基于秒级探空资料分析四川重力波统计特征

A Statistical Study of Gravity Wave with Second-level Radiosonde Data in Sichuan

利用2014年6月-2017年9月的秒级探空资料,选取四川地区5个代表性站点研究重力波在对流层(2~10km)和平流层(18~25km)的时空特征。选取结果表明:重力波能量在四川地区各个高度均存在明显的季节变化,冬季强,夏季弱;在对流层由于地形影响,川西和川北高原地区的能量小于其他地区。垂直波长没有明显的时空变化,在对流层和平流层分别集中分布于1.5~3km和1.5~3.5km;水平波长则差别较大,分别分布于0~300km和100~700km,平均值分别为100km和350km。重力波固有频率在对流层有较大的区域差异,表现为在四川西北部的高原地区固有频率平均值为3f(f为地转参数),其他地区则仅为2.4f;平流层则没有明显的差异存在,均约为2f。四川地区重力波的垂直传播方向特征基本相同,在对流层约有50%的波动向上传播,平流层则有90%以上的波动向上传播。水平传播则存在明显的不确定性,特别是对流层;平流层水平传播方向存在明显的季节变化,表现为夏季重力波多向偏东方向传播,而其他季节则向偏西方向传播。

High vertical resolution radiosonde data of Sichuan Province from June 2014 to September 2017 are analyzed to derive important gravity wave parameters, such as wave energy, intrinsic frequencies, vertical and horizontal wavelengths, and propagation directions. The sampling period of these data is 1.2 s and the vertical resolution is 5-8 m. Five representative stations of Sichuan Province are investigated, including Ganzi, Hongyuan, Chengdu, Xichang and Dazhou. Data in troposphere (2-10 km) and stratosphere (18-25 km), and the latest upper-air wind measurement algorithm for L-band radiosonde sounding system are used to process the original data. Results show that there are obvious seasonal variabilities of gravity waves energy at various areas in Sichuan, strong in winter and weak in summer. In the troposphere, due to the influence of terrain, the energy in the western Sichuan and northern Sichuan regions is significantly smaller than that in other regions. And gravity wave activity is also affected by latitudes. There is no obvious spatial variation in vertical wavelength, and vertical wavelength in winter is slightly larger than summer. The vertical wavelength is concentrated at 1.5-3 km and 1.5-3.5 km in the troposphere and stratosphere, respectively. The horizontal wavelength is quite different, distributed in 0-300 km and 100-700 km, or averaged of 100 km and 350 km in the troposphere and stratosphere, respectively. The ratio of horizontal wavelength to vertical wavelength is 35:1 in the troposphere and 150:1 in the stratosphere. It indicates that gravity waves mainly propagate vertically in the troposphere and propagate horizontally in the stratosphere. In order to get more accurate intrinsic frequency of gravity waves, filtering is essential perform before calculation. There is a large regional difference for intrinsic frequency in the troposphere. The averaged intrinsic frequency in the Plateau regions in northwestern Sichuan is 3 (represents the Coriolis force parameter), while only 2.4 in other regions. There is no obvious spatial difference in the stratosphere, and the mean value is about 2. The vertical propagation directions of gravity waves at different stations in Sichuan are similar, with about 50% of the waves propagating upward in the troposphere and more than 90% in the stratosphere. Horizontal propagation direction of gravity wave is always influenced by background wind field, and it has significant uncertainty, especially in the troposphere. The horizontal propagation of gravity waves in stratosphere strongly depends on season, eastward in summer and westward in other seasons.