Variability of virtual layered phenomena in the mesosphere observed with medium frequency radars at 69°N

Abstract

The MF-Saura radar positioned at polar latitudes is very sensitive to enhanced ionization caused by solar and geomagnetic activity. Differing from the intensities normally detected by partial reflections from the ionospheric D region during quiet conditions, distinct layers can be seen due to intense increase of electron number density at as low as 50 km altitude caused by particle precipitation. Effects of energetic particle precipitation on observations by medium frequency (MF) radars have been rarely reported so far, generally associated with solar proton events, which are rather scarce especially during solar minimum conditions. Here, we focus on events associated with precipitation of particles with lower energy (<10 MeV), which are seen by the MF radar with occurrence rates of as much as 40% at times. Such situations are studied for a period of continuous observations for one solar cycle and statistical results like diurnal and annual distributions are presented.