Increase and decrease in depolarization of Ka-band satellite beacon signal in thunderstorm events

Abstract

In the thunderstorms, the significant depolarization of microwave and millimeter waves is often caused by raindrops and ice crystals in the thunder clouds on the satellite-to-ground path. Moreover, it is well known that rapid changes in depolarization with time scale of a second or less are frequently observed in the thunderstorm events. These rapid changes are considered to be caused by the alignment of ice crystals in thunder clouds due to aerodynamic-gravitational and/or electrostatic forces. Detailed mechanisms for producing this type of depolarization are, however, still poorly understood, and very little is yet known about the behavior of ice crystals concerning aerodynamic-gravitational and electrostatic forces in thunder clouds. This paper discusses the depolarization characteristics in thunderstorm events using Japan's CS-3 satellite beacon signal (19.45 GHz, right-hand circular polarization). The cross-polarization discrimination (XPD) and cross-polar phase relative to the co-polar phase of the satellite signal radiowave have been observed every second in thunderstorm events that occurred in the period between 1990 to 1995. These data showing conspicuous rapid changes in thunderstorm events are then compared with time and location of lightning strokes detected by the lightning location and protection system (LEPS) of a nearby electric power company.