TY - JOUR
T1 - Statistical Study of Chromospheric Evaporation in Impulsive Phase of Solar Flares
AU - Sadykov, Viacheslav M.
AU - Kosovichev, Alexander G.
AU - Sharykin, Ivan N.
AU - Kerr, Graham S.
N1 - Funding Information:
IRIS is a NASA small explorer mission developed and operated by LMSAL, with mission operations executed at NASA Ames Research Center and major contributions to downlink communications funded by ESA and the Norwegian Space Centre. We acknowledge the RHESSI team for the availability of the high-quality scientific data. The research leading to these results has received funding from the European Community’s Seventh Framework Programme (FP7/2007-2013) under grant agreement No. 606862 (F-CHROMA). We also acknowledge the Stanford Solar Observatories Group and NASA Ames Research Center for the ability to use the computational resources. G.S.K. is supported by an appointment to the NASA Postdoctoral Program at Goddard Space Flight Center, administered by USRA through a contract with NASA. The research was partially supported by NASA grants NNX14AB68G and NNX16AP05H and NSF grant 1639683.
Publisher Copyright:
© 2019. The American Astronomical Society. All rights reserved.
PY - 2019/1/20
Y1 - 2019/1/20
N2 - We present a statistical study of chromospheric evaporation in solar flares using simultaneous observations by the RHESSI X-ray telescope and the Interface Region Imaging Spectrograph UV spectrograph. The results are compared with radiation hydrodynamic flare models from the F-CHROMA RADYN database. For each event, we study spatially resolved Doppler shifts of spectral lines formed in the transition region (C ii 1334.5) and hot coronal plasma (Fe xxi 1354.1) to investigate the dynamics of the solar atmosphere during the flare impulsive phase. We estimate the energy fluxes deposited by high-energy electrons using X-ray imaging spectroscopy and assuming the standard thick-target model. Using the RADYN flare models, the RH 1.5D radiative transfer code, and the Chianti atomic line database, we calculate C ii and Fe xxi line profiles and compare with the observations. While the RADYN models predict a correlation between the Doppler shifts and deposited energy flux for both lines, this was only observed in the C ii data. Several quantitative discrepancies are found between the observations and models: the Fe xxi Doppler shifts are substantially stronger in the models than in the data, and the C ii mean blueshifts are absent in the observations but predicted by the models. The transition energies between "gentle" and "explosive" evaporation regimes estimated from the observations ( erg cm -2 s -1 ) and derived from the models ( erg cm -2 s -1 ) are comparable with each other. The results illustrate relationships among the processes of chromospheric evaporation, the response of the colder layers, and the flare energy flux deposited by high-energy electrons, although demonstrating discrepancy between analyzed observations and RADYN models.
AB - We present a statistical study of chromospheric evaporation in solar flares using simultaneous observations by the RHESSI X-ray telescope and the Interface Region Imaging Spectrograph UV spectrograph. The results are compared with radiation hydrodynamic flare models from the F-CHROMA RADYN database. For each event, we study spatially resolved Doppler shifts of spectral lines formed in the transition region (C ii 1334.5) and hot coronal plasma (Fe xxi 1354.1) to investigate the dynamics of the solar atmosphere during the flare impulsive phase. We estimate the energy fluxes deposited by high-energy electrons using X-ray imaging spectroscopy and assuming the standard thick-target model. Using the RADYN flare models, the RH 1.5D radiative transfer code, and the Chianti atomic line database, we calculate C ii and Fe xxi line profiles and compare with the observations. While the RADYN models predict a correlation between the Doppler shifts and deposited energy flux for both lines, this was only observed in the C ii data. Several quantitative discrepancies are found between the observations and models: the Fe xxi Doppler shifts are substantially stronger in the models than in the data, and the C ii mean blueshifts are absent in the observations but predicted by the models. The transition energies between "gentle" and "explosive" evaporation regimes estimated from the observations ( erg cm -2 s -1 ) and derived from the models ( erg cm -2 s -1 ) are comparable with each other. The results illustrate relationships among the processes of chromospheric evaporation, the response of the colder layers, and the flare energy flux deposited by high-energy electrons, although demonstrating discrepancy between analyzed observations and RADYN models.
KW - Sun: UV radiation
KW - Sun: chromosphere
KW - Sun: flares
KW - methods: statistical
KW - techniques: spectroscopic
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U2 - 10.3847/1538-4357/aaf6b0
DO - 10.3847/1538-4357/aaf6b0
M3 - Article
AN - SCOPUS:85061998993
SN - 0004-637X
VL - 871
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 1
M1 - 2
ER -