Preflare changes in the solar photosphere observed using the THEMIS telescope

Abstract

The physical state of the photosphere 1 h 50 min before a C1 solar flare on May 24, 2012, was studied. The spectropolarimetric data from the French-Italian THEMIS telescope (Tenerife Island, Spain) were used. The modeling was carried out through the inversion method using SIR [B. Ruiz Cobo and J. C. del Toro Iniesta, Astrophys. J. 398, 375–385 (1992)] code. Height distributions of temperature, magnetic field strength, and line-of-sight velocity were obtained. Nine semiempirical models of the photosphere were constructed. Each model has a two-component (a magnetic field component and nonmagnetic surroundings) structure. According to the obtained models, the magnetic field parameters and thermodynamic parameters did change significantly in the course of observations that lasted for 8 min. The models contain layers with increased and decreased temperature values. The magnetic field strength in these models varied, on average, from 0.2 T (lower photospheric layers) to 0.13 T (upper layers). The line-of-sight velocities did not exceed 2 km/s in lower and middle photospheric layers and rose to 5–6 km/s in the upper layers. The differences in the physical state and its changes occurring at different sites within the active region prior to the flare were revealed.