## Dissertations

Spring 5-31-2019

Dissertation

#### Degree Name

Doctor of Philosophy in Applied Physics - (Ph.D.)

#### Department

Physics

Alexander G. Kosovichev

Haimin Wang

Bin Chen

Zhen Wu

Gelu M. Nita

For a comprehensive understanding of the energy release and chromospheric evaporation processes in solar flares it is necessary to perform a combined multi-wavelength analysis using observations from space-based and ground-based observatories, and compare the results with predictions of the radiative hydrodynamic (RHD) flare models. Initially, the case study of spatially-resolved chromospheric evaporation properties for an M\,1.0-class solar flare (SOL2014-06-12T21:12) using data form IRIS (Interface Region Imaging Spectrograph), HMI/SDO (Helioseismic and Magnetic Imager onboard Solar Dynamics Observatory), and VIS/GST (Visible Imaging Spectrometer at Goode Solar Telescope), demonstrate a complicated nature of evaporation and its connection to the magnetic field topology. Following this study, the Interactive Multi-Instrument Database of Solar Flares (IMIDSF) is designed for efficient search, integration, and representation of solar flares for statistical studies. Comparison of the energy release and chromospheric evaporation properties for seven solar flares simultaneously observed by IRIS and RHESSI (Reuven Ramaty High Energy Solar Spectroscopic Imager) with predictions of the RHD electron beam-heating flare models reveals weak correlations between deposited energy fluxes and Doppler shifts of IRIS lines for observations and strong fore models, together with other quantitative discrepancies. Statistical analysis of properties of Soft X-Ray (SXR) emission, plasma temperature (T), and emission measure (EM), derived from GOES (Geostationary Operational Environmental Satellite) observations demonstrate that flares form two groups, T-controlled'' and EM-controlled'', distinguished by different contribution of T and EM to the SXR peak formation and presumably evolving in loops of different lengths. Also, the modeling of the SDO/HMI line-of-sight observables for RHD flare models highlights that for relatively high deposited energy fluxes ($\ge{}5.0\times{}10^{10}$ erg\,cm$^{-2}$\,s$^{-1}$) the sharp magnetic transients and Doppler velocities observed during the solar flares by HMI/SDO should be interpreted with caution. Finally, problems of the solar flare prediction and the role of the magnetic field Polarity Inversion Lines (PIL) in the initiation and development of flares are considered. In particular, the possibility to enhance the daily operational forecasts of M-class flares by considering jointly PIL and other magnetic field and SXR characteristics is demonstrated, with corresponding Brier Skill Scores ($BSS=0.29\pm{}0.04$) higher than for the SWPC NOAA operational probabilities ($BSS=0.09\pm{}0.04$).