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Thermodynamic and Microphysics Interactions in the Formation of a Meso-β-Scale Downburst: A Numerical Case Study of a Thunderstorm in Shanghai
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DOI：10.1029/2025JD045512.png)
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Abstract
En 中文
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.
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