The extreme ultraviolet emissions of solar flares: A comparison between OSO-6 spectroheliograph observations and SFDs

Solar Physics ◽  
1973 ◽  
Vol 29 (1) ◽  
pp. 107-123 ◽  
Author(s):  
R. F. Donnelly ◽  
A. T. Wood ◽  
R. W. Noyes
Keyword(s):  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Ultraviolet Emissions

scholarly journals Solar flares observed by Rosetta at comet 67P/Churyumov-Gerasimenko

2019 ◽  
Vol 630 ◽  
pp. A49 ◽  
Author(s):  
N. J. T. Edberg ◽  
F. L. Johansson ◽  
A. I. Eriksson ◽  
D. J. Andrews ◽  
R. Hajra ◽  
...  
Keyword(s):  
Plasma Density ◽  
Solar Flares ◽  
Langmuir Probe ◽  
Extreme Ultraviolet ◽  
Vantage Point ◽  
Spectral Model ◽  
Time Of Arrival ◽  
Observable Effect ◽  
Density Measurements ◽  
Comet 67P

Context. The Rosetta spacecraft made continuous measurements of the coma of comet 67P/Churyumov-Gerasimenko (67P) for more than two years. The plasma in the coma appeared very dynamic, and many factors control its variability. Aims. We wish to identify the effects of solar flares on the comet plasma and also their effect on the measurements by the Langmuir Probe Instrument (LAP). Methods. To identify the effects of flares, we proceeded from an existing flare catalog of Earth-directed solar flares, from which a new list was created that only included Rosetta-directed flares. We also used measurements of flares at Mars when at similar longitudes as Rosetta. The flare irradiance spectral model (FISM v.1) and its Mars equivalent (FISM-M) produce an extreme-ultraviolet (EUV) irradiance (10–120 nm) of the flares at 1 min resolution. LAP data and density measurements obtained with the Mutual Impedence Probe (MIP) from the time of arrival of the flares at Rosetta were examined to determine the flare effects. Results. From the vantage point of Earth, 1504 flares directed toward Rosetta occurred during the mission. In only 24 of these, that is, 1.6%, was the increase in EUV irradiance large enough to cause an observable effect in LAP data. Twenty-four Mars-directed flares were also observed in Rosetta data. The effect of the flares was to increase the photoelectron current by typically 1–5 nA. We find little evidence that the solar flares increase the plasma density, at least not above the background variability. Conclusions. Solar flares have a small effect on the photoelectron current of the LAP instrument, and they are not significant in comparison to other factors that control the plasma density in the coma. The photoelectron current can only be used for flare detection during periods of calm plasma conditions.

Solar flares in the extreme ultraviolet

Solar Physics ◽  
1972 ◽  
Vol 24 (1) ◽  
pp. 169-179 ◽  
Author(s):  
A. T. Wood ◽  
R. W. Noyes ◽  
A. K. Dupree ◽  
M. C. E. Huber ◽  
W. H. Parkinson ◽  
...  
Keyword(s):  
Solar Flares ◽  
Extreme Ultraviolet

scholarly journals Solar flares as proxy for the young Sun: satellite observed thermosphere response to an X17.2 flare of Earth's upper atmosphere

2012 ◽  
Vol 30 (8) ◽  
pp. 1129-1141 ◽  
Author(s):  
S. Krauss ◽  
B. Fichtinger ◽  
H. Lammer ◽  
W. Hausleitner ◽  
Yu. N. Kulikov ◽  
...  
Keyword(s):  
Solar Flares ◽  
Radiation Flux ◽  
Extreme Ultraviolet ◽  
Upper Atmosphere ◽  
Radiation Environment ◽  
The Sun ◽  
Satellite Drag ◽  
Grace Satellites ◽  
Early Phases ◽  
Activity Indices

Abstract. We analyzed the measured thermospheric response of an extreme solar X17.2 flare that irradiated the Earth's upper atmosphere during the so-called Halloween events in late October/early November 2003. We suggest that such events can serve as proxies for the intense electromagnetic and corpuscular radiation environment of the Sun or other stars during their early phases of evolution. We applied and compared empirical thermosphere models with satellite drag measurements from the GRACE satellites and found that the Jacchia-Bowman 2008 model can reproduce the drag measurements very well during undisturbed solar conditions but gets worse during extreme solar events. By analyzing the peak of the X17.2 flare spectra and comparing it with spectra of young solar proxies, our results indicate that the peak flare radiation flux corresponds to a hypothetical Sun-like star or the Sun at the age of approximately 2.3 Gyr. This implies that the peak extreme ultraviolet (EUV) radiation is enhanced by a factor of about 2.5 times compared to today's Sun. On the assumption that the Sun emitted an EUV flux of that magnitude and by modifying the activity indices in the Jacchia-Bowman 2008 model, we obtain an average exobase temperature of 1950 K, which corresponds with previous theoretical studies related to thermospheric heating and expansion caused by the solar EUV flux.

scholarly journals ON THE ORIGIN OF THE EXTREME-ULTRAVIOLET LATE PHASE OF SOLAR FLARES

2013 ◽  
Vol 768 (2) ◽  
pp. 150 ◽  
Author(s):  
Kai Liu ◽  
Jie Zhang ◽  
Yuming Wang ◽  
Xin Cheng
Keyword(s):  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Late Phase

scholarly journals Preflare very long-periodic pulsations observed in Hα emission before the onset of a solar flare

2020 ◽  
Vol 639 ◽  
pp. L5
Author(s):  
Dong Li ◽  
Song Feng ◽  
Wei Su ◽  
Yu Huang
Keyword(s):  
Solar Flare ◽  
Light Curve ◽  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Light Curves ◽  
Trigger Mechanism ◽  
X Ray ◽  
Hα Emission ◽  
Plasma Loop ◽  
Full Disk

Context. Very long-periodic pulsations during preflare phases (preflare-VLPs) have been detected in the full-disk solar soft X-ray (SXR) flux. They may be regarded as precursors to solar flares and may help us better understand the trigger mechanism of solar flares. Aims. In this Letter, we report a preflare-VLP event prior to the onset of an M1.1 circular-ribbon flare on 2015 October 16. It was simultaneously observed in Hα, SXR, and extreme ultraviolet (EUV) wavelengths. Methods. The SXR fluxes in 1−8 Å and 1−70 Å were recorded by the Geostationary Operational Environmental Satellite (GOES) and Extreme Ultraviolet Variability Experiment, respectively; the light curves in Hα and EUV 211 Å were integrated over a small local region, which were measured by the 1 m New Vacuum Solar Telescope and the Atmospheric Imaging Assembly (AIA), respectively. The preflare-VLP is identified as the repeat and quasi-periodic pulses in light curves during preflare phase. The quasi-periodicity can be determined from the Fourier power spectrum with Markov chain Monte Carlo-based Bayesian. Results. Seven well-developed pulses are found before the onset of an M1.1 circular-ribbon flare. They are firstly seen in the local light curve in Hα emission and then discovered in full-disk SXR fluxes in GOES 1−8 Å and ESP 1−70 Å, as well as the local light curve in AIA 211 Å. These well-developed pulses can be regarded as the preflare-VLP, which might be modulated by LRC-circuit oscillation in the current-carrying plasma loop. The quasi-period is estimated to be ∼9.3 min. Conclusions. We present the first report of a preflare-VLP event in the local Hα line and EUV wavelength, which could be considered a precursor of a solar flare. This finding should therefore prove useful for the prediction of solar flares, especially for powerful flares.

scholarly journals Post-flare Coronal Activity on AU Mic Detected by EUVE

1995 ◽  
Vol 151 ◽  
pp. 146-147
Author(s):  
Maria Katsova ◽  
Jeremy Drake ◽  
Moissei Livshits
Keyword(s):  
Solar Flares ◽  
Extreme Ultraviolet ◽  
Emission Measure ◽  
Coronal Loops ◽  
Stellar Radius ◽  
Euv Emission ◽  
Long Duration ◽  
Red Dwarfs ◽  
Coronal Activity ◽  
Region Scale

Data of long-duration emission arising after the impulsive rise and decay in a flaring event on the red dwarf star AU Mic are discussed. Intensive EUV emission in the band 65-190 Å was registered by the Extreme Ultraviolet Explorer (EUVE) after both impulses during half a day. A similar behavior of the flux in the Fe XVIII 93.9 Å line is detected after the first powerful impulse. The decay of the intensity in the 65-190 Å band and in the Fe XVIII line during this prolonged event is 10 times slower than the time of radiative cooling of coronal loops with a typical flare plasma density. Some difficulties with two explanations of this event proposed earlier are discussed. Explanation (i) - the radiation of dense loops at main phase of the flare, and (ii) - the emission of the low-dense plasma of coronal transients (CME). The temporal behavior of the emission measure is determined for both the 65-190 Å band and the Fe XVIII line fluxes. The total energy emitted in the 1-2000 Å region for the long-duration event lasting almost 12 hours is 3 · 1035 ergs. The following physical model is proposed to explain the prolonged event (Fig. 1): the source of emission is the system of high coronal loops, the size of which is more than the active region scale, but is less than the stellar radius. The temperature of the plasma in the loops decreases from 107 K slowly, during a few hours. The densities in these loops are in the range 1013 cm−3 to 5 · 109 cm−3. Such systems, when the plasma therein becomes cool, are observed in the Hα line during large solar flares (for instance, June 15, 1991) after CME. Some additional post-flare energy input into this high coronal loop systems can be caused by the reconnection in vertical current sheet, and this post-eruptive energy release provides prolonged and intensive EUV emission.Apparently, we are faced here with a new kind of surface activity on late-type stars which is intermediate between impulsive flares on red dwarfs and long-duration, powerful events on subgiants, which are components of RS CVn binaries.The full version of this contribution will be published in Astronomicheskij Zhurnal (Astronomy Reports), 1995, Vol. 72.

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