Magnetic field peculiarities in limb solar flare of 12 July 2012 on heigh about 40 megameters

Abstract

We present results of magnetic field measurements in limb solar flare of 12 July 2012 of M7.7 class based of analysis of I ± V profiles of Нα line. Our results relate to moment 06:45:50 UT when top of flare arcade reached ≈ 40 Mm according to observations of space observatory SDO. Observed Нα profiles have specific signs of magnetic field inhomogeneity, in particular, unequal splitting of bisectors of I ± V profiles on various distances from their centers. In general, splitting of bisectors increases from line wings to its core, and value of this splitting corresponds to magnetic field in range 400–1200 G. In addition to this trend, local peak of bisector splitting was found on distance about 420 mÅ which may indicate local magnetic field with strength about 20 kG. As the authors know, observational indications of such very strong magnetic fields at a height of 40 mm have been detected for the first time. Obviously, such magnetic fields can exist in the rarefied solar corona only with a certain special structure of the magnetic field, obviously of the force-free type, which implies strong twisting of the lines of force.