Variability of rain microphysics using long-term disdrometer observations

摘要

This study explores variability of rain microphysics in terms of drop size distributions (DSD) using seven years of Joss-Waldvogel disdrometer data in a long-term perspective. Firstly, self-consistency evaluation of the disdrometer is performed against four raingauges. The result indicates that the disdrometer derived rain totals are in a good agreement to the raingauges with correlation coefficients ranging from 0.89 to 0.99. In addition, a total of 162 415 one-minute filtered raindrop spectra obtained from the disdrometer are fitted to the normalized gamma DSD model to understand DSD variability in different seasonal and atmospheric states. To characterize rain microphysics, four sets of DSDs are created from the entire raindrop spectra - two are based on seasonal "equinox" criteria and the other two are based on wet bulb temperature. It has been revealed that the normalized gamma DSD parameters, N_w, D_m, and μ vary from set to set because of seasonal and atmospheric variability. Finally, radar Z-R relations for the four DSD sets are developed and it is shown that coefficients differ meaningfully from state to state. In particular, the variability is found to be more substantial between those DSDs which have been separated using the wet bulb temperature.