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.