Physics of auroral phenomena : proceedings of the 33rd Annual seminar, Apatity, 02 - 05 March, 2010 / [ed.: A.G. Yahnin, A. A. Mochalov]. - Апатиты : Издательство Кольского научного центра РАН, 2011. - 206 с. : ил.

А. V. Germanenko at al. monitor data collection systems at these stations with a frequency of 1 times per minute. During the observations spectrometers detected sporadic increases o f the intensity of X-ray radiation. It was also noted that the increase events almost always were accompanied by intense precipitations, with dense and low altitude (200-600 meters) cloudiness. There were observed 99 X-ray increase events from June 2009 to April 2010. The intensity increased from 5 to 45% of the background and duration of an increase varied from one hour to two days. 97% o f these events were accompanied by precipitations of varying duration and intensity. The amplitude o f increases differs for different seasons. In winter the amplitude o f increases was on the average less and there was not fixed any increase greater than 25%. In addition, the connection o f the type of precipitation with the increase amplitude was noted. Fine, dry snow with the wind (blizzard) or permanent drizzling rain rarely were accompanied with an increase. Most o f the increase events were accompanied by heavy rains or snowfall with no strong wind. 242.40 242.65 242.90 243.15 243.40 Days of year Fig. 1. X-ray increase and precipitations (rain) in the event of September 16,2009, Apatity Days Fig. 2. X-ray increase and precipitations (snowfall) in the event of November 12, 2009, Barentsburg Figure 1 shows typical profiles of the count rate increase in the X-ray channel > 20keV and precipitations (rain) for the Apatity station. The good correlation between the strengthening o f rain and increases of the X- ray intensity is seen. Typically, a peak of a rainfall occurs 10-40 minutes prior to the corresponding increase in X-rays. Figure 2 shows the typical profiles o f X-rays > 20keV increase and the precipitations (snow) for the station Barentsburg. Unfortunately, here we were only available data on precipitation averaged for 3 hours, but still it is seen the link between the X-ray increase with a period of snowfall. 4. D iscussion We assume that the increase in a count rate of gamma-ray spectrometers is caused by the X-ray bremsstrahlung produced by electrons accelerated in a rain cloud. Near the Earth’s surface the electric field in quiet weather is about 100 V/m. Inside rain clouds the electric field strength is much higher and may reach of kilovolts and even tens o f kV/m [4]. This is enough to accelerate electrons up to such energies, that produced by them X-ray quanta could reach a terrestrial surface and cause appreciable increases o f the count rate o f gamma - detectors. The intensity o f the photons is determined by the generation o f energetic electrons and positrons in the form o f bremsstrahlung and the alternative process o f absorption in the air [3]. When passing through the matter, the electron loses energy due to ionization and radiation losses. In our low-energy energy domain (Ee < IMeV) a decisive contribution to the energy losses gives the ionization process. Radiation losses become significant at much higher energies [2]. The energy spectrum of electrons in the energy range (E < IMeV) can be approximated by an exponential law [3]. dN (E ) dE ■= N n - E / E „ ( 1 ) where E0 is characteristic energy, which varies in the range 10-100 keV. Number of photons with energies hv in the range d(hv), produced by an electron with energy E when changing it on dE on distance dx, is equal to: 164