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.