A Study on Long-Term Rain Attenuation Characteristics in Ka and Ku Band Satellite Communications Links

Long-term rain attenuation statistics and variability are discussed using Ka and Ku band satellite signal observations conducted at Osaka Electro-Communication University in Neyagawa, Japan, during 37 years from 1986 to 2023. Before 2006, the long-term rain attenuation statistics agree well with the ITU-R predictions. Yearly 0.01% values of the attenuation indicate fairly large variations which amount to about 20% around the mean value. Besides the yearly rainfall rate statistics, these variations seem to be caused by difference in equivalent path length in each year. However, the increase in the equivalent path length is not fully explained by that of rain height determined by the ground temperature, but rather related to the types of rainfall which frequently appear in summer time, such as shower and typhoon. The occurrence time of shower and typhoon is newly found to be correlated with the sea surface temperature anomalies off the coast of Japan in Pacific Ocean, possibly caused by the tropical climate change in the equatorial region. After 2007, the long-term rain attenuation statistics are considerably larger than the ITU-R predictions. This is found to be even caused by the increase in the occurrence time of warm, cold, and stationary fronts rather than shower and typhoon due to the recent rise of the sea surface temperature due to the climate change.