青藏高原上空UTLS区域一次地形重力波过程中的物质上传

利用美国航空航天局MERRA(Modern-Era Retrospective Analysis for Research and Applications)再分析资料和MODIS(Moderate-Resolution Imaging Spectroradiometer)卫星资料以及欧洲气象中心ECMWF-Interim(European Centre for Medium-Range Weather Forecasts)再分析资料,分析了发生于青藏高原北侧上空的一次地形重力波事件,并使用中尺度预报模式WRF-ARW.V3.0(Weather Research and Forecasting model,V3.0)对其进行了数值模拟.在此基础上,诊断分析了此次地形重力波在UTLS(Upper Troposphere and Lower Stratosphere)区域造成的物质和能量垂直传输特征.分析结果表明这一中尺度地形重力波信号的水平波长约为600km,与地形扰动水平尺度接近,重力波在对流层中传播的垂直波长约为3km,在垂直方向上随着高度的增加呈现出由东向西倾斜的结构特征.此次地形重力波上传进入平流层并在150hPa附近破碎,波破碎后动量通量在短时间内发生了强烈的衰减,重力波携带的能量在破碎高度附近释放.重力波破碎的同时垂直方向湍流混合变得异常强烈,湍流交换系数可在短时间内增加到背景值的8倍以上,剧烈湍流混合过程导致了对流层上层的空气进入平流层,使下平流层空气出现了位势涡度和臭氧的低值区,在浮力频率的垂直剖面中也可以看到由于地形重力波过程造成的平流层下层浮力频率异常低值区.

Upward transport of air mass during a generation of orographic waves in the UTLS over the Tibetan Plateau

This work examined the characteristics of an orographic gravity wave event during 0:00~6:00 UTC on 1 May 2008 and its impacts on stratosphere and troposphere exchange, using NASA MERRA(Modern-Era Retrospective Analysis for Research and Applications) and European Centre for Medium-Range Weather Forecasts(ECMWF) Interim reanalysis data and Moderate Resolution Imaging Spectroradiometer(MODIS) data, in combination with the Weather Research and Forecasting model(WRF). The results show that the horizontal wavelength is about 600 km throughout the troposphere and stratosphere, close to the terrain width, and the vertical wavelength is about 3 km in the troposphere. The wave structure shows a westward tilt with height. Orographic waves propagate upward into the stratosphere and break up near 150 hPa, leading to a strong attenuation of momentum flux and the release of energy into basic flows. Meanwhile, vertical turbulent mixing is extremely increased and turbulent exchange coefficient enhances more than eight times during a short period(within 1 hour). Large turbulent mixing process causes air transport from the troposphere to the stratosphere, corresponding to the low value of ozone, potential vorticity and buoyancy frequency in the lower stratosphere.