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Author name code: neidig
ADS astronomy entries on 2022-09-14
author:"Neidig, Donald F. Jr."
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Title: On the Size of the Flare Associated with the Solar Proton
Event in 774 AD
Authors: Cliver, E. W.; Hayakawa, H.; Love, Jeffrey J.; Neidig, D. F.
2020ApJ...903...41C Altcode:
The 774 AD solar proton event (SPE) detected in cosmogenic nuclides
had an inferred >1 GV (>430 MeV) fluence estimated to have been
∼30-70 times larger than that of the 1956 February 23 ground level
event (GLE). The 1956 GLE was itself ∼2.5 times larger at >430 MeV
than the episode of strong GLE activity from 1989 August-October. We use
an inferred soft X-ray (SXR) class of X20 ± 10 for the 1956 February
23 eruptive flare as a bridge to the source flare for the 774 SPE. A
correlation of the >200 MeV proton fluences of hard-spectra post-1975
GLEs with the SXR peak fluxes of their associated flares yields an
SXR flare class of X285 ± 140 (bolometric energy of ∼(1.9 ± 0.7)
× 10<SUP>33</SUP> erg) for the 774 flare. This estimate is within
theoretical determinations of the largest flare the Sun could produce
based on the largest spot group yet observed. Assuming a single eruptive
flare source for the 774 SPE, the above estimate indicates that the Sun
can produce a threshold-level 10<SUP>33</SUP> erg superflare. If the 774
event originated in two closely timed, equal-fluence SPEs, the inferred
flare size drops to X180 ± 90 (∼(1.4 ± 0.5) × 10<SUP>33</SUP>
erg). We speculate on favorable solar conditions that can lead to
enhanced shock acceleration of high-energy protons in eruptive flares.
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Title: On the Origin of the Solar Moreton Wave of 2006 December 6
Authors: Balasubramaniam, K. S.; Cliver, E. W.; Pevtsov, A.; Temmer,
M.; Henry, T. W.; Hudson, H. S.; Imada, S.; Ling, A. G.; Moore, R. L.;
Muhr, N.; Neidig, D. F.; Petrie, G. J. D.; Veronig, A. M.; Vršnak,
B.; White, S. M.
2010ApJ...723..587B Altcode:
We analyzed ground- and space-based observations of the eruptive flare
(3B/X6.5) and associated Moreton wave (~850 km s<SUP>-1</SUP> ~270°
azimuthal span) of 2006 December 6 to determine the wave driver—either
flare pressure pulse (blast) or coronal mass ejection (CME). Kinematic
analysis favors a CME driver of the wave, despite key gaps in coronal
data. The CME scenario has a less constrained/smoother velocity versus
time profile than is the case for the flare hypothesis and requires an
acceleration rate more in accord with observations. The CME picture is
based, in part, on the assumption that a strong and impulsive magnetic
field change observed by a GONG magnetograph during the rapid rise phase
of the flare corresponds to the main acceleration phase of the CME. The
Moreton wave evolution tracks the inferred eruption of an extended
coronal arcade, overlying a region of weak magnetic field to the west
of the principal flare in NOAA active region 10930. Observations of
Hα foot point brightenings, disturbance contours in off-band Hα
images, and He I 10830 Å flare ribbons trace the eruption from 18:42
to 18:44 UT as it progressed southwest along the arcade. Hinode EIS
observations show strong blueshifts at foot points of this arcade
during the post-eruption phase, indicating mass outflow. At 18:45
UT, the Moreton wave exhibited two separate arcs (one off each flank
of the tip of the arcade) that merged and coalesced by 18:47 UT to
form a single smooth wave front, having its maximum amplitude in
the southwest direction. We suggest that the erupting arcade (i.e.,
CME) expanded laterally to drive a coronal shock responsible for the
Moreton wave. We attribute a darkening in Hα from a region underlying
the arcade to absorption by faint unresolved post-eruption loops.
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Title: The Solar Moreton Wave Of 6 December 2006: Evidence For A
CME Driver
Authors: Pevtsov, Alexei A.; Balasubramaniam, K. S.; Cliver, E. W.;
Neidig, D. F.; Petrie, G. J. D.
2009SPD....40.3703P Altcode:
We analyze ground- and space-based observations of the major eruptive
flare and associated Moreton wave of 6 December 2006. The Moreton wave
spanned 270° in azimuth and exhibited a variable speed time profile
as it propagated away from the source region. The Hα wave traveled
1.2 Rsun from the S06E63 site of the eruption and white-light flare
toward the southwest in 15 minutes where it disrupted a large quiescent
filament. A preceding coronal wave was observed in a single He 10830 Å
image. Potential field analysis of the active region magnetic fields
and a comparison of ISOON images of the eruptive flare in line-center
Hα with off-band images of the wave indicate that the Moreton wave
was driven by a coronal mass ejection.
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Title: Sunspot Numbers and Sunspot Irradiance Reductions as Obtained
with OSPAN Semi- automatic Analysis
Authors: Balasubramaniam, K. S.; Neidig, D. F.; Radick, R. R.;
Henry, T.
2007AGUFMSH13A1108B Altcode:
The USAF/AFRL Optical Solar PAtrol Network telescope (OSPAN) acquires
true continuum solar images (0.08 Å bandwidth) in the optical
region(6303.15 Å). OSPAN analysis software includes semi-automatic
routines for measuring (1) sunspot counts, which we compare with
counts obtained by traditional methods, and (2) solar irradiance
reductions due tosunspot blocking. We present measurements of the
variation of irradiance reductions as a function of the solar cycle,
including examples of irradiance reduction due to sunspot activity
during solarcycle maximum. This work was supported by US Air Force
Office of Scientific Research (AFOSR).
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Title: Moreton Waves And Filament Eruptions
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.
2007AAS...210.2504B Altcode: 2007BAAS...39..131B
Moreton waves are traditionally associated with large flares, and may
accompany filament and mass ejections. Using high-spectral resolution
and high cadence full-disk chromospheric imaging measurements, we track
two exceptional Moreton waves (2003 October 29 and 2006 December 6)
to understand the nature of this phenomenon. We employ arguments drawn
from spectroscopy, wave propagation and formation of prominences to
affirm the location of Moreton waves to coronal heights. We present
evidence that the Moreton wave sweeps filamentary material and thus
became visible in chromospheric spectral line. We suggest a model to
describe the associations between the flares, filament eruptions and
coronal mass ejections.
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Title: Are Moreton Waves Coronal Phenomena?
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.
2007ApJ...658.1372B Altcode:
We report on permeability characteristics of the upper solar atmosphere
due to the progression of a Moreton wave. An exceptional Moreton wave
is tracked to cover most of the Sun, following an unusually large
solar X-ray flare observed on 2003 October 29. Using Hα intensity
and Doppler measurements, the Moreton wave is tracked for as long as
12 minutes. Moving outward, the wave circumnavigates strong-field
active regions. The wave sweeps through solar magnetic neutral
lines, disrupting material from filament and filament channels,
thereby accentuating the visibility of the wave. We establish that
the requirement for the visibility of a Moreton wave is the necessary
presence of higher density material in the layers of the corona, besides
reaffirming that Moreton waves are observed only when the speed of the
disturbance exceeds Mach 2. We suggest that the cause can be a removal
of significant amount of material from the solar upper atmosphere due
to a coronal mass ejection.
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Title: Large scale solar chromospheric eruptive activity - a signature
of magnetic reconnection
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Hock,
R. A.
2006ilws.conf...65B Altcode:
A new class of large-scale solar chromospheric eruptive activity,
sequential chromospheric brightenings (SCBs), has been reported by
Balasubramaniam et al. (2005). SCBs are chromospheric network points
(outside of active regions) that sequentially brighten over a narrow
path of chromospheric network points. SCBs appear as single or multiple
trains of brightenings, the underlying magnetic poles of each train
having the same (negative or positive) polarity. SCBs may be associated
with the following phenomena: solar flares, filament eruptions, CMEs,
disappearing transequatorial loops, Moreton and EIT waves. We present
an understanding of SCBs and their place in respect to these related
eruptive phenomena.
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Title: Accumulation of Filament Material at the Boundaries of
Supergranular Cells
Authors: Pevtsov, A. A.; Neidig, D.
2005ASPC..346..219P Altcode:
We use ISOON full disk H-alpha images to study fragmented filaments
whose main body consists of non-connected clumps of dark filament
material. Fragmented filaments may represent the early evolution
of filament development. We describe two filaments that began
their formation with a few individual clumps, which later grew and
interconnected to form a continuous body typical of a chromospheric
filament. We show that there is a tendency for clumps to be situated
over the boundaries of supergranular cells. We suggest that this
preference in initial accumulation of material above areas of persistent
downflows (boundary of supergranules) may be a key in understanding why
the chromospheric filaments show a much stronger hemispheric helicity
rule than other solar features (e.g. sunspots).
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Title: Sequential Chromospheric Brightenings beneath a Transequatorial
Halo Coronal Mass Ejection
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.; Cliver,
E. W.; Thompson, B. J.; Young, C. A.; Martin, S. F.; Kiplinger, A.
2005ApJ...630.1160B Altcode:
Analyses of multiwavelength data sets for a solar eruption at ~21:30
UT on 2002 December 19 show evidence for the disappearance of a
large-scale, transequatorial coronal loop (TL). In addition, coronal
manifestations of the eruption (based on SOHO EIT and LASCO images)
include large-scale coronal dimming, flares in each associated active
region in the northern and southern hemispheres, and a halo CME. We
present detailed observations of the chromospheric aspects of this
event based on Hα images obtained with the ISOON telescope. The
ISOON images reveal distant flare precursor brightenings, sympathetic
flares, and, of most interest herein, four nearly cospatial propagating
chromospheric brightenings. The speeds of the propagating disturbances
causing these brightenings are 600-800 km s<SUP>-1</SUP>. The inferred
propagating disturbances have some of the characteristics of Hα
and EIT flare waves (e.g., speed, apparent emanation from the flare
site, subsequent filament activation). However, they differ from
typical Hα chromospheric flare waves (also known as Moreton waves)
because of their absence in off-band Hα images, small angular
arc of propagation (<30°), and their multiplicity. Three of
the four propagating disturbances consist of a series of sequential
chromospheric brightenings of network points that suddenly brighten in
the area beneath the TL that disappeared earlier. SOHO MDI magnetograms
show that the successively brightened points that define the inferred
propagating disturbances were exclusively of one polarity, corresponding
to the dominant polarity of the affected region. We speculate that
the sequential chromospheric brightenings represent footpoints of
field lines that extend into the corona, where they are energized in
sequence by magnetic reconnection as coronal fields tear away from
the chromosphere during the eruption of the transequatorial CME. We
report briefly on three other events with similar narrow propagating
disturbances that were confined to a single hemisphere.
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Title: ISOON + SOLIS: Merging the Data Products
Authors: Radick, R.; Dalrymple, N.; Mozer, J.; Wiborg, P.; Harvey,
J.; Henney, C.; Neidig, D.
2005AGUSMSP51A..03R Altcode:
The combination of AFRL's ISOON and NSO's SOLIS offers significantly
greater capability than the individual instruments. We are working
toward merging the SOLIS and ISOON data products in a single central
facility. The ISOON system currently includes both an observation
facility and a remote analysis center (AC). The AC is capable of
receiving data from both the ISOON observation facility as well as
external sources. It archives the data and displays corrected images
and time-lapse animations. The AC has a large number of digital tools
that can be applied to solar images to provide quantitative information
quickly and easily. Because of its convenient tools and ready archival
capability, the ISOON AC is a natural place to merge products from
SOLIS and ISOON. We have completed a preliminary integration of the
ISOON and SOLIS data products. Eventually, we intend to distribute
viewing stations to various users and academic institutions, install
the AC software tools at a number of user locations, and publish
ISOON/SOLIS data products jointly on a common web page. In addition,
SOLIS data products, separately, are and will continue to be fully
available on the NSO,s Digital Library and SOLIS web pages, and via the
Virtual Solar Observatory. This work is being supported by the National
Science Foundation and the Air Force Office of Scientific Research.
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Title: ISOON Observations of Late-Cycle Solar Flares and Associated
Activity During October and November 2003
Authors: Neidig, D.
2004AAS...204.4710N Altcode: 2004BAAS...36..738N
The ISOON system (Improved Solar Observing Optical Network) recorded
numerous large flares associated with the disk passage of several highly
active regions during late October and early November 2003. Included is
the 1947 UT X28 superflare on November 4. Wavelengths covered include
hydrogen-alpha (line center and wings) abd 6303 A continuum. Results
are presented showing the evolution of the sunspot groups (motions
and areas) prior to these flares, as well as the associated phenomena,
development, and light curves of the flares themselves. Chromospheric
signatures of coronal eruptive events may be evident in the form of
nearly simultaneous, widely-spaced flares, brightenings, and propagating
disturbances. Several Moreton waves were observed, including one that
appears to be a wave train encompassing two or more full wavelengths,
with measurable propagation velocity, velocity amplitude, and period.
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Title: How big was the Carrington 1859 Flare?
Authors: Cliver, E. W.; Svalgaard, L.; Neidig, D. F.
2004AGUSMSH43A..03C Altcode:
The 1859 space weather event was distinguished by its great geomagnetic
storm, widespread low-latitude aurora, and intense solar energetic
particle event (inferred from the NO<SUB>3</SUB> concentration in
polar ice cores). Arguably each of these three effects was the largest
ever observed. What can we say about the size of the associated solar
flare? We have two observations with which to make such an assessment:
(1) Carrington's and Hodgson's report of the white-light flare and (2)
the solar flare effect or magnetic crochet observed in the Kew and
Greenwich magnetograms. Estimates of the area, duration, spectrum,
and intensity of the white-light emission indicate a large (~2 x
10<SUP>30</SUP> erg) but not unequalled event (the white-light emission
of the 24 April 1984 >X13 flare contained ~6 x 10<SUP>30</SUP>
erg). The magnetic crochet of 130 nT in the horizontal force,
however, exceeds that for all >X10 soft X-ray flares observed from
1984-2002 (we are presently compiling magnetic data for the recent
October-November 2003 activity for comparison with the 1859 event). Thus
at this point, we can conservatively say that Carrington's flare likely
had a soft X-ray classification >X10 and was at least comparable
to the largest flares recorded during the spacecraft era.
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Title: Introducing ISOON, The Improved Solar Observing Optical Network
Authors: Neidig, D.; Wiborg, P.; Mozer, J.; Dalrymple, N.; Dunn, R.;
Gregory, S.; Gullixson, C.
2003SPD....34.2021N Altcode: 2003BAAS...35..848N
ISOON is a semi-autonomous, remotely commandable solar patrol telescope
for studies of solar activity in support of space weather specifications
and forecasts. ISOON was originally planned to consist of a world-wide
three-site network with high speed networking to a central command and
analysis facility. Under USAF funding, the prototype unit is currently
in operation, providing H-alpha, off-band, and continuum images. This
paper briefly describes the ISOON system and its capabilities, analysis
software, data archive, products, and its research and space weather
support applications. Further information as well as real time images
can be found on the ISOON web page at www.nso.edu/nsosp/isoon.
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Title: Signatures of Large Scale Coronal Eruptive Activity, Associated
Flares, and Propagating Chromospheric Disturbances
Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F.;
Cliver, E. W.; Young, C. A.; Martin, S. F.; Kiplinger, A. L.
2003SPD....34.0505B Altcode: 2003BAAS...35..814B
Analyses of multi-wavelength data sets on 2002 December 19 at
approximately 2150 UT show evidence of a large-scale, transequatorial
coronal eruption associated with simultaneous flares in active
regions in both hemispheres. The coronal manifestations (based on
EIT, LASCO, and TRACE images) include a large coronal dimming,
an opening/restructuring of magnetic fields, the formation of a
transient coronal hole, and a halo CME. In the chromosphere, ISOON
H-alpha images show distant flare precursor brightenings and several
sympathetic flares. Originating near the main flare is a rapidly
propagating (800 km/s), narrowly channeled disturbance detectable as a
sequential brightening of numerous pre-existing points in the H-alpha
chromospheric network. This disturbance is not a chromospheric Moreton
wave, but it does produce a temporary activation of a transequatorial
filament. This filament does not erupt nor do any other filaments
in the vicinity. MDI magnetograms show that the brightened network
points are all of the same polarity (the dominant polarity among the
points in the disturbance's path), suggesting that the affected field
lines extend into the corona where they are energized in sequence
as the eruption tears away. <P />Three other similar eruptive events
(non-transequatorial) that we studied, while they are less impressive,
show most of the same phenomena including distant sympathetic flares and
a propagating disturbance showing close adherence to the monopolarity
rule. Two of these events do include filament eruptions near the main
flare. We conclude that the observations of these four events are
consistent with large scale coronal eruptive activity that triggers
nearly simultaneous surface activity of various forms separated by
distances on the same scale as the coronal structures themselves. A
filament eruption at the main flare site appears not to be a necessity
in this type of eruptive activity.
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Title: The USAF Improved Solar Observing Optical Network (ISOON)
and its Impact on Solar Synoptic Data Bases
Authors: Neidig, D.; Wiborg, P.; Confer, M.; Haas, B.; Dunn, R.;
Balasubramaniam, K. S.; Gullixson, C.; Craig, D.; Kaufman, M.; Hull,
W.; McGraw, R.; Henry, T.; Rentschler, R.; Keller, C.; Jones, H.;
Coulter, R.; Gregory, S.; Schimming, R.; Smaga, B.
1998ASPC..140..519N Altcode: 1998ssp..conf..519N
No abstract at ADS
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Title: ISOON: The Improved Solar Observing Optical Network
Authors: Neidig, D.; Confer, M.; Wiborg, P.; Dunn, R.; Balasubramaniam,
K. S.; Frederick, R.; Kutzman, R.; Soli, R.; Keller, C.; Gullixson,
C.; Alios, Inter
1997SPD....28.0224N Altcode: 1997BAAS...29..897N
Efforts are under way to replace the existing SOON system, which was
designed in the 1970s, with a new system (ISOON) based on a fully
tunable narrow-band filter and CCD detector. ISOON would feature
autonomous, rapid-cadence solar imaging and remote operation at four
sites, and would transmit solar images in near real time to central
facilities at Falcon AFB and Boulder CO, for use in space weather
forecasting. The ISOON technical approach is to retain the front
end of the existing SOON telescope, but replace the optical bench,
birefringent filter, and spectrograph with a dual Fabry-Perot filter
system and secondary optics contained in a single pod. ISOON data
products will include full-disk H-alpha, continuum, and line-of-sight
magnetograms on 1-arcsecond pixels. High- resolution images (limited
field, 0.3-arcsecond pixels) would be available via a future upgrade
in the secondary optics. ISOON will also be capable of acquiring
vector magnetic field images via a software upgrade to be added at a
future time.
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Title: Observations of Faint, Outlying Loop Systems in Large Flares
Authors: Neidig, Donald F.; Švestka, Zdeněk; Cliver, Edward W.;
Airapetian, Vladimir; Henry, Timothy W.
1997SoPh..170..321N Altcode:
Faintly visible, darkened regions in Hα lying outside but
adjacentto bright flare emissionwere found to occur in 10 of 31 major
flares investigated. Without exception, the darkenings occur over
`magnetically neutral' areas, and these are usually bordered by ridges
ofoppositely-poled field, where one border is shared in common with a
flare ribbon. Thedarkenings probably result from the formation of faint,
outlying loop systems, similar topost-flare loops seen in absorption,
but which are connected to magnetic features outsidethe flare and
are unresolved or only marginally resolved in patrol images. Simple
modelsfor post-flare loops incorporating the results of statistical
equilibrium calculations readilydemonstrate that darkenings of several
percent (consistent with our photometric measurements) can be produced
by loop structures of cross-sectional diameter ≈ 10<SUP>2</SUP> km
(unresolved by patrol instruments) and containing gas at densities 5 ×
10<SUP>10</SUP>-5 × 10<SUP>11</SUP> cm<SUP>-3</SUP> andtemperatures
8000-15000 K. Outlying loop systems might be formed by magnetic
fieldreconnection, analogous to the mechanism ascribed to eruptive
two-ribbon flares, butassociated with field structures adjacent to the
flare. Alternatively, these outlying loopsystems may not erupt but
become visible as a result of heating and chromospheric evaporation
at the footpoints shared with the flare ribbon. In either case, the
observations presented here have interesting implications for both
the spatial scale and the topology of thecoronal magnetic fields in
which eruptions occur.
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Title: The Role of High-Energy Protons and Electrons in Powering
the Solar White-Light Flare Emission
Authors: Rieger, E.; Neidig, D. F.; Engfer, D. W.; Strelow, D.
1996SoPh..167..307R Altcode:
The temporal histories of three intense and impulsive gamma-ray flares,
for which also white-light emission had been observed, are analyzed
in order to test the role of high-energy particles- electrons and
protons - in powering the optical continuum. By comparing the light
curves at optical wavelengths and at X-ray and gamma-ray energies, we
find a good correlation of the main peaks of emission, which confirms
previous findings that the continuum emission is most likely associated
with the energy loss of energetic particles. The power carried by
the greater-than-50 keV nonthermal electrons may be sufficient to
balance the optical emission. The power residing in protons or ions
with energies greater than 1 MeV depends largely on the spectral shape
of the particle distribution. Only if this is similar to a power law,
may the energy carried by these high-energy particles be sufficient
to balance the white-light flare emission.
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Title: White-Light Reflecting Corona graph for the SWATH Mission
Authors: Smartt, Raymond N.; Dunn, Richard B.; Carmichael, Roger
B.; Gregory, B. Scott; Plum, Douglas W.; Neidig, Donald F.; Golub,
Leon; Bookbinder, Jay A.; Koutchmy, George U.; Nystrom, Serge L.;
Zimmermann, Jean-Paul
1996ASPC...95..531S Altcode: 1996sdit.conf..531S
No abstract at ADS
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Title: An Objective Test of Magnetic Shear as a Flare Predictor
Authors: Smith, Jesse B., Jr.; Neidig, Donald F.; Wiborg, Philip H.;
West, Edward A.; Hagyard, Mona J.; Adams, Mitzi; Seagraves, Paul H.
1996ASPC...95...55S Altcode: 1996sdit.conf...55S
No abstract at ADS
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Title: Flare-Associated Darkenings in H-Alpha: Possible Evidence
for Faint Outlying, Unresolved Loop Systems
Authors: Neidig, D. F.; Cliver, E. W.; Svestka, Z.; Airapetian, V.;
Henry, T. W.
1995SPD....26.1215N Altcode: 1995BAAS...27..986N
No abstract at ADS
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Title: CLEAR : A Concept for a "Coronagraph and Low Emissivity
Astronomical Reflector" for Solar and Nighttime Observations
Authors: Beckers, J. M.; Kuhn, J.; Neidig, D.; Rabin, R.; Rimmele,
T.; Smartt, R. N.
1995SPD....26..722B Altcode: 1995BAAS...27..971B
No abstract at ADS
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Title: Near-Infrared Coronagraphic Detection of Space Debris
Authors: Neidig, D. F.; Smartt, R. N.; Kim, I. S.; Koutchmy, S.
1995itsa.conf..253N Altcode:
No abstract at ADS
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Title: Mirror Coronagraphic Device and Its Application
Authors: Kim, I. S.; Bougaenko, O. I.; Brouevitch, V. V.; Koutchmy,
S.; Neidig, D. F.; Smartt, R. N.; Evseev, O. A.
1995itsa.conf..239K Altcode:
No abstract at ADS
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Title: Extreme "Propagation" of Solar Energetic Particles
Authors: Cliver, E. W.; Kahler, S. W.; Neidig, D. F.; Cane, H. V.;
Richardson, I. G.; Kallenrode, M. B.; Wibberenz, G.
1995ICRC....4..257C Altcode: 1995ICRC...24d.257C
No abstract at ADS
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Title: Optical output of the 24 April 1984 white-light flare
Authors: Neidig, Donald F.; Grosser, Hartmut; Hrovat, Mary
1994SoPh..155..199N Altcode:
Results of quantitative, two-dimensional photographic photometry of
the spectacular 24 April 1984 white-light flare (WLF) are presented,
including measurements of optical continuum peak flux, spectrum,
and power. The WLF light curve peaks nearly simultaneously with the
flare hard x-rays, but precedes the peak soft x-ray thermal emission
by several minutes.
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Title: Consequences of chromospheric irradiation in white light
flares: An observer's point of view
Authors: Neidig, D. F.
1993AdSpR..13i.317N Altcode: 1993AdSpR..13..317N
Irradiation of the photosphere by chromospheric flare continuum has
been suggested as a mechanism of energy transport in white light
flares. In this model the flare optical continuum originates from
both the chromosphere (H<SUB>fb</SUB> emission) and the photosphere
(H<SUP>-</SUP> emission). Consequences of the irradiation model include
different dependences on viewing angle of the two continuum components
and reduction in minimum required chromospheric energy deposition
rate, for a given visible light flare intensity, relative to models
which assume only a chromospheric source. Testable predictions of the
irradiation model, relating to specific effects on spatial variation
and timing of flare emissions, are discussed.
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Title: Inferring the Spatial Variation of the Thick Target Nonthermal
Electron Spectrum in a White Light Flare
Authors: Neidig, D. F.; Kiplinger, A. L.
1993BAAS...25.1196N Altcode:
No abstract at ADS
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Title: Physical properties of white-light flares derived from their
center-to-limb distribution
Authors: Neidig, Donald F.; Wiborg, Philip H.; Gilliam, Lou B.
1993SoPh..144..169N Altcode:
We compare the observed center-to-limb distribution of 86 white-light
flares (WLFs) with calculated distributions derived from five flare
models, each covering different heights, temperatures, and densities
in the solar atmosphere. Considering the limited statistics and the
possibility of selection effects in reporting WLFs, the following
results may be considered tentative: (1) WLFs cannot be modeledsolely by
high-altitude optically thin sources, by optically thin chromospheric
sources, or by photospheric sources located less than 150 km above
the τ<SUB>5000</SUB> = 1 level; (2) middle photospheric sources
extending somewhat higher than 150 km provide the best fit to the
observed center-to-limb distribution, and (3) middle photospheric
sources not exceeding 150 km altitude combined with chromospheric or
higher-altitude sources are acceptable. An important feature of this
work is that the methods used in the analysis are entirely independent
of spectral analysis; yet spectral analysis has provided evidence for
both photospheric and chromospheric components in WLFs.
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Title: The Mechanisms of Solar Variability (MSV) program
Authors: Leibacher, John W.; Noyes, Robert W.; Simon, George W.;
Neidig, Donald F.
1993STIN...9328585L Altcode:
The Mechanisms of Solar Variability (MSV) Program aims toward
understanding physical causes of variations in the radiative, magnetic,
and particle emissions from the Sun. Solar particle and field variations
influence the interplanetary medium and the magnetosphere; UV and X-ray
variations affect the Earth's upper atmosphere; and total irradiance
variations are a possibly significant perturber of tropospheric
climate. Solar magnetic variability provides a close-up arena for
studying important but otherwise unobservable astrophysical phenomena
as well. The MSV program will advance our understanding of the causes
of solar variability through high angular resolution observations
of the interaction of solar surface magnetic fields and convective
motions, as well as related x-ray, ultraviolet, and visible brightness
variations. Through these high resolution studies, MSV will complement
national programs aimed at monitoring integrated solar outputs, thus
contributing to the better understanding and ultimate predictability
of global solar variability.
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Title: The Solar White-Light Flare of 1989 March 7: Simultaneous
Multiwavelength Observations at High Time Resolution
Authors: Neidig, Donald F.; Kiplinger, Alan L.; Cohl, Howard S.;
Wiborg, Philip H.
1993ApJ...406..306N Altcode:
Observational data for the March 7, 1989 white light flare (WLF) are
presented. The flare kernel shows an impulsive rise in both H-alpha
and continuum that is well correlated with impulsive hard X-rays. The
H-alpha emission shows a red asymmetry interpreted as Doppler redshift
associated with explosive heating of the chromosphere. The flare kernel
is separated into a bright inner core and a fainter outer region, where
the two components display distinctly different temporal behavior and
amount of H-alpha and red asymmetry. A delay, relative to hard X-rays,
of about 1 s is seen in the impulsive rise of the H-alpha wing emission,
followed by an additional 1-2 s delay in the 5000 A continuum. The
observed fluxes and timing of the hard X-ray and WLF optical emission
are consistent with chromospheric heating by nonthermal electrons,
with additional visible light continuum possibly being contributed
by a backwarmed photosphere irradiated by intense chromospheric
recombination continua.
---------------------------------------------------------
Title: A Flare Prediction Algorithm Based on Evidence of Energy
Storage in Sheared Magnetic Fields (Abstract)
Authors: Smith, J. B., Jr.; Neidig, D. F.
1993stp2.conf..406S Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Energetics and Timing of the Hard and Soft X-Ray Emissions
in White-Light Flares
Authors: Neidig, Donald F.; Kane, Sharad R.
1993SoPh..143..201N Altcode:
By comparing the light curves in optical, hard x-ray, and soft x-ray
wavelengths for 8 well-observed flares, we confirm previous results
indicating that the white light flare (WLF) is associated with the
flare impulsive phase. The WLF emission peaks within secondsafter the
associated hard x-ray peak, and nearly two minutesbefore the 1-8 å
soft x-ray peak. It is further shown that the peak power in nonthermal
electrons above 50 keV is typically an order of magnitudelarger, and
the power in 1-8 å soft x-rays radiated over 2π strdn at the time of
the WLF peak is an order of magnitudesmaller, than the peak WLF power.
---------------------------------------------------------
Title: The X-ray ultraviolet imager for the orbiting solar laboratory
Authors: Antonucci, Ester; Malvezzi, Marco; Ciminiera, Luigi; Angrilli,
Francesco; Bruner, Marilyn E.; Perona, Giovanni; Adele Dodero, Maria;
Evans, Brian L.; Golub, Leon; Landini, Massimo; Noci, Giancarlo;
McWhirter, Peter; Fossi, Brunella Monsignori; Poletto, Giannina;
Neidig, Donald F.; Schmidt, Wolfgang K. H.; Thomas, Roger J.;
Tondello, Giuseppe
1992AIPC..267..126A Altcode: 1992ecsa.work..126A
A normal incidence multimirror telescope, the X-ray Ultraviolet
Imager, for high resolution imaging of the solar atmosphere in the
soft X-ray/XUV region, is being developed as part of the scientific
payload of the NASA Orbiting Solar Laboratory. The X-ray Ultraviolet
Imager is formed by two units: a high resolution telescope (0.25
arcsec pixel size and 8×8 arcmin2 field of view) and a wide field one
(2.3 arcsec pixel size and 5×5 solar radii2 field of view). The two
systems complement each other and allow a full coverage of solar
features from the small scale (200 km on the sun) to the global
phenomena. Each system consists of 8 channels with multilayer mirrors,
imaging at different wavelengths. In each channel the mirror coating
is optimized to select a narrow spectroscopic window corresponding to
an intense line in the region 40-400 A˚. In order to provide imaging
and temperature diagnostics from the chromosphere to the upper corona,
8 wavelengths are chosen to cover the broad temperature range from 105
to 107 K. Four images, two high resolution and two full disk ones,
are simultaneously obtained by the X-ray Ultraviolet Imager, at a
cadence which in flares can be of 0.4-1 s.
---------------------------------------------------------
Title: Characteristics of White Light Flares as Derived from their
Observed Center-to-Limb Distribution
Authors: Neidig, D. F.; Wiborg, P. H.; Gilliam, L. B.
1991BAAS...23.1026N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The XUV imager for the OSL.
Authors: Landini, M.; Noci, G.; Antonucci, E.; Bruner, M. E.; Evans,
B. L.; Golub, L.; Malvezzi, M.; McWhirter, R. W.; Monsignori Fossi,
B. C.; Poletto, G.; Neidig, D.; Perona, G.; Thomas, R.; Tondello, G.
1990BAAS...22.1148L Altcode:
No abstract at ADS
---------------------------------------------------------
Title: High Time Resolution Hα, Continuum, and Hard X-Ray
Observations of a White Light Flare
Authors: Neidig, D. F.; Kiplinger, A.; Cohl, H.
1990BAAS...22..846N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - Solar Physics in the 1990'S
Authors: Neidig, D. F.; Hudson, H. S.
1989Sci...246..246N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Importance of Solar White-Light Flares
Authors: Neidig, Donald F.
1989SoPh..121..261N Altcode: 1989IAUCo.104..261N
The basic results of white-light flare (WLF) photometric and
spectrographic observations are reviewed. WLFs represent the most
extreme density conditions in solar optical flares and are similar
to stellar flares in many respects. It is shown that WLFs originate
in the low chromosphere and upper photosphere, and that their huge
radiative losses remain difficult to explain within the context of
known mechanisms of energy transport.
---------------------------------------------------------
Title: The M8.1 Flare of 1988JUN23 - Part One
Authors: Herant, M.; Golub, L.; Neidig, D. F.
1989SoPh..124..145H Altcode:
Hα observations of two-ribbon flares often show secondary brightenings
which are not directly spatially connected with the main center of
activity but which are correlated in time with the primary impulsive
flare. We present here a mechanism which explains these secondary
brightenings via the reconnection of magnetic loops which are tied to
only one of the two ribbons, in contrast with the loops responsible for
the main flare which are tied to both ribbons. The distant footpoint is
then interpreted as the site of the secondary brightening. We apply our
model to the two-ribbon flare of 17:52 UT, 23 June, 1988, which started
during the rocket flight of the Normal Incidence X-ray Telescope.
---------------------------------------------------------
Title: The Identification of Optical Continuum Emission with the
Phase of Electron Acceleration in Solar Flares
Authors: Neidig, D. F.; Kane, S. R.; Hrovat, M.; Grosser, H.
1989BAAS...21..846N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1989epos.conf..225C Altcode:
The work of this group was concerned with how the energy released
in a solar flare is transported through the solar atmosphere before
escaping in the form of radiant and mechanical energy.
---------------------------------------------------------
Title: Multi-Wavelength Observations of the 23 June 1745UT M8 Flare
Authors: Herant, M.; Golub, L.; Mickey, D.; Neidig, D.; Slater, G.
1988BAAS...20R.977H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Foreword
Authors: Neidig, Donald F.
1988AdSpR...8k...3N Altcode: 1988AdSpR...8....3N
No abstract at ADS
---------------------------------------------------------
Title: Solar physics in the 1990s. Proceedings. Workshop XV and
the COSPAR Interdisciplinary Scientific Commission E (Meeting E1)
of the 27. COSPAR Plenary Meeting: Solar physics in the 1990s, Espoo
(Finland), 18 - 29 Jul 1988.
Authors: Neidig, D. F.; Hudson, H. S.
1988AdSpR...8k....N Altcode: 1988AdSpR...8.....N
Papers concerning developments in solar physics are presented, focusing
on scientific planning for the solar maximum and high-energy detector
calibration and observation of nonthermal and superhot sources. Specific
topics include solar radioastronomy, VLA observations of the sun,
coronal loops, solar observation in the Phobos mission, the Solar-A
mission, the Solar and Heliospheric Observatory satellite, the Global
Oscillation Network Group, the relation between convection flows and
magnetic structure and the solar surface, and solar flares research
programs including quasi-dedicated mm-wave imaging, H-alpha, far IR,
X-ray spectroscopy, and optical observations. Additional subjects
include the manifestation of supergranulation structure of active
regions during solar flares, post-flare loops, the relationship of peak
emission measure and temperature to peak flare X-ray flux, turbulent
and directed motions in solar flares, coronal temperature diagnostics
from high-resolution soft W-ray spectra, the study of coronal densities
from X-ray line ratios of Ne IX and Mg XI, electron densities in the
solar atmosphere, the Coronal Magnetic Structures Observing Campaign,
observations of a giant filament, the determination of coronal fieldline
connectivity from photospheric flare observations, MHD simulation of
mass injection, numerical simulation of solar atmospheric dynamics,
intercalibration of hard X-ray spectrometers, the influence of the
energy calibration of broad-band X-ray detectors on the determination
of plasma parameters, and space experiments measuring solar X-rays.
---------------------------------------------------------
Title: Multi-thermal observations of newly formed loops in a
dynamic flare
Authors: Švestka, Zdeněk F.; Fontenla, Juan M.; Machado, Marcos E.;
Martin, Sara F.; Neidig, Donald F.; Poletto, Giannina
1987SoPh..108..237S Altcode:
The dynamic flare of 6 November, 1980 (max ≈ 15:26 UT) developed a
rich system of growing loops which could be followed in Hα for 1.5
hr. Throughout the flare, these loops, near the limb, were seen in
emission against the disk. Theoretical computations of deviations from
LTE populations for a hydrogen atom reveal that this requires electron
densities in the loops close to, or in excess of 10<SUP>12</SUP>
cm <SUP>-3</SUP>. From measured widths of higher Balmer lines the
density at the tops of the loops was found to be 4 x 10<SUP>12</SUP>
cm <SUP>-3</SUP> if no non-thermal motions were present, or 5 ×
10<SUP>11</SUP> cm <SUP>-3</SUP> for a turbulent velocity of ~ 12 km
s <SUP>-1</SUP>.
---------------------------------------------------------
Title: The largest white light flare ever observed: 25 April 1984,
0001 UT
Authors: Neidig, D. F.; Grosser, H.; Kiplinger, A. L.
1987sici.symp....6N Altcode:
The X13/3B flare of 25 April 1984, 0001 UT, was accompanied by intense
white light emission that reached a peak power output approx 2x10
to the 29 erg/sec in the optical/near UV continuum; the total energy
radiated in the continuum alone reached 10 to the 32 power ergs. This
was the most powerful white light flare yet recorded, exceeding the peak
output of the largest previously known event by more than one order
of magnitude. The flare was a two-ribbon type with intense embedded
kernels as observed in both Balmer-alpha line and Balmer continuum, and
each of these flare ribbons covered separate umbrae shortly after the
maximum of the event. The onset and peak of the white light emission
coincided with the onset and peak of the associated E greater than
100 KeV hard X-ray burst, while the 1-8 angstrom soft X-ray emission
reached its maximum 4 minutes after the peak in white light.
---------------------------------------------------------
Title: The Spectrum and Energetics of the 25 April 1984 White
Light Flare
Authors: Neidig, D. F.; Kiplinger, A. L.; Grosser, H.
1987BAAS...19..920N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Book-Review - the Lower Atmosphere of Solar Flares,
Relationships Between Low Temperature Plasmas and High Energy
Emissions
Authors: Neidig, D. F.; Hick, P.
1987SoPh..108..201N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Impulsive Phase Observations and Their Interpretation
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf..3.4C Altcode: 1986epos.confC...4C
No abstract at ADS
---------------------------------------------------------
Title: Theoretical Studies of Transport Processes
Authors: Canfield, R. C.; Bely-Dumau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986epos.conf.3.34C Altcode: 1986epos.confBC.34C
No abstract at ADS
---------------------------------------------------------
Title: Impulsive phase transport
Authors: Canfield, Richard C.; Bely-Dubau, Francoise; Brown, John C.;
Dulk, George A.; Emslie, A. Gordon; Enome, Shinzo; Gabriel, Alan H.;
Kundu, Mukul R.; Melrose, Donald; Neidig, Donald F.
1986epos.conf..3.1C Altcode: 1986epos.confC...1C
The transport of nonthermal electrons is explored. The thick-target
electron beam model, in which electrons are presumed to be accelerated
in the corona and typically thermalized primarily in the chromosphere
and photosphere, is supported by observations throughout the
electromagnetic spectrum. At the highest energies, the anisotropy
of gamma-ray emission above 10 MeV clearly indicates that these
photons are emitted by anisotropically-directed particles. The timing
of this high-energy gamma-radiation with respect to lower-energy
hard X-radiation implies that the energetic particles have short
life-times. For collisional energy loss, this means that they are
stopped in the chromosphere or below. Stereoscopic (two-spacecraft)
observations at hard X-ray energies (up to 350 keV) imply that these
lower-energy (but certainly nonthermal) electrons are also stopped deep
in the chromosphere. Hard X-ray images show that, in spatially resolved
flares whose radiation consists of impulsive bursts, the impulsive
phase starts with X-radiation that comes mostly from the foot-points
of coronal loops whose coronal component is outlined by microwaves.
---------------------------------------------------------
Title: Solar Gradual Hard X-Ray Bursts and Associated Phenomena
Authors: Cliver, E. W.; Dennis, B. R.; Kiplinger, A. L.; Kane, S. R.;
Neidig, D. F.; Sheeley, N. R., Jr.; Koomen, M. J.
1986ApJ...305..920C Altcode:
White-light coronagraph, H-alpha and radio data are presented as well
as hard X-ray data for a sample of 10 gradual hard X-ray bursts (GHBs)
in an attempt to better understand the nature of these events. It is
found that: (1) the hard X-ray photon energy spectrum began to harden
near the onset of the GHBs and continued in this fashion during the
decay phase; (2) a coronal mass ejection (CME) occurred in association
with at least nine of the GHBs; (3) the GHBs occurred in the late phase
of major flares; (4) the centimeter wavelength bursts associated with
the GHBs had relatively low frequency spectral maxima, and in relation
to the observed hard X-ray emission, they were microwave-rich; (5) the
associated decimetric bursts showed significant intensity variations
on time scales ranging from 0.1 to approximately greater than 1 minute;
and (6) the GHBs were most strongly associated with type IV events. It
is concluded that the acceleration and trapping of radiating electrons
occurs in the postflare loop systems following CMEs.
---------------------------------------------------------
Title: Why P/OF should look for evidences of over-dense structures
in solar flare hard X-ray sources
Authors: Neidig, D. F.; Kane, S. R.; Love, J. J.; Cliver, E. W.
1986sfcp.nasa..142N Altcode:
White-light and hard X-ray (HXR) observations of two white-light flares
(WLFs) show that if the radiative losses in the optical continuum
are powered by fast electrons directly heating the WLF source, then
the column density constraints imposed by the finite range of the
electrons requires that the WLF consist of an over-dense region in the
chromosphere, with density exceeding 10 to the 14th power/cu cm. Thus,
we recommend that P/OF search for evidences of over-dense structures in
HXR images obtained simultaneously with optical observations of flares.
---------------------------------------------------------
Title: The lower atmosphere of solar flares. Relationships between
low temperature plasmas and high energy emissions. Proceedings of
the National Solar Observatory/Solar Maximum Mission Symposium,
held at National Solar Observatory, Sacramento Peak, Sunspot, NM,
USA, 20 - 24 August 1985.
Authors: Neidig, D. F.; Machado, M. E.
1986lasf.conf.....N Altcode: 1986lasf.symp.....N
The topics discussed by the present conference encompass the
chromospheric flare phenomenon, white light flares, UV emission and the
flare transition region, the flare corona and high energy emissions,
stellar flares, and flare energy release and transport. Attention
is given to radiative shocks and condensation in flares, impulsive
brightening of H-alpha flare points, the structure and response
of the chromosphere to radiation backwarming during solar flares,
the interpretation of continuum emissions in white light flares,
and the radiation properties of solar plasmas. Also discussed are EUV
images of a solar flare and C III intensity, an active region survey in
H-alpha and X-rays, dynamic thermal plasma conditions in large flares,
the evolution of the flare mechanism in dwarf stars, the evidence
concerning electron beams in solar flares, the energetics of the
nonlinear tearing mode, macroscopic electric fields during two-ribbon
flares, and the low temperature signatures of energetic particles.
---------------------------------------------------------
Title: Impulsive phase transport.
Authors: Canfield, R. C.; Bely-Dubau, E.; Brown, J. C.; Dulk, G. A.;
Emslie, A. G.; Enome, S.; Gabriel, A. H.; Kundu, M. R.; Melrose,
D.; Neidig, D. F.; Ohki, K.; Petrosian, V.; Poland, A.; Rieger, E.;
Tanaka, K.; Zirin, H.
1986NASCP2439....3C Altcode:
Contents: 1. Introduction: motivation for transport studies, historical
perspective, overview of the chapter. 2. Impulsive phase observations
and their interpretation: gamma-ray emission above 10 MeV, hard
X-ray and microwave morphology, combined soft and hard X-ray spectra,
iron Kα emission, ultraviolet and hard X-ray emission, white light
emission, Hα emission. 3. Theoretical studies of transport processes:
electron beams and reverse currents, proton transport, radiative energy
transport by amplified decimetric waves. 4. Summary.
---------------------------------------------------------
Title: Working Group "C" Report: Short-Term Solar Predictions
Authors: Smith, J.; Neidig, D.
1986stp..conf..167S Altcode: 1986STP.....2..167S
No abstract at ADS
---------------------------------------------------------
Title: Limitations in the Use of H Filament and Fibril Activity as
a Short Term (30 Minute) Predictor of Flares and Flare-Like Events
Authors: Neidig, D.
1986stp..conf..187N Altcode: 1986STP.....2..187N
No abstract at ADS
---------------------------------------------------------
Title: Solar Activity Measurement Experiment (SAMEX)
Authors: Keil, Stephen L.; Neidig, Donald F.
1986aiaa.meetQ....K Altcode:
SAMEX is the first step in providing the Air Force with a Solar Activity
Forecasting and Monitoring System in Space (SAFMSS). SAMEX will provide
the test bed for a high spatial resolution soft X-ray/EUV imager (20-150
A) and a high resolution vector magnetograph. The proposed payload
will be flown as part of the Space Test Program and subsequently used
to form the kernel of a Solar Activity Monitoring Satellite (SAMSAT)
that has been proposed by the Air Weather Service.
---------------------------------------------------------
Title: White light flares and atmospheric modeling (Working Group
report).
Authors: Machado, M. E.; Avrett, E. H.; Falciani, R.; Fang, C.;
Gesztelyi, L.; Henoux, J. -C.; Hiei, E.; Neidig, D. F.; Rust, D. M.;
Sotirovski, P.; Svestka, Z.; Zirin, H.
1986lasf.conf..483M Altcode:
The authors give a short summary of their discussions, and a set
of recommendations which may help in the study of white light flare
emission processes.
---------------------------------------------------------
Title: Solar gradual hard X-ray bursts: Observations and an
interpretation
Authors: Cliver, E. W.; Dennis, B. R.; Kiplinger, A.; Kane, S.;
Neidig, D. F.; Sheeley, N.; Koomen, M.
1986AdSpR...6f.249C Altcode: 1986AdSpR...6..249C
A recent study of solar gradual hard X-ray bursts is summarized. The
data are interpreted in terms of a model involving the acceleration
and trapping of electrons in post flare loop systems following coronal
mass ejections. A controversy about the classification of the metric
continuum that typically accompanies gradual hard X-ray events is
addressed.
---------------------------------------------------------
Title: Why P/OF should look for evidences of over-dense structures
in solar flare hard X-ray sources.
Authors: Neidig, D. F.; Kane, S. R.; Love, J. J.; Cliver, E. W.
1986NASCP2421..142N Altcode:
White-light and hard X-ray (HXR) observations of two white-light
flares (WLFs) show that if the radiative losses in the optical
continuum are powered by fast electrons directly heating the
WLF source, then the column density constraints imposed by the
finite range of the electrons requires that the WLF consist of
an over-dense region in the chromosphere, with density exceeding
10<SUP>14</SUP>cm<SUP>-3</SUP>. Thus, the authors recommend that P/OF
search for evidences of over-dense structures in HXR images obtained
simultaneously with optical observations of flares.
---------------------------------------------------------
Title: Direct measurements of the optical thickness and radiative
source function in the optical continuum of solar flares.
Authors: Neidig, Donald F.
1986lasf.conf..152N Altcode: 1986lasf.symp..152N
Spectrograms of a number of white-light flares (WLFs) recently obtained
at Sacramento Peak indicate that the optical continuum originates
in a layer of finite optical thickness, probably elevated above the
photosphere. If so, this circumstance allows the radiative source
function and optical thickness of the flare layer to be measured
directly, using the observed changes in the contrast of spectral
features in the photospheric background as seen through the flare
layer. The method is briefly described and an example of its application
to the 24 April 1981 WLF is given. The effects of spatially-unresolved
flare structures and of spatial/spectral non-uniformities in the
background photosphere are discussed in terms of the limitations they
impose on the method.
---------------------------------------------------------
Title: Objective Forecasts for Solar Flares Using Multivariate
Discriminant Analysis
Authors: Neidig, D.; Wiborg, P.; Seagraves, P.; Hirman, J.; Flowers, W.
1986stp..conf..300N Altcode: 1986STP.....2..300N
No abstract at ADS
---------------------------------------------------------
Title: Flare activity, sunspot motions, and the evolution of vector
magnetic fields in Hale region 17244
Authors: Neidig, Donald F.; Smith, Jesse B.; Hagyard, Mona J.; Machado,
Marcos E.
1986AdSpR...6f..25N Altcode: 1986AdSpR...6...25N
We study the magnetic and dynamical circumstances leading to the 1B/M4
flare of November 5, 1980, and find a strong association between the
buildup of magnetic shear and the onset of flare activity within the
active region. The development of shear, as observed directly in vector
magnetograms, is consistent in detail with the dynamical history of
the active region and identifies the precise location of the optical
and hard x-ray kernels of the flare emission. <P />NAS/NRC Research
Associate on leave from CNIE, Argentina
---------------------------------------------------------
Title: A dynamic flare with anomalously dense flare loops
Authors: Svestka, Z.; Fontenla, J. M.; Machado, M. E.; Martin, S. F.;
Neidig, D. F.; Poletto, G.
1986AdSpR...6f.253S Altcode: 1986AdSpR...6..253S
The dynamic flare of 6 November 1980 (max. ~ 15:26 UT) developed a
rich system of growing loops which could be followed in Hα for 1.5
hours. Throughout the flare, these loops, near the limb, were seen in
emission against the disk. Theoretical computations of b-values for
a hydrogen atom reveal that this requires electron densities in the
loops to be close to 10<SUP>12</SUP> cm<SUP>-3</SUP>. From measured
widths of higher Balmer lines the density at the loops of the loops
was found to be 4 × 10<SUP>12</SUP> cm<SUP>-3</SUP> if no non-thermal
motions were present. It is now general knowledge that flare loops
are initially observed in X-rays and become visible in Hα only after
cooling. For such a high density a loop would cool through radiation
from 10<SUP>7</SUP> K to 10<SUP>4</SUP> K within a few minutes so that
the dense Hα loops should have heights very close to the heights of
the X-ray loops. This, however, contradicts the observations obtained by
the HXIS and FCS instruments on board SMM which show the X-ray loops at
much higher altitudes than the loops in Hα. Therefore, the density must
have been significantly smaller when the loops were formed and the flare
loops were apparently both shrinking and becoming denser while cooling.
---------------------------------------------------------
Title: On the possibility of a purely chromospheric origin for the
bright kernels in white light flares.
Authors: Neidig, Donald F.
1986lasf.conf..142N Altcode: 1986lasf.symp..142N
Optical spectra derived from images of white light flares
(WLFs), obtained in broad (≡50 Å) bands at several wavelengths
between 3600 and 6200 Å, are compared with H<SUB>fb</SUB> and
H<SUB>ff</SUB> emission originating from a homogeneous, isothermal
slab at dense chromospheric flare conditions. It is found that
good agreement with observations can be obtained for temperatures
10<SUP>4</SUP> - 25,000K, linear emission measures 10<SUP>35</SUP>
- 10<SUP>36</SUP>cm<SUP>-5</SUP> and relatively small departures
from LTE for hydrogen atoms in level n = 3. These simple models are
able to account for both the observed large intensity in the Balmer
continuum and the relatively flat Paschen continuum at λ ⪆ 5000
Å. In addition, a relative brightening in the calculated Paschen
continuum at λ ⪉ 4500 Å arises as an unavoidable consequence of
comparing the flare spectrum with the quiescent solar background. The
latter effect may be responsible, in part, for the "blue continuum"
observed in WLFs.
---------------------------------------------------------
Title: Characteristics of the white-light source in the 1981 April
24 solar flare
Authors: Kane, S. R.; Love, J. J.; Neidig, D. F.; Cliver, E. W.
1985ApJ...290L..45K Altcode:
The large white-light flare on 1981 April 24 (≡1358 UT) was very well
observed at the hard X-ray, optical, and radio wavelengths. Energetic
particles escaping from the Sun were detected in the interplanetary
space and in the vicinity of the Earth. The flare had distinct impulsive
and gradual phases and provided the best available measurements of
the optical continuum in a solar flare. In this letter the authors
present these observations and discuss their interpretation in terms
of the energetics of the flare and the role of energetic electrons in
the production of optical continuum emission.
---------------------------------------------------------
Title: Non-thermal Excitation of the White Light Source in the 24
April 1981 (~1358 UT) Solar Flare
Authors: Kane, S. R.; Love, J. J.; Neidig, D. F.; Cliver, E. W.
1985BAAS...17..628K Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Hydrogen Emission Spectrum in Three White Light Flares
Authors: Neidig, D. F.; Wiborg, P. H., Jr.
1984SoPh...92..217N Altcode:
We present spectral data for three white-light flares (WLFs) showing
Balmer continuum at wavelengths ≲ 3700 Å. These flares also have
a weaker continuum extending toward longer wavelengths, from which,
in one flare where this continuum is sufficiently bright, we are able
to identify a Paschen jump near 8500 Å. The presence of the latter
suggests that the Paschen continuum may be a substantial contributor
to the WLF continuum at visible wavelengths. We note the possibility,
therefore, that the entire continuum of this particular flare may be
dominated by H<SUB>fb</SUB> emission.
---------------------------------------------------------
Title: Hydrogen Recombination as an Emission Mechanism in White-Light
Flares
Authors: Neidig, D. F.
1984BAAS...16..545N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: The Occurrence Frequency of White Light Flares
Authors: Neidig, D. F.; Cliver, E. W.
1983SoPh...88..275N Altcode:
We derive an occurrence frequency for white-light flares (WLF) of 15.5
± 4.5 yr<SUP>−1</SUP> during a 2.6 year period following the maximum
of solar cycle 21. This compares with a frequency 5-6 yr<SUP>−1</SUP>
derived by McIntosh and Donnelly (1972) during solar cycle 20. We
find that the higher frequency of the more recently observed WLFs is
due to the availability of patrol data at shorter wavelengths (λ ≲
4000 Å), where the contrast of the flare emission is increased; the
improved contrast has allowed less energetic (and hence more frequently
occurring) events to be classified as WLFs. We find that sufficient
conditions for the occurrence of a WLF are: active region magnetic
class = delta; sunspot penumbra class = K, with spot group area ≥
500 millionths of the solar hemisphere; 1-8 Å X-ray burst class ≥ X2.
---------------------------------------------------------
Title: A catalog of solar white-light flares, including their
statistical properties and associated emissions, 1859 - 1982
Authors: Neidig, D. F.; Cliver, E. W.
1983STIN...8424521N Altcode:
This catalog of 57 solar white-light flares reported between 1859
and 1982 includes H-alpha, soft X-ray, and radio emissions associated
with the white-light flares. The following are among the conclusions
resulting from statistical examination of the listed flares and the
active regions in which they occurred: (1) The active regions that
produce white-light flares tend to have the following characteristics:
(a) magnetic class = Delta; (b) classification of the penumbra of the
largest spot = K; and (c) sunspot group area > 500 millionths of the
solar hemisphere. (2) Northern Hemisphere white-light flare activity
begins abruptly about 1 or 2 years before solar maximum, and declines
slowly thereafter. Southern hemisphere white-light flare activity
follows the same pattern, but begins approximately 1 year after solar
maximum. (3) White light flares have a mean latitude of 13 + or - 2 deg
in the Southern Hemisphere but a mean latitude of 18 + or - 1 deg in
the Northern Hemisphere. (4) White-light flares exhibit a north-south
asymmetry with 70% more events having been observed in the Northern
Hemisphere as compared to the southern (the current solar cycle is a
possible exception with southern hemisphere activity dominating) as of
December 1982. (5) There is no compelling evidence of preferred solar
longitudes for white-light flare active regions. Southern Hemisphere
activity during the current cycle is a possible exception.
---------------------------------------------------------
Title: Spectral analysis of the optical continuum in the 24 April
1981 flare
Authors: Neidig, D. F.
1983SoPh...85..285N Altcode:
Spectrograph and multiple-band polarimeter observations of the 24 April
1981 white-light flare indicate the presence of an optical continuum
with intensity increasing strongly below 4000 Å. The flare emission
(lines and continuum combined) is unpolarized and, at 3600 Å, exceeds
the brightness of the background solar surface by 360%. Analysis of the
spectrum between 3600 and 8200 Å, at a location three arc sec from the
brightest point in the kernel, yields a probable temperature of 6700
K for the continuum emitting layer. The wavelength dependence of the
continuum indicates emission by both negative hydrogen (H<SUP>−</SUP>)
and Balmer continuum, with the H<SUP>−</SUP> probably originating
in the upper photosphere at a height (above τ<SUB>5000 Å</SUB> = 1)
in the range 200-300 km. Analysis of the Balmer lines and continuum
yields an electron density 5.3 × 10<SUP>13</SUP> cm<SUP>−3</SUP>
and a second-level hydrogen column density 1.1 × 10<SUP>16</SUP>
cm<SUP>−2</SUP>. The peak radiative output integrated over wavelength
is 6.1 × 10<SUP>27</SUP> erg s<SUP>−1</SUP>. The observed continuum
intensity, if originating at a height of 300 km, implies an energy
loss rate of 10<SUP>3</SUP> erg s<SUP>−1</SUP> cm<SUP>−3</SUP>.
---------------------------------------------------------
Title: Observing White-Light Flares
Authors: Neidig, D. F.; Beckers, J. M.
1983S&T....65..226N Altcode:
Observational techniques and instrumentation for tracking the occurrence
of solar white light flares back to their origin are discussed. The
rare events have been found to happen in the chromospheric and coronal
regions over sunspots, and are thought to be the release of accumulated
energy breaking free from the magnetic field lines and reforming into
simpler structures. Use of an achromatic f/15 objective lens, together
with a reimaging system for field magnification as a prelude to 35
mm photography, at the Sacramento Peak Observatory is described. A
Wollaston prism is also used to split the image into two beams for
detection of intensity variations due to polarization, which has thus
far not been observed in the white light flares. Spectroscopic data
indicate visual emission due to negatively-charged hydrogen ions in
the upper photosphere, and shorter wavelength neutral hydrogen Balmer
continuum features. A white light flare can be up to 300% as brilliant
as the surrounding region, and involve several percent of the total
spontaneous solar output.
---------------------------------------------------------
Title: Motion Picture of the 24 April 1981 White-Light Flare
Authors: Neidig, D. F.
1983BAAS...15R.698N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: On the color of the 26 February 1981 white light flare
Authors: Neidig, D. F.; Beck, R. O.
1982SoPh...78..225N Altcode:
We describe visual observations of a white light flare which displayed
a pink color in a part of the flare which covered a sunspot umbra. We
then show that visible pink tint, if attributable to strong Hα
emission, requires a minimum equivalent emission line width of
approximately 140 A, or three times larger than in any flare previously
measured. Such extreme line broadening might be interpreted to result
from flare penetration to unusually high chromospheric densities
(≳ 10<SUP>14</SUP> cm<SUP>−3</SUP>), or from anomalous Stark
broadening due to turbulent electric fields in an unstable plasma
(Spicer and Davis, 1975) at lower density.
---------------------------------------------------------
Title: Continuum emission in the 1980 July 1 solar flare
Authors: Zirin, H.; Neidig, D. F.
1981ApJ...248L..45Z Altcode:
Comparison of continuum measurements of the July 1, 1980 flare at Big
Bear Solar Observatory and Sacramento Peak Observatory show strong
blue emission kernels with the ratio of Balmer continuum (Bac):3862 A
continuum:continuum above 4275 A to be about 10:5:1. The blue continuum
at 3862 A is too strong to be explained by unresolved lines. The
Bac intensity was 2.5 times the photosphere and the strongest 3826 A
continuum was 2 times the photosphere. The brightest continuum kernel
occurred late in the flare, after the hard X-ray peak and related in
time to an isolated peak in the 2.2 MeV line, suggesting that that
continuum was excited by protons above 20 MeV.
---------------------------------------------------------
Title: Optical Properties of Bipolar Flare Kernels Associated with
Asymmetric Magnetic Loops
Authors: Neidig, D. F.
1981SoPh...70..129N Altcode:
Observations are presented for nine flares containing two principal
patches of emission, or kernels, in which the kernel associated with
weaker magnetic field has the greater Hα line width. The observations
are interpreted in terms of an asymmetric bipolar magnetic loop from
which high energy electrons precipitate predominantly at the loop
footpoint of weaker field. Calculations are presented which indicate
that, for an isotropic distribution of electron velocity vectors at
their initial point of injection, the observations are consistent with
a location for the injection in the upper part of the loop. The same
type of model predicts the associated microwave burst to be stronger
near the opposite (strong field) footpoint (Kundu and Vlahos, 1979).
---------------------------------------------------------
Title: The Continuous Opacity Function in a White-Light Flare
Authors: Neidig, D. F.
1981BAAS...13..820N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: An objective method for forecasting solar flares
Authors: Neidig, D. F.; Wiborg, P. H.; Seagraves, P. H.; Hirman,
J. W.; Flowers, W. E.
1981aifo.reptQ....N Altcode:
Solar parameters derived from the region analysis program at the
NOAA Space Environment Services Center (SESC) are submitted to a
multivariate discriminant analysis (MVDA) in which the parameters
relevant to flare prediction are identified and incorporated in a
classification procedure to produce a flare forecast. The analysis
uses two years of data (6095 solar active region-days). The MVDA
forecast is compared with a subjective forecast derived from the SESC
forecast during the same period, and is found to have greater accuracy
overall. Specific recommendations are made concerning the application
of the technique in a forecasting operation, and in the types of data
required for future improvement.
---------------------------------------------------------
Title: Observation of the 1 July 1980 Flare with a Multiband
Polarimeter
Authors: Neidig, D. F.
1980BAAS...12..910N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Solar rotation studies using sunspot data (1967 1974)
Authors: Neidig, D. F.
1980SoPh...66..205N Altcode:
The solar rotation rate during 1967-1974 was measured from photographic
observations of sunspots. The rates derived from isolated single spots
and from bipolar groups were 14.38 ±0.02 and 14.71±0.05 deg per day
equatorial sidereal, respectively. Year-to-year fluctuations in the
bipolar group rates correlate with fluctuations in the Mt. Wilson
spectroscopic rotation rates, while the isolated single spots show
smaller, uncorrelated variations. A possible explanation for the
fluctuations in the bipolar rates is year-to-year changes in the
separation rates of the bipolar groups, rather than changes in the
global solar rotation rate. The latter interpretation requires caution
because (1) the sunspot rotation rates were derived from a limited
amount of data (one month per year), and (2) the rotation rates were
reduced to equatorial values assuming a differential rotation law
{ie205-01}.
---------------------------------------------------------
Title: Impulsive phase of solar flares
Authors: Kane, S. R.; Crannell, C. J.; Datlowe, D.; Feldman, U.;
Gabriel, A.; Hudson, H. S.; Kundu, M. R.; Maetzler, C.; Neidig, D.;
Petrosian, V.
1980sfsl.work..187K Altcode: 1980sofl.symp..187K
The present understanding of the impulsive phase of a solar flare,
characterized by short-duration bursts of impulsive hard X-ray,
EUV, optical and radio emission indicating the release of energetic
electrons is reviewed. Observations of the spectral distribution
of impulsive hard X-ray bursts and of Type III and radio continuum
bursts are presented and interpreted in terms of energetic electron
distributions, and impulsive EUV, XUV, soft X-ray and optical
observations, which provide a lower limit to total energy release
during the impulsive phase, are discussed. The role of energetic
electrons in exciting the hard X-ray, EUV and microwave emissions is
considered, and thin-target, thick-target, partial-precipitation and
thermal models of impulsive phase electron acceleration are evaluated
in light of the observations. It is noted that available data do
not allow discrimination between a thermal or a nonthermal electron
distribution, on which depends the proportion of flare energy supplied
by the energetic electrons, and that data favors models which permit
at least partial electron precipitation. Future observational and
theoretical work is indicated.
---------------------------------------------------------
Title: High resolution observations of fibril changes in a small
flare.
Authors: Neidig, D. F.
1979SoPh...61..121N Altcode:
Changes in the fibril geometry associated with a subflare are tracked in
detail in both time and space. The fibril morphology at the location of
the subflare is a spiral configuration surrounding a sunspot. Despite
the rotation of this sunspot, which tends to tighten the spiral
structure, a relaxation toward a more nearly radial structure is
associated with the occurrence of the subflare. The relaxation is
confined to those fibrils which connect the poles of the optical
flare emission, and in addition, tends to reflect the different time
evolutions of different parts of the subflare. Comparison of the changes
in the fibril geometry with the soft X-ray burst indicates that the
reorganization of the fibril structures lags the energy release in
the subflare by more than one hour.
---------------------------------------------------------
Title: Hα, hard X-ray, and microwave emissions in the impulsive
phase of solar flares
Authors: Neidig, D. F., Jr.
1978SoPh...57..385N Altcode:
I have studied the observational relationship between the location
of flare sites in active regions and three other observables, viz.,
Hα line width, hard X-ray burst parameters, and peak microwave
fluxes. Results suggest that the strength of the magnetic field plays
a role in governing the magnitudes of these emissions. Qualitative
relationships are derived on the assumption of proportionality between
the spectral maximum frequency of the associated microwave burst and
the field strength in the microwave source.
---------------------------------------------------------
Title: Flares, Force-free Fields, Emerging Flux and other Phenomena
in McMath 14943
Authors: Neidig, D. F.
1978AFGL...78..194N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Microwave burst spectra and solar flare magnetic fields.
Authors: Neidig, D. F., Jr.
1977SoPh...54..165N Altcode:
Microwave burst spectra are compared with the position, within the
active region, of their associated flares observed in Hα. The magnetic
fields predicted by Takakura's burst model (1972) are found to be in
reasonable agreement with the fields expected at the flare locations.
---------------------------------------------------------
Title: Nonthermal electrons in solar flares
Authors: Neidig, Donald Foster, Jr.
1976PhDT........50N Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Nonthermal Electrons in Solar Flares.
Authors: Neidig, D. F.
1976PhDT.........1N Altcode:
Coordinated microwave and H alpha patrol observations verify the
existence of a near-proportionality between the strength of the
magnetic field in the flare and the frequency of the peak in the
impulsive microwave burst. This relationship is then used to determine
that the peak flux in the impulsive microwave burst, the peak 20-keV
flux in the impulsive X-ray burst, and the maximum H alpha line width
are modulated by the magnetic field strength. These observations are
consistent with the hypothesis that the density of nonthermal electrons
in these flares varies roughly as the 2.5 power of the characteristic
magnetic field strength. H alpha observations of the bipolar kernels in
flares are interpreted in terms of a model magnetic field consisting of
a flux tube connecting two regions of opposite polarity. The relative
H alpha line widths of the kernels appear to be controlled only by
the relative strength of the magnetic fields in the kernels.
---------------------------------------------------------
Title: A Chromospheric Temperature Inversion and Its Implicacations
on Millimeter Brightness Distribution
Authors: Neidig, D. F., Jr.
1973SoPh...33...63N Altcode:
The brightness temperature curve of the quiet Sun at millimeter
wavelengths suggests a possible inversion in the mid-millimeter
range. Interpreting this as a result of an actual inversion in
the chromospheric temperature structure, and example of a model
chromoshere is presented whose calculated temperature curve exhibits
such an inversion. This model is then tested for radial brightness
distribution at millimeter wavelengths. Comparing the calculated
distributions at 3.2 mm and 6 mm with eclipse measurements made with
parabolic cylinders at 3.2 mm and 8.6 mm shows qualitative agreement,
allowing for instrumental smoothing. It is conluded that a chromospheric
temperature inversion, either actual or effective, could account for the
inversion suggested by millimeter data and also the complex brightness
distributions measured during eclipses with parabolic cylinders.
---------------------------------------------------------
Title: Identification of Two Distinctive Types of Centimeter Radio
Bursts with Flare Location
Authors: Hagen, John P.; Neidig, Donald F., Jr.
1971SoPh...18..305H Altcode:
Two distinct types of centimeter solar bursts, classified `simple',
have been identified and related to the position (with respect to
a sunspot) of the related flare. Type S in which the flare occurs
directly over the spot has a radio spectrum with a maximum beyond 10
GHz, type P which occurs away from the spot has its maximum occurring
near 3 GHz. Considering the structure of the spot magnetic field and
invoking the synchrotron effect, it is shown that the origin of the
radio burst may be attributed to a burst of energetic electrons with
an energy peak near 3 MeV.
---------------------------------------------------------
Title: Identification of Two Distinctive Types of Centimeter Radio
Bursts with Flare Location.
Authors: Hagen, J. P.; Neidig, D. F.
1971BAAS....3..246H Altcode:
No abstract at ADS
---------------------------------------------------------
Title: Observation of a Vortex Ring in the Solar Atmosphere
Authors: Hagen, John P.; Neidig, Donald F., Jr.
1970ApJ...161..751H Altcode:
A vortex ring, or "smoke ring," formed in the solar atmosphere above
a class iB flare was photographed in Ha light on 1969 December 2. The
ring persisted for less than 2 minutes, with the fast-moving material
out of which it was formed being reflected back toward the photosphere.
