北京北郊冬季大风过程湍流通量演变特征的分析研究

Characteristics of Turbulent Transfer during the Strong Wind Period in the Northern Suburbs of Beijing

利用中国科学院大气物理研究所325m气象观测塔1993年12月～1994年1月大气边界层实验资料,计算分析了大风过境过程中47m和120m高度湍流通量演变特征及其影响因子,以及与风速、稳定度等参数的关系。结果表明:大风过程对近地面层的物质能量输送有着重要影响,大风之前出现短时间动量上传和热量下传;大风过程中的湍流通量数值明显高于过境后,水平方向湍流通量数值和能量增加幅度大于垂直方向;当风速大于临界值5m/s时,湍流通量与风速、湍流动能的相关迅速增大;湍流谱特征表现为湍流能量的低频部分增加、湍流谱曲线变宽;大风能强烈影响近地面层的能量收支。

The modulation of the intraseasonal oscillation（ISO） on the typhoon tracks over the western North Pacific is studied by observational data analysis.The authors divide the main classes of typhoon tracks into five types based on the traditional methods.The results show that the ISO may affect the tracks of typhoons.The low-frequency cyclone（LFC） or low-frequency anticyclone（LFAC） influences the intensity and position of the monsoon trough and subtropical high in the lower and middle troposphere.The LFC east of the Philippines will strengthen the monsoon trough,and its northward propagation will influence the position of the subtropical high so as to influence the typhoon activity.Afterward,typhoons are more inclined to move along the zone of positive vorticity of the LFC.The ISO westward propagation in the form of wave trains in the subtropics also influences the position of subtropical high.The interaction of tropical and subtropical ISOs performs an important function on the typhoon tracks.The low-frequency circulation at 200 hPa can also have an indicative effect on the typhoon tracks.As a whole,the circulation field of ISO can be used as a basis for forecasting the typhoon tracks.