Yanan Liu

Downbursts pose severe threats to socioeconomic development due to their abruptness and unpredictability, yet forecasting whether a convective system will produce a downburst remains a major operational challenge. Although synoptic and mesoscale conditions facilitate probabilistic forecasting of convection, more accurate prediction of downburst demands an understanding of cloud microphysical processes. By means of a cloud‐resolving simulation at 333 m horizontal grid spacing of an observed downburst event associated with a multi‐cell mesoscale convective system in Shanghai, we examine the thermodynamic–microphysical interaction mechanisms responsible for generating intense downdraft. We find that latent cooling from rainwater evaporation and graupel melting establishes a persistent source of negative horizontal vorticity at lower levels. This vorticity anomaly, which prevails along the direction of storm motion, plays a pivotal role in accelerating descending motion and driving downdraft development. These findings extend the Rotunno‐Klemp‐Weisman (RKW) theory by highlighting how horizontal vorticity dynamically couples microphysical and thermodynamic processes in downburst‐producing non‐linearly organized convective systems. Furthermore, our research indicates that the low‐level virtual potential temperature contrast between the ambient inflow and the storm interior may provide a critical precursor signal, substantially elevating the probability of occurrence of strong downdraft and damaging straight‐line winds in deep moist convection evolution.

This study on the warm-sector heavy rainfall event in Guangzhou on 7 May 2017, examined the effects and mechanisms of incorporating 30 m high-resolution land surface data into its numerical simulation. The updated 1km numerical model, integrating 30 m high-resolution land surface data, successfully captured the initiation, back-building, and organized development of warm-sector convections in Huadu and Zengcheng District. The analysis revealed that the high spatial resolution of the surface data led to a reduced urban area footprint (urban −6.31%), increased vegetation cover (forest 11.63%, croplands 1%), and enhanced surface runoff (water 2.77%) compared with a model’s default land cover (900 m). These changes mitigated the urban heat island (UHI) effect within the metropolitan area and decreased the surface sensible heat flux. This reduction contributed to a pronounced temperature gradient between Huadu Mountain and the urban area. Additionally, a stronger high-pressure recirculation and sea–land breezes facilitated the transport of warm and moist air from the sea inland, creating a humid corridor along the sea–land interface. The consistent influx of warm and moist air near the mountain front, where strong temperature gradients were present, forcibly triggered warm-sector convection, intensifying its organization. This study highlighted the critical role of high-resolution land surface data in the accurate numerical simulation of warm-sector heavy rainfall.