Microphysical Characteristics of Precipitating Stratiform Clouds in North China Revealed by Joint Observations of an Aircraft and a Polarimetric Radar

Abstract

Abstract Microphysical structures and processes in a case of precipitating stratiform clouds in North China on 21 May 2018 are investigated using joint observations from an aircraft and an X-band polarimetric radar. The results show that there are enhancements in differential reflectivity (ZDR) and specific differential phase (KDP) above the 7-km altitude, consistent with the existence of dendrites and platelike ice crystals. The horizontal reflectivity factor (ZH) increases and ZDR decreases downward above the melting layer (ML), due to the prevalent aggregation process, which is confirmed by the downward increasing volume-weighted mean diameter (Dm) and decreasing total number concentration (Nt) observed by the aircraft. Within the ML, the concentration of median-sized particles (2–5 mm) decreases rapidly downward due to the melting process. Within approximately the top 2/3 of the ML, the melting particles’ mean and maximum sizes increase, demonstrating the dominance of the aggregation process. This causes the enhancements of ZH and ZDR within the radar bright band together with the increase in the dielectric constant. Within the bottom 1/3 of the ML, the breakup process is responsible for the decreasing Dm and increasing Nt observed by the aircraft. Below the ML, the measurements by the polarimetric radar and the aircraft only show slight variance with altitude, indicating the near balance between microphysical processes favored by the nearly saturated air. The results of the microphysics in the stratiform case would help improve the microphysical parameterization of numerical modeling in the future.