KEYWORDS: Radar, Ka band, Clouds, Reflectivity, Doppler effect, Convection, Atmospheric propagation, Signal attenuation, Signal to noise ratio, Data modeling
Using the observations of both ground based disdrometer and Micro Rain Radar, Drop size distribution (DSD) parameters were derived using gamma function over coastal station Thumba. Stratiform rain and transition rain regime has been considered to study the vertical variability of DSD parameters for different monsoon seasons during 2006- 2008. The analysis clearly reveals a significant variation in DSD parameters for different seasons. Contour Frequency by Altitude Diagram (CFAD) of DSD parameters is carried out to examine salient microphysical characteristics of DSD during these two rain regimes. Results show that the observed variability of gamma parameters and median volume diameter is attributed to microphysical processes like evaporation, break-up and collision-coalescence. The significance of the present results demonstrates the capability of Ka band radar in understanding the microphysics of rain during light to moderate rain regimes
Variation of raindrop size distribution (DSD) are investigated using long-term (2007-2014) measurements made at Thumba (8.5°N, 76.9°E) by Joss-Waldvogel disdrometer. The DSD is observed to be distinctly different for NE and SW monsoon seasons. Results show a significant difference in the diurnal pattern of rainfall with large amplitude in the diurnal variation of rainfall in the monsoon with an evening (19:00 LT) to midnight (04:00 LT) peak and a weak diurnal variation in the Pre-monsoon and Post monsoon seasons. Probability of occurrence of rain is minimum during 10:00 – 13:00 LT for all seasons. The diurnal variation of DSD parameter Dm (mass-weighted mean diameter) also shows a distinct pattern with smaller values in monsoon compared to pre-, and post monsoon seasons. During monsoon season due to the presence of large number of small drops reduces the Dm value. While the presence of fewer small drops and relatively more big drops in the post and pre monsoon increases the values of Dm.
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