基于秒级探空资料的中国地区浮力频率分布

浮力频率用来描述大气层结稳定性，反映大气扰动强弱。利用2014年6月-2017年5月中国地区高垂直分辨率的秒级探空资料，分析了中国地区浮力频率的时空分布特征。结果表明:中国地区大气浮力频率总体随高度的增加而增大，低平流层值大于对流层值；对流层和低平流层中浮力频率随高度变化均较小可视为常数，过渡层浮力频率随高度变化较大，对流层中浮力频率受地形影响较平流层大。对流层中北方地区5 km高度以下的浮力频率随时间呈现出较弱的周期变化，周期为1年，峰值出现在冬季，南方地区随时间无明显变化；在过渡层中南北地区的浮力频率随时间均呈现出1年的周期变化，峰值出现在冬季，谷值出现在夏季；在低平流层中南北地区浮力频率随时间均无明显变化。浮力频率的大小变化对重力波参数有较大影响，秒级探空资料计算的的浮力频率和风速切变更精细，较常规探空资料更准确地反映大气稳定度的变化。

A Statistical Study of Brunt-vaisala Frequency with Second-level Radiosonde Data in China

Based on the second-level sounding data of high vertical resolution in China from June 2014 to May 2017, time and space distribution characteristics of brunt-vaisala frequency in China are analyzed. Results show that the distribution of atmospheric brunt-vaisala frequency increases with height, data of lower stratosphere is larger than the troposphere, and the brunt-vaisala frequency remains constant in the vertical direction in the troposphere and low stratosphere. The brunt-vaisala frequency in the troposphere is greatly affected by the topography, and gradually increases from west to east with the change of longitude, with a small value area in the plateau region. The brunt-vaisala frequency in the low stratosphere is less affected by the topography and mainly changes with latitude, and it''s greater in the southern region than that in the northern region. The brunt-vaisala frequency of the transition layer varies greatly with height. The southern part of lower transition layer changes faster with height than the northern part. The middle and southern parts of the upper transition layer change faster with height than the northern part. The brunt-vaisala frequency in the transition layer increases with latitude. The brunt-vaisala frequency doesn''t change significantly with seasons at 5-10 km height and low stratosphere, but in the transition layer between troposphere and stratosphere (10-18 km), the seasonal change is significant. It changes most significantly in winter, less significantly in spring and autumn, and minimally in summer. Below 5 km, the seasonal variation is obvious, and it changes the most in winter. The brunt-vaisala frequency below 5 km in the northern region troposphere shows annually variation characteristics, and the peak value is in winter. The brunt-vaisala frequency doesn''t change significantly with time in the stratosphere of north and south regions, and changes little with time in the troposphere in north and south regions. The brunt-vaisala frequency shows annually variation characteristics in the lower troposphere over the northern region, with peaks appearing in the winter, and there is also a one-year periodic variation in the transition layer, the peak is in winter and the valley is in summer. The brunt-vaisala frequency changes at the same height of the southern region and the northern region are similar in the transition layer. There is an annual change, the peak is in winter and the valley is in summer, but the central value of the transition layer in the southern region is smaller than the central value in the northern region. In the transition layer, the influence of the brunt-vaisala frequency with the height on the gravity-wave momentum flux is considered. The brunt-vaisala frequency and wind speed calculated by second-level sounding data are finely changed, and the change of atmospheric stability can be grasped more accurately than the conventional sounding.