日喀则南部冬末春初一次强降雪天气过程的成因及模式检验分析

Causes and Model Verification Analysis of a Heavy Snowfall Event in Southern Shigatse in Late Winter and Early Spring

摘要: 本文以2024年3月2~4日日喀则南部区域性强降雪为研究对象，利用ERA5再分析资料、常规观测及探空数据，结合多数值模式产品，从环流背景、水汽输送、动力热力机制及模式预报性能四方面开展系统分析，旨在揭示高原南部冬末春初暴雪成因，为同类天气预报提供参考。结果表明：(1) 此次暴雪由500 hPa南支槽东移与低空西南急流协同作用引发，中高纬“两槽一脊”经向环流为冷暖气流交汇提供了有利条件；(2) 阿拉伯海与孟加拉湾的水汽通过西南急流持续输送至降雪区，700~250 hPa整层相对湿度维持85%以上，配合200 hPa高空急流右后侧强辐散场，形成“上散下合”的垂直环流与强烈上升运动；(3) 探空资料显示风随高度顺转的暖平流特征显著，逆温层的建立与破坏过程调控不稳定能量的积聚与释放，影响降雪强度变化；(4) 聂拉木、吉隆特殊地形对水汽辐合与上升运动具有显著促进作用，是暴雪落区集中的重要因素；(5) 各数值模式对降雪落区预报一致性较好，GERMAN模式对降水量级的预报最接近实况，ECMWF模式预报偏强，CMA-GFS和CMA-TYM模式预报偏弱。本研究揭示的高原南部强降雪成因机制及模式表现，可为同类天气的预报准确率提升提供理论支撑与技术参考。

Abstract: To reveal the formation mechanism of heavy snowfall in the southern Qinghai-Xizang Plateau in late winter and early spring and improve forecast accuracy, this study takes the regional heavy snowfall event in southern Shigatse from March 2 to 4, 2024 as the research object. Using ERA5 reanalysis data (spatial resolution 0.25°×0.25°; temporal resolution 1 h), surface and sounding observation data (observation times at 08:00 and 20:00), combined with forecast products from four numerical models including GERMAN, ECMWF, CMA-GFS and CMA-TYM, a systematic analysis was carried out from four dimensions: circulation background, water vapor transport, dynamic and thermal mechanisms, and model forecast performance. The results show that: (1) This heavy snowfall was triggered by the synergistic effect of the eastward movement of the 500 hPa southern branch trough and the low-level southwest jet, under the favorable background of the “two troughs and one ridge” meridional circulation in the middle and high latitudes, which provided conditions for the convergence of cold and warm air masses. (2) Water vapor from the Arabian Sea and the Bay of Bengal was continuously transported to the snowfall area via the southwest jet, with the whole-layer relative humidity between 700 hPa and 250 hPa maintaining above 85%, combined with the strong divergence field on the right rear side of the 200 hPa upper-level jet, a vertical circulation of “upper divergence and lower convergence” was formed, inducing strong upward motion. (3) Sounding data showed significant warm advection with wind turning clockwise with height; the establishment and destruction of the inversion layer regulated the accumulation of unstable energy, which affected the variation of snowfall intensity. (4) The special terrain of Nyalam and Gyirong has a significant promoting effect on water vapor convergence and upward motion, and is an important factor for the concentration of heavy snowfall areas. (5) All models had good consistency in forecasting the snowfall area, among which the GERMAN model had the closest prediction to the observed precipitation magnitude, the ECMWF model overestimated the precipitation, and the CMA-GFS and CMA-TYM models underestimated it. The research results can provide theoretical support and technical reference for the forecast and early warning of similar heavy snowfall events in the southern Qinghai-Xizang Plateau.