地形强迫在高纬地区30～60天低频振荡中的作用

Topographic Forcing Role in the 30～60 Day Oscillation in the High Latitudes

利用３０～６０天带通滤波器对高纬地区５００ｈＰａ１～２波的振幅及位相角进行滤波。发现３０～６０天低频振荡沿纬圈方向的传播是围绕一个平衡位置的振荡，其振荡范围在１００°之内，而在不同振荡周期之间表现出不同的特点。它们分别是：（１）振荡型，即波向西或向东传播速度大致相等；（２）向西传播较慢而向东传播较快型；（３）向东传播较快而向西传播较慢型。还利用以地形为强迫的二层斜压模式对产生低频振荡机理进行了分析和数值研究，结果表明，在一定的选定参数之下，地形强迫可使模式大气产生３０～６０天的低频振荡，且具有３种振荡类型，其图像与观测结果的图像有较好的一致性，产生这种振荡的机制是地形强迫波在某些位相是发展的，而在另一些位相则是衰减的。而波的传播速度与振幅的大小有关。当波振幅较小时，地形强迫作用会迫使波的位相回到被激发时的位相，从而形成周期振荡。

The amplitude and phase of 1～2 waves at 500 hPa in the high latitude are filtered by using the 30～60 day band-pass filter The results show that the propagating characteristic of 30～60 day oscillation is an oscillation around the balance place along latitude within 100 degree There are different kinds of oscillating types among different oscillating periods, which contain (1) oscillating type, that is, the wave speeds are almost same westward or eastward, (2) larger eastward than westward, and (3) larger westward than eastward The mechanism of 30～60 day oscillation is studied analytically and numerically by using a two-layer baroclinic model with topographic forcing The results show that under certain parameters, the topographic forcing can excite three kinds of 30～60 day oscillation The figures of these oscillations are consistent with ones of observation The mechanism producing oscillation is that topographic forcing wave increases in same phases and reduces as the others The wave speed is related to the amplitude itself When the amplitude becomes enough small, the topographic forcing can force the wave phase to return to the excited phase and thus the periodic oscillation is formed