Microphysical Characteristics of Raindrop Size Distribution in Rainfall Caused by the Northeast China Cold Vortex (NCCV) Based on Disdrometer Observations

Abstract Northeast China experiences significant rainfall events driven by the Northeast China Cold Vortex (NCCV) during the warm season. However, the microphysical processes associated with this precipitation require further investigation. This study aims to fill this gap by comparing the microphysical characteristics of local stratiform and convective rain under the influence of the NCCV (NCCV precipitation or rain) and by exploring the underlying meteorological mechanisms. The results indicate that both stratiform and convective NCCV precipitation in Northeast China are characterized by sparser raindrops compared to similar rainfall types in other regions of China. In addition, convective NCCV rain consists of much larger raindrops than any other types of rainfall across China, leading to rain rates over 10 times greater than those of stratiform NCCV precipitation. The accelerated generation and growth of raindrops reinforce both stratiform and convective NCCV precipitation, whereas convective NCCV rain exhibits a more complex intensifying mechanism. If the rain rate ( R ) ≤ 9 mm h −1 , raindrops are sparse but large. With the increase in precipitation intensity, raindrops become denser but also collide and break up into smaller particles. When R > 16 mm h −1 , dense and large raindrops prevail, deriving from the melting of numerous large solid hydrometeors formed through deep convection. The convection is stimulated by higher mid- to low-level temperatures and greater convective available potential energy, causing clouds to ascend to higher altitudes with faster upward movement, thereby fostering the formation of larger raindrops. Additionally, convective NCCV precipitation is usually enhanced by divergence induced by upper-level jet streams.