Experimental study of meteorological parameters variation using hf-signal during solar proton events

Nowadays there are many experimental facts showing the Solar activity influence on a weather and climate. Nevertheless we still do not have a model explaining all the problems of Solar-terrestrial links. This lack is due to the deficit of the experimental data about variations of the meteorological conditions before, during and after a solar flare. This type of data could be obtained by use of weather balloon, rocket or aircraft sounding, etc. But all of these methods could not be used for achieving of large arrays of continuous data due to their large cost. Refractive index, which plays a significant role in radiowave propagation, relates to the main meteorological parameters such as temperature, pressure and vapor pressure [1]. So, statistical studies of the signal level variation processes can give some information about meteorological processes in troposphere. To solve this problem an experimental radio link from telecommunication satellite Asiasat-3S (elevation angle in Kharkov, Ukraine is 4.5o) was constructed. The experiment was carried out from May-2002 till November-2003 at the frequency 3.6GHz. More than 20 solar flare events were analyzed. It was found that during strong solar flare with proton flux index (p.f.u.) >200 a deep rapid fading appears. The fading rate of the signal increased in 10-15 times at the level -6dB and in 5-10 times at the level -4dB from the signal mean value in 3-6 hours after solar flare had begun. It is necessary to note that during solar flare with p.f.u <200 this effects are not registered. The duration of the signal fading increased, too. Two to three days later the behavior of the received signal returns to the normal, non-flare state. This fading can be connected to phenomena of the interference between few signals originating at different sources like tropospheric inhomogeneouses and the satellite. These inhomogeneouses are linked to small-scale fluctuation of refractive index. It is necessary to note that radio waves reflected from ground were shielded. So, we do not have to examine an influence of the variations of properties of the ground on signal level variation. When analyzing time delays between beginnings of the solar flare and the fade distribution variation it is possible to assume that solar flare products influencing on tropospheric parameters may be ultra-violet or X- rays or high energy solar protons. The first two appear in the Earth's atmosphere in 8-9 minutes after the flare beginning, whereas the latter appear in near-earth space in 1-2 hours after solar flare beginning. A positive charged ions and electrons appear in neutral atmospheric gas interacting with the solar protons and their secondary particles. These charged particles can be condensation nuclei for atmospheric vapor. This aerosol layer can be cause of low and middle atmospheric temperature profile variations mentioned in [2] and is connected with descending stratospheric air flow, first described in [3]. This stratospheric air has lower refractivity index than surrounding tropospheric air due to its low humidity. So, the tropospheric inhomogeneouses linked to stratospheric air flow can play a significant role in UHF radiowaves propagation. From 48 to 72 hours after beginning of the solar flare the high energy solar protons density comes back to the previous level and tropospheric inhomogeneouses disappear. This fact was confirmed in the described experiment, too. References: 1. Francois Du Castel Tropospheric Radiowave Propagation beyond the Horizon // Oxford: Repgamon Press, 1966, 331p 2. Pudovkin M.I., Morozova A.L. Time evolution of the temperature altitudinal profile in the lower atmosphere during solar proton events // J. Atmosphere and Solar-Terrestrial Physics, 1997., v.59,N17, pp. 2159-2166 3. Reiter R. Increased influx of stratospheric air into the lower troposphere after solar Ha and X-ray flares // J. Geophys. Res.,v.78,p.6167