Severe Convection over the Central Yangtze–Huai River Basin Modulated by Northeast China Cold Vortex: A 10-Year Refined Observational Analysis

The Northeast China Cold Vortex (NCCV) has frequently induced severe convection over the Yangtze–Huai River basin in recent years. Anhui Province, centrally located within the YHRB and traversed by both the Yangtze and Huaihe Rivers, is selected as the core study area to exploit its dense, high-resolution observational network. However, the mechanisms by which the NCCV modulates convection specifically over Anhui remain poorly understood. This study investigates how the NCCV influences the spatial distribution, environmental conditions, and weather types of severe convection in Anhui. Based on 6-min mosaic composite reflectivity (MCR) from six Doppler radars, hourly surface observations, and ERA5 reanalysis data during May–September 2014–2023, a total of 153 NCCV days were identified. Herein, NCCV days are defined as days when Anhui is located within 15° of latitude from the NCCV center and is influenced by the associated trough. Severe convection events (MCR ≥ 45 dBZ with duration ≥ 30 min and area ≥ 10 km²) were classified into three types according to their spatial locations. Composite circulation analysis, one-way analysis of variance of environmental parameters, and three typical cases were conducted to elucidate the underlying mechanisms. Under the NCCV influence, severe convection develops along three distinct northwest–southeast oriented corridors over northern, central, and southern Anhui. Each corridor is associated with a unique configuration involving NCCV, its boundary-layer secondary vortex (strongest at 925 hPa), and the western North Pacific subtropical high (WNPSH). The northern type features a strong, westward-shifted secondary vortex that directly triggers convection with minimal warm-moist air involvement, favoring thunderstorm winds. The southern type involves a weak, southward-shifted secondary vortex converging with robust WNPSH-driven southerly flow, favoring heavy rainfall. The middle type exhibits intermediate characteristics, favoring the development of both thunderstorm winds and heavy rainfall. These results suggest that the NCCV modulates severe convection in Anhui through controlling the position and intensity of its induced boundary-layer secondary vortices. These vortices then interact with the WNPSH-modulated warm-moist flow, jointly determining the location, environment, and weather of convection. The proposed three-type conceptual model provides a mechanistic basis for predicting severe weather in Anhui under the NCCV influence.