湖南江永县大风时空分布特征分析

Analysis of Spatial and Temporal Distribution Characteristics of Gale in Jiangyong County, Hunan

摘要: 利用1991~2023年湖南省江永县气象自动站大风数据和ERA5再分析数据，采用统计分析等方法，分析江永县大风分布特征，并以典型大风过程为例，分析气象条件和地形作用对大风的影响，并尝试凝练大风预报因子阈值，所得结论如下：(1) 江永县大风事件在春夏季更明显，全年均以偏北风为主，江永站和花楼站风速更大，出现大风的日期更早，北部地区大风事件发生频率高于南部地区；(2) 分析江永县典型雷暴大风过程，发现副热带高压和西风带槽脊波动，配合地面低压倒槽为此次雷暴大风过程提供了持续的暖湿辐合与抬升条件，较大的气压梯度叠加雷暴下沉气流，形成极端大风，加之气流受地形扰动，进一步增加了雷暴大风的不确定性。动力条件方面，低层暖湿急流与中层干冷空气交汇激发的强烈垂直上升运动和局地地形的强迫抬升作用加剧了对流层结不稳定性，进一步促进了局地雷暴大风的发展。(3) 通过线性回归方程凝练大风预报因子阈值，当江永县发生6级以上大风时，200 hPa和850 hPa散度差小于1.4342 × 10⁻⁵/s，925 hPa全风速大于21.8221 m/s，200 hPa和850 hPa全风速差大于−19.2331 m/s，500 hPa位势高度低于599.4651 dagpm，构成大风发生的有利条件。

Abstract: Based on the strong wind data and ERA5 reanalysis data of Jiangyong meteorological automatic station in Hunan Province from 1991 to 2023, the distribution characteristics of strong wind in Jiangyong County were analyzed by statistical analysis and other methods. Taking the typical strong wind process as an example, the influence of meteorological conditions and topography on strong wind was analyzed, and the threshold of strong wind forecast factor was tried to be condensed. The conclusions are as follows: (1) The strong wind event in Jiangyong County is more obvious in spring and summer, and the northerly wind is the main wind throughout the year. The wind speed of Jiangyong Station and Hualou Station is larger, and the date of strong wind is earlier. The frequency of strong wind events in the northern region is higher than that in the southern region. (2) The typical thunderstorm gale process in Jiangyong County was analyzed. It was found that the subtropical high and the westerly trough and ridge fluctuations, combined with the ground low pressure inverted trough, provided continuous warm and wet convergence and lifting conditions for the thunderstorm gale process. The large pressure gradient superimposed the thunderstorm downdraft to form extreme gale. In addition, the airflow was disturbed by the terrain, which further increased the uncertainty of the thunderstorm gale. In terms of dynamic conditions, the strong vertical ascending motion excited by the intersection of low-level warm and humid jets and middle-level dry and cold air and the forced uplift of local terrain aggravate the instability of tropospheric stratification and further promote the development of local thunderstorms. (3) Through the linear regression equation, the threshold value of the wind forecast factor is condensed. When the strong wind above grade 6 occurs in Jiangyong County, the divergence difference between 200 hPa and 850 hPa is less than 1.4342 × 10⁻⁵/s, the total wind speed at 925 hPa is greater than 21.8221 m/s, the total wind speed difference between 200 hPa and 850 hPa is greater than −19.2331 m/s, and the 500 hPa geopotential height is lower than 599.4651 dagpm, which constitutes the favorable conditions for the occurrence of strong wind.