一次东移西南涡过程的平流层重力波特征研究

基于WRF模式对2011年6月16—19日一次东移西南涡过程的模拟,开展了西南涡激发平流层重力波的特征研究。东移西南涡可以分为发展、强盛和减弱3个阶段,每个阶段均伴随着强降雨天气,但由于降水位置和强度的不同,平流层重力波的分布和强度也不同。西南涡发展阶段,平流层重力波主要位于低涡的东侧,并向东北传播;西南涡强盛阶段,伴随对流降水的强度和范围明显增大,平流层重力波的振幅和范围也显著增大,且围绕西南涡的东侧和南侧呈现出半环状的重力波分布特征可分为两支,东侧波动波列表现为东北西南向分布,南侧的波列表现为东—西向分布;西南涡减弱阶段,重力波的振幅和范围均减小。波谱分析表明,重力波的纬向波数频率谱关于零频率呈非对称分布,且随着西南涡的增强,波谱在小尺度范围显著增大,即强对流更容易激发出小尺度的高频波;经向波数频率谱在波数较小谱段关于零频率基本呈对称分布,但在波数较大谱段,也呈非对称分布,这说明受平流层东风气流的影响,重力波主要向东传播。

Characteristics of stratospheric gravity waves in an eastward moving southwest vortex process

The characteristics of stratospheric gravity waves generated by the southwest vortex from June 16 to 19, 2011 were investigated by using the Weather Research and Forecasting (WRF) model. The eastward moving southwest vortex can be divided into three stages:development stage, mature stage and decaying stage. Each stage is accompanied with heavy rainfall, and the stratospheric gravity waves show different distribution and intensity due to the distinct location and magnitude of precipitation. In the development stage of the southwest vortex, the stratospheric gravity waves are mainly located in the east of the southwest vortex, which propagate northeastward. During the mature stage of the southwest vortex, the intensity and range of convective precipitation enhance obviously, while the amplitude and range of stratospheric gravity waves also increase significantly. Besides, these semi-annular waves around the east and south of the southwest vortex can be divided into two branches. The wave on the east side is distributed in the northeast-southwest direction, and the wave on the south side is distributed in the east-west direction. During the decaying stage of the southwest vortex, the main amplitude and wavelength are reduced correspondingly. The spectral analysis shows that the zonal wave number-frequency spectrum of the gravity waves is asymmetrically distributed with respect to the zero frequency. The sptectrum increases significantly in the small-scale range with the enhancement of the southwest vortex, which indicates that strong convection is easier to generate small-scale high-frequency waves. The meridional wave number frequency spectrum mainly presents symmetrical distribution about the zero frequency in the small wave number, but it also presents asymmetric distribution in the large wave number. This also illustrates that the gravity waves mainly propagate eastward under the influence of the stratospheric easterly flow.