Observations of rain drop size distribution and rain attenuation of a satellite signal at a tropical location

Measurement of rain drop size distribution (DSD) along with rain attenuation have been carried out at Kolkata (22.65°N, 88.45°E), India, a tropical location since 2004. On analyzing the rain event, it has been noted that the distribution of the larger drops have been found to dominate the growing phase of the event in comparison to the later part for identical rain rates. At the same time, the analysis of monthly variation of rain DSD spectrum shows that the number density of larger drops are greater for the pre-monsoon months in comparison to the monsoon period for similar rain rates. The seasonal variation of rain attenuation at Ku-band indicates the larger attenuation values in the pre-monsoon months than in the monsoon period for identical rain rates during the years, 2005-2007. This is basically due to the convective nature of the rainfall, accompanying thunderstorm that occur mostly in the pre-monsoon period. The convective process increases the rain height, which in turn results in high attenuation values in the pre-monsoon months of the year.