Raindrop Size Distribution Characteristics of Summer and Winter Season Rainfall Over North Taiwan

摘要

Raindrop size distribution (RSD) characteristics of summer and winter seasons over north Taiwan are analyzed by using long-term (~12 years) raindrop spectra from Joss-Waldvogel disdrometer located at National Central University (24°580N, 121°100E), Taiwan. Along with the disdrometer data, radar reflectivity mosaic from six ground-based radars, Tropical Rainfall Measuring Mission, Moderate Resolution Imaging Spectroradiometer, and ERA-Interim data sets are used to establish the dynamical and microphysical characteristics of summer and winter rainfall. Significant differences in raindrop spectra of summer and winter rainfall are noticed. Winter rainfall has a higher concentration of small drops and a lower concentration of midsize and large drops when compared to summer rainfall. RSD stratified on the basis of rain rate showed a higher mass-weighted mean diameter (D_m) and a lower normalized intercept parameter (log_(10)N_w) in summer than winter. Similarly, diurnal variation of RSD showed higher D_m and lower log_(10)N_w values in summer as compared to winter rainfall. In addition, for both seasons, the mean value of Dm is higher in convective precipitation than stratiform. Radar reflectivity (Z) and rain rate (R) relations (Z = A*R~b) showed a clear demarcation between summer and winter rainfall. Higher ground temperatures, deeply extended clouds with intense convective activity in summer modified the RSD through evaporation, drop sorting, and collision-coalescence processes resulting with higher D_m and lower log_(10)N_w values in summer as compared to winter rainfall.