Microphysical Characteristics of Three Convective Events with Intense Rainfall Observed by Polarimetric Radar and Disdrometer in Eastern China

Abstract

Polarimetric radar and disdrometer observations obtained during the 2014 Observation, Prediction, and Analysis of Severe Convection of China (OPACC) field campaign are used in this study to investigate the microphysical characteristics of three primary types of organized intense rainfall events (meiyu rainband, typhoon outer rainband, and squall line) in eastern China. Drop size distributions (DSDs) of these three events on the ground are derived from measurements of a surface disdrometer, while the corresponding three-dimensional microphysical structures are obtained from the Nanjing University C-band polarimetric radar (NJU-CPOL). Although the environmental moisture and instability conditions are different, all three events possess relatively high freezing level favorable for warm-rain processes where the high medium to small raindrop concentration at low levels is consistent with the high surface rainfall rates. Convection is tallest in the squall line where abundant ice-phase processes generate large amounts of rimed particles (graupel and hail) above the freezing level and the largest surface raindrops are present among these three events. The storm tops of both the typhoon and meiyu rainbands are lower than that in the squall line, composed of less active ice processes above the freezing level. The typhoon rainrate is more intense than that of meiyu, enhanced by higher coalescence efficiency. A revised generalized intercept parameter versus mass-weighted mean diameter (Nw-Dm) space diagram is constructed to describe the DSD distributions over the three events and illustrate the relative DSD positions for heavy precipitation. DSDs of these intense rainfall convections observed in this midlatitude region of eastern Asia somewhat represent the typical DSD characteristics in low latitudes, suggesting that the parameterization of microphysical characteristics in eastern China in numerical models needs to be further investigated to improve rain fall forecasts in these heavy rainfall events.

Microphysics of Stratiform and Convective Precipitation During Meiyu Season in Eastern China

“…The melting of these particles is indispensable for heavy rainfall at the surface. However, warm rain processes are still vital pathways for the growth of raindrops and the eventual production of heavy rainfall, as also documented in previous precipitation microphysics studies for Meiyu cases (e.g., G. Chen et al, 2019).…”

“…Generally, during this Meiyu event, D m shows a more inhomogeneous distribution (mostly around 1-1.4 mm) than the other rainfall system occurred in this region, that is, squall line (G. Chen et al, 2019;J. Wen et al, 2017).…”

“…Generally, during this Meiyu event, D m shows a more inhomogeneous distribution (mostly around 1–1.4 mm) than the other rainfall system occurred in this region, that is, squall line (G. Chen et al., 2019; J. Wen et al., 2017). On the contrary, the distribution of log 10 N w and LWC is highly relevant to Z H variation (see Figure 4a).…”

“…The low Z H but relatively high K DP above the melting layer indicate a high concentration of small ice particles aloft. This implies that the contribution of ice‐formed particles which melted into raindrops is relatively minor compared with classical continental storms with deep convection (e.g., G. Chen et al., 2019). Meanwhile, both convective and stratiform D m vary within ±0.1 mm while descending toward the ground, suggesting that the intensification of Meiyu rainfall largely benefits from the increase in raindrop concentration through the warm rain process.…”

“…Chen, 2009). Recently, the microphysics of Meiyu extreme rainfall and convective events in Eastern China were investigated by Yang et al (2019) and G. Chen et al (2019). However, the statistical characteristics of near-surface DSD observed by disdrometers are not well confirmed, and the statistics in terms of the evolution and structure of Meiyu stratiform and convective precipitation have not yet been resolved in this particular region.…”