Theory of 'crotchet' impulse component generation

It is known that increasing of the electromagnetic emissions flux during the solar flares is accompanied by sudden disturbance of the geomagnetic field, which manifests itself on the ground magnetograms as a 'crotchet'. This disturbance can be understood as a geomagnetic field response to a current intensification in the global ionosphere system due to the conductivity growing. Investigations for the past few years have showed that a temporal structure of the 'crotchet' at solar flares, characterized by harder spectra (presence of a gamma rays), is more complicated and, in reality, is the mixture of the two components: a classic or gradual component and an impulse one. It has been suggested that such impulse disturbance be called 'crotchet' impulse component (CIC). The possible generation mechanism of CIC is the main concern of this paper. According to the mechanism to be discussed, CIC is a geomagnetic field reaction to the changes in the global atmosphere-ionosphere current system related to the stratosphere absorption of solar flare gamma rays (0.1-10 MeV). In this energy band, the most important role the gamma rays absorption plays is the Compton scattering, providing favourable conditions for the vertical transfer of the Compton electrons being produced. The presence of this vertical electric current changes the parameters of the global ionosphere current system and causes the suitable geomagnetic field effect - the CIC event. The theoretical estimates demonstrate good agreement with the characteristics of the CIC event observed on the ground magnetograms. (author)