Abstract:

To investigate the mechanisms underlying dust events in southern China, this study examined a representative dust intrusion that affected Hunan Province from 12 to 14 April 2025. ERA5 reanalysis data from the European Centre for Medium-Range Weather Forecasts (ECMWF), wind-profiler radar observations, air-quality monitoring data, and the Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT) backward-trajectory model combined with topographic data were used to examine the role of Hunan’s terrain in pollutant transport and retention during the dust event. The results are as follows: (1) Although Hunan lies in the humid region of southern China, it can be significantly affected by long-range dust transport. The dust originating from Mongolia and southern Xinjiang moved southward along the northwest path, forming the first province-wide dust event since 2000, with pollutants dominated by exogenous coarse dust particles. (2) The dual “channel-retention” effect of Hunan’s horseshoe-shaped terrain was the major cause of this multi-day dust event. The northern plain accelerated the southward spread of dust, while the surrounding mountains blocked airflows and prolonged pollution retention in southern Hunan, and this effect may be common in complex-terrain regions of southern China. (3) A conceptual model for dust intrusion into Hunan was established, and the key forecasting and early-warning indicators were identified as follows: strong dust storms lasting for more than 2 d over northwestern China and adjacent regions, the coupling of a Mongolian cyclone with a surface cold front, and widespread northerly winds exceeding Beaufort Force 5. Under these conditions, dust aerosols were transported over long distances along a westerly pathway, reached Hunan within 48-72 h, and were rapidly removed after the prevailing wind shifted to a southerly direction.

Key words: dust transport, orographic modulation, Hunan Province, backward trajectory analysis, early-warning criterion

摘要：

为探究中国南方沙尘事件的影响机制，本文选取2025年4月12—14日入侵湖南省的一次典型沙尘过程，利用欧洲中期天气预报中心ERA5再分析资料、风廓线雷达观测数据、空气质量监测数据和叠加地形资料的HYSPLIT后向轨迹分析模型（Hybrid Single-Particle Lagrangian Integrated Trajectory model），重点讨论了湖南地形对沙尘过程中污染物输送与滞留的作用。结果表明：（1）处于南方湿润区的湖南省可受远距离沙尘暴显著影响，此次源自蒙古国与南疆的沙尘沿西北路径南下，成为2000年以来首个覆盖全省的沙尘过程，污染物以外来粗颗粒沙尘为主。（2）湖南马蹄形地形的“通道—滞留”双模态效应是此次沙尘过程持续多日的重要原因，北部平原加速沙尘南下，周边山地阻挡气流使湘南污染长时间滞留，该效应在南方复杂地形区具有普遍性。（3）构建沙尘入侵湖南的概念模型，确定关键预报预警指标：西北及周边地区持续2 d以上的强沙尘暴，蒙古气旋与地面冷锋耦合，以及大范围5级以上偏北风；在此条件下，沙尘气溶胶通过偏西路径进行远距离输送，在48~72 h内影响湖南，并在风向转为偏南后迅速清除。

关键词: 沙尘过程, 地形影响, 湖南, 后向轨迹, 预报预警指标