Attenuation relations for monsoonal rain at the X band from disdrometric measurements: Dependency on temperature, raindrop size distribution and drop shape models

Four years of disdrometric measurements made at Gadanki (13.5 ° N, 79.18 ° E), which receives rainfall during both southwest and northeast monsoons, have been used to (a) derive optimal attenuation relations for monsoonal rainfall at the X band, (b) study the impact of seasonal variation in raindrop size distribution (DSD) on attenuation relations and (c) analyze the dependency of these relations on the controlling parameters/models, such as temperature ( T ) and drop shape model. The results clearly show that the coefficients of these relations vary significantly with DSD (season and rain type), T and drop shape model, and are quite different for monsoonal rain than for those obtained elsewhere. The traditional relations that involve a specific attenuation ( A H )‐reflectivity factor at horizontal polarization ( Z H ) and A H ‐rain rate depend heavily on DSD and to some extent on T , while the relations involving a specific differential phase ( K DP ) and differential attenuation ( A DP ) show strong dependency on the drop shape model and DSD, but depend weakly on T . A detailed investigation has been carried out to decipher reasons for the observed intriguing seasonal variation in K DP ‐based relations and their temperature dependency. The resonance scattering effects that are thought to be negligible at the X band in earlier studies appear to play a dominant role here and are primarily responsible for the observed features.