scholarly journals Observation of Seismic Effects of Solar Flares from the SOHO Michelson Doppler Imager

1998 ◽  
Vol 185 ◽  
pp. 191-194
Author(s):  
A.G. Kosovichev ◽  
V.V. Zharkova
Keyword(s):  
Solar Flares ◽  
Seismic Waves ◽  
Solar Surface ◽  
Active Regions ◽  
Impulsive Phase ◽  
High Energy ◽  
Solar Interior ◽  
Michelson Doppler Imager ◽  
Seismic Effects ◽  
Doppler Imager

Solar flares are the strongest localized seismic disturbances on the solar surface. During the impulsive phase a high-energy electron beam heats the chromosphere, resulting in explosive evaporation of chromospheric plasma at supersonic velocities. This upward motion is balanced by a downward recoil in the lower part of the chromosphere that excites propagating waves in the solar interior. On the solar surface the outgoing circular flare waves resemble ripples from a pebble thrown into a pond. We report on first observations of the seismic effects of a solar flare from the SOHO Michelson Doppler Imager (MDI) and compare the results with a theoretical model. Observation of flare seismic waves provide important information about the flare mechanism and about the subphotospheric structure of active regions.

Characteristics of Sunquake Events Observed in Solar Cycle 24

2021 ◽  
Author(s):  
Alexander Kosovichev ◽  
Ivan Sharykin
Keyword(s):  
Solar Cycle ◽  
Solar Flares ◽  
Active Regions ◽  
Impulsive Phase ◽  
High Energy ◽  
Lower Atmosphere ◽  
Solar Dynamics Observatory ◽  
X Ray ◽  
Solar Cycle 24 ◽  
Cycle 24

<p>Helioseismic response to solar flares ("sunquakes") occurs due to localized force or/and momentum impacts observed during the flare impulsive phase in the lower atmosphere. Such impacts may be caused by precipitation of high-energy particles, downward shocks, or magnetic Lorentz force. Understanding the mechanism of sunquakes is a key problem of the flare energy release and transport. Our statistical analysis of M-X class flares observed by the Solar Dynamics Observatory during Solar Cycle 24 has shown that contrary to expectations, many relatively weak M-class flares produced strong sunquakes, while for some powerful X-class flares, helioseismic waves were not observed or were weak. The analysis also revealed that there were active regions characterized by the most efficient generation of sunquakes during the solar cycle. We found that the sunquake power correlates with maximal values of the X-ray flux derivative better than with the X-ray class. The sunquake data challenge the current theories of solar flares.</p>

scholarly journals The behavior of the spotless active regions during the solar minimum 23-24

2016 ◽  
Vol 12 (S328) ◽  
pp. 137-139
Author(s):  
Alexandre José de Oliveira e Silva ◽  
Caius Lucius Selhorst
Keyword(s):  
Solar Minimum ◽  
Solar Surface ◽  
Active Regions ◽  
Physical Parameters ◽  
Michelson Doppler Imager ◽  
Heliospheric Observatory ◽  
Doppler Imager

AbstractIn this work, we analysed the physical parameters of the spotless actives regions observed during solar minimum 23 – 24 (2007 – 2010). The study was based on radio maps at 17 GHz obtained by the Nobeyama Radioheliograph (NoRH) and magnetograms provided by the Michelson Doppler Imager (MDI) on board the Solar and Heliospheric Observatory (SOHO). The results shows that the spotless active regions presents the same radio characteristics of a ordinary one, they can live in the solar surface for long periods (>10 days), and also can present small flares.

scholarly journals High Energy Phenomena in the Sun

1981 ◽  
Vol 94 ◽  
pp. 367-372
Author(s):  
Claudio Chiuderi
Keyword(s):  
Solar Flares ◽  
Solar Surface ◽  
Solar Physics ◽  
Total Duration ◽  
Cosmic Ray ◽  
Total Surface Area ◽  
High Energy ◽  
Energy Scale ◽  
Image Position ◽  
Large Flare

High energy phenomena in the solar physics context, simply means solar flares. To be sure, the energies attained during flares are certainly not very impressive on a cosmic-ray scale. The most energetic particles belong the GeV range, the highest temperatures are of the order of 107 K, γ-ray emission is occasional and the total energy emitted remains below 1033 ergs for all the flares so far observed. Apart from an absolute energy scale, flares are also energetically irrelevant on a solar scale. In fact in a large flare a few units in 1032 ergs are emitted, with a total duration of about one hour and a total surface area involved of a few units in 10−4 of the solar surface. Recalling the values of the luminosity, L⊙ ≃ 4 × 1033 erg s−1 and the solar flux F⊙6.3 × 1010 erg cm−2s−1, we see that

scholarly journals Machine learning reveals systematic accumulation of electric current in lead-up to solar flares

2019 ◽  
Vol 116 (23) ◽  
pp. 11141-11146 ◽  
Author(s):  
Dattaraj B. Dhuri ◽  
Shravan M. Hanasoge ◽  
Mark C. M. Cheung
Keyword(s):  
Magnetic Field ◽  
Machine Learning ◽  
Solar Flares ◽  
Active Regions ◽  
High Energy ◽  
Field Observations ◽  
High Energy Radiation ◽  
Before And After ◽  
Class Flare ◽  
Maxwell Stresses

Solar flares—bursts of high-energy radiation responsible for severe space weather effects—are a consequence of the occasional destabilization of magnetic fields rooted in active regions (ARs). The complexity of AR evolution is a barrier to a comprehensive understanding of flaring processes and accurate prediction. Although machine learning (ML) has been used to improve flare predictions, the potential for revealing precursors and associated physics has been underexploited. Here, we train ML algorithms to classify between vector–magnetic-field observations from flaring ARs, producing at least one M-/X-class flare, and nonflaring ARs. Analysis of magnetic-field observations accurately classified by the machine presents statistical evidence for (i) ARs persisting in flare-productive states—characterized by AR area—for days, before and after M- and X-class flare events; (ii) systematic preflare buildup of free energy in the form of electric currents, suggesting that the associated subsurface magnetic field is twisted; and (iii) intensification of Maxwell stresses in the corona above newly emerging ARs, days before first flares. These results provide insights into flare physics and improving flare forecasting.

scholarly journals On the seismic emission in sunspots associated with Lorentz force changes accompanying major solar flares

2020 ◽  
Vol 497 (1) ◽  
pp. 976-987
Author(s):  
Hirdesh Kumar ◽  
Brajesh Kumar
Keyword(s):  
Lorentz Force ◽  
Solar Flares ◽  
Seismic Waves ◽  
Acoustic Power ◽  
High Energy ◽  
Space Mission ◽  
Solar Dynamics Observatory ◽  
Seismic Emission ◽  
X Ray ◽  
Power Maps

ABSTRACT Solar flares are known to generate seismic waves in the Sun. We present a detailed analysis of seismic emission in sunspots accompanying M- and X-class solar flares. For this purpose, we have used high-resolution Dopplergrams and line-of-sight magnetograms at a cadence of 45 s, along with vector magnetograms at a cadence of 135 s obtained from Helioseismic and Magnetic Imager instrument aboard the Solar Dynamics Observatory space mission. In order to identify the location of flare ribbons and hard X-ray footpoints, we have also used Hα chromospheric intensity observations obtained from Global Oscillation Network Group instruments and hard X-ray images in 12–25 keV band from the Reuvan Ramaty High Energy Solar Spectroscopic Imager spacecraft. The fast Fourier transform technique is applied to construct the acoustic velocity power map in 2.5–4 mHz band for pre-flare, spanning flare, and post-flare epochs for the identification of seismic emission locations in the sunspots. In the power maps, we have selected only those locations which are away from the flare ribbons and hard X-ray footpoints. These regions are believed to be free from any flare related artefacts in the observational data. We have identified concentrated locations of acoustic power enhancements in sunspots accompanying major flares. Our investigation provides evidence that abrupt changes in the magnetic fields and associated impulsive changes in the Lorentz force could be the driving source for these seismic emissions in the sunspots during solar flares.

Millimeter, Microwave, Hard X-Ray, and Soft X-Ray Observations of Energetic Electron Populations in Solar Flares

1994 ◽  
Vol 142 ◽  
pp. 599-610
Author(s):  
M. R. Kundu ◽  
S. M. White ◽  
N. Gopalswamy ◽  
J. Lim
Keyword(s):  
Solar Flares ◽  
Energetic Electron ◽  
Impulsive Phase ◽  
High Energy ◽  
X Rays ◽  
High Turnover ◽  
X Ray ◽  
Nonthermal Electrons ◽  
Time Profiles ◽  
Wavelength Emission

AbstractWe present comparisons of multiwavelength data for a number of solar flares observed during the major campaign of 1991 June. The different wavelengths are diagnostics of energetic electrons in different energy ranges: soft X-rays are produced by electrons with energies typically below 10 keV, hard X-rays by electrons with energies in the range 10-200 keV, microwaves by electrons in the range 100 keV-1 MeV, and millimeter-wavelength emission by electrons with energies of 0.5 MeV and above. The flares in the 1991 June active period were remarkable in two ways: all have very high turnover frequencies in their microwave spectra, and very soft hard X-ray spectra. The sensitivity of the microwave and millimeter data permit us to study the more energetic (>0.3 MeV) electrons even in small flares, where their high-energy bremsstrahlung is too weak for present detectors. The millimeter data show delays in the onset of emission with respect to the emissions associated with lower energy electrons and differences in time profiles, energy spectral indices incompatible with those implied by the hard X-ray data, and a range of variability of the peak flux in the impulsive phase when compared with the peak hard X-ray flux which is two orders of magnitude larger than the corresponding variability in the peak microwave flux. All these results suggest that the hard X-ray-emitting electrons and those at higher energies which produce millimeter emission must be regarded as separate populations. This has implications for the well-known “number problem” found previously when comparing the numbers of nonthermal electrons required to produce the hard X-ray and radio emissions.Subject headings: Sun: flares — Sun: radio radiation — Sun: X-rays, gamma rays

scholarly journals The Model of the Impulsive Phase of Stellar Flares

1989 ◽  
Vol 104 (2) ◽  
pp. 297-300
Author(s):  
V.P. Grinin ◽  
V.V. Sobolev
Keyword(s):  
Radiative Transfer ◽  
Solar Flares ◽  
Charged Particles ◽  
Impulsive Phase ◽  
High Energy ◽  
Stellar Flares ◽  
Flare Region ◽  
Optical Continuum

AbstractThe arguments in favour of that the primary heating of the gas at the impulsive phase of stellar flares is caused by charged particles of higher energies than in the solar flares are given. It is shown that the model of the deep heating by high energy protons (E ≃ 10 MeV) or electrons (E ≃ 100 keV) with taken into account of the radiative transfer in flare region explane the main properties of the optical continuum of the flare.

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