Comparison of drop size distribution between stations in Eastern and Western coasts of India

A Joss-Waldvogel type disdrometer was installed at Thiruvananthapuram, Kochi, and Sreeharikotta (SHAR) during various periods. This paper presents results from the analysis of the data. Drop Size Distribution (DSD) and rainfall rate for each minute were computed from the disdrometer data, and the entire data for each month were sorted by rainfall rate. The data were then divided into different ranges of rainfall rate and DSD computed for each. The average DSD for each range was fitted with a lognormal distribution function of the form N(D) = (a0/D) exp (-0.5(ln ( D)-a1)/a2) 2 where D = drop diameter, N(D) = number of drops/m3/mm interval. The results show the following: For the lowest rainfall intensity, the distribution is narrow and is dominated by small drops. With increase in intensity, the distribution spreads out and more larger drops appear. However, in some cases, the data does not follow the lognormal distribution. The total number of drops, NT, geometric mean diameter, Dg and standard geometric deviation, σ was derived from the ai. NT showed a tendency to increase slightly with rainfall rate. Dg followed a simple power relationship of the form Dg = b0R b1. The standard geometric deviation did not show any significant dependence on rainfall rate. The characteristics of rainfall in terms of the three parameters for coastal stations on the west coast are similar. The rate of increase of NT is higher at SHAR than at Kochi. NT is higher at SHAR than at Kochi for any particular rainfall rate, indicating that, unlike Kochi and other stations on the western coast, rainfall at SHAR is made up of more number of smaller drops