An Observational Overview of Solar Flares

Fletcher, L.; Dennis, B. R.; Hudson, H. S.; Krucker, S.; Phillips, K. J. H.; Veronig, A.; Battaglia, Marina; Bone, L.; Caspi, Amir; Chen, Q.; Gallagher, Peter T.; Grigis, P. C.; Ji, Haisheng; Liu, W.; Milligan, Ryan O.; Temmer, Manuela

doi:10.1007/978-1-4614-3073-5_3

Cited by 24 publications

(26 citation statements)

References 455 publications

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“…The signal absorption calculated for a flare with k b T = 0.55, 0.5, and 0.45 keV spectra corresponds well to the features of the measured attenuation for 5-7 September, respectively. These temperatures fall within the range of solar flare 0.1-to 10-keV soft X-ray emission (Caspi et al, 2015;Fletcher et al, 2011;Jeffrey, 2015;Mitra, 1974). Before the peak fluence, the data for attenuation are higher than the calculated absorption for the X9.3 and X1.3 flares.…”

Section: Resultsmentioning

confidence: 61%

“…The spectral energy density of solar flares is a complex function of flare plasma dynamics, with changing magnitude and spectral distribution over the duration of the flare. Flare spectroscopy is still an active area of research, with continued efforts underway to measure and model the time-dependent spectrum (Chaimberlin et al, 2008;Fletcher et al, 2011;Jeffrey, 2015;Lin et al, 2002;Savchenko et al, 2017). We approximate the vacuum spectral energy density for a flare at a distance D away to be…”

Section: X-ray Solar Flares Spectral Energy Densitymentioning

confidence: 99%

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A Parameterized Model of X‐Ray Solar Flare Effects on the Lower Ionosphere and HF Propagation

2019

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We present a parameterized X-ray solar flare effects model relating the physics of radiation transport to the observable impact of solar flares on low-altitude ionospheric absorption of High Frequency (HF) signals. Tunable parameters of time-varying flare spectral energy density and characteristic flare temperature provide a novel capability to simulate HF experiments over a wide range of X-ray solar flare behavior. Results from our model are consistent with HF propagation data collected over a period of heightened solar flare activity during 5-7 September 2017, including M and X class solar flares. Our predictions and measurements are compared with results from D Region Absorption Prediction (Akmaev et al., 2010, https://www.ngdc.noaa.gov/stp/drap/DRAP-V-Report1.pdf) and the Wait Very Low Frequency (VLF)-driven model (Wait & Spies, 1964). Plain Language SummaryWe present a physics-based model for high-frequency (HF) signal absorption resulting from the effects of X-ray solar flares on the low-altitude ionosphere. Our model calculates the extent of ionization enhancement in the D region due to an X-ray flare and predicts the altitude-dependent change of electron density and consequent increase in HF signal absorption. We demonstrate that results from our model are consistent with ionosonde data collected during three solar flare events. This model provides a novel approach to analyzing the impact of X-ray solar flares on HF propagation and is complementary to the widely used empirical D Region Absorption Prediction and Wait models. Key Points:• We developed a physics-based model of HF absorption due to X-ray solar flare impact on the low-altitude ionosphere • Model results are consistent with ionosonde data collected during flare events on a 3-day experimental campaign • The model is a novel approach to X-ray flare impact on HF propagation, complementing existing empirical modelsCorrespondence to:

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Section: Resultsmentioning

confidence: 61%

Section: X-ray Solar Flares Spectral Energy Densitymentioning

confidence: 99%

A Parameterized Model of X‐Ray Solar Flare Effects on the Lower Ionosphere and HF Propagation

2019

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“…For the centimeter range, these mechanisms are mainly related to the gyrosynchrotron electron emis sion mechanism (Fletcher et al, 2011). The relation between the radioemission flux and the area of heated regions in the Ca II K line found in this work should also be studied.…”

Section: Discussionmentioning

confidence: 78%

“…It is considered that the energy that is expended on particle acceleration and the formation of a nonthermal (synchrotron) microwave emission and hard X rays is released during the flare impulsive phase. This energy is also expended on the chromo spheric line, continuum, and ultraviolet emissions (Fletcher et al, 2011). A rather high correlation exists between the total X ray flux and the maximal intensity in the Ca II K line during the event in this region (Fig.…”

Section: Discussionmentioning

confidence: 88%

Synoptic and fast events on the sun according to observations at the center and wings of the Ca II K line at the Kislovodsk Mountain station patrol telescope

et al. 2015

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Observations performed at the solar telescope-spectroheliograph, which has continuously auto matically operated at MAS MAO RAS, were analyzed. Measurements of the activity index in the Ca II K line, which were performed according to the program of synoptic observations, are presented. The development of the solar flares observed at the center and on the wings of the Ca II K line was compared with observations in the X ray and radio bands. It was shown that the time variations in the intensity in the 1-8 Å range according to the Geostationary Orbiting Environmental Satellites' (GOES) data and in the Ca II K line are close to each other and that the total X ray flux and Ca II K intensity amplitude substantially correlate during the entire flare.

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“…Spine reconnection in 3-D MHD reconnection simulations can naturally produce two symmetric jets of energetic particles escaping along the spine, while the fan reconnection produces azimuthally localized ribbons of high energy particles in the fan plane. Both features, in principle, are often observed in flares, e.g., magnetic jets and two-ribbon flares as discussed in Fletcher et al (2011). Jet-like structure can also be important in ejecting solar energetic particles into space.…”

Section: Acceleration Via Magnetic Reconnectionmentioning

confidence: 94%

Particle Acceleration in the Sun and Beyond

Lee¹

2017

Proceedings of 35th International Cosmic Ray Conference — PoS(ICRC2017)

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This article reviews recent studies on cosmic rays originating in the heliosphere with emphasis on the role played by solar flares. In the first part, the physical drivers for high-energy particle acceleration in the heliosphere including solar flares, coronal mass ejections (CMEs), corotating interaction regions (CIR) and solar wind termination shocks are briefly discussed. We then introduce solar particle acceleration mechanisms in which shocks, turbulence, Alfvén waves, and magnetic reconnection respectively play a role. It is demonstrated that the properties of accelerated particles in the Sun are known in considerable detail because magnetic reconnection geometry is visible through electromagnetic radiations, and imaging spectroscopy at hard X-ray and radio wavelengths is available. In the second part, we attempt to relate our knowledge of solar flare particles to several research topics on solar energetic particles (SEPs). The topics include: (1) possible influence of solar magnetic field structure upon the energy spectra and time profiles of the resulting SEPs, (2) temporal, spatial and spectral properties of SEP electrons measured in interplanetary space in comparison with those remotely observed in the Sun, and (3) the energydependent onset time of SEP protons and its implication on the proton acceleration beyond the Sun. It is argued that we should take advantage of solar imaging spectroscopy at X-ray and radio wavelengths to complement the cosmic ray studies largely based on in-situ observations in order to disentangle the roles played by solar flares and CMEs in accelerating SEPs and better understand the relationship between solar flares and SEPs.

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An Observational Overview of Solar Flares

Cited by 24 publications

References 455 publications

A Parameterized Model of X‐Ray Solar Flare Effects on the Lower Ionosphere and HF Propagation

A Parameterized Model of X‐Ray Solar Flare Effects on the Lower Ionosphere and HF Propagation

Synoptic and fast events on the sun according to observations at the center and wings of the Ca II K line at the Kislovodsk Mountain station patrol telescope

Particle Acceleration in the Sun and Beyond

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