Author name code: neidig ADS astronomy entries on 2022-09-14 author:"Neidig, Donald F. Jr." ------------------------------------------------------------------------ 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. Bibcode: 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) × 1033 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 1033 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) × 1033 erg). We speculate on favorable solar conditions that can lead to enhanced shock acceleration of high-energy protons in eruptive flares. 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. Bibcode: 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-1 ~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. 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. Bibcode: 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. 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. Bibcode: 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). Title: Moreton Waves And Filament Eruptions Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F. Bibcode: 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. Title: Are Moreton Waves Coronal Phenomena? Authors: Balasubramaniam, K. S.; Pevtsov, A. A.; Neidig, D. F. Bibcode: 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. 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. Bibcode: 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. Title: Accumulation of Filament Material at the Boundaries of Supergranular Cells Authors: Pevtsov, A. A.; Neidig, D. Bibcode: 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). 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. Bibcode: 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-1. 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. Title: ISOON + SOLIS: Merging the Data Products Authors: Radick, R.; Dalrymple, N.; Mozer, J.; Wiborg, P.; Harvey, J.; Henney, C.; Neidig, D. Bibcode: 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. Title: ISOON Observations of Late-Cycle Solar Flares and Associated Activity During October and November 2003 Authors: Neidig, D. Bibcode: 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. Title: How big was the Carrington 1859 Flare? Authors: Cliver, E. W.; Svalgaard, L.; Neidig, D. F. Bibcode: 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 NO3 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 1030 erg) but not unequalled event (the white-light emission of the 24 April 1984 >X13 flare contained ~6 x 1030 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. Title: Introducing ISOON, The Improved Solar Observing Optical Network Authors: Neidig, D.; Wiborg, P.; Mozer, J.; Dalrymple, N.; Dunn, R.; Gregory, S.; Gullixson, C. Bibcode: 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. 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. Bibcode: 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.

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. 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. Bibcode: 1998ASPC..140..519N Altcode: 1998ssp..conf..519N No abstract at ADS 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 Bibcode: 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. Title: Observations of Faint, Outlying Loop Systems in Large Flares Authors: Neidig, Donald F.; Švestka, Zdeněk; Cliver, Edward W.; Airapetian, Vladimir; Henry, Timothy W. Bibcode: 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 ≈ 102 km (unresolved by patrol instruments) and containing gas at densities 5 × 1010-5 × 1011 cm-3 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. 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. Bibcode: 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. 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 Bibcode: 1996ASPC...95..531S Altcode: 1996sdit.conf..531S No abstract at ADS 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. Bibcode: 1996ASPC...95...55S Altcode: 1996sdit.conf...55S No abstract at ADS 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. Bibcode: 1995SPD....26.1215N Altcode: 1995BAAS...27..986N No abstract at ADS 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. Bibcode: 1995SPD....26..722B Altcode: 1995BAAS...27..971B No abstract at ADS Title: Near-Infrared Coronagraphic Detection of Space Debris Authors: Neidig, D. F.; Smartt, R. N.; Kim, I. S.; Koutchmy, S. Bibcode: 1995itsa.conf..253N Altcode: No abstract at ADS 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. Bibcode: 1995itsa.conf..239K Altcode: No abstract at ADS 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. Bibcode: 1995ICRC....4..257C Altcode: 1995ICRC...24d.257C No abstract at ADS Title: Optical output of the 24 April 1984 white-light flare Authors: Neidig, Donald F.; Grosser, Hartmut; Hrovat, Mary Bibcode: 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. Title: Consequences of chromospheric irradiation in white light flares: An observer's point of view Authors: Neidig, D. F. Bibcode: 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 (Hfb emission) and the photosphere (H- 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. Title: Inferring the Spatial Variation of the Thick Target Nonthermal Electron Spectrum in a White Light Flare Authors: Neidig, D. F.; Kiplinger, A. L. Bibcode: 1993BAAS...25.1196N Altcode: No abstract at ADS Title: Physical properties of white-light flares derived from their center-to-limb distribution Authors: Neidig, Donald F.; Wiborg, Philip H.; Gilliam, Lou B. Bibcode: 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 τ5000 = 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. Title: The Mechanisms of Solar Variability (MSV) program Authors: Leibacher, John W.; Noyes, Robert W.; Simon, George W.; Neidig, Donald F. Bibcode: 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. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1990BAAS...22..846N Altcode: No abstract at ADS Title: Book-Review - Solar Physics in the 1990'S Authors: Neidig, D. F.; Hudson, H. S. Bibcode: 1989Sci...246..246N Altcode: No abstract at ADS Title: The Importance of Solar White-Light Flares Authors: Neidig, Donald F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1988BAAS...20R.977H Altcode: No abstract at ADS Title: Foreword Authors: Neidig, Donald F. Bibcode: 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. Bibcode: 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 Bibcode: 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 1012 cm -3. From measured widths of higher Balmer lines the density at the tops of the loops was found to be 4 x 1012 cm -3 if no non-thermal motions were present, or 5 × 1011 cm -3 for a turbulent velocity of ~ 12 km s -1. Title: The largest white light flare ever observed: 25 April 1984, 0001 UT Authors: Neidig, D. F.; Grosser, H.; Kiplinger, A. L. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1986stp..conf..187N Altcode: 1986STP.....2..187N No abstract at ADS Title: Solar Activity Measurement Experiment (SAMEX) Authors: Keil, Stephen L.; Neidig, Donald F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 1014cm-3. 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.

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. Bibcode: 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 1012 cm-3. From measured widths of higher Balmer lines the density at the loops of the loops was found to be 4 × 1012 cm-3 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 107 K to 104 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. Bibcode: 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 Hfb and Hff 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 104 - 25,000K, linear emission measures 1035 - 1036cm-5 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. Bibcode: 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. Bibcode: 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. Bibcode: 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 Hfb emission. Title: Hydrogen Recombination as an Emission Mechanism in White-Light Flares Authors: Neidig, D. F. Bibcode: 1984BAAS...16..545N Altcode: No abstract at ADS Title: The Occurrence Frequency of White Light Flares Authors: Neidig, D. F.; Cliver, E. W. Bibcode: 1983SoPh...88..275N Altcode: We derive an occurrence frequency for white-light flares (WLF) of 15.5 ± 4.5 yr−1 during a 2.6 year period following the maximum of solar cycle 21. This compares with a frequency 5-6 yr−1 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. Bibcode: 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. Bibcode: 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) and Balmer continuum, with the H probably originating in the upper photosphere at a height (above τ5000 Å = 1) in the range 200-300 km. Analysis of the Balmer lines and continuum yields an electron density 5.3 × 1013 cm−3 and a second-level hydrogen column density 1.1 × 1016 cm−2. The peak radiative output integrated over wavelength is 6.1 × 1027 erg s−1. The observed continuum intensity, if originating at a height of 300 km, implies an energy loss rate of 103 erg s−1 cm−3. Title: Observing White-Light Flares Authors: Neidig, D. F.; Beckers, J. M. Bibcode: 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. Bibcode: 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. Bibcode: 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 (≳ 1014 cm−3), 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1980BAAS...12..910N Altcode: No abstract at ADS Title: Solar rotation studies using sunspot data (1967 1974) Authors: Neidig, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 1978AFGL...78..194N Altcode: No abstract at ADS Title: Microwave burst spectra and solar flare magnetic fields. Authors: Neidig, D. F., Jr. Bibcode: 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. Bibcode: 1976PhDT........50N Altcode: No abstract at ADS Title: Nonthermal Electrons in Solar Flares. Authors: Neidig, D. F. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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. Bibcode: 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.