures of ~30 km s-1 in coronal (Fe XVI and Mg IX) emission lines, where the enhanced velocities coincide with the locations of coronal dimming. This provides direct evidence that the dimmings are associated with outflowing material. We also see larger (~100 km s-1) Doppler velocities in transition region (O V and He I) emission lines, which are likely to be associated with motions of a prominence and loops at transition region temperatures. An ``EIT wave'' accompanies the disk event, and a dimming region behind the wave shows strong blueshifted Doppler signatures of ~100 km s-1 in O V, suggesting that material from the dimming regions behind the wave may be feeding the CME. Title: EIT and SXT Observations of a Quiet-Region Filament Ejection: First Eruption, Then Reconnection Authors: Sterling, Alphonse C.; Moore, Ronald L.; Thompson, Barbara J. Bibcode: 2001ApJ...561L.219S Altcode: We observe a slow-onset quiet-region filament eruption with the EUV Imaging Telescope (EIT) on the Solar Heliospheric Observatory (SOHO) and the soft X-ray telescope (SXT) on Yohkoh. This event occurred on 1999 April 18 and was likely the origin of a coronal mass ejection detected by SOHO at 08:30 UT on that day. In the EIT observation, one-half of the filament shows two stages of evolution: stage 1 is a slow, roughly constant upward movement at ~1 km s-1 lasting ~6.5 hr, and stage 2 is a rapid upward eruption at ~16 km s-1 occurring just before the filament disappears into interplanetary space. The other half of the filament shows little motion along the line of sight during the time of stage 1 but erupts along with the rest of the filament during stage 2. There is no obvious emission from the filament in the SXT observation until stage 2; at that time, an arcade of EUV and soft X-ray loops forms first at the central location of the filament and then expands outward along the length of the filament channel. A plot of EUV intensity versus time of the central portion of the filament (where the postflare loops initially form) shows a flat profile during stage 1 and a rapid upturn after the start of stage 2. This light curve is delayed from what would be expected if ``tether-cutting'' reconnection in the core of the erupting region were responsible for the initiation of the eruption. Rather, these observations suggest that a loss of stability of the magnetic field holding the filament initiates the eruption, with reconnection in the core region occurring only as a by-product. Title: Internal and external reconnection in a series of homologous solar flares Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2001JGR...10625227S Altcode: Using data from the extreme ultraviolet imaging telescope (EIT) on SOHO and the soft X-ray telescope (SXT) on Yohkoh, we examine a series of morphologically homologous solar flares occurring in National Oceanic and Atmospheric Administration (NOAA) active region 8210 over May 1-2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coronal hole to the east is the source of the repeated flaring. An SXT sigmoid parallels the EFR's neutral line at the site of the initial flaring in soft X rays. In EIT each flaring episode begins with the formation of a crinkle pattern external to the EFR. These EIT crinkles move out from, and then in toward, the EFR with velocities ~20 km s-1. A shrinking and expansion of the width of the coronal hole coincides with the crinkle activity, and generation and evolution of a postflare loop system begins near the time of crinkle formation. Using a schematic based on magnetograms of the region, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions but are modified by the presence of the additional magnetic fields of the sunspot and coronal hole. In the schematic, internal reconnection begins inside of the EFR-associated fields, unleashing a flare postflare loops, and a coronal mass ejection (CME). External reconnection, first occurring between the escaping CME and the coronal hole field and second occurring between fields formed as a result of the first external reconnection, results in the EIT crinkles and changes in the coronal hole boundary. By the end of the second external reconnection, the initial setup is reinstated; thus the sequence can repeat, resulting in morphologically homologous eruptions. Our inferred magnetic topology is similar to that suggested in the ``breakout model'' of eruptions [Antiochos, 1998], although we cannot determine if our eruptions are released primarily by the breakout mechanism (external reconnection) or, alternatively, primarily by the internal reconnection. Title: EIT Crinkles as Evidence for the Breakout Model of Solar Eruptions Authors: Sterling, Alphonse C.; Moore, Ronald L. Bibcode: 2001ApJ...560.1045S Altcode: We present observations of two homologous flares in NOAA Active Region 8210 occurring on 1998 May 1 and 2, using EUV data from the EUV Imaging Telescope (EIT) on board the Solar and Heliospheric Observatory, high-resolution and high-time cadence images from the soft X-ray telescope on Yohkoh, images or fluxes from the hard X-ray telescope on Yohkoh and the BATSE experiment on board the Compton Gamma Ray Observatory, and Ca XIX soft X-ray spectra from the Bragg crystal spectrometer (BCS) on Yohkoh. Magnetograms indicate that the flares occurred in a complex magnetic topology, consisting of an emerging flux region (EFR) sandwiched between a sunspot to the west and a coronal hole to the east. In an earlier study we found that in EIT images, both flaring episodes showed the formation of a crinkle-like pattern of emission (``EIT crinkles'') occurring in the coronal hole vicinity, well away from a central ``core field'' area near the EFR-sunspot boundary. With our expanded data set, here we find that most of the energetic activity occurs in the core region in both events, with some portions of the core brightening shortly after the onset of the EIT crinkles, and other regions of the core brightening several minutes later, coincident with a burst of hard X-rays there are no obvious core brightenings prior to the onset of the EIT crinkles. These timings are consistent with the ``breakout model'' of solar eruptions, whereby the emerging flux is initially constrained by a system of overlying magnetic field lines, and is able to erupt only after an opening develops in the overlying fields as a consequence of magnetic reconnection at a magnetic null point. In our case, the EIT crinkles would be a signature of this pre-impulsive phase magnetic reconnection, and brightening of the core only occurs after the core fields begin to escape through the newly created opening in the overlying fields. Morphology in soft X-ray images and properties in hard X-rays differ between the two events, with complexities that preclude a simple determination of the dynamics in the core at the times of eruption. From the BCS spectra, we find that the core region expends energy at a rate of ~1026 ergs s-1 during the time of the growth of the EIT crinkles; this rate is an upper limit to energy expended in the reconnections opening the overlying fields. Energy losses occur at an order of magnitude higher rate near the time of the peak of the events. There is little evidence of asymmetry in the spectra, consistent with the majority of the mass flows occurring normal to the line of sight. Both events have similar electron temperature dependencies on time. Title: Velocity observations of an active region during the onset phase of a coronal mass ejection Authors: Harra, Louise K.; Sterling, Alphonse C. Bibcode: 2001ESASP.493..237H Altcode: 2001sefs.work..237H No abstract at ADS Title: Energetics of an Active Region Observed from Helium-Like Sulphur Lines Authors: Watanabe, Tetsuya; Sterling, Alphonse C.; Hudson, Hugh S.; Harra, Louise K. Bibcode: 2001SoPh..201...71W Altcode: We report temperature diagnostics derived from helium-like ions of sulphur for an active region NOAA 7978 obtained with Bragg Crystal Spectrometer (BCS) on board the Yohkoh satellite. For the same region we estimate conductive flux downward to the chromosphere by the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO) satellite. This region appeared as a region of soft X-ray enhancement in May 1996, underwent a period of enhanced activity coinciding with flux emergence between 6 July and 12 July, and then continued to exist in a nearly flareless state for several solar rotations until November 1996. Energy balance of the non-flaring active region is basically consistent with a model of an arcade of coronal loops having an average loop-top temperature of 4×106 K. Energy from flare activity during a period of flux emergence is comparable to the energy requirements of the non-flaring active region. However, the non-flaring energy is roughly constant for the subsequent solar rotations following the birth of the active region even after the flare activity essentially subsided. Energy partition between flare activity and steady active-region heating thus varies significantly over the lifetime of the active region, and active-region emission cannot always be identified with flaring. Title: Onset of the Magnetic Explosion in Solar Flares and Coronal Mass Ejections Authors: Moore, Ronald L.; Sterling, Alphonse C.; Hudson, Hugh S.; Lemen, James R. Bibcode: 2001ApJ...552..833M Altcode: We present observations of the magnetic field configuration and its transformation in six solar eruptive events that show good agreement with the standard bipolar model for eruptive flares. The observations are X-ray images from the Yohkoh soft X-ray telescope (SXT) and magnetograms from Kitt Peak National Solar Observatory, interpreted together with the 1-8 Å X-ray flux observed by GOES. The observations yield the following interpretation. (1) Each event is a magnetic explosion that occurs in an initially closed single bipole in which the core field is sheared and twisted in the shape of a sigmoid, having an oppositely curved elbow on each end. The arms of the opposite elbows are sheared past each other so that they overlap and are crossed low above the neutral line in the middle of the bipole. The elbows and arms seen in the SXT images are illuminated strands of the sigmoidal core field, which is a continuum of sheared/twisted field that fills these strands as well as the space between and around them. (2) Although four of the explosions are ejective (appearing to blow open the bipole) and two are confined (appearing to be arrested within the closed bipole), all six begin the same way. In the SXT images, the explosion begins with brightening and expansion of the two elbows together with the appearance of short bright sheared loops low over the neutral line under the crossed arms and, rising up from the crossed arms, long strands connecting the far ends of the elbows. (3) All six events are single-bipole events in that during the onset and early development of the explosion they show no evidence for reconnection between the exploding bipole and any surrounding magnetic fields. We conclude that in each of our events the magnetic explosion was unleashed by runaway tether-cutting via implosive/explosive reconnection in the middle of the sigmoid, as in the standard model. The similarity of the onsets of the two confined explosions to the onsets of the four ejective explosions and their agreement with the model indicate that runaway reconnection inside a sheared core field can begin whether or not a separate system of overlying fields, or the structure of the bipole itself, allows the explosion to be ejective. Because this internal reconnection apparently begins at the very start of the sigmoid eruption and grows in step with the explosion, we infer that this reconnection is essential for the onset and growth of the magnetic explosion in eruptive flares and coronal mass ejections. Title: EIT Crinkles as Evidence for the Breakout Model of Solar Eruptions Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2001AGUSM..SH51B02S Altcode: Ejective solar eruptions generally involve: (i) a strong magnetic field ``core'' region, which envelops a magnetic inversion line and is the site of the earliest post-flare loop footpoints, and (ii) weaker magnetic fields surrounding the core. Determining whether the eruption begins in the core or in the surrounding fields is vital to understanding the eruption process. Here we discuss observational tests of two different models with opposing views on where the eruption begins. The ``tether-cutting model'' suggests that magnetic reconnection among fields in the core is the primary cause of the eruption; in this case, we expect the earliest signature of the start of the eruption to be brightenings inside the core. In contrast, the ``breakout model'' (Antiochos et al.~1999, ApJ, 510, 485) suggests that the eruption begins when overlying coronal fields are eroded away by low-energy reconnection far from the core; in this case, we would expect initial brightenings at sites remote from the core. To test these ideas, we examine relative timings of brightenings inside and outside the core region of a series of homologous flares in NOAA AR~8210 over 1998 May 1-2. As we previously reported (Sterling and Moore 2001, JGR, in press), these events displayed a crinkle-like pattern of emission in EIT 195 images (``EIT crinkles'') near the time of the eruptions, at locations remote from the core. We examine the onset of these remote brightenings relative to the core brightenings, observing the core using EIT data and high-cadence ( ~ 10~s), high resolution (2.5'' pixels) data from the Soft X-ray Telescope (SXT) on Yohkoh. We find that the EIT crinkles precede the core brightenings by several minutes, which is consistent with the breakout model, but inconsistent with the tether-cutting model. ACS is an NRC---MSFC Research Associate. Title: Sigmoid CME source regions at the Sun: some recent results Authors: Sterling, A. C. Bibcode: 2000JASTP..62.1427S Altcode: 2000JATP...62.1427S Identifying coronal mass ejection (CME) precursors in the solar corona would be an important step in space weather forecasting, as well as a vital key to understanding the physics of CMEs. Twisted magnetic field structures are suspected of being the source of at least some CMEs. These features can appear sigmoid (S or inverse-S) shaped in soft X-ray (SXR) images. We review recent observations of these structures and their relation to CMEs, using SXR data from the Soft X-ray Telescope (SXT) on the Yohkoh satellite, and EUV data from the EUV Imaging Telescope (EIT) on the SOHOsatellite. These observations indicate that the pre-eruption sigmoid patterns are more prominent in SXRs than in EUV, and that sigmoid precursors are present in over 50% of CMEs. These findings are important for CME research, and may potentially be a major component to space weather forecasting. So far, however, the studies have been subject to restrictions that will have to be relaxed before sigmoid morphology can be used as a reliable predictive tool. Moreover, some CMEs do not display a SXR sigmoid structure prior to eruption, and some others show no prominent SXR signature of any kind before or during eruption. Title: Solar Spicules: A Review of Recent Models and Targets for Future Observations - (Invited Review) Authors: Sterling, Alphonse C. Bibcode: 2000SoPh..196...79S Altcode: Since their discovery over 100 years ago, there have been many suggestions for the origin and development of solar spicules. Because the velocities of spicules are comparable to the sound and Alfvén speeds of the low chromosphere, linear theory cannot fully describe them. Consequently, detailed tests of theoretical ideas had to await the development of computing power that only became available during the 1970s. This work reviews theories for spicules and spicule-like features over approximately the past 25 years, with an emphasis on the models based on nonlinear numerical simulations. These models have given us physical insight into wave propagation in the solar atmosphere, and have helped elucidate how such waves, and associated shock waves, may be capable of creating motions and structures on magnetic flux tubes in the lower solar atmosphere. So far, however, it has been difficult to reproduce the most-commonly-quoted parameters for spicules with these models, using what appears to be the most suitable input parameters. A key impediment to developing satisfactory models has been the lack of reliable observational information, which is a consequence of the small angular size and transient lifetime of spicules. I close with a list of key observational questions to be addressed with space-based satellites, such as the currently operating TRACE satellite, and especially the upcoming Solar-B mission. Answers to these questions will help determine which, if any, of the current models correctly explains spicules. Title: Internal and External Reconnection in a Series of Homologous Solar Flares Authors: Sterling, A. C.; Moore, R. L. Bibcode: 2000SPD....31.1405S Altcode: 2000BAAS...32..847S Using data from the Extreme Ultraviolet Telescope (EIT) on SOHO and the Soft X-ray Telescope (SXT) on Yohkoh, we examine a series of morphologically homologous solar flares occurring in NOAA AR 8210 over May 1---2, 1998. An emerging flux region (EFR) impacted against a sunspot to the west and next to a coronal hole to the east is the source of the repeated flaring. An SXT sigmoid traces the EFR's neutral line at the site of the initial flaring in soft X-rays. In EIT, each flaring episode begins with the formation of a crinkle pattern external to the EFR\@. These EIT crinkles move out from, and then in toward, the EFR with velocities ~ 20 km s-1. A shrinking and expansion of the width of the coronal hole coincides with the crinkle activity, and generation and evolution of a postflare loop system begins near the time of crinkle formation. Using a schematic based on magnetograms of the region, we suggest that these observations are consistent with the standard reconnection-based model for solar eruptions, but modified by the presence of the additional magnetic fields of the sunspot and coronal hole. In the schematic, internal reconnection begins inside of the EFR-associated fields, unleashing a flare, postflare loops, and a CME\@. External reconnection, occurring between the escaping CME and the surrounding fields, results in the EIT crinkles and changes in the coronal hole boundary. Our inferred magnetic topology is similar to that suggested in the ` ` breakout model" of eruptions [Antiochos, 1998], although we cannot determine if the ultimate source of the eruptions in this case is due to the breakout mechanism or, alternatively, is primarily released by the internal reconnection. ACS is an NRC---MSFC Research Associate Title: Yohkoh SXT and SOHO EIT Observations of Sigmoid-to-Arcade Evolution of Structures Associated with Halo Coronal Mass Ejections Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Thompson, Barbara J.; Zarro, Dominic M. Bibcode: 2000ApJ...532..628S Altcode: A subset of the solar-disk counterparts to halo coronal mass ejections (CMEs) displays an evolution in soft X-rays (SXR) that is characterized by a preflare S-shaped structure, dubbed a ``sigmoid,'' which evolves into a postflare cusp or arcade. We examine the morphological properties of the evolution of sigmoids into cusps and arcades for four such regions associated with SXR flares, using the Soft X-Ray Telescope (SXT) on the Yohkoh satellite and the EUV Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO) satellite. Most of our EIT observations are with the 1.5 MK 195 Å Fe XII channel. At most, there is only a weak counterpart to the SXR sigmoid in the preflare 195 Å EUV images, indicating that the preflare sigmoid has a temperature greater than 1.5 MK. While more identifiable than in the 195 Å channel, a clear preflare sigmoid is also not observed in the 2.0 MK EIT 284 Å Fe XV channel. During the time of the flare, however, an EUV sigmoid brightens near the location of the SXR preflare sigmoid. Initially the SXR sigmoid lies along a magnetic neutral line. As the SXR flare progresses, new field lines appear with orientation normal to the neutral line and with footpoints rooted in regions of opposite polarity; these footpoints are different from those of the preflare sigmoid. The cusp structures in SXRs develop from these newly ignited field lines. In EIT images, the EUV sigmoid broadens as the flare progresses, forming an arcade beneath the SXR cusp. Our findings are consistent with a standard picture in which the origin of the flare and CME is caused by the eruption of a filament-like feature, with the stretching of field lines producing a cusp. We infer that the cusp-producing fields may be overlying the sigmoid fields in the preflare phase, but we do not directly observe such preflare overlying fields. Title: Variation of Thermal Structure with Height of a Solar Active Region Derived from SOHO CDS and YOHKOH BCS Observations Authors: Sterling, Alphonse C.; Pike, C. D.; Mason, Helen E.; Watanabe, Tetsuya; Antiochos, Spiro K. Bibcode: 1999ApJ...524.1096S Altcode: We present observations of NOAA solar Active Region 7999 when it was near the west solar limb on 1996 December 2 and 3, using data from the Coronal Diagnostic Spectrometer (CDS) experiment on the SOHO satellite. Ratios of intensities of 2 MK material (as observed in CDS Fe XVI images) to 1 MK material (from CDS Mg IX images) indicate that there is a drop in the ratio of the hotter to the cooler material with height in the region, up to an altitude of about 105 km. At low altitudes the relative amount of 2 MK emission measure to 1 MK emission measure ranges from 8 to 10, while the ratio is minimum near 105 km, ranging from 1.3 to 3.5. The decrease with height of the CDS ratio qualitatively resembles the decrease in S XV election temperature with height (measurable up to ~85,000 km) in the same active region obtained from the Bragg crystal spectrometer instrument on Yohkoh. The CDS images indicate that the highest S XV temperatures and largest CDS ratios correspond to regions of microflares, and somewhat lower S XV temperatures and CDS ratios correspond to diffuse regions. Above 105 km, the trend of the CDS ratios changes, either increasing or remaining approximately constant with height. At these altitudes the CDS images show faint, large-scale diffuse structures. Title: SOHO EIT Observations of Extreme-Ultraviolet ``Dimming'' Associated with a Halo Coronal Mass Ejection Authors: Zarro, Dominic M.; Sterling, Alphonse C.; Thompson, Barbara J.; Hudson, Hugh S.; Nitta, Nariaki Bibcode: 1999ApJ...520L.139Z Altcode: A solar flare was observed on 1997 April 7 with the Soft X-ray Telescope (SXT) on Yohkoh. The flare was associated with a ``halo'' coronal mass ejection (CME). The flaring region showed areas of reduced soft X-ray (SXR) brightness--``dimmings''--that developed prior to the CME observed in white light and persisted for several hours following the CME. The most prominent dimming regions were located near the ends of a preflare SXR S-shaped (sigmoid) feature that disappeared during the event, leaving behind a postflare SXR arcade and cusp structure. Based upon these and similar soft X-ray observations, it has been postulated that SXR dimming regions are the coronal signatures (i.e., remnants) of magnetic flux ropes ejected during CMEs. This Letter reports new observations of coronal dimming at extreme-ultraviolet (EUV) wavelengths obtained with the Extreme-ultraviolet Imaging Telescope (EIT) on the Solar and Heliospheric Observatory (SOHO). A series of EIT observations in the 195 Å Fe XII wavelength band were obtained simultaneously with SXT during the 1997 April 7 flare/CME. The EIT observations show that regions of reduced EUV intensity developed at the same locations and at the same time as SXR dimming features. The decrease in EUV intensity (averaged over each dimming region) occurred simultaneously with an increase in EUV emission from flaring loops in the active region. We interpret these joint observations within the framework of flux-rope eruption as the cause of EUV and SXR coronal dimmings, and as the source of at least part of the CME. Title: Electron temperatures of a late-phase solar active region from it YOHKOH BCS and SXT observations Authors: Sterling, Alphonse C. Bibcode: 1999A&A...346..995S Altcode: We deduce electron temperatures in a 2-3 month old active region from 1996 September and October, using soft X-ray S Xv spectra from the Bragg Crystal Spectrometer (BCS) and images from the Soft X-ray Telescope (SXT), both on board the Yohkoh satellite. Our observations cover a full transit of the region, from before its appearance around the east limb until after it disappeared around the west limb. Over most of this transit the region is diffuse and extremely quiescent, with few strong X-ray intensity enhancements (microflares) seen in plots of the GOES flux. During the passage the region's temperature is roughly constant at 2.5+/-0.2 MK in S Xv and at 1.9+/-0.1 MK from SXT, with emission measures of about 10(48) cm(-3) for both instruments. Temperatures obtained from SXT are consistently lower then the S Xv values, indicating a multithermal plasma. A high-temperature (>~ 5 MK) component, seen in younger active regions, is virtually absent in this mature active region. Our findings, combined with earlier work, provide a method for estimating S Xv temperatures of structures based on their intensity in SXT, even when these structures are not isolated on the Sun and hence not directly resolvable with the full-Sun BCS instrument. Our work also suggests that old active regions form a fundamental component of the quiet-Sun corona during periods of high solar activity. Title: YOHKOH SXT and SOHO EIT Observations of ``Sigmoid-to-Arcade'' Evolution of Structures Associated with Halo CMEs Authors: Sterling, A. C.; Hudson, H. S.; Thompson, B. J.; Zarro, D. M. Bibcode: 1999AAS...19410107S Altcode: 1999BAAS...31..999S A subset of the solar-disk counterparts to halo coronal mass ejections (CMEs) display an evolution in soft X-rays (SXR) characterized by a preflare ``S''-shaped structure, dubbed a ``sigmoid,'' evolving into a postflare cusp or arcade. We examine the morphological properties of the evolution of sigmoids into cusps and arcades for four such regions associated with SXR flares, using the Soft X-ray Telescope (SXT) on Yohkoh and the 195 Angstroms Fe xii\ channel of the EUV Imaging Telescope (EIT) on SOHO. There is, at most, only a weak counterpart to the SXR sigmoid in the preflare EUV images, indicating that the preflare sigmoid has a temperature >1.5 MK\@. During the time of the flare itself, however, an EUV sigmoid brightens near the location of the SXR preflare sigmoid. Initially the SXR sigmoid lies along a magnetic neutral line. As the SXR flare progresses new field lines appear with orientation normal to the neutral line and with footpoints rooted in opposite polarity regions; these footpoints are different from those of the preflare sigmoid. The cusp structures in SXRs develop from these newly-ignited field lines. In EIT images the EUV sigmoid broadens out as the flare progresses, forming an arcade which resides beneath the SXR cusp. In many respects, our findings are consistent with a standard picture where the origin of the flare and CME is due to the eruption of a filament-like feature, and the stretching of overlying preflare fields produces the cusp. We do not, however, observe these preflare overlying fields prior to flare onset. This work was supported by the NRL Naval basic research program and NASA. Title: Alfvénic Resonances on Ultraviolet Spicules Authors: Sterling, Alphonse C. Bibcode: 1998ApJ...508..916S Altcode: We consider the propagation of small-amplitude torsional Alfvén waves on spicule-like structures seen at UV and EUV wavelengths. We assume that such UV spicules have densities an order of magnitude lower than chromospheric spicules. Extending the earlier analysis of Sterling & Hollweg, we find that UV spicules can act as resonance cavities, whereby Alfvén waves of preferred frequencies have strong transmission into the structures. The resonance cavity forms because of the sharp changes in Alfvén velocity between the photosphere/chromosphere and the UV spicule at the UV spicule's base and between the UV spicule and the corona at the top of the UV spicule. For a canonical UV spicule residing on a magnetic flux tube of strength B0 = 40 G with length L = 10,000 km and density ρ = 1.0 × 10-14 g cm-3, we predict a fundamental resonance period of about 35 s, some 3 times shorter than for a corresponding chromospheric spicule. Velocities along the length of the UV spicule vary from about 30 to 150 km s-1, increasing with height along the structure. Longer UV spicules have longer resonance periods and lower rotational velocities, and stronger magnetic fields result in shorter resonance periods and higher velocities. The same qualitative parameter dependencies also hold for chromospheric spicules. Damping flattens out the velocity amplitude's profile along the structure and reduces the maximum velocity but does not appreciably change the periods of the resonances. Title: X-ray coronal changes during Halo CMEs Authors: Hudson, H. S.; Lemen, J. R.; St. Cyr, O. C.; Sterling, A. C.; Webb, D. F. Bibcode: 1998GeoRL..25.2481H Altcode: Using the Yohkoh soft X-ray images, we examine the coronal structures associated with “halo” coronal mass ejections (CMEs). These may correspond to events near solar disk center. Starting with a list of eleven confirmed halo CMEs over the time range from December 1996 through May 1997, we find seven with surface features identifiable in soft X-rays, with GOES classifications ranging from A1 to M1.3. These have a characteristic pattern of sigmoid → arcade development. In each of these events, the pre-flare structure disrupted during the flare, leaving the appearance of compact transient coronal holes. The four remaining events had weak or indistinguishable signatures in the X-ray images. For the events for which we could see well-defined coronal changes, we confirm our previous result that the estimated mass loss inferred from the soft X-ray dimming is a small fraction of typical CME masses [Sterling & Hudson 1997]. Title: S XV Spectral Properties of an Active Region from the YOHKOH Bragg Crystal Spectrometer Authors: Sterling, A. C. Bibcode: 1998ASSL..229..245S Altcode: 1998opaf.conf..245S No abstract at ADS Title: Numerical simulations of solar spicules Authors: Sterling, A. Bibcode: 1998ESASP.421...35S Altcode: 1998sjcp.conf...35S No abstract at ADS Title: NOAA 7978: the Last best Old-Cycle Region Authors: Hudson, H. S.; Labonte, B. J.; Sterling, A. C.; Watanabe, Te. Bibcode: 1998ASSL..229..237H Altcode: 1998opaf.conf..237H No abstract at ADS Title: Yohkoh SXT Observations of X-Ray ``Dimming'' Associated with a Halo Coronal Mass Ejection Authors: Sterling, Alphonse C.; Hudson, Hugh S. Bibcode: 1997ApJ...491L..55S Altcode: A sudden depletion or intensity ``dimming'' of the X-ray corona sometimes accompanies a solar eruptive flare or coronal mass ejection (CME). We have identified a dimming that occurred just prior to a ``halo'' CME, observed on 1997 April 7 using the Soft X-ray Telescope (SXT) on Yohkoh. Halo CMEs are prime candidates for ``space weather'' effects. The dimming occurred in compact regions near a flare of 14 UT on April 7, over a projected area of about 1020 cm-2, and indicate that a mass of a few times 1014 g was ejected. This is a lower limit imposed by the obscuration of the dimming volume by the brightness of the accompanying flare and other factors. Most of the mass deficit comes from two regions close to the ends of a preflare S-shaped active-region structure, and the resulting dimmings in these regions persisted for more than three days following the flare. A cusp-shaped loop--not apparent prior to the flare--dominates the emission in the flare decay phase, and has a mass comparable to that lost in the dimming regions. Our findings are consistent with the source of the CME being a flux rope that erupted, leaving behind the dimming regions. The cusp-shaped loop probably represents magnetic fields reconfigured or reconnected by the eruption. We do not see an X-ray analog of the wavelike disturbance evident in SOHO EUV images. Title: X-ray spectral observations of a solar active region corona Authors: Sterling, Alphonse C. Bibcode: 1997GeoRL..24.2263S Altcode: We study the X-ray flux and electron temperature variation of the corona above a solar active region. Electron temperatures are determined using data from the S xv channel of the Bragg crystal spectrometer (BCS) instrument on board the Yohkoh satellite. The active region, designated NOAA AR 7999, rotated from just inside the west solar limb to beyond the limb over the period December 2-4, 1996, allowing us to map the electron temperature as a function of height in the active region's corona. Consistent with previous findings, we find two components to the active region coronal temperature, with a hotter (Te ≳5.0 MK) component due to transient flares and microflares, and a cooler component present in between the times of the microflares. There is a steady decrease in the frequency of occurrence of flares and microflares as the occultation progresses, implying that the flaring structures are low lying. For the cool component, the average electron temperature is about 4.5 MK when the region is just inside the limb, and gradually decreases to under 3.0 MK as the region rotates around the limb, indicating that temperature decreases with height. Title: Electron Temperatures of the Corona Above a Solar Active Region Determined from S XV Spectra Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Watanabe, Tetsuya Bibcode: 1997SPD....28.0136S Altcode: 1997BAAS...29..885S We present high resolution soft X-ray spectral observations of the corona above an active region, using data from the Bragg crystal spectrometer (BCS) on board the Yohkoh satellite. We observed NOAA AR 7978 as it rotated beyond the solar limb so that the lower portions of the region were occulted. Long integrations from times after the region had totally disappeared some days later show a substantial background in S xv. Since the background spectrum is featureless, spectral lines obtained from the time of occultation must originate from the upper corona of the active region. Our results support previous findings that the corona consists of two components: a cooler, steady component with T_e ~ 3 MK, and a hotter, transient component in excess of 5 MK. This hotter component is due to microflares; outside the time of microflares there is relatively little or no active region upper coronal plasma with T_e gtrsim 3.5 MK. There is evidence for a decrease in T_e with height for the cool component. Title: Temporal Variations of Solar Flare Spectral Properties: Hard X-Ray Fluxes and Fe XXV, Ca XIX, and Wide-Band Soft X-Ray Fluxes, Temperatures, and Emission Measures Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Lemen, James R.; Zarro, Dominic A. Bibcode: 1997ApJS..110..115S Altcode: We present fluxes, temperatures, and emission measures for nine solar flares, using data from both the Fe XXV and Ca XIX channels of the Bragg Crystal Spectrometer (BCS) experiment on the Yohkoh satellite and from the wide-band soft X-ray spectrometers on the GOES spacecraft. We also present hard X-ray fluxes from the Hard X-ray Telescope (HXT) on Yohkoh and the BATSE spectrometer on the Compton Gamma-Ray Observatory (CGRO). All events occurred during 1992 and ranged in size from GOES class C5 to M2. Three of the events occurred near the solar limb. For each flare we give two sets of plots. The first set shows flux, electron temperature, and emission measures for Fe XXV, Ca XIX, and GOES as functions of time. The second set of plots gives log electron temperature as functions of log (emission measure)1/2 for these three wavelength ranges; we refer to these plots as E1/2-T diagrams. Hard X-ray flux information is included in both sets of plots. Our observations indicate that (1) cooler plasmas are located along the legs of, or are evenly distributed along, the flaring loops, while hotter plasmas are concentrated near the loop tops, (2) peaks in temperature in each of the wavelength bands are closely associated with hard X-ray enhancements, and (3) the emission from both relatively hot and relatively cool flaring plasmas emanates from the same loop or from closely related loops. Title: Electron Temperatures of the Corona Above a Solar Active Region Determined from S XV Spectra Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Watanabe, Tetsuya Bibcode: 1997ApJ...479L.149S Altcode: We present the first high-resolution soft X-ray spectral observations of the corona above an active region, using the Bragg crystal spectrometer (BCS) on board the Yohkoh satellite. We observed NOAA AR 7978 as it rotated beyond the solar limb so that the lower portions of the region were occulted. Long integrations from times after the region had totally disappeared some days later show a substantial, variable background in S XV. Since the background spectrum is featureless, spectral lines obtained from the time of occultation must originate from the upper corona of the active region. Our results support previous findings that the active region corona consists of two components: a cooler, steady component with Te ~ 3 MK and a hotter, transient component in excess of 5 MK. This hotter component is due to microflares; outside the time of microflares there is relatively little or no active region upper coronal plasma with Te >~ 3.5 MK. There is evidence for a decrease in Te with height for the cool component. Title: S XV Spectral Properties of an Active Region from the Yohkoh Bragg Crystal Spectrometer Authors: Sterling, Alphonse C. Bibcode: 1997ApJ...478..807S Altcode: Using the Bragg crystal spectrometer (BCS) on board the Yohkoh satellite, we examine the spectral properties of a solar active region from 1996 March 22-24. Because the region, NOAA AR 7953, was the only one on the Sun over the 3-day period, it was possible to obtain quality spectra for that region alone despite the BCS being a full-Sun instrument. We analyzed about 150 S XV spectra with integration times ranging from about 15 to 3000 s. At least one sub-C-class flare and one C-class flare were observed during the period. Lower level transient brightenings occur nearly continuously in the region. We find average electron temperatures for the nonflaring active region ranging from 5.5 to 6.2 MK, and an average nonthermal velocity of 43.5 +/- 11.8 km s-1 over the 3 days. Temporal variations of S XV values for flux and electron temperature, for electron temperature and emission measure, and for flux and emission measure are all strongly correlated both when the region is nonflaring and when it is flaring. Correlations between nonthermal velocity and flux and between nonthermal velocity and electron temperature are strong when flares are included in the analysis, but the correlation is weak when spectra from times of flares are excluded. It is, however, difficult to deconvolve the contribution of the source distribution to the nonthermal velocity estimate when flux from the region is low. Title: Isolating the Footpoint Characteristics of a Solar Flare Loop Authors: Harra-Murnion, L. K.; Culhane, J. L.; Hudson, H. S.; Fujiwara, T.; Kato, T.; Sterling*, A. C. Bibcode: 1997SoPh..171..103H Altcode: We analyse the physical characteristics of a C5.7 class flare which was observed on 27 September, 1993 using data from the soft X-ray telescope (SXT), the Bragg crystal spectrometer (BCS), and the hard X-ray telescope (HXT) on Yohkoh. The flare takes the form of a simple loop which is much brighter at one of its footpoints than anywhere else for a period of 2 min. During this time there is an increase in the soft X-ray fluxes, and a corresponding peak in hard X-rays. The parameters derived from the hard X-ray and soft X-ray spectra and images are assumed to be from the footpoint. This flare showed two peaks in the non-thermal velocity, the first one simultaneous with the footpoint brightening. The non-thermal velocity corresponding to these first few minutes is unusually large - by a factor of 80%, 68%, and 26% relative to the second peak in the Fexxv, Caxix, and Sxv channels respectively. Title: Active Region Coronal Temperatures from YOHKOH BCS Sxv Spectra Authors: Sterling, A. C.; Hudson, H. S.; Watanabe, T. Bibcode: 1997IAUJD..19E...9S Altcode: Using the Bragg crystal spectrometer (BCS) on board the Yohkoh satellite, we present high resolution soft X-ray spectral observations of the corona above an active region. We observed NOAA AR 7978 as it rotated beyond the solar limb so that the lower portions of the region were occulted. Long integrations from times after the region had totally disappeared some days later show a substantial background in Sxv. Since the background spectrum is featureless, spectral lines obtained from the time of occultation must originate from the upper corona of the active region. Our results support previous findings that the active region corona consists of two components: a cooler, steady component with electron temperature T_e ~3 MK, and a hotter, transient component in excess of 5 MK @. This hotter component is due to micro-flares; outside the time of micro-flares there is relatively little or no active region upper coronal plasma with T_e higher than about 3.5 MK @. There is evidence for a decrease in T_e with height for the cool component. Title: Active Region Energetics via Yohkoh/BCS and SOHO/CDS Authors: Watanabe, T.; Sterling, Alphonse C.; Hudson, Hugh S.; Harra-Murnion, Louise K. Bibcode: 1997ESASP.404..723W Altcode: 1997cswn.conf..723W No abstract at ADS Title: YOHKOH Observations of Fe XXVI X-Ray Line Emission from Solar Flares Authors: Pike, C. D.; Phillips, K. J. H.; Lang, J.; Sterling, A.; Watanabe, T.; Hiei, E.; Culhane, J. L.; Cornille, M.; Dubau, J. Bibcode: 1996ApJ...464..487P Altcode: We report on observations from the Bragg Crystal Spectrometer (B CS) on board the Japanese solar flare spacecraft Yohkoh showing Fe XXVI Lyα X-ray line emission at 1.78 Å. Some 75 events over a 2 yr period between 1991 December 6 and 1993 December 31 have been analyzed. The greater sensitivity of the BCS compared with previous instruments has enabled such emission to be detected from a wider group of flares than has previously been possible. The likelihood of detecting Fe XXVI lines in a flare is found to increase sharply with the electron temperature obtained from the Fe XXV line spectrum, also observed by the BCS, and with GOES X-ray class. The width of the Lyα1, line, measured after the impulsive stage, is greater than that determined by thermal Doppler broadening, but this is explained by the nonzero spatial extent of flares. Electron temperatures from the intensity ratio of a nearby feature due to Fe XXV dielectronic satellites and the Fe XXVI Lyα1 line are obtained from new atomic parameters from the superstructure code, details of which are described. This revises earlier calculations that have been extensively used. Comparison of these temperatures with those from the Fe XXV spectra provides evidence for a single loose grouping of flares, with the difference between the two temperatures ranging from nearly zero to about 20 MK. A "superhot" component would seem to be more or less developed according to whether the temperature difference is large or nearly zero. Flares at both extremes are examined in detail. The gradually varying part of the 14-33 keV X-ray emission for these events, as observed by the Hard X-ray Telescope on Yohkoh, has a hardness ratio corresponding to temperatures and emission measures similar to those from Fe XXVI line ratios, pointing to a common origin for their emission. Many of the flares studied occurred in particular active regions with great magnetic complexity, although Fe XXVI flares do not seem to be a distinct class within large X-ray flares. Title: Solar coronal abundances: Some recent X-ray flare observations Authors: Sterling, Alphonse C. Bibcode: 1996AIPC..374..343S Altcode: 1996hesp.conf..343S I review recent elemental abundance studies from X-ray flare spectra obtained with Bragg crystal spectrometer experiments on board the SMM, P78-1, and Yohkoh spacecraft. Using the line-to-continuum method, data from all three satellites indicate an enhancement of the abundance of low-FIP Ca relative to H. But the average magnitude of the enhancement is somewhat uncertain. Flare-to-flare variations in the enhancement are also seen. Fe flare abundances seem to be close to photospheric values, with differing methods giving somewhat differing values. These findings, in conjunction with results for S, leave open the possibility that H may behave as an intermediate-FIP element or that a more complex characterization may apply. Further studies of the Yohkoh data, and studies comparing different analysis methods are needed to clarify these issues. Title: YOHKOH Observations of an Over-the-Limb Solar Flare with Large Spectral Line Shifts Authors: Sterling, Alphonse C.; Harra-Murnion, Louise K.; Hudson, Hugh S.; Lemen, James R. Bibcode: 1996ApJ...464..498S Altcode: We present observations of a solar flare of 1993 April 15 near 9 UT, using data from the Yohkoh Bragg crystal spectrometer (BC S) and soft X-ray telescope (SXT). Observations from SXT indicate that the flare occurred well beyond the solar limb, meaning that our observations are restricted to the uppermost portions of the flaring structure. BCS spectra show strong bulk blueshifts of the spectral line profiles for a short period near the start of the event, followed by an extended period of strong bulk redshifts of the line profiles. Concurrent with these bulk line shifts, the spectra show "blue wing" asymmetries. Both bulk line shifts and blue wings are infrequent characteristics of flares observed near the solar limb. Our observations are consistent with strong upward mass motions occurring on a high-altitude flaring loop oriented edge-on with the Earth. We find nonthermal line broadenings in the spectra which are qualitatively and quantitatively similar to line broadenings in spectra of disk flares. Near peak intensity of the flare, ≤10% of the residual nonthermal broadening can be explained by the spatial distribution of the soft X-ray flaring structure. Title: Temporal Variations of Solar Flare Spectral Properties in CA XIX and GOES Authors: Sterling, A. C.; Hudson, H. S.; Lemen, J. R.; Zarro, D. A. Bibcode: 1996AAS...188.1905S Altcode: 1996BAAS...28..850S Since the advent of space borne X-ray observations, there has been a strong interest in the nature of the X-ray solar flare. Examining the relationships between radiations produced in different portions of the X-ray spectrum gives us information on the properties of the constituent flaring plasmas. We have studied the joint variation of electron temperatures and emission measures for a number of flares in two different wavelength ranges, using data from the narrow band Ca xix channel (near 3.18 Angstroms) of the Bragg crystal spectrometer (BCS) experiment on board the Yohkoh spacecraft, and data from the wide band X-ray monitors on the Geostationary Operational Environmental Satellites (GOES, covering 0.5---8 Angstroms). A power law relationship often describes the relationship between temperature and emission measure during the decay phase in both wavelength ranges. According to work of Sylwester et al. (1993, A&A 267, 586), energy input parameters and physical properties of the flaring loop(s) determine the slope of this power law. We find that ratios of Ca xix to GOES slopes generally fall between .6 and 1.0, when slopes in both channels are measured during the flare decay in each respective wavelength range. This relatively good agreement between slopes in the two channels suggests that emissions in both wavelength ranges originate from either the same flaring loop, or differing loops with similar global properties. Title: Fe XXVI line emission observed by YOHKOH Authors: Pike, C. D.; Pillips, K. J. H.; Lang, J.; Sterling, A.; Watanabe, T.; Hiei, E.; Culhane, J. L. Bibcode: 1996AdSpR..17d..51P Altcode: 1996AdSpR..17...51P Observations from the Bragg Crystal Spectrometer (BCS) on board the Japanese solar flare space-craftYohkoh showing Fe xxvi Ly-alpha X-ray line emission at about 1.78 Angstroms are reported. Some 75 events over a two-year-long period between December 1991 and December 1993 have been analyzed. The greater sensitivity of the BCS compared with previous instruments has enabled such emission to be detected from a wider group of flares than has previously been possible. The likelihood of detecting Fe xxvi lines in a flare is found to increase sharply with the electron temperature obtained from the Fe xxv line spectrum, also observed by the BCS, and with GOES X-ray class. The width of the Lyalpha_1 line, measured after the impulsive stage, is rather greater than that determined by thermal Doppler broadening, and if the excess broadening is attributed to turbulence, velocities of up to 70 km s^-1 are indicated. Comparison of electron temperatures obtained from the Fe xxvi spectrum with Fe xxv temperatures provides evidence for a single loose grouping of flares, with the difference between the two temperatures ranging from nearly zero to about 20 x 10^6K. A ``superhot'' component would seem to be more or less developed according as the temperature difference is large or nearly zero. Title: YOHKOH SXT and BCS Observations of the "Reconnection Region" of a Solar Flare Authors: Sterling, Alphonse C.; Hudson, Hugh S.; Lemen, James R. Bibcode: 1996ASPC..111..177S Altcode: 1997ASPC..111..177S The authors find strong line shifts in Bragg crystal spectrometer (BCS) spectra of a flare which occurred well beyond the solar limb on 1993 April 15. Since the flare is beyond the limb, only the uppermost regions of the flare are visible. If reconnection is acting in flares, than one may expect that the line shifts from this event are due to reconnection jets emanating from above the region of the main flaring loops. The authors show, however, that details of the line shifts are not consistent with this picture. Rather than being a result of reconnection jets, it is more likely that the line shifts are due to plasma motions on a flaring loop oriented edge on with respect to the Earth. Title: Isolating the Footpoint Characteristics of a Solar Flare Loop Authors: Harra-Murnion, L. K.; Culhane, J. L.; Fujiwara, T.; Hudson, H. S.; Kato, T.; Sterling, A. C. Bibcode: 1996mpsa.conf..527H Altcode: 1996IAUCo.153..527H No abstract at ADS Title: X-ray Observations of an Over-the-Limb Solar Flare with Large Spectral Line Shifts Authors: Sterling, A. C.; Harra-Murnion, L. K.; Hudson, H. S.; Lemen, J. R.; Strong, K. T. Bibcode: 1996mpsa.conf..557S Altcode: 1996IAUCo.153..557S No abstract at ADS Title: A Loop Flare Observed by YOHKOH on 1992 July 11 Authors: Khan, Josef I.; Hudson, Hugh S.; Sterling, Alphonse C.; Lemen, James R. Bibcode: 1996ASPC..111..162K Altcode: 1997ASPC..111..162K The authors present Yohkoh soft and hard X-ray observations of a flare. Soft X-ray morphology shows the structure of this flare to be a relatively simple loop. Nonetheless several interesting points were found including: (i) bright soft X-ray footpoints persist long after completion of the impulsive hard X-ray bursts; (ii) both legs and footpoints of the flare loop appear to move together rather than apart during the course of the flare; (iii) initially the flare loop appears to have a fairly uniform thickness but as the flare progresses the loop-top region becomes broader; (iv) 'low energy' hard X-rays appear to originate from high in the loop near the loop apex; and (v) soft X-ray spectra show strong line asymmetries suggesting the presence of upflowing plasma oriented nearly directly towards the Earth. Title: Yohkho Soft X-Ray Spectroscopic Observations of the Bright Loop-Top Kernels of Solar Flares Authors: Khan, Josef I.; Harra-Murnion, Louise K.; Hudson, Hugh S.; Lemen, James R.; Sterling, Alphonse C. Bibcode: 1995ApJ...452L.153K Altcode: Observations of solar flares by the Soft X-ray Telescope (SXT) on board Yohkoh frequently show strongly enhanced brightenings near the tops of the magnetic loops containing hot plasma. The Yohkoh Bragg Crystal Spectrometer (BCS) cannot normally make observations of these loop-top sources in the absence of contamination by the legs and the feet of the loops since it has no spatial resolution. We have overcome this limitation by using the solar limb as an occulting edge in a sequence of similar flares that occurred over an interval of ~10 hr near the west limb on 1992 November 24. The progressive occultation by the limb restricts the line of sight to higher and higher altitudes during this sequence, with the final event showing only a compact source of the type often found at loop tops. BCS observations in Fe XXV, Ca XIX, and S XV show that electron temperatures and nonthermal velocities in these compact sources are similar to those quantities determined for disk flares in previous studies. As with disk flares, the nonthermal line broadening persists late into the decay phase of the flaring isolated loop tops. Our results favor mechanisms for nonthermal-velocity generation that are either independent of height or place the source near the apex of the flaring loop. In addition, there may be a temporal relationship between the hard X-ray emission and the nonthermal velocity, which suggests a possible association between the primary energy release of the flare, the nonthermal-velocity generation mechanism, and the loop top. Title: Yohkoh Multi-Wavelength Observations of the Bright Loop-Top Kernels in Solar Flares Authors: Sterling, A.; Khan, J.; Harra-Murnion, L.; Hudson, H.; Lemen, J. Bibcode: 1995SPD....26.1211S Altcode: 1995BAAS...27..985S No abstract at ADS Title: Fe XXV Temperatures in Flares from the YOHKOH Bragg Crystal Spectrometer Authors: Sterling, Alphonse C.; Doschek, George A.; Pike, C. David Bibcode: 1994ApJ...435..898S Altcode: Studies by Doschek et al. using P78-1 and Solar Maximum Misson (SMM) data have shown that the ratio of intensities of the Fe XXV and Ca XIX resonance lines can be expressed as a function of Fe XXV temperature. Using a more recent data set consisting of 13 flares observed by the Bragg crystal spectrometer (BCS) experiment on board Yohkoh, we find a nearly identical functional relationship between the same resonance line ratios and Fe XXV temperatures. We use this functional relationship to obtain resonance line ratio temperatures (TRLR) for each flare in our data set, and compare them with temperatures resulting from application of a simple spectral fitting method. (TSSF) to individal Fe XXV spectra. We also use a more involved free-parameter spectral fitting method to deduce temperatures (TFSF) from some of these spectra. On average, agreement between TRLR and TSSF improves as a flare progresses in time, with average agreements of 10.0% +/- 5.2%, 6.4% +/- 5.4%, and 5.0% +/- 3.9% over the rise, peak, and decay phases, respectively. Deviations between TRLR and TFSF are about the same or smaller. Thus, for most analysis purposes, all three methods yield virtually identical temperatures in flares. The somewhat poorer agreement between TSSF and TRLR during the earlier phases may be partially a result of difficulties in obtaining precise values for temperatures from spectral fits when blueshifts and large nonthermal broadenings are present in the spectra. Because of the high sensitivity of the Yohkoh BCS compared to that of BCS experiments on earlier spacecraft, we can for the first time consistently observe the heating phase of flares in Fe XXV. Title: Jets and brightenings generated by energy deposition in the middle and upper solar chromosphere Authors: Sterling, Alphonse C.; Shibata, Kazunari; Mariska, John T. Bibcode: 1994SSRv...70...77S Altcode: Numerical simulations of energy depositions in the middle and upper solar chromosphere result in ejection of chromospheric material into the corona and heating of the chromospheric gas. These simulations may be capable of describing some of the features seen by the soft X-ray telescope on board theYohkoh satellite. Title: The 1991 November 9 Flare at 03.2 UT: Observations from YOHKOH Authors: Doschek, G. A.; Mariska, J. T.; Strong, K. T.; Bentley, R. D.; Brown, C. M.; Culhane, J. L.; Lang, J.; Sterling, A. C.; Watanabe, T. Bibcode: 1994ApJ...431..888D Altcode: We discuss X-ray spectra and soft X-ray images of an M1.9 flare that occurred on 1991 November 9 near 03.2 UT. These data were obtained with instrumentation on the Japanese Yohkoh spacecraft. They cover the entire rise phase and peak flare emission, and the beginning of the decay phase. We determine the dynamics, temperature, and emission measure of the flare as inferred from the X-ray line profiles of resonance lines of Fe XXV, Ca XIX, and S XV. We discuss the morphology of the flare as inferred from the soft X-ray images. The November 9 flare is atypical in that a stronger than usual blueshifted emission component (relative to the stationary component) is observed for the resonance lines at flare onset. We discuss several methods for deconvolving the blueshifted component from the stationary component. The X-ray line profiles are consistent with predictions of numerical simulations of chromospheric evaporation. The X-ray images reveal a flare with a complicated loop geometry that is not fully understood. Many of the features in the images are moving upwards at speeds ranging from a few km/s to about 800 km/s. The blueshifted emission begins near the onset of hard X-ray emission, implying that particle acceleration and upflowing plasma have a common energy source. Title: YOHKOH Bragg Crystal Spectrometer(BCS) Observations of the 6-Feb-1992 Limb Flare Authors: Sterling, A. C. Bibcode: 1994kofu.symp..131S Altcode: We present Yohkoh BCS observations of a near-limb solar flare of 6 Feb 1992. SXT images show that the event was composed of at least two flaring loops. The first of these to flare had a maximum Fe XXV temperature of about 19 MK and no substantial Fe XXVI component, while the second flaring loop achieved a Fe XXV temperature in excess of 21 MK and had a superhot (30--40 MK) Fe XXVI component. Title: YOHKOH Observations of Weak Events Within AR7218 Authors: Linford, G. A.; Hudson, H.; Sterling, A. Bibcode: 1994xspy.conf...49L Altcode: No abstract at ADS Title: A Resonance Line Rations Method for Determining Flare Temperatures Using YOHKOH BCS Spectra Authors: Sterling, A. C.; Doschek, G.; Mariska, J. T.; Hiei, E.; Watanabe, T. Bibcode: 1994xspy.conf..127S Altcode: No abstract at ADS Title: Non-Thermal Effects in Slow Solar Flares Authors: Hudson, H. S.; Acton, L. W.; Sterling, A. C.; Tsuneta, S.; Fishman, J.; Meegan, C.; Paciesas, W.; Wilson, R. Bibcode: 1994xspy.conf..143H Altcode: No abstract at ADS Title: The 1992 January 5 Flare at 13.3 UT: Observations from YOHKOH Authors: Doschek, G. A.; Strong, K. T.; Bentley, R. D.; Brown, C. M.; Culhane, J. L.; Fludra, A.; Hiei, E.; Lang, J.; Mariska, J. T.; Phillips, K. J. H.; Pike, C. D.; Sterling, A. C.; Watanabe, T.; Acton, L. W.; Bruner, M. E.; Hirayama, T.; Tsuneta, S.; Rolli, E.; Kosugi, T.; Yoshimori, M.; Hudson, H. S.; Metcalf, T. R.; Wuelser, J. -P.; Uchida, Y.; Ogawara, Y. Bibcode: 1993ApJ...416..845D Altcode: We discuss X-ray spectra and soft X-ray images of an M1.9 flare that occurred on 1992 January 5 near 13.3 UT. These data were obtained with instrumentation on the Japanese Yohkoh spacecraft. They cover the entire rise phase of the flare. To supplement these data we have ground-based magnetograms and Hα spectroheliograms. We calculate the electron temperature and emission measure of the flare as a function of time during the early rise phase using X-ray spectral line intensities and line ratios. Using spectral line widths, line profile asymmetries, and wavelength shifts due to the Doppler effect, we calculate the dynamical properties of the flare. The time development of the morphology of the flare, as revealed by the soft X-ray images and the Hα spectroheliograms, and the physical quantities inferred from the X-ray spectra, are compared with chromospheric evaporation models. There is an enhancement of blueshifted emission that is closely correlated with the hard X-ray bursts. Heating of one loop in the flare is consistent with a conduction-evaporation model, but heating is found in several structures that do not appear to be physically associated with each other. No standard evaporation model can adequately explain all of the observations. Title: Yohkoh observations of plasma upflows during solar flares Authors: Culhane, J. L.; Phillips, A. T.; Pike, C. D.; Fludra, A.; Bentley, R. D.; Bromage, B.; Doschek, G. A.; Hiei, E.; Inda, M.; Mariska, J. T.; Phillips, K. J. H.; Sterling, A. C.; Watanabe, T. Bibcode: 1993AdSpR..13i.303C Altcode: 1993AdSpR..13..303C Observations of two flares, an M 2.2 event on 16 December, 1991 and the precursor to an X1 flare on 15 November, 1991 are presented. Spectra obtained with the Bragg Crystal Spectrometer (BCS) are compared with data from the Hard and Soft X-ray Telescopes (HXT, SXT) and the Wide Band Spectrometer (WBS) on the satellite. For both events the creation of upflowing plasma is detected. While the first event seems to conform well to the chromospheric evaporation model for high temperature plasma production, the behaviour for the second event is more complex. Title: Determination of coronal abundances of sulphur, calcium and iron using the yohkoh bragg crystal spectrometer Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.; Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T. Bibcode: 1993AdSpR..13i.395F Altcode: 1993AdSpR..13..395F Using spectra from the Bragg Crystal Spectrometer on Yohkoh we have derived coronal abundances of sulphur, calcium and iron during several flares from the ratio of the flux in the resonance line to the nearby continuum. Multi-thermal effects have been taken into account using differential emission measure analysis. We have also determined the abundance of S in cool active regions during a period of very low solar activity. We compare the coronal abundances of S, Ca and Fe with their photospheric values. Title: Temperatures in Flares Determined from Fe XXV Spectra, Resonance Line Ratios, and GOES X-ray Flux Authors: Sterling, A. C.; Doschek, G. A.; Pike, C. D.; Hudson, H. S.; Lemen, J. R.; Zarro, D. M. Bibcode: 1993BAAS...25.1178S Altcode: No abstract at ADS Title: Solar Chromospheric and Transition Region Response to Energy Deposition in the Middle and Upper Chromosphere Authors: Sterling, Alphonse C.; Shibata, Kazunari; Mariska, John T. Bibcode: 1993ApJ...407..778S Altcode: A series of numerical simulations modeling the chromosphere and transition region response to deposition of thermal energy ranging from about 5 x 10 exp 24 to 5 x 10 exp 28 ergs in the middle or upper chromosphere is reported. The dissipative effects of heat conduction, optically thin radiation losses in the corona, and an approximate expression for the radiation losses of lower temperature plasma are calculated. In response to the energy deposition, chromospheric material is ejected into the corona in the form of pressure gradient generated jets, jets with pressure-gradient, and shock-generated components, or high-speed gas plugs. Category of ejection depends on the spatial and temporal distribution and the magnitude of the input energy source. Title: On the Absolute Abundance of Calcium in Solar Flares Authors: Sterling, Alphonse C.; Doschek, George A.; Feldman, Uri Bibcode: 1993ApJ...404..394S Altcode: The abundance of calcium relative to hydrogen in soft X-ray-emitting solar flare plasmas is determined. Results were obtained for 25 flares. An average calcium-to-hydrogen abundance of about 5 x 10 exp -6, which is about a factor of 2 greater than measured for the photosphere, is found. This result is consistent with an enhancement of low first ionization elements in soft X-ray flare plasmas. For one flare, the calcium abundance was higher, at about 1.6 times the average results. It is inferred that the calcium abundance can vary among flares. Significant variations of the calcium abundance during the course of a flare were not detected. Title: Determination of element abundances using the Yohkoh Bragg Crystal Spectrometer. Authors: Fludra, A.; Culhane, J. L.; Bentley, R. D.; Doschek, G. A.; Hiei, E.; Phillips, K. J. H.; Sterling, A.; Watanabe, T. Bibcode: 1993uxrs.conf..542F Altcode: 1993uxsa.conf..542F No abstract at ADS Title: Observations of Several Small Flares with the Bragg Crystal Spectrometer on YOHKOH Authors: Culhane, J. Leonard; Fludra, Andrzej; Bentley, Robert D.; Doschek, George A.; Watanabe, Tetsuya; Hiei, Eijiro; Lang, James; Carter, Martin K.; Mariska, John T.; Phillips, Andrew T.; Phillips, Kenneth J. H.; Pike, C. David; Sterling, Alphonse C. Bibcode: 1992PASJ...44L.101C Altcode: We have analysed data from two flares of GOES class C7.1 and C8.5 observed by the Yohkoh Bragg Crystal Spectrometer. The high sensitivity of the Yohkoh instrument allows us to observe the very early stages of flare development and to study small events with a high signal-to-noise ratio. Spectral fitting programs have been used to derive plasma temperatures, emission measures and velocities from spectra of S XV, Ca XIX and Fe XXV. Large plasma motions indicative of chromospheric evaporation have been found. A more detailed analysis of a flare which occurred on 1991 October 30 is presented. Title: YOHKOH Bragg Crystal Spectrometer Observations of the Dynamics and Temperature Behavior of a Soft X-Ray Flare Authors: Doschek, George A.; Mariska, John T.; Watanabe, Tetsuya; Hiei, Eijiro; Lang, James; Culhane, J. Leonard; Bentley, Robert D.; Brown, Charles M.; Feldman, Uri; Phillips, Andrew T.; Phillips, Kenneth J. H.; Sterling, Alphonse C. Bibcode: 1992PASJ...44L..95D Altcode: We describe X-ray spectra of an M1.5 flare that occurred on 1991 November 9, starting at about 0313 UT. This flare is unusual in that very intense blueshifted components are observed in the resonance lines of Fe XXV, Ca XIX, and S XV. During the onset of the flare, the resonance lines of Ca XIX and Fe XXV are primarily due to this blueshifted component, which from the Doppler effect indicates line-of-sight speeds and turbulent motions that in combination extend up to 800 km s(-1) . Title: Yohkoh BCS Observations of Doppler Shifts Early in Solar Flares Authors: Mariska, J. T.; Doschek, G. A.; Sterling, A. C.; Culhane, J. L.; Hiei, E.; Watanabe, T.; Lang, J. Bibcode: 1992AAS...180.2308M Altcode: 1992BAAS...24..761M No abstract at ADS Title: Time Variation of Solar Flare Temperatures Determined from YOHKOH BCS Spectra Authors: Sterling, A. C.; Doschek, G. A.; Mariska, J. T.; Pike, C. D.; Culhane, J. L.; Hiei, E.; Watanabe, T.; YOHKOH BCS Team Bibcode: 1992AAS...180.3001S Altcode: 1992BAAS...24..775S Bragg Crystal Spectrometer (BCS) X-ray spectra analysis from past satellite missions indicate that it is possible to estimate temperatures in highly ionized flare plasmas to within about 12\ resonance lines in different He-like ions. This procedure is particularly valuable in cases where other temperature measuring methods are insufficient, such as during the rise phase of flares with strong X-ray spectra blue shifts. Here we examine this ratio variation in several flares using data from the Fe XXV, Ca XIX, and S XV channels of the BCS experiment onboard the Yohkoh satellite. We select flares for which we have good rise phase data, and calibrate the ratios using dielectronic-to-resonance line ratios in selected Fe XXV spectra assuming constant elemental abundances in each event. The Yohkoh BCS is about an order of magnitude more sensitive than previous X-ray flare spectrometers, and is therefore able to examine the early stages of flare development in greater detail than previously possible. For this study we select events for which we have good rise phase data, but data well into the decay phase is available for a number of the selected events. This allows us, for the first time, to follow the evolution of flare spectra from relatively cool temperatures (~ 12 MK in Fe XXV) to previously quoted ``typical" flare temperatures (~ 17 MK in Fe XXV). Title: Emergence of Magnetic Flux from the Convection Zone into the Solar Atmosphere. I. Linear and Nonlinear Adiabatic Evolution of the Convective-Parker Instability Authors: Nozawa, S.; Shibata, K.; Matsumoto, R.; Sterling, A. C.; Tajima, T.; Uchida, Y.; Ferrari, A.; Rosner, R. Bibcode: 1992ApJS...78..267N Altcode: The linear and nonlinear properties of the evolution of emerging magnetic flux from the solar convection zone into the photosphere, chromosphere, and corona are studied. A linear stability analysis of the partially magnetized convection zone is presented. The growth rate of this combined convective-Parker instability is found to differ significantly from that of the Parker instability in the absence of convection. When beta(=pg/pm) is greater than 10 in the initial flux sheet, the growth rate increases with horizontal wavenumber, and there is no maximum growth rate. A local maximum can occur when the flux is initially located near the top of the convection zone. When beta is less than 10, the convective-Parker instability behaves like the Parker instability for long-wavelength modes, and like the convective instability for short-wavelength modes. A 2D MHD code is used to study the nonlinear evolution of the system. When the initial flux sheet has beta less than 10, the long-wavelength mode dominates the nonlinear evolution of the system, independently of the initial perturbation wavelength. Title: Numerical Simulations of Microflare Evolution in the Solar Transition Region and Corona Authors: Sterling, Alphonse C.; Mariska, John T.; Shibata, Kazunari; Suematsu, Yoshinori Bibcode: 1991ApJ...381..313S Altcode: Several observers report transient ultraviolet brightenings, often referred to as microflares, in the solar atmosphere. In this paper, the results are presented of a series of one-dimensional numerical simulations examining possible relationships between microflares and the generation of dynamical chromospheric and transition region features. Low-energy and medium-energy microflares eject long-lived cool, dense gas plugs into the corona, with the gas plug traversing the loop apex in the medium energy case. In the case of high-energy microflares, the gas plug is rapidly heated to the temperature of the surrounding corona, and the results resemble the dynamics occurring in standard solar flare thick-target electron beam models. Title: On the Absolute Abundance of Ca in Solar Flares Authors: Sterling, A. C.; Doschek, G. A. Bibcode: 1991BAAS...23.1467S Altcode: No abstract at ADS Title: Numerical Studies of Atmospheric Dynamics Driven by Energy Deposition in the Chromosphere Authors: Sterling, A. C.; Mariska, J. T.; Shibata, K. Bibcode: 1991BAAS...23.1029S Altcode: No abstract at ADS Title: Numerical Simulations of Ultraviolet and X-ray Microflares Authors: Sterling, A. C.; Shibata, K.; Mariska, J. T. Bibcode: 1991LNP...387...71S Altcode: 1991fpsa.conf...71S A series of numerical simulations indicates that thermal energy releases of 1025 - 1027 ergs in the middle chromosphere can produce ejections into the corona in the form of pressure gradient generated jets, jets with pressure gradient and shock generated components, or high speed gas plugs. Heating of the chromosphere to X-ray emitting temperatures occurs in association with gas plugs, perhaps generating X-ray microflares observable by Solar-A. Chromospheric UV-microflares can occur in association with some jets, but do not generally occur with spicules. Title: Atmospheric Heating in Emerging Flux Regions (With 2 Figures) Authors: Shibata, K.; Nozawa, S.; Matsumoto, R.; Tajima, T.; Sterling, A. C. Bibcode: 1991mcch.conf..609S Altcode: No abstract at ADS Title: Numerical Simulation of Microflare Evolution in the Solar Transition Region and Corona (With 4 Figures) Authors: Sterling, A. C.; Mariska, J. T. Bibcode: 1991mcch.conf..630S Altcode: No abstract at ADS Title: Emergence of Solar Magnetic Flux from the Convection Zone into the Photosphere and Chromosphere Authors: Shibata, K.; Nozawa, S.; Matsumoto, R.; Sterling, A. C.; Tajima, T. Bibcode: 1990ApJ...351L..25S Altcode: A two-dimensional MHD code is used to study the nonlinear dynamics of solar magnetic flux emerging from the convection zone into the photosphere and chromosphere. An isolated horizontal magnetic flux with beta of about 4 is initially located in a convectively unstable layer (solar convection zone) beneath a two-temperature layered atmosphere (solar corona-chromosphere/photosphere). The combined effects of convection and magnetic buoyancy carry the magnetic flux from the convection zone into the photosphere, where it then expands through the photosphere and chromosphere. Gas slides down the expanding loop, resulting in its evacuation and subsequent rise due to enhanced magnetic buoyancy. Initially, weak convection zone magnetic flux (B of about 600 G) is amplified up to 1000 G or more after emerging into the photosphere. The resulting velocity fields are similar to those observed in arch filament systems. Title: Numerical Simulations of the Rebound Shock Model for Solar Spicules Authors: Sterling, Alphonse C.; Mariska, John T. Bibcode: 1990ApJ...349..647S Altcode: Using time-dependent numerical simulations, the proposed rebound shock mechanism for spicules has been examined. At temperatures above a critical value, T(c), the radiation is characteristic of the conditions in the optically thin corona and near optically thin transition region. When T less than T(c), the atmosphere has a radiative cooling time, tau(rad) characteristic of chromosphere. The spicule is initiated with a quasi-impulsive force in the low chromosphere, which drives a train of upward propagating rebound shocks along the rigid magnetic flux tube. These shocks then move the transition region upward. The material below the displaced transition region has temperatures and densities similar to those of spicules when T(c) = 20,000 K or more and tau(rad) = 500 s or more, but not when T(c) = 10,000 K, and probably not when tau(rad) = 100 s. For all the cases where the cross sectional area diverges rapidly with height, the upward velocity of the transition region is less than that of spicules. Moreover, the maximum height is less than that of average spicules. Taller, higher velocity spicules result when the magnetic field cross sectional area is constant. In all cases, the rebound shock mechanism produces substantial motions and temperature and density variations in chromospheric and transition region material. It is suggested that this may be a partial explanation for the continuous dynamic state of the lower solar atmosphere. Title: Emergence of Solar Magnetic Flux from the Convection Zone into the Photosphere aand Chromosphere Authors: Sterling, A. C.; Shibata, K.; Nozawa, S.; Matsumoto, R.; Tajima, T. Bibcode: 1989BAAS...21.1179S Altcode: No abstract at ADS Title: A Rebound Shock Mechanism for Solar Fibrils Authors: Sterling, Alphonse C.; Hollweg, Joseph V. Bibcode: 1989ApJ...343..985S Altcode: Flows along a rigid solar magnetic flux tube which is horizontal over a substantial portion of its length are numerically investigated. A single, quasi-impulsive force near the base of the first vertical segment drives a series of upward propagating rebound shocks on the flux tube. When the horizontal segment is in the corona, the shocks raise the transition region onto the horizontal segment and eventually onto the coronal vertical segment. The material behind the displaced transition region resembles a fibril on the horizontal segment, and a short spicule on the second vertical segment. A full-sized spicule does not develop. The resulting density of the material on the horizontal segment is 10 to the -14th g/cu cm, which is consistent with the observed densities in fibrils. When the horizontal segment is in the chromosphere, the motions and densities induced on the horizontal segment do not resemble those of observed fibrils, and a full-sized spicule again does not develop. Title: Numerical Simulations of the Rebound Shock Model for Spicules Authors: Sterling, A. C.; Mariska, J. T. Bibcode: 1988BAAS...20Q.989S Altcode: No abstract at ADS Title: The Rebound Shock Model for Solar Spicules: Dynamics at Long Times Authors: Sterling, Alphonse C.; Hollweg, Joseph V. Bibcode: 1988ApJ...327..950S Altcode: The spicule model due to Hollweg is extended and developed. The dynamics is emphasized here; radiative and ionization losses, heat conduction, and nonshock heat input, are not included. In the model, a series of rebound shocks results in chromospheric material with spicule-like properties below a raised transition region. The shocks result from a single quasi-impulsive source in the photosphere. It is found that at long times, the model approaches a new hydrostatic equilibrium with the transition region remaining raised, and with a region of shock-heated chromosphere below it. Attention is given to the variation of the properties of the model in response to different values for the magnitude and location of the source, and to different initial transition region heights. It is concluded that the model is capable of generating structures with properties consistent with observations of spicules (with the exception of temperature) when only the dynamics is considered. Title: A Rebound Shock Model for Solar Fibrils Authors: Sterling, A. C.; Hollweg, J. V. Bibcode: 1988BAAS...20..690S Altcode: No abstract at ADS Title: Dynamics of the Solar Atmosphere: Spicules and Fibrils. Authors: Sterling, Alphonse Christopher Bibcode: 1988PhDT.........2S Altcode: Numerical and analytical studies of MHD waves on magnetic flux tubes are applied to problems of the solar atmosphere. In particular, theoretical analysis of the chromospheric features known as spicules and fibrils are undertaken. The thesis consists of three principal segments:. i. A preexisting spicule model is extended and developed. In the model, a series of rebound shocks propagating on a vertical magnetic flux tube results in chromospheric material with spicule-like properties below a raised transition region. The model emphasizes dynamic motions and shock heating, but excludes radiative and ionization losses. At long times, the model approaches a new hydrostatic equilibrium with the transition region remaining raised, and with a region of shock-heated chromosphere below it. The variation of the model properties in response to different initial parameters is investigated. One conclusion is that the model is capable of generating structures with properties consistent with observations of spicules (with the exception of temperature) when only the dynamics is considered. ii. An analytical study is performed using linearized MHD equations to demonstrate that spicules may act as resonance cavities for MHD Alfven waves propagating along a vertical magnetic flux tube. When the resonances are excited, large amounts of wave energy from the photosphere and lower chromosphere can propagate into the spicule. This may result in the observed heating, fading, and twisting motions of spicules. It is assumed that the wave energy can be dissipated as heat via a turbulent cascade which follows a Kolmogorov. iii. The spicule model used in the first segment of the thesis is applied to a magnetic field geometry which is vertical through the photosphere and chromosphere, turns horizontal in the low corona, and eventually turns vertical again and extends into the outer corona. Radiative and ionization losses are again omitted. A structure develops on the horizontal segment which may be identifiable with a fibril, but a full spicule does not develop. At long times, the fibril and short spicule remain extended, and a standing wave develops on the flux tube. Title: Spicule Dynamics: Long Time Behavior Authors: Sterling, A. C.; Hollweg, J. V. Bibcode: 1985BAAS...17Q.631S Altcode: No abstract at ADS Title: Alfvenic resonances on solar spicules Authors: Sterling, A. C.; Hollweg, J. V. Bibcode: 1984ApJ...285..843S Altcode: It is suggested that twisting and heating of solar spicules can be produced by Alfven waves which enter the spicule from below. The spicule is treated as a region of constant Alfven speed which is bounded above by a region of much higher Alfven speed (the corona) and below by a region of exponentially increasing Alfven speed (the photosphere and chromosphere). It is shown how the spicule can act as a resonant cavity. The transmission of the waves into the cavity is analytically determined to be enhanced at certain resonant frequencies. With reasonable spicule parameters, and assuming the spicule damping to be moderately large, it is found that twisting velocities of approximately 20-30 km/s can be induced on the spicule. It is suggested that the Alfven waves are dissipated via a turbulent cascade of their energy to higher wavenumbers. It is shown that the waves can thereby heat the spicules to the observed temperatures. It is further suggested that the continued input of energy can explain why H-alpha spicules fade, since the predicted heating rate is sufficient to heat the spicules to temperatures at which the hydrogen is fully ionized; thus H-alpha spicules may evolve into EUV spicules. Title: Resonant heating - an interpretation of coronal loop data Authors: Hollweg, J. V.; Sterling, A. C. Bibcode: 1984ApJ...282L..31H Altcode: The authors show that the resonant heating theory of Hollweg can be used to organize the coronal loop data of Golub et al. When combined with a reasonable form for the input power spectrum, the resonant heating theory is fully compatible with the loop data. Title: Coronal Loop Heating: Theory and Data Authors: Hollweg, J. V.; Sterling, A. C. Bibcode: 1984BAAS...16..527H Altcode: No abstract at ADS Title: Alfvenic Heating: An Interpretation of Coronal Loop Data Authors: Sterling, A. C.; Hollweg, J. V. Bibcode: 1984BAAS...16Q.527S Altcode: No abstract at ADS Title: Resonances of Solar Spicules Authors: Hollweg, J. V.; Sterling, A. C. Bibcode: 1983BAAS...15R.994H Altcode: No abstract at ADS Title: Study of Earth Tides, Earthquakes and Terrestrial Spectroscopy by Analysis of the Level Fluctuations in a Borehole at Heibaart (Belgium) Authors: Sterling, A.; Smets, E. Bibcode: 1971GeoJ...23..225S Altcode: 1971GeoJI..23..225S No abstract at ADS Title: Etude des marées terrestres et des séismes par l'analyse des variations du niveau d'eau dans un puits à Heibaart Authors: Sterling, A.; Smets, E. Bibcode: 1970C&T....86...23S Altcode: No abstract at ADS Title: Effets de dilatations cubiques dues aux marées terrestres observés sous forme de variations de niveau dans un puits à Basècles (Hainaut) Authors: Melchior, P.; Sterling, A.; Wery, A. Bibcode: 1963C&T....79..353M Altcode: No abstract at ADS