Figure 2. A pattern of the EOSO progress at the end of the storm on Aragats on 24 May. Disturbances of the NS electric field (blue), count rate of ASNT spectrometer (black), and distance to lightning (red). By the vertical green lines, we outline 12 minutes of TGE duration and graupel fall. In the inset, we show the relation of electron-to-gamma ray ratio to the recovered height above ground where the strong accelerating field is terminated obtained according to the algorithm described in (Chilingarian et al., 2021c).
The energy spectra, those parameters are posted in Table 1 were approximated by the power-law dependence; the power-law indices were roughly constant during 8 minutes of the TGE mature phase and equal to ≈2.0 for electron spectrum and ≈2.4 – for gamma ray spectrum (Table 1). As it is expected due to large ionization losses of electrons the intensities and maximal energies of the electron flux are smaller than the same parameters of the gamma ray flux. However, the proximity of maximal energies of both TGE species demonstrates that the strong accelerating electric field in the atmosphere was rather low above the earth’s surface. The electron-to-gamma ray ratio is a very good indicator of the strong electric field height above the ground. At the exit from the strong electric field, the electron flux attenuates very fast and if this height is larger than 200 m practically it is impossible to recover the electron energy spectrum, the flux was dominated by the gamma ray flux, which is 50 times more intensive than the electron flux. In (Chilingarian et al., 2021c) we present a simplified algorithm of the strong field height estimation based on the maximum energies of the gamma ray and electron energy spectra.
In Table 1 we present the main characteristics of the EOSO-TGE event for 8 minutes of the maximum TGE flux. In the second and third columns – the power law fit indices for the electron and gamma ray spectra; in the fourth and fifth the integral energy spectrum of both fluxes for energies larger than 7 MeV; in the sixth – the electron-to-gamma ray ratio; in the seventh and eighth – maximal energies of differential energy spectra for both species; and in the last – an approximate estimate of termination height of the strong accelerating electric field (according to the algorithm from Chilingarian et al., 2021c). We can see in the table very large values of the electron-to-gamma ray ratio , corresponding to low locations of the strong electric field above the earth’s surface.