Recent Tendencies of Increase in Yearly Cumulative Time Percentages of Rain Attenuation in Ku-Band Satellite Communications Links

摘要

The long-term rain attenuation statistics of cumulative time percentages are obtained from Ku band satellite signal observations conducted at Osaka Electro-Communication University in Neyagawa, Osaka, from 1988 to 2016. Besides the yearly rainfall rate statistics, the variation of rain attenuation statistics seems to be caused by those of the equivalent rain path length at each year, which becomes longer as the average ground temperature at rain time from May to October becomes higher. However, the increase of the equivalent rain path length is not simply explained in term of the rise of rain height proportional to the ground temperature, but rather related to the occurrence of rain attenuation due to tropical-type rainfall such as shower and typhoon in summer time. Also, the equivalent path length tends to increase further for the last ten years since 2006, and the rain attenuation statistics are becoming larger than the ITU-R predictions. This tendency seems to be related to the overall increase of the average ground temperature at rain time in each year, as well as the increase of the effects of stationary fronts that cause longer rain attenuation duration time.