اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدTransition Region Emission and Energy Input to Thermal Plasma During the Impulsive Phase of Solar Flares
77
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
The energy released in a solar flare is partitioned between thermal and non-thermal particle energy and lost to thermal conduction and radiation over a broad range of wavelengths. It is difficult to determine the conductive losses and the energy radiated at transition region temperatures during the impulsive phases of flares. We use UVCS measurements of O VI photons produced by 5 flares and subsequently scattered by O VI ions in the corona to determine the 5.0 < log T < 6.0 transition region luminosities. We compare them with the rates of increase of thermal energy and the conductive losses deduced from RHESSI and GOES X-ray data using areas from RHESSI images to estimate the loop volumes, cross-sectional areas and scale lengths. The transition region luminosities during the impulsive phase exceed the X-ray luminosities for the first few minutes, but they are smaller than the rates of increase of thermal energy unless the filling factor of the X-ray emitting gas is ~ 0.01. The estimated conductive losses from the hot gas are too large to be balanced by radiative losses or heating of evaporated plasma, and we conclude that the area of the flare magnetic flux tubes is much smaller than the effective area measured by RHESSI during this phase of the flares. For the 2002 July 23 flare, the energy deposited by non-thermal particles exceeds the X-ray and UV energy losses and the rate of increase of the thermal energy.
قيم البحث
اقرأ أيضاً
There are relatively few observations of UV emission during the impulsive phases of solar flares, so the nature of that emission is poorly known. Photons produced by solar flares can resonantly scatter off atoms and ions in the corona. Based on off-l
imb measurements by SOHO/UVCS, we derive the O VI $lambda$1032 luminosities for 29 flares during the impulsive phase and the Ly$alpha$ luminosities of 5 flares, and we compare them with X-ray luminosities from GOES measurements. The upper transition region and lower transition region luminosities of the events observed are comparable. They are also comparable to the luminosity of the X-ray emitting gas at the beginning of the flare, but after 10-15 minutes the X-ray luminosity usually dominates. In some cases we can use Doppler dimming to estimate flow speeds of the O VI emitting gas, and 5 events show speeds in the 40 to 80 $rm km s^{-1}$ range. The O VI emission could originate in gas evaporating to fill the X-ray flare loops, in heated chromospheric gas at the footpoints, or in heated prominence material in the coronal mass ejection. All three sources may contribute in different events or even in a single event, and the relative timing of UV and X-ray brightness peaks, the flow speeds, and the total O VI luminosity favor each source in one or more events.
Using a recently developed analytical procedure, we determine the rate of magnetic reconnection in the standard model of eruptive solar flares. During the late phase, the neutral line is located near the lower tip of the reconnection current sheet, a
nd the upper region of the current sheet is bifurcated into a pair of Petschek-type shocks. Despite the presence of these shocks, the reconnection rate remains slow if the resistivity is uniform and the flow is laminar. Fast reconnection is achieved only if there is some additional mechanism that can shorten the length of the diffusion region at the neutral line. Observations of plasma flows by the X-Ray Telescope (XRT) on Hinode imply that the diffusion region is in fact quite short. Two possible mechanisms for reducing the length of the diffusion region are localized resistivity and MHD turbulence.
We report solar flare plasma to be multi-thermal in nature based on the theoretical model and study of the energy-dependent timing of thermal emission in ten M-class flares. We employ high-resolution X-ray spectra observed by the Si detector of the S
olar X-ray Spectrometer (SOXS). The SOXS onboard the Indian GSAT-2 spacecraft was launched by the GSLV-D2 rocket on 8 May 2003. Firstly we model the spectral evolution of the X-ray line and continuum emission flux F(epsilon) from the flare by integrating a series of isothermal plasma flux. We find that multi-temperature integrated flux F(epsilon) is a power-law function of epsilon with a spectral index (gamma) approx -4.65. Next, based on spectral-temporal evolution of the flares we find that the emission in the energy range E= 4 - 15 keV is dominated by temperatures of T= 12 - 50 MK, while the multi-thermal power-law DEM index (gamma) varies in the range of -4.4 and -5.7. The temporal evolution of the X-ray flux F(epsilon,t) assuming a multi-temperature plasma governed by thermal conduction cooling reveals that the temperature-dependent cooling time varies between 296 and 4640 s and the electron density (n_e) varies in the range of n_e= (1.77-29.3)*10^10 cm-3. Employing temporal evolution technique in the current study as an alternative method for separating thermal from non-thermal components in the energy spectra, we measure the break-energy point ranging between 14 and 21pm1.0 keV.
It is well established that elemental abundances vary in the solar atmosphere and that this variation is organized by first ionization potential (FIP). Previous studies have shown that in the solar corona low-FIP elements, such as Fe, Si, Mg, and Ca,
are generally enriched relative to high-FIP elements, such as C, N, O, Ar, and Ne. In this paper we report on measurements of plasma composition made during impulsive heating events observed at transition region temperatures with the Extreme Ultraviolet Imaging Spectrometer (EIS) on Hinode. During these events the intensities of O IV, V, and VI emission lines are enhanced relative to emission lines from Mg V, VI, and VII and Si VI and VII and indicate a composition close to that of the photosphere. Long-lived coronal fan structures, in contrast, show an enrichment of low-FIP elements. We conjecture that the plasma composition is an important signature of the coronal heating process, with impulsive heating leading to the evaporation of unfractionated material from the lower layers of the solar atmosphere and higher frequency heating leading to long-lived structures and the accumulation of low-FIP elements in the corona.
The aim of the thesis is the study of properties of solar flares via reconstruction of energy distributions of accelerated/heated electrons, diagnostics of flare plasma based on EUV and X-ray observations, as well as the estimation of the thermal bal
ance within the standard flare model. The X-ray data were obtained from the Ramaty High Energy Solar Spectroscopic Imager (RHESSI) and the Russian solar observatory KORONAS-F (IRIS experiment). The EUV data were obtained from the Solar Dynamics Observatory / Atmospheric Imaging Assembly (SDO/AIA). In the first chapter a new technique is presented, which allowed to determine at first the photon spectra based on the KORONAS-F/IRIS observations and then to reconstruct the energy spectra of the emitting electrons using the random search method and the Tikhonov regularization method. In the second chapter the developed technique of simultaneously fitting the model differential emission measure functions (DEM) to RHESSI and SDO/AIA data is introduced, which allowed to infer the electron distribution from X-ray and EUV observations. The proposed method allows to reconstruct of both the spectra of accelerated/heated electrons and the basic parameters of the flare plasma, such as temperature, emission measure, total electron number density, and flare energy. In addition, the analytical function suitable for both DEM analysis and mean electron flux spectra in flares has been developed and applied, as well as kappa-distribution in the form of differential emission measure. The thermal balance and hard X-ray emission of coronal loops from different flare regions within the standard flare model is considered in the third chapter. This thesis is based on the next papers: Motorina et al., TePh, 2012, Motorina & Kontar, Ge&Ae, 2015, Battaglia et al., ApJ, 2015, Motorina et al., TePh, 2016, Tsap et al., Ge&Ae, 2016.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
