论热带大气垂直环流圈的结构和海洋加热尺度间的关系

ON RELATIONSHIP BETWEEN THE STRUCTURE OF VERTICAL CIRCULATION AND THE OCEAN HEATING SCALE IN THE TROPICS

应用本征模式的浅水运动方程,研究了热带大气中Walker环流和Hadley环流圈的垂直结构和海洋加热尺度间的关系,如热源的纬圈尺度为L,赤道Rossby变形半径为L_0,Ray-leigh摩擦和Newton冷却系数为ε,则垂直环流圈的结构依赖于加热尺度L的大小。当α(=L_0/L)>α_0(ε)时(即小尺度热源),其结果和Gill的定常解相似,即在热源中心西侧的Rossby波活动区,与Walker环流相联系的Hadley环流,是热力性的正环流。低层空气是向赤道辐合,高层空气是向极地的,并在副热带地区下沉;而在热源以东的Kelvin波活动区,经圈速度的垂直分布反过来,即低层气流是向极地的,高层气流是向赤道的。但当热源尺度变得适当大后,例如当α<α_0(ε)时,经圈环流在Rossby波和Kelvin波区的大部分地区,都是正的Hadley环流,而原来在Kelvin波区的反Hadley环流,将东移到离热源中心相当远的地区(例如超过10个赤道Rossby变形半径)。在后面这种情况下,一个大尺度的正的Hadley环流,将把大气从海洋中得到的热量或能量大量地输送到副热带或中纬度地区,使那里的大气环流发生异常性的变化。后面这一理论结果与统计事实相当符合,可以看成是对Bjerknes提出的遥相关现象的一个理论支持。

A steady, shallow water atmospheric model is used to study the relationship between the structures of Walker and Hadley circulation in the tropic atmosphere and the scale of ocean heating. It is showed that the structure of vertical cell depends on the oceanic heating scale. When a is larger than α0(ε) (that is, the small scale), results are similar to Gill (1980) ones. Whereas α is smaller than α0(ε), a Hadley cell exists in the entire heating region. An anti-Hadley circulation which appears in the area of Kelvin wave will move eastward for a long distance, i. e. 10 units of Rossby deformation radius. In the last case, a larger scale Hadley cell can transfer a lot of heating and energy to extratropical and midlatitude regions. This causes the atmospheric circulation there to be anomalous. The results are coherent with statistical facts, and in theoretically support the teleconnection_ phenomena which Bejerknes put forward in 1960's.