东亚季风区冬季经向风的季节内变化及其可能机理

利用1979—2013年ERA-interim再分析资料,通过均方差分析、功率谱分析、带通滤波及合成分析等统计方法系统地分析了东亚季风区冬季经向风的季节内变化及其可能机理。结果表明,东亚季风区冬季经向风异常在我国华南一带变化显著,振荡周期为10~20 d(准双周振荡)。在准双周尺度上,水平方向上,850 h Pa异常北风主要呈现从高纬向低纬传播的特点,60°N附近异常经向风向东南方向传播,副热带30°N附近弱的异常经向风向东传播,二者在华南汇合,随后分为两支中心,分别向南和向东继续传播,我国华南一带存在基本气流向准双周尺度波动的能量转换,因此异常经向风在华南会显著增强;垂直方向上,对流层上层、中层、下层的经向风呈现强—弱—强的异常中心特征,对流层下层850 h Pa和上层200~300 h Pa均存在经向风大值中心;我国东部上空300 h Pa上,副热带地区波动比850 h Pa更明显,60°N附近波动向东南方向移动,同样在我国东部地区合并,波动辐合导致波动能量增强。

Intraseasonal variation of winter meridional wind in East Asian monsoon region and its possible mechanism

Based on the ERA-interim reanalysis data of the ECMRWF(European Center for Medium-Range Weather Forecasts) from 1979 to 2013,this paper systematically analyzes the intraseasonal variation of winter meridional wind in East Asian monsoon region and its possible mechanism by using the mean square analysis,power spectrum analysis,Butterworth filtering,synthesis analysis and other statistical methods.Results show that the winter meridional wind anomaly of East Asian monsoon area significantly changes in South China area,with an oscillation period of 10-20 d (Quasi-BiWeekly Oscillation,QBWO).In the horizontal direction,the 850 hPa anomalous north wind has the characteristics of propagation from the high latitudes to the low latitudes.The anomalous meridional wind near 60°N spreads southeastward,and the anomalous weak meridional wind near 30°N spreads eastward in the subtropical zone.They converge in South China,then are divided into two centers,which continue to spread southward and eastward respectively.The oscillating evolution of winter meridional wind has the characteristics of anti-phase between Lake Baikal and South China.There exists the energy conversion from the basic air flow to the quasi-biweekly fluctuation in South China,therefore the anomalous meridional wind will enhance significantly there.In the vertical direction,the anomalous meridional wind exhibits strong-weak-strong anomalous center features in the upper,middle and lower layers of the troposphere.There is a large center of meridional wind in the lower (850 hPa) and upper (200-300 hPa) layers of the troposphere.However,the quasi-biweekly oscillations of meridional wind are relatively weak in the middle troposphere.Rossby wave changes significantly at 300 hPa.Over the eastern part of China,there is also a large value center of meridional wind with quasi-biweekly oscillation period.The fluctuations in the subtropical regions at 300 hPa are more obvious than those at 850 hPa,and the fluctuations near 60°N move southeastward,similarly merging in the eastern part of China.The Rossby waves from Europe spread eastward and the Rossby waves from North Pacific spread westward,and their convergence near the eastern part of China results in an increase of fluctuation energy.