Author name code: panesar ADS astronomy entries on 2022-09-14 author:"Panesar, Navdeep Kaur" ------------------------------------------------------------------------ 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: The Magnetic Origin of Solar Campfires: Observations by Solar Orbiter and SDO Authors: Panesar, Navdeep Kaur; Zhukov, Andrei; Berghmans, David; Auchere, Frederic; Müller, Daniel; Tiwari, Sanjiv Kumar; Cheung, Mark Bibcode: 2022cosp...44.2564P Altcode: Solar campfires are small-scale, short-lived coronal brightenings, recently observed in 174 Å images by Extreme Ultraviolet Imager (EUI) on board Solar Orbiter (SolO). Here we investigate the magnetic origin of 52 campfires, in quiet-Sun, using line-of-sight magnetograms from Solar Dynamics Observatory (SDO)/Helioseismic and Magnetic Imager (HMI) together with extreme ultraviolet images from SolO /EUI and SDO/Atmospheric Imaging Assembly (AIA). We find that the campfires are rooted at the edges of photospheric magnetic network lanes; (ii) most of the campfires reside above neutral lines and 77% of them appear at sites of magnetic flux cancelation between the majority-polarity magnetic flux patch and a merging minority-polarity flux patch, with a flux cancelation rate of ∼1018 Mx hr‑1; some of the smallest campfires come from the sites where magnetic flux elements were barely discernible in HMI; (iii) some of the campfires occur repeatedly from the same neutral line; (iv) in the large majority of instances (79%), campfires are preceded by a cool-plasma structure, analogous to minifilaments in coronal jets; and (v) although many campfires have "complex" structure, most campfires resemble small-scale jets, dots, or loops. Thus, "campfire" is a general term that includes different types of small-scale solar dynamic features. They contain sufficient magnetic energy (∼1026-1027 erg) to heat the solar atmosphere locally to 0.5-2.5 MK. Their lifetimes range from about 1 minute to over 1 hour, with most of the campfires having a lifetime of <10 minutes. The average lengths and widths of the campfires are 5400 ± 2500 km and 1600 ± 640 km, respectively. Our observations suggest that (a) the presence of magnetic flux ropes may be ubiquitous in the solar atmosphere and not limited to coronal jets and larger-scale eruptions that make CMEs, and (b) magnetic flux cancelation, most likely driven by magnetic reconnection in the lower atmosphere, is the fundamental process for the formation and triggering of most campfires. Title: Fine-scale, Dot-like, Brightenings in an Emerging Flux Region: SolO/EUI Observations, and Bifrost MHD Simulations Authors: Tiwari, Sanjiv Kumar; Berghmans, David; De Pontieu, Bart; Hansteen, Viggo; Panesar, Navdeep Kaur Bibcode: 2022cosp...44.2529T Altcode: Numerous tiny bright dots are observed in SolO's EUI/\hri\ data of an emerging flux region (a coronal bright point) in 174 \AA, emitted by the coronal plasma at $\sim$1 MK. These dots are roundish, with a diameter of 675$\pm$300 km, a lifetime of 50$\pm$35 seconds, and an intensity enhancement of 30% $\pm$10% from their immediate surroundings. About half of the dots remain isolated during their evolution and move randomly and slowly ($<$10 \kms). The other half show extensions, appearing as a small loop or surge/jet, with intensity propagations below 30\,\kms. Some dots form at the end of a fine-scale explosion. Many of the bigger and brighter EUI/HRI dots are discernible in SDO/AIA 171 \AA\ channel, have significant EM in the temperature range of 1--2 MK, and are often located at polarity inversion lines observed in HMI LOS magnetograms. Bifrost MHD simulations of an emerging flux region do show dots in synthetic Fe IX/X images, although dots in simulations are not as pervasive as in observations. The dots in simulations show distinct Doppler signatures -- blueshifts and redshifts coexist, or a redshift of the order of 10 \kms\ is followed by a blueshift of similar or higher magnitude. The synthetic images of O V/VI and Si IV lines, which form in the transition region, also show the dots that are observed in Fe IX/X images, often expanded in size, or extended as a loop, and always with stronger Doppler velocities (up to 100 \kms) than that in Fe IX/X lines. Our results, together with the field geometry of dots in the simulations, suggest that most dots in emerging flux regions form in the lower solar atmosphere (at $\approx$1 Mm) by magnetic reconnection between emerging and pre-existing/emerged magnetic field. The dots are smaller in Fe IX/X images (than in O V/VI & Si IV lines) most likely because only the hottest counterpart of the magnetic reconnection events is visible in the hotter emission. Some dots might be manifestations of magneto-acoustic shocks (from the lower atmosphere) through the line formation region of Fe IX/X. A small number of dots could also be a response of supersonic downflows impacting transition-region/chromospheric density. Title: Observations of magnetic reconnection and particle acceleration locations in solar coronal jets Authors: Zhang, Yixian; Musset, Sophie; Glesener, Lindsay; Panesar, Navdeep; Fleishman, Gregory Bibcode: 2022arXiv220705668Z Altcode: We present a multi-wavelength analysis of two flare-related jets on November 13, 2014, using data from SDO/AIA, RHESSI, Hinode/XRT, and IRIS. Unlike most coronal jets where hard X-ray (HXR) emissions are usually observed near the jet base, in these events HXR emissions are found at several locations, including in the corona. We carry out the first differential emission measure (DEM) analysis that combines both AIA (and XRT when available) bandpass filter data and RHESSI HXR measurements for coronal jets, and obtain self-consistent results across a wide temperature range and into non-thermal energies. In both events, hot plasma first appeared at the jet base, but as the base plasma gradually cooled, hot plasma also appeared near the jet top. Moreover, non-thermal electrons, while only mildly energetic, are found in multiple HXR locations and contain a large amount of total energy. Particularly, the energetic electrons that produced the HXR sources at the jet top were accelerated near the top location, rather than traveling from a reconnection site at the jet base. This means that there was more than one particle acceleration site in each event. Jet velocities are consistent with previous studies, including upward and downward velocities around ~200 km/s and ~100 km/s respectively, and fast outflows of 400-700 km/s. We also examine the energy partition in the later event, and find that the non-thermal energy in accelerated electrons is most significant compared to other energy forms considered. We discuss the interpretations and provide constraints on mechanisms for coronal jet formation. 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: SolO/EUI Observations of Ubiquitous Fine-scale Bright Dots in an Emerging Flux Region: Comparison with a Bifrost MHD Simulation Authors: Tiwari, Sanjiv K.; Hansteen, Viggo H.; De Pontieu, Bart; Panesar, Navdeep K.; Berghmans, David Bibcode: 2022ApJ...929..103T Altcode: 2022arXiv220306161T We report on the presence of numerous tiny bright dots in and around an emerging flux region (an X-ray/coronal bright point) observed with SolO's EUI/HRIEUV in 174 Å. These dots are roundish and have a diameter of 675 ± 300 km, a lifetime of 50 ± 35 s, and an intensity enhancement of 30% ± 10% above their immediate surroundings. About half of the dots remain isolated during their evolution and move randomly and slowly (<10 km s-1). The other half show extensions, appearing as a small loop or surge/jet, with intensity propagations below 30 km s-1. Many of the bigger and brighter HRIEUV dots are discernible in the SDO/AIA 171 Å channel, have significant emissivity in the temperature range of 1-2 MK, and are often located at polarity inversion lines observed in SDO/HMI LOS magnetograms. Although not as pervasive as in observations, a Bifrost MHD simulation of an emerging flux region does show dots in synthetic Fe IX/X images. These dots in the simulation show distinct Doppler signatures-blueshifts and redshifts coexist, or a redshift of the order of 10 km s-1 is followed by a blueshift of similar or higher magnitude. The synthetic images of O V/VI and Si IV lines, which represent transition region radiation, also show the dots that are observed in Fe IX/X images, often expanded in size, or extended as a loop, and always with stronger Doppler velocities (up to 100 km s-1) than that in Fe IX/X lines. Our observation and simulation results, together with the field geometry of dots in the simulation, suggest that most dots in emerging flux regions form in the lower solar atmosphere (at ≍ 1 Mm) by magnetic reconnection between emerging and preexisting/emerged magnetic field. Some dots might be manifestations of magnetoacoustic shocks through the line formation region of Fe IX/X emission. 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: Multi-wavelength Analysis of Two Flare-related RHESSI Coronal Jets Authors: Zhang, Yixian; Musset, Sophie; Glesener, Lindsay; Panesar, Navdeep K.; Fleishman, Gregory Bibcode: 2021AGUFMSH25E2142Z Altcode: Current models for solar coronal jets generally suggest that they are formed by magnetic reconnection between open and closed magnetic field lines, but details of triggering process for such magnetic reconnection are still not fully clear. Here we present multi-wavelength analysis of two flare-rated jets on November 13, 2014, using data from the Atmospheric Imaging Assembly (AIA) onboard the Solar Dynamic Observatory (SDO) and the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI). Usually, hot plasma in a coronal jet is located near the reconnection site or the base of the jet, as suggested by most models. However, for these two events, both the differential emission measure (DEM) analysis and RHESSI observations suggested that hot plasma appeared not only at the base of the jet at the beginning of each event, but also near the top of the jet a few minutes after the starting time. We performed the first comparison of the DEM in extreme ultraviolet (EUV) and the hard X-ray (HXR) spectrum for coronal jets, which qualitatively validated the hot component of the DEM. In one of the events, HXR emissions were observed at three different locations and different times: first at the base of the jet, then near the top of the jet, and finally at a location to the north of the jet. These HXR sources showed evidence of accelerated electrons which extended to fairly low energies. Jet velocities were consistent with previous studies, including major upward and downward velocities of 200km/s and 100km/s respectively, and fast outflows of 680km/s or 390km/s only visible in the 131A filter. Combining the temperature profile, the velocity profile, and the accelerated electron population for these two events, this work will provide new constraints on mechanisms for coronal jet formation. 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: Characterizing Steady and Bursty Coronal Heating of a Solar Active Region Authors: Wilkerson, Lucy; Tiwari, Sanjiv; Panesar, Navdeep K.; Moore, Ronald Bibcode: 2021AGUFMSH15E2060W Altcode: One of the biggest problems in solar physics today is our inability to explain why the solar corona is so hot. In this project, we aimed to quantify transient and background coronal heating for a given active region in order to better understand coronal heating. We used SDO/AIA data of the active region NOAA 12712 observed on May 29, 2018 over a period of 24 hours with a 3-minute cadence. We calculated FeXVIII emission (hot component of AIA 94 Å channel) by removing warm components using AIA 171 and 193 Å channels. From the maximum, minimum, and mean brightness values of each pixel over the full 24 hour period, we made maximum, minimum, and mean brightness maps. We repeated this process in moving time windows of 16 hours, 8 hours, 5 hours, 3 hours, 1 hour, and 30 minutes. We used the total luminosity for each of these maps over time to make lightcurves that show the evolution of maximum, minimum, and mean brightness over time for each running window. Finally, we took the ratio of the total maximum and total minimum luminosity to total mean luminosity, and plotted these ratios over time. The average maximum to mean ratio was 8.40±0.00, 6.36±0.46, 5.29±0.34, 4.73±0.24, 4.19±0.19, 3.21±0.17, and 2.64±0.15 and the average minimum to mean ratio was 0.053±0.00, 0.08±0.00, 0.12±0.01, 0.14±0.02, 0.17±0.02, 0.26±0.02, and 0.33±0.03 for 24h, 16h, 8h, 5h, 3h, 1h, and 30m windows, respectively. As expected, the ratio of background to mean luminosity increased as the time window decreased, and the ratio of transient to mean luminosity decreased as the time window decreased. As such, the ratio of background to mean luminosity is a new and effective technique to quantify the background intensity of the active region. Our 24h window result suggests that at most 5% of the luminosity of the AR at a given time comes from the steady background heating. This upper limit increases to 33% of the luminosity of the AR for the 30 min running window. Title: Solar Jet Hunter: a citizen science investigation of coronal solar jets Authors: Musset, Sophie; Glesener, Lindsay; Fortson, Lucy; Kapsiak, Charles; Ostlund, Erik; Alnahari, Suhail; Jeunon, Mariana; Zhang, Yixian; Panesar, Navdeep; Fleishman, Gregory; Hurlburt, Neal Bibcode: 2021AGUFMSA32A..07M Altcode: The Sun is the source of energetic particles that fill the heliosphere, interact with planets magnetospheres, and impact human activities. The origins of those energetic particles are still under investigation, as well as the mechanisms responsible for their escape from the solar atmosphere where they are energized. Solar jets, collimated ejections of solar plasma along magnetic field lines extending to the interplanetary medium, offer a possible route for particle escape. Coronal solar jets are commonly observed in soft X-rays and extreme ultraviolet (EUV) and are ubiquitous in the solar atmosphere, assuming various shapes, sizes and velocities. To date, autonomous algorithms are not detecting solar jets reliably, and they are usually reported manually by human observers, resulting in an incomplete and inhomogeneous database of jets. In order to produce a reliable, extensive, and consistent database of jets, that will be used to statistically study the jet phenomenon and its relationship to solar energetic particles, we initiated a citizen science project called Solar Jet Hunter whose goal is to explore the huge amount of EUV observations of the Sun in order to identify and characterize the solar jets in the dataset. The resulting database will also be used to train algorithms to identify solar jets in the EUV data. We will present here the preliminary results of this Zooniverse project. Title: Campfires observed by EUI: What have we learned so far? Authors: Berghmans, David; Auchere, F.; Zhukov, Andrei; Mierla, Marilena; Chen, Yajie; Peter, Hardi; Panesar, Navdeep; Chitta, Lakshmi Pradeep; Antolin, Patrick; Aznar Cuadrado, Regina; Tian, Hui; Hou, Zhenyong; Podladchikova, Olena Bibcode: 2021AGUFMSH21A..02B Altcode: Since its very first light images of the corona, the EUI/HRIEUV telescope onboard Solar Orbiter has observed small localised brightenings in the Quiet Sun. These small localised brightenings, have become known as campfires, and are observed with length scales between 400 km and 4000 km and durations between 10 sec and 200 sec. The smallest and weakest of these HRIEUV brightenings have not been previously observed. Simultaneous observations from the EUI High-resolution Lyman- telescope (HRILYA) do not show localised brightening events, but the locations of the HRIEUV events clearly correspond to the chromospheric network. Comparisons with simultaneous AIA images shows that most events can also be identified in the 17.1 nm, 19.3 nm, 21.1 nm, and 30.4 nm pass-bands of AIA, although they appear weaker and blurred. Some of the larger campfires have the appearance of small interacting loops with the brightening expanding from the contact point of the loops. Our differential emission measure (DEM) analysis indicated coronal temperatures. We determined the height for a few of these campfires to be between 1 and 5 Mm above the photosphere. We interpret these events as a new extension to the flare-microflare-nanoflare family. Given their low height, the EUI campfires could stand as a new element of the fine structure of the transition region-low corona, that is, as apexes of small-scale loops that undergo internal heating all the way up to coronal temperatures. 3D MHD simulations with the MURaM code revealed brightenings that are in many ways similar to the campfires by EUI. The brightenings in the simulations suggest that campfires are triggered by component reconnection inside flux bundles rather than flux emergence or cancellation. Nevertheless, some of the observed campfires can be clearly linked to flux cancellation events and, intriguingly, are preceded by an erupting cool plasma structure. Analysis of the dynamics of campfires revealed that some have the appearance of coronal microjets, the smallest coronal jets observed in the quiet Sun. The HRIEUV images also reveal transient jets on a somewhat bigger scale with repeated outflows on the order of 100 km s1. In this paper we will provide an overview of the campfire related phenomena that EUI has observed and discuss the possible relevance for coronal heating. Title: The Magnetic Origin of Solar Campfires Authors: Panesar, Navdeep K.; Tiwari, Sanjiv K.; Berghmans, David; Cheung, Mark C. M.; Müller, Daniel; Auchere, Frederic; Zhukov, Andrei Bibcode: 2021ApJ...921L..20P Altcode: 2021arXiv211006846P Solar campfires are fine-scale heating events, recently observed by Extreme Ultraviolet Imager (EUI) on board Solar Orbiter. Here we use EUI 174 Å images, together with EUV images from Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA), and line-of-sight magnetograms from SDO/Helioseismic and Magnetic Imager (HMI) to investigate the magnetic origin of 52 randomly selected campfires in the quiet solar corona. We find that (i) the campfires are rooted at the edges of photospheric magnetic network lanes; (ii) most of the campfires reside above the neutral line between majority-polarity magnetic flux patch and a merging minority-polarity flux patch, with a flux cancelation rate of ~1018 Mx hr-1; (iii) some of the campfires occur repeatedly from the same neutral line; (iv) in the large majority of instances, campfires are preceded by a cool-plasma structure, analogous to minifilaments in coronal jets; and (v) although many campfires have "complex" structure, most campfires resemble small-scale jets, dots, or loops. Thus, "campfire" is a general term that includes different types of small-scale solar dynamic features. They contain sufficient magnetic energy (~1026-1027 erg) to heat the solar atmosphere locally to 0.5-2.5 MK. Their lifetimes range from about 1 minute to over 1 hr, with most of the campfires having a lifetime of <10 minutes. The average lengths and widths of the campfires are 5400 ± 2500 km and 1600 ± 640 km, respectively. Our observations suggest that (a) the presence of magnetic flux ropes may be ubiquitous in the solar atmosphere and not limited to coronal jets and larger-scale eruptions that make CMEs, and (b) magnetic flux cancelation is the fundamental process for the formation and triggering of most campfires. Title: Multi-wavelength analysis of flare-related RHESSI coronal jets Authors: Zhang, Y.; Musset, S.; Glesener, L.; Panesar, N.; Fleishman, G. Bibcode: 2021AAS...23821315Z Altcode: Current models for solar coronal jets generally suggest that they are formed by magnetic reconnection between open and closed magnetic field lines, but details of the triggering process for such magnetic reconnection are still not fully clear. Here we report observations of a set of coronal jets on November 13 2014 using data from the Reuven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Atmospheric Imaging Assembly (AIA). Usually, hot plasma in a coronal jet is located near the reconnection site or the base of the jet, as suggested by most models. However, for the first and one of the later jets in this series, RHESSI found strong hard x-ray (HXR) emissions at the top of the jet, well-modeled by an isothermal distribution, which indicates the existence of hot material at the top. The differential emission measure (DEM) analysis with AIA data shows qualitatively consistent results with RHESSI observations, and we present a comparison between HXR flux deduced from AIA DEMs and HXR flux directly measured by RHESSI. To identify possible drivers for those jets, we calculate the jet speeds in multiple AIA filters and compare them with, for example, the upper limit of chromospheric evaporation. This work will provide new constraints on mechanisms for coronal jet formation. 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: 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: What Percentage Of The Brightest Coronal Loops Are Rooted In Mixed-polarity Magnetic Flux? Authors: Tiwari, S. K.; Evans, C. L.; Panesar, N.; Prasad, A.; Moore, R. Bibcode: 2021AAS...23820502T Altcode: We have previously shown (Tiwari et al. 2017, ApJ Letters, 843, L20) that the heating in active region (AR) coronal loops depends systematically on their photospheric magnetic setting. There, we found that the brightest and hottest loops of ARs are the ones connecting sunspot umbra/penumbra at one end to (a) penumbra, (b) unipolar plage, or (c) mixed-polarity plage on the other end. The coolest loops are the ones that connect sunspot umbra at both ends. In this work we study the brightest loops during 24 hours in the core of the active region that was observed by Hi-C 2.1. These loops have neither foot in sunspot umbra or penumbra, but in plage. We investigate what percentage of the brightest coronal loops (in SDO/AIA Fe XVIII emission) have mixed-polarity magnetic flux at least at one of their feet, and so the heating could be driven by magnetic flux cancellation. We confirm the footpoint locations of loops via non-force-free field extrapolations (using SDO/HMI magnetograms) and find that ∼40% of the loops have both feet in unipolar flux, and ∼60% of the loops have at least one foot in mixed-polarity flux. The loops having mixed-polarity foot-point flux are ∼15% longer lived on average than the ones with both feet unipolar, but their peak-intensity averages do not show any significant difference. While the presence of mixed-polarity magnetic flux at least at one foot in majority of loops strongly supports the cancellation idea, the absence of mixed-polarity magnetic flux (to the detection limit of HMI) in about 40% of the loops suggests cancellation may not be necessary for heating coronal loops, but rather might enhance heating by some factor. We will further discuss some points that support, and some points that challenge, the flux cancellation idea of coronal heating. 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: 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: Are the Brightest Coronal Loops Always Rooted in Mixed-polarity Magnetic Flux? Authors: Tiwari, Sanjiv K.; Evans, Caroline L.; Panesar, Navdeep K.; Prasad, Avijeet; Moore, Ronald L. Bibcode: 2021ApJ...908..151T Altcode: 2021arXiv210210146T A recent study demonstrated that freedom of convection and strength of magnetic field in the photospheric feet of active-region (AR) coronal loops, together, can engender or quench heating in them. Other studies stress that magnetic flux cancellation at the loop-feet potentially drives heating in loops. We follow 24 hr movies of a bipolar AR, using extreme ultraviolet images from the Atmospheric Imaging Assembly/Solar Dynamics Observatory (SDO) and line-of-sight (LOS) magnetograms from the Helioseismic and Magnetic Imager (HMI)/SDO, to examine magnetic polarities at the feet of 23 of the brightest coronal loops. We derived Fe XVIII emission (hot-94) images (using the Warren et al. method) to select the hottest/brightest loops, and confirm their footpoint locations via non-force-free field extrapolations. From 6″ × 6″ boxes centered at each loop foot in LOS magnetograms we find that ∼40% of the loops have both feet in unipolar flux, and ∼60% of the loops have at least one foot in mixed-polarity flux. The loops with both feet unipolar are ∼15% shorter lived on average than the loops having mixed-polarity foot-point flux, but their peak-intensity averages are equal. The presence of mixed-polarity magnetic flux in at least one foot in the majority of the loops suggests that flux cancellation at the footpoints may drive most of the heating. But the absence of mixed-polarity magnetic flux (to the detection limit of HMI) in ∼40% of the loops suggests that flux cancellation may not be necessary to drive heating in coronal loops—magnetoconvection and field strength at both loop feet possibly drive much of the heating, even in the cases where a loop foot presents mixed-polarity magnetic flux. Title: Fine-scale explosive energy release at sites of magnetic flux cancellation in the core of a solar active region: Hi-C 2.1, IRIS and SDO observations Authors: Tiwari, Sanjiv Kumar; Moore, Ronald; De Pontieu, Bart; Winebarger, Amy; Panesar, Navdeep Kaur Bibcode: 2021cosp...43E1779T Altcode: The second sounding-rocket flight of the High-Resolution Coronal Imager (Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution (~250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 A, of a solar active region (AR NOAA 12712) near solar disk center. Three morphologically-different types (I: dot-like, II: loop-like, & III: surge/jet-like) of fine-scale sudden brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is resemble IRIS bombs (in size, and brightness with respect to surroundings), our dot-like events are apparently much hotter, and shorter in span (70 s). Because Dot-like brightenings are not as clearly discernible in AIA 171 A as in Hi-C 172 A, they were not reported before. We complement the 5-minute-duration Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying flux cancellation at the microflare's polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light curves from Hi-C, AIA and IRIS peak nearly simultaneously for many of these events and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening events have chromospheric/transition-region origin. 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: Citizen science to identify and analyze coronal jets in SDO/AIA data Authors: Musset, S.; Glesener, L.; Fortson, L.; Wright, D.; Kapsiak, C.; Hurlburt, N. E.; Panesar, N. K.; Fleishman, G. D. Bibcode: 2020AGUFMSH0240006M Altcode: Coronal jets are collimated ejections of plasma that are found to be ubiquitous in the solar atmosphere, at different scales and in different regions of the Sun. They are interpreted as the result of energy release in the solar atmosphere when magnetic reconnection involves both closed and open magnetic field lines. Jets are therefore suspected to be associated with the escape of energetic particles from the solar atmosphere and possibly with perturbations of the solar wind. The Atmospheric Imaging Assembly (AIA) on board the Solar Dynamic Observatory (SDO) provides high-cadence and high-resolution images of the solar atmosphere in which coronal jets can be identified and studied. However, the detection of such events via automatic algorithms has been limited and is better achieved by human annotation of the data. In order to detect and catalog coronal jets in the AIA data set, we designed a citizen science project on the Zooniverse platform, where participants can report the precise position and timing of solar jets, along with an indication of their extent. The use of citizen science provides the opportunity to perform this kind of analysis on a large amount of data, and to derive the average values of the jet properties reported by multiple volunteers, removing some of the bias inherent in a single expert observer reporting such properties. This catalog of jet events will provide a useful database for future jet studies, including statistical studies, and a training set for a machine learning approach to the problem of the detection of coronal jets in EUV data sets. Title: Fine-scale explosive energy release at sites of magnetic flux cancellation in the core of a solar active region: Hi-C 2.1, IRIS and SDO observations Authors: Tiwari, S. K.; Panesar, N. K.; Moore, R. L.; De Pontieu, B.; Winebarger, A. R. Bibcode: 2020AGUFMSH0010007T Altcode: The second sounding-rocket flight of the High-Resolution Coronal Imager (Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution (~250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 Å, of a solar active region (AR NOAA 12712) near solar disk center. Three morphologically-different types (I: dot-like, II: loop-like, & III: surge/jet-like) of fine-scale sudden brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is resemble IRIS bombs (in size, and brightness with respect to surroundings), our dot-like events are apparently much hotter, and shorter in span (70 s). Because Dot-like brightenings are not as clearly discernible in AIA 171 Å as in Hi-C 172 Å, they were not reported before. We complement the 5-minute-duration Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying flux cancellation at the microflare's polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light curves from Hi-C, AIA and IRIS peak nearly simultaneously for many of these events and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening events have chromospheric/transition-region origin. 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: 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: 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: A Solar Magnetic-fan Flaring Arch Heated by Nonthermal Particles and Hot Plasma from an X-Ray Jet Eruption Authors: Lee, Kyoung-Sun; Hara, Hirohisa; Watanabe, Kyoko; Joshi, Anand D.; Brooks, David H.; Imada, Shinsuke; Prasad, Avijeet; Dang, Phillip; Shimizu, Toshifumi; Savage, Sabrina L.; Moore, Ronald; Panesar, Navdeep K.; Reep, Jeffrey W. Bibcode: 2020ApJ...895...42L Altcode: 2020arXiv200509875L We have investigated an M1.3 limb flare, which develops as a magnetic loop/arch that fans out from an X-ray jet. Using Hinode/EIS, we found that the temperature increases with height to a value of over 107 K at the loop top during the flare. The measured Doppler velocity (redshifts of 100-500 km s-1) and the nonthermal velocity (≥100 km s-1) from Fe XXIV also increase with loop height. The electron density increases from 0.3 × 109 cm-3 early in the flare rise to 1.3 × 109 cm-3 after the flare peak. The 3D structure of the loop derived with Solar TErrestrial RElations Observatory/EUV Imager indicates that the strong redshift in the loop-top region is due to upflowing plasma originating from the jet. Both hard X-ray and soft X-ray emission from the Reuven Ramaty High Energy Solar Spectroscopic Imager were only seen as footpoint brightenings during the impulsive phase of the flare, then, soft X-ray emission moved to the loop top in the decay phase. Based on the temperature and density measurements and theoretical cooling models, the temperature evolution of the flare arch is consistent with impulsive heating during the jet eruption followed by conductive cooling via evaporation and minor prolonged heating in the top of the fan loop. Investigating the magnetic field topology and squashing factor map from Solar Dynamics Observatory/HMI, we conclude that the observed magnetic-fan flaring arch is mostly heated from low atmospheric reconnection accompanying the jet ejection, instead of from reconnection above the arch as expected in the standard flare model. 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: A CME-Producing Solar Eruption from the Interior of a Twisted Emerging Bipole Authors: Moore, R. L.; Adams, M.; Panesar, N. K.; Falconer, D. A.; Tiwari, S. K. Bibcode: 2019AGUFMSH43D3355M Altcode: In a negative-polarity coronal hole, magnetic flux emergence, seen by the Solar Dynamics Observatory's (SDO) Helioseismic Magnetic Imager (HMI), begins at approximately 19:00 UT on March 3, 2016. The emerged magnetic field produced sunspots with penumbrae by 3:00 UT on March 4, which NOAA numbered 12514. The emerging magnetic field is largely bipolar with the opposite-polarity fluxes spreading apart overall, but there is simultaneously some convergence and cancellation of opposite-polarity flux at the polarity inversion line (PIL) inside the emerging bipole. The emerging bipole shows obvious overall left-handed shear and/or twist in its magnetic field and corresponding clockwise rotation of the two poles of the bipole about each other as the bipole emerges. The eruption comes from inside the emerging bipole and blows it open to produce a CME observed by SOHO/LASCO. That eruption is preceded by flux cancellation at the emerging bipole's interior PIL, cancellation that plausibly builds a sheared and twisted flux rope above the interior PIL and finally triggers the blow-out eruption of the flux rope via photospheric-convection-driven slow tether-cutting reconnection of the legs of the sheared core field, low above the interior PIL, as proposed by van Ballegooijen and Martens (1989, ApJ, 343, 971) and Moore and Roumeliotis (1992, in Eruptive Solar Flares, ed. Z. Svestka, B.V. Jackson, and M.E. Machado [Berlin:Springer], 69). The production of this eruption is a (perhaps rare) counterexample to solar eruptions that result from external collisional shearing between opposite polarities from two distinct emerging and/or emerged bipoles (Chintzoglou et al., 2019, ApJ, 871:67). Title: Are the brightest coronal loops always rooted in mixed-polarity magnetic flux? Authors: Evans, C.; Tiwari, S. K.; Panesar, N. K.; Prasad, A.; Moore, R. L. Bibcode: 2019AGUFMSH41F3324E Altcode: Magnetic energy dissipated in coronal loops heats the Sun's corona to millions of Kelvin. Some recent investigations indicate that in addition to the required magnetoconvection and field strength, heating in the brightest coronal loops are driven by flux cancellation at the loop-feet. To find coronal loop footpoints , we selected extreme ultraviolet (EUV) data from the Atmospheric Imaging Assembly (AIA) and line- of-sight (LOS) magnetograms from the Helioseismic and Magnetic Imager (HMI), both on-board the Solar Dynamics Observatory (SDO). We located the footpoints of 28 brightest coronal loops of the bipolar active region NOAA 12712 on 28 May 2018 in hot 94 images (calculated using the Warren et al. method) and confirm the location of these footpoints via non-force free field extrapolations. We examine the photospheric magnetic field in 6" boxes centered at each footpoint and find that ~20% of loops have both feet in unipolar magnetic flux, ~10% loops have both feet in mixed-polarity flux, and ~70% of loops have one foot in unipolar and one in mixed-polarity flux. The presence of mixed-polarity magnetic flux in at least one foot of majority of the brightest coronal loops suggests that flux cancellation at the footpoints may drive heating in them. However, the absence of mixed-polarity magnetic flux (to the detection limit of HMI) in a significant number of the brightest coronal loops suggests that flux cancellation may not be necessary to drive heating in the loops - the combination of magnetoconvection and the magnetic field strength at the footpoints could be responsible for much of the coronal loop heating even in cases where a footpoint presents mixed-polarity magnetic flux. 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: Fine-scale explosive energy release at sites of magnetic flux cancellation in the core of the solar active region observed by Hi-C 2.1, IRIS and SDO Authors: Tiwari, S. K.; Panesar, N. K.; Moore, R. L.; De Pontieu, B.; Winebarger, A. R. Bibcode: 2019AGUFMSH31C3323T Altcode: The second sounding-rocket flight of the High-Resolution Coronal Imager (Hi-C 2.1) provided unprecedentedly-high spatial and temporal resolution 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: Fine-scale Explosive Energy Release at Sites of Prospective Magnetic Flux Cancellation in the Core of the Solar Active Region Observed by Hi-C 2.1, IRIS, and SDO Authors: Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.; De Pontieu, Bart; Winebarger, Amy R.; Golub, Leon; Savage, Sabrina L.; Rachmeler, Laurel A.; Kobayashi, Ken; Testa, Paola; Warren, Harry P.; Brooks, David H.; Cirtain, Jonathan W.; McKenzie, David E.; Morton, Richard J.; Peter, Hardi; Walsh, Robert W. Bibcode: 2019ApJ...887...56T Altcode: 2019arXiv191101424T The second Hi-C flight (Hi-C 2.1) provided unprecedentedly high spatial and temporal resolution (∼250 km, 4.4 s) coronal EUV images of Fe IX/X emission at 172 Å of AR 12712 on 2018 May 29, during 18:56:21-19:01:56 UT. Three morphologically different types (I: dot-like; II: loop-like; III: surge/jet-like) of fine-scale sudden-brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. Although type Is (not reported before) resemble IRIS bombs (in size, and brightness with respect to surroundings), our dot-like events are apparently much hotter and shorter in span (70 s). We complement the 5 minute duration Hi-C 2.1 data with SDO/HMI magnetograms, SDO/AIA EUV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying likely flux cancellation at the microflare’s polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. In types I and II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow. The light curves from Hi-C, AIA, and IRIS peak nearly simultaneously for many of these events, and none of the events display a systematic cooling sequence as seen in typical coronal flares, suggesting that these tiny brightening events have chromospheric/transition region origin. 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: Fine-scale explosive energy release at sites of magnetic flux cancellation in the core of the solar active region observed by HiC2.1, IRIS and SDO Authors: Tiwari, Sanjiv K.; Panesar, Navdeep; Moore, Ronald L.; De Pontieu, Bart; Testa, Paola; Winebarger, Amy R. Bibcode: 2019AAS...23411702T Altcode: The second sounding-rocket flight of the High-Resolution Coronal Imager (HiC2.1) provided unprecedentedly-high spatial and temporal resolution (150 km, 4.5 s) coronal EUV images of Fe IX/X emission at 172 Å, of a solar active region (AR NOAA 12712) near solar disk center. Three morphologically-different types (I: dot-like, II: loop-like, & III: surge/jet-like) of fine-scale sudden brightening events (tiny microflares) are seen within and at the ends of an arch filament system in the core of the AR. We complement the 5-minute-duration HiC2.1 data with SDO/HMI magnetograms, SDO/AIA EUV and UV images, and IRIS UV spectra and slit-jaw images to examine, at the sites of these events, brightenings and flows in the transition region and corona and evolution of magnetic flux in the photosphere. Most, if not all, of the events are seated at sites of opposite-polarity magnetic flux convergence (sometimes driven by adjacent flux emergence), implying flux cancellation at the polarity inversion line. In the IRIS spectra and images, we find confirming evidence of field-aligned outflow from brightenings at the ends of loops of the arch filament system. These outflows from both ends of the arch filament system are seen as bi-directional flows in the arch filament system, suggesting that the well-known counter-streaming flows in large classical filaments could be driven in the same way as in this arch filament system: by fine-scale jet-like explosions from fine-scale sites of mixed-polarity field in the feet of the sheared field that threads the filament. Plausibly, the flux cancellation at these sites prepares and triggers a fine scale core-magnetic-field structure (a small sheared/twisted core field or flux rope along and above the cancellation line) to explode. In types I & II the explosion is confined, while in type III the explosion is ejective and drives jet-like outflow in the manner of larger jets in coronal holes, quiet regions, and active regions. 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: Invisibility of Solar Active Region Umbra-to-Umbra Coronal Loops: New Evidence that Magnetoconvection Drives Solar-Stellar Coronal Heating Authors: Moore, Ronald L.; Tiwari, Sanjiv; Thalmann, Julia; Panesar, Navdeep; Winebarger, Amy Bibcode: 2019AAS...23410603M Altcode: How magnetic energy is injected and released in the solar corona, keeping it heated to several million degrees, remains elusive. The corona is shaped by the magnetic field that fills it and the heating of the corona generally increases with increasing strength of the field. For each of two bipolar solar active regions having one or more sunspots in each of the two main opposite-polarity domains of magnetic flux, from comparison of a nonlinear force-free model of the active region's three-dimensional coronal magnetic field to observed extreme-ultraviolet coronal loops, we find that (1) umbra-to-umbra loops, despite being rooted in the strongest magnetic flux at both ends, are invisible, and (2) the brightest loops have one foot in a sunspot umbra or penumbra and the other foot in another sunspot's penumbra or in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra loops is new evidence that magnetoconvetion drives solar-stellar coronal heating: evidently, the strong umbral field at both ends quenches the magnetoconvection and hence the heating. Broadly, our results indicate that depending on the field strength in both feet, the photospheric feet of a coronal loop on any convective star can either engender or quench coronal heating in the body of the loop.

This work was supported by funding from the Heliophysics Division of NASA's Science Mission Directorate, from NASA's Postdoctoral Program, and from the Austrian Science Fund. The results have been published in The Astrophysical Journal Letters (Tiwari, S. K., Thalmann, J. K., Panesar, N. K., Moore, R. L., & Winebarger, A. R. 2017, ApJ Letters, 843:L20). Title: A CME-Producing Solar Eruption from the Interior of an Emerging Bipolar Active Region Authors: Adams, Mitzi L.; Moore, Ronald L.; Panesar, Navdeep; Falconer, David Bibcode: 2019AAS...23430501A Altcode: In a negative-polarity coronal hole, magnetic flux emergence, seen by the Solar Dynamics Observatory's (SDO) Helioseismic Magnetic Imager (HMI), begins at approximately 19:00 UT on March 3, 2016. The emerged magnetic field produced sunspots, which NOAA numbered 12514 two days later. The emerging magnetic field is largely bipolar with the opposite-polarity fluxes spreading apart overall, but there is simultaneously some convergence and cancellation of opposite-polarity flux at the polarity inversion line (PIL) inside the emerging bipole. In the first fifteen hours after emergence onset, three obvious eruptions occur, observed in the coronal EUV images from SDO's Atmospheric Imaging Assembly (AIA). The first two erupt from separate segments of the external PIL between the emerging positve-polarity flux and the extant surrounding negative-polarity flux, with the exploding magnetic field being prepared and triggered by flux cancellation at the external PIL. The emerging bipole shows obvious overall left-handed shear and/or twist in its magnetic field. The third and largest eruption comes from inside the emerging bipole and blows it open to produce a CME observed by SOHO/LASCO. That eruption is preceded by flux cancellation at the emerging bipole's interior PIL, cancellation that plausibly builds a sheared and twisted flux rope above the interior PIL and finally triggers the blow-out eruption of the flux rope via photospheric-convection-driven slow tether-cutting reconnection of the legs of the sheared core field, low above the interior PIL, as proposed by van Ballegooijen and Martens (1989, ApJ, 343, 971) and Moore and Roumeliotis (1992, in Eruptive Solar Flares, ed. Z. Svestka, B.V. Jackson, and M.E. Machado [Berlin:Springer], 69). The production of this eruption is a (perhaps rare) counterexample to solar eruptions that result from external collisional shearing between opposite polarities from two distinct emerging and/or emerged bipoles (Chintzoglou et al., 2019, ApJ, 871:67).

This work was supported by NASA, the NASA Postdoctoral Program (NPP), and NSF. 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: 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: Critical Magnetic Field Strengths for Solar Coronal Plumes in Quiet Regions and Coronal Holes? Authors: Avallone, Ellis A.; Tiwari, Sanjiv K.; Panesar, Navdeep K.; Moore, Ronald L.; Winebarger, Amy Bibcode: 2018ApJ...861..111A Altcode: 2018arXiv180511188A Coronal plumes are bright magnetic funnels found in quiet regions (QRs) and coronal holes (CHs). They extend high into the solar corona and last from hours to days. The heating processes of plumes involve dynamics of the magnetic field at their base, but the processes themselves remain mysterious. Recent observations suggest that plume heating is a consequence of magnetic flux cancellation and/or convergence at the plume base. These studies suggest that the base flux in plumes is of mixed polarity, either obvious or hidden in Solar Dynamics Observatory (SDO)/HMI data, but do not quantify it. To investigate the magnetic origins of plume heating, we select 10 unipolar network flux concentrations, four in CHs, four in QRs, and two that do not form a plume, and track plume luminosity in SDO/AIA 171 Å images along with the base flux in SDO/HMI magnetograms, over each flux concentration’s lifetime. We find that plume heating is triggered when convergence of the base flux surpasses a field strength of ∼200-600 G. The luminosity of both QR and CH plumes respond similarly to the field in the plume base, suggesting that the two have a common formation mechanism. Our examples of non-plume-forming flux concentrations, reaching field strengths of 200 G for a similar number of pixels as for a couple of our plumes, suggest that a critical field might be necessary to form a plume but is not sufficient for it, thus advocating for other mechanisms, e.g., flux cancellation due to hidden opposite-polarity field, at play. 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: 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: Birth of a Bipolar Active Region in a Small Solar Coronal Hole Authors: Adams, Mitzi; Panesar, Navdeep Kaur; Moore, Ronald L. Bibcode: 2018tess.conf20235A Altcode: We report on an the emergence of an anemone active region in a very small 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: Critical Magnetic Field Strengths for Unipolar Solar Coronal Plumes in Quiet Regions and Coronal Holes? Authors: Avallone, E. A.; Tiwari, S. K.; Panesar, N. K.; Moore, R. L. Bibcode: 2017AGUFMSH43A2797A Altcode: Coronal plumes are sporadic fountain-like structures that are bright in coronal emission. Each is a magnetic funnel rooted in a strong patch of dominant-polarity photospheric magnetic flux surrounded by a predominantly-unipolar magnetic network, either in a quiet region or a coronal hole. The heating processes that make plumes bright evidently involve the magnetic field in the base of the plume, but remain mysterious. Raouafi et al. (2014) inferred from observations that plume heating is a consequence of magnetic reconnection in the base, whereas Wang et al. (2016) showed that plume heating turns on/off from convection-driven convergence/divergence of the base flux. While both papers suggest that the base magnetic flux in their plumes is of mixed polarity, these papers provide no measurements of the abundance and strength of the evolving base flux or consider whether a critical magnetic field strength is required for a plume to become noticeably bright. To address plume production and evolution, we track the plume luminosity and the abundance and strength of the base magnetic flux over the lifetimes of six coronal plumes, using Solar Dynamics Observatory (SDO)/Atmospheric Imaging Assembly (AIA) 171 Å images and SDO/Helioseismic and Magnetic Imager (HMI) line-of-sight magnetograms. Three of these plumes are in coronal holes, three are in quiet regions, and each plume exhibits a unipolar base flux. We track the base magnetic flux over each plume's lifetime to affirm that its convergence and divergence respectively coincide with the appearance and disappearance of the plume in 171 Å images. We tentatively find that plume formation requires enough convergence of the base flux to surpass a field strength of ∼300-500 Gauss, and that quiet Sun and coronal-hole plumes both exhibit the same behavior in the response of their luminosity in 171 Å to the strength of the magnetic field in the base. 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: Invisibility of Solar Active Region Umbra-to-Umbra Coronal Loops: New Evidence that Magnetoconvection Drives Solar-Stellar Coronal Heating Authors: Tiwari, S. K.; Thalmann, J. K.; Panesar, N. K.; Moore, R. L.; Winebarger, A. R. Bibcode: 2017AGUFMSH43A2789T Altcode: Coronal heating generally increases with increasing magnetic field strength: the EUV/X-ray corona in active regions is 10-100 times more luminous and 2-4 times hotter than that in quiet regions and coronal holes, which are heated to only about 1.5 MK, and have fields that are 10-100 times weaker than that in active regions. From a comparison of a nonlinear force-free model of the three-dimensional active region coronal field to observed extreme-ultraviolet loops, we find that (1) umbra-to-umbra coronal loops, despite being rooted in the strongest magnetic flux, are invisible, and (2) the brightest loops have one foot in an umbra or penumbra and the other foot in another sunspot's penumbra or in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra loops is new evidence that magnetoconvection drives solar-stellar coronal heating: evidently, the strong umbral field at both ends quenches the magnetoconvection and hence the heating. Our results from EUV observations and nonlinear force-free modeling of coronal magnetic field imply that, for any coronal loop on the Sun or on any other convective star, as long as the field can be braided by convection in at least one loop foot, the stronger the field in the loop, the stronger the coronal heating. 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 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: 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: New Evidence that Magnetoconvection Drives Solar-Stellar Coronal Heating Authors: Tiwari, Sanjiv K.; Thalmann, Julia K.; Panesar, Navdeep K.; Moore, Ronald L.; Winebarger, Amy R. Bibcode: 2017ApJ...843L..20T Altcode: 2017arXiv170608035T How magnetic energy is injected and released in the solar corona, keeping it heated to several million degrees, remains elusive. Coronal heating generally increases with increasing magnetic field strength. From a comparison of a nonlinear force-free model of the three-dimensional active region coronal field to observed extreme-ultraviolet loops, we find that (1) umbra-to-umbra coronal loops, despite being rooted in the strongest magnetic flux, are invisible, and (2) the brightest loops have one foot in an umbra or penumbra and the other foot in another sunspot’s penumbra or in unipolar or mixed-polarity plage. The invisibility of umbra-to-umbra loops is new evidence that magnetoconvection drives solar-stellar coronal heating: evidently, the strong umbral field at both ends quenches the magnetoconvection and hence the heating. Broadly, our results indicate that depending on the field strength in both feet, the photospheric feet of a coronal loop on any convective star can either engender or quench coronal heating in the loop’s body. 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: 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: 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: Suppression of heating of coronal loops rooted in opposite polarity sunspot umbrae Authors: Tiwari, Sanjiv K.; Thalmann, Julia; Moore, Ronald; Panesar, Navdeep; Winebarger, Amy Bibcode: 2016shin.confE..61T Altcode: EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 Å images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-polarity plage region. The AIA 94 Å images show dim regions in the umbrae of the sunspots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the Heliosesmic Magnetic Imager (HMI) onboard SDO. The NLFFF model, validated by comparison of calculated model field lines with observed loops in AIA 193 and 94 Å, specifies the photospheric roots of the model field lines. Some model coronal magnetic field lines arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed. 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: 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: Suppression of heating of coronal loops rooted in opposite polarity sunspot umbrae Authors: Tiwari, Sanjiv K.; Thalmann, Julia K.; Moore, Ronald L.; Panesar, Navdeep; Winebarger, Amy R. Bibcode: 2016SPD....47.0336T Altcode: EUV observations of active region (AR) coronae reveal the presence of loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 A images we identify many clearly discernible coronal loops that connect plage or a sunspot of one polarity to an opposite-polarity plage region. The AIA 94 A images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the HMI onboard SDO. After validation of the NLFFF model by comparison of calculated model field lines and observed loops in AIA 193 and 94, we specify the photospheric roots of the model field lines. The model field then shows the coronal magnetic loops that arch from the dim umbral areas of the opposite polarity sunspots. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.We hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. In particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbra. Many transient, outstandingly bright, loops in the AIA 94 movie of the AR do have this expected rooting pattern. We will also present another example of AR in which we find a similar rooting pattern of coronal loops. 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: 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: 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: 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: Evidence of suppressed heating of coronal loops rooted in opposite polarity sunspot umbrae Authors: Tiwari, Sanjiv K.; Thalmann, Julia K.; Winebarger, Amy R.; Panesar, Navdeep K.; Moore, Ronald Bibcode: 2015TESS....120404T Altcode: Observations of active region (AR) coronae in different EUV wavelengths reveal the presence of various loops at different temperatures. To understand the mechanisms that result in hotter or cooler loops, we study a typical bipolar AR, near solar disk center, which has moderate overall magnetic twist and at least one fully developed sunspot of each polarity. From AIA 193 and 94 A images we identify many clearly discernible coronal loops that connect opposite-polarity plage or a sunspot to a opposite-polarity plage region. The AIA 94 A images show dim regions in the umbrae of the spots. To see which coronal loops are rooted in a dim umbral area, we performed a non-linear force-free field (NLFFF) modeling using photospheric vector magnetic field measurements obtained with the Heliosesmic Magnetic Imager (HMI) onboard SDO. After validation of the NLFFF model by comparison of calculated model field lines and observed loops in AIA 193 and 94 A, we specify the photospheric roots of the model field lines. The model field then shows the coronal magnetic loops that arch from the dim umbral area of the positive-polarity sunspot to the dim umbral area of a negative-polarity sunspot. Because these coronal loops are not visible in any of the coronal EUV and X-ray images of the AR, we conclude they are the coolest loops in the AR. This result suggests that the loops connecting opposite polarity umbrae are the least heated because the field in umbrae is so strong that the convective braiding of the field is strongly suppressed.From this result, we further hypothesize that the convective freedom at the feet of a coronal loop, together with the strength of the field in the body of the loop, determines the strength of the heating. In particular, we expect the hottest coronal loops to have one foot in an umbra and the other foot in opposite-polarity penumbra or plage (coronal moss), the areas of strong field in which convection is not as strongly suppressed as in umbrae. Many transient, outstandingly bright, loops in the AIA 94 A movie of the AR do have this expected rooting pattern. Title: On the Structure and Evolution of a Polar Crown Prominence/Filament System Authors: Panesar, N. K.; Innes, D. E.; Schmit, D. J.; Tiwari, S. K. Bibcode: 2014SoPh..289.2971P Altcode: 2014arXiv1402.4989P; 2014SoPh..tmp...50P Polar crown prominences, that partially circle the Sun's poles between 60° and 70° latitude, are made of chromospheric plasma. We aim to diagnose the 3D dynamics of a polar crown prominence using high-cadence EUV images from the Solar Dynamics Observatory (SDO)/AIA at 304, 171, and 193 Å and the Ahead spacecraft of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195 Å. Using time series across specific structures, we compare flows across the disk in 195 Å with the prominence dynamics seen on the limb. The densest prominence material forms vertical columns that are separated by many tens of Mm and connected by dynamic bridges of plasma that are clearly visible in 304/171 Å two-colour images. We also observe intermittent but repetitious flows with velocity 15 km s−1 in the prominence that appear to be associated with EUV bright points on the solar disk. The boundary between the prominence and the overlying cavity appears as a sharp edge. We discuss the structure of the coronal cavity seen both above and around the prominence. SDO/HMI and GONG magnetograms are used to infer the underlying magnetic topology. The evolution and structure of the prominence with respect to the magnetic field seems to agree with the filament-linkage model. Title: A Study of quiescent prominences using SDO and STEREO data Authors: Panesar, Navdeep Kaur Bibcode: 2014PhDT........78P Altcode: In this dissertation, we have studied the structure, dynamics and evolution of two quiescent prominences. Quiescent prominences are large structures and mainly associated with the quiet Sun region. For the analysis, we have used the high spatial and temporal cadence data from the Solar Dynamic Observatory (SDO), and the Solar Terrestrial Relations Observatory (STEREO). We combined the observations from two different directions and studied the prominence in 3D. In the study of polar crown prominence, we mainly investigated the prominence flows on limb and found its association with on-disk brightenings. The merging of diffused active region flux in the already formed chain of prominence caused the several brightenings in the filament channel and also injected the plasma upward with an average velocity of 15 km/s. In another study, we investigated the triggering mechanism of a quiescent tornado-like prominence. Flares from the neighboring active region triggered the tornado-like motions of the top of the prominence. Active region field contracts after the flare which results in the expansion of prominence cavity. The prominence helical magnetic field expands and plasma moves along the field lines which appear as a tornado-like activity. In addition, the thermal structure of the tornado-like prominence and neighbouring active region was investigated by analysing emission in six of the seven EUV channels from the SDO. These observational investigations led to our understanding of structure and dynamics of quiescent prominences, which could be useful for theoretical prominence models. Title: A solar tornado caused by flares Authors: Panesar, N. K.; Innes, D. E.; Tiwari, S. K.; Low, B. C. Bibcode: 2014IAUS..300..235P Altcode: An enormous solar tornado was observed by SDO/AIA on 25 September 2011. It was mainly associated with a quiescent prominence with an overlying coronal cavity. We investigate the triggering mechanism of the solar tornado by using the data from two instruments: SDO/AIA and STEREO-A/EUVI, covering the Sun from two directions. The tornado appeared near to the active region NOAA 11303 that produced three flares. The flares directly influenced the prominence-cavity system. The release of free magnetic energy from the active region by flares resulted in the contraction of the active region field. The cavity, owing to its superior magnetic pressure, expanded to fill this vacated space in the corona. We propose that the tornado developed on the top of the prominence due to the expansion of the prominence-cavity system. Title: A solar tornado triggered by flares? Authors: Panesar, N. K.; Innes, D. E.; Tiwari, S. K.; Low, B. C. Bibcode: 2013A&A...549A.105P Altcode: 2012arXiv1211.6569P Context. Solar tornados are dynamical, conspicuously helical magnetic structures that are mainly observed as a prominence activity.
Aims: We investigate and propose a triggering mechanism for the solar tornado observed in a prominence cavity by SDO/AIA on September 25, 2011.
Methods: High-cadence EUV images from the SDO/AIA and the Ahead spacecraft of STEREO/EUVI are used to correlate three flares in the neighbouring active-region (NOAA 11303) and their EUV waves with the dynamical developments of the tornado. The timings of the flares and EUV waves observed on-disk in 195 Å are analysed in relation to the tornado activities observed at the limb in 171 Å.
Results: Each of the three flares and its related EUV wave occurred within ten hours of the onset of the tornado. They have an observed causal relationship with the commencement of activity in the prominence where the tornado develops. Tornado-like rotations along the side of the prominence start after the second flare. The prominence cavity expands with the accelerating tornado motion after the third flare.
Conclusions: Flares in the neighbouring active region may have affected the cavity prominence system and triggered the solar tornado. A plausible mechanism is that the active-region coronal field contracted by the "Hudson effect" through the loss of magnetic energy as flares. Subsequently, the cavity expanded by its magnetic pressure to fill the surrounding low corona. We suggest that the tornado is the dynamical response of the helical prominence field to the cavity expansion.

Movies are available in electronic form at http://www.aanda.org Title: A study of quiescent prominences using SDO and STEREO data Authors: Panesar, Navdeep Kaur Bibcode: 2013PhDT.......414P Altcode: No abstract at ADS