A case study on microphysical characteristics of mesoscale convective system using generalized DSD parameters retrieved from dual-polarimetric radar observations

The microphysical characteristics of a mesoscale convective system(MCS) during a summer monsoon of South Korea are investigated using the generalized drop size distributions (DSD) that are derived from S-band dual-polarization radar data. The characteristics parameters of generalized DSDs (generalized number concentration, N₀' and generalized mean diameter, D_m) are directly calculated from DSD's two moments without any assumption on the DSD model. Relationships between ZDR and generalized DSD parameters normalized by Z_H are derived in the form of the polynomial equation. Verification of the retrieved DSD parameters is conducted with the 2-D video disdrometer (2DVD) located about 23 km from the radar. The standard deviations (SD) of retrieved DSD parameters are about 0.26 for log N₀', and about 0.11 for D_m because of the variability of DSDs. The SD of the retrieved log N₀' from the dual-polarimetric measurement reaches to about 0.46 (almost double) for 11 rain events while the accuracy of retrieved D_m is quite higher (~0.19). This higher error in retrieved log N₀' is likely attributed to the larger discrepancy in radar-observed and DSD-calculated ZDR when Z_H is low. This retrieval technique is applied to a mesoscale convective system (MCS) case to investigate the Lagrangian characteristics of the microphysical process. The MCS is classified into the leading edge and trailing stratiform region by using the storm classification algorithm. The leading edge dominated by strong updraft showed the broad DSD spectra with a steady temporal increase of Dm throughout the event, likely because of the dominant drop growth by the collision-coalescence process. On the other hand, the drop growth is less significant in the trailing stratiform region as shown by the nearly constant D_m for the entire period. The DSD variation is also controlled by the new generation of drops in the leading edge and less extent in the trailing stratiform during the early period when precipitation systems grow. When the system weakens, the characteristic number concentration decreases with time, indicating the new generation of drops becomes less significant in both regions.