A Numerical Investigation of the Atmospheric General Circulation and Stratospheric-Tropospheric Mass Exchange : II. Lagrangian Motion of the Atmosphere
A Numerical Investigation of the Atmospheric General Circulation and Stratospheric-Tropospheric Mass Exchange : II. Lagrangian Motion of the Atmosphere
复制标题
大气环流和平流层-对流层质量交换的数值研究：II。
DOI：
10.2151/jmsj1965.55.1_71
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发表时间：
1977
影响因子：
3.1
通讯作者：
H. Kida
中科院分区：
文献类型：
--
作者：
H. Kida
利用一个简化的大气环流模式，通过追踪大量源于平流层的空气粒子，对平流层 - 对流层质量交换进行了数值模拟。结果表明，平流层空气向对流层流出的最合理机制是与中纬度气旋相关的穿越对流层顶的运动。空气粒子运动的具体过程是：气旋后部且纬度约60度附近的最低平流层空气粒子最有效地向下和向赤道方向移动，并到达对流层中部约40度纬度处，而许多其他平流层空气粒子只是在西风带中随南北向的蜿蜒曲折向东流动。一些进入对流层的源于平流层的空气粒子会在气旋东侧返回原来的高度。尽管有这种返回运动，但由于气旋的动力作用导致空气粒子长期存在净向下运动，它们最终还是会在对流层中下降并融合。另一方面，该模式显示平流层空气通过亚热带对流层顶缺口的准水平流出并未发生。文中讨论并给出了空气粒子可能的大气环流情况，将其称为大气的拉格朗日大气环流。其结构在一个半球上呈现出一个环流圈，在高纬度和低纬度分别有向下和向上的分支，且与平流层下部所谓的布鲁尔 - 多布森环流相符。因此，可以认为平流层 - 对流层质量交换的个体短程机制和统计长程机制分别是气旋后部的优先下沉运动和布鲁尔 - 多布森型经向环流。实验表明，拉格朗日大气环流在中纬度对流层顶高度处的垂直向下速度约为100毫巴/月，这意味着平流层空气完全被替换所需的停留时间量级为半年。然而，由于有一些理由认为这个值被低估了2 - 3倍，所以可以推断在实际大气中其量级为1 - 2年，这与观测研究的结果相符。
A numerical simulation of Stratospheric-Tropospheric mass exchange was performed by tracing a large number of air particles of the stratospheric origin with a simplified general circulation model. It shows that the most plausible mechanism of outflow of the stratospheric air to the troposphere is cross-tropopause motion associated with the mid-latitude cyclone. The individual process of air particle's movement is that the lowest stratospheric air particles in the rear of the cyclone and around at 60 degrees of latitude most-effectively move downward and equatorward and arrive around at 40 degrees of latitude in the middle troposphere, while many other stratospheric air particles merely flow eastward with north and south meander in the westerlies. Some air particles of the stratospheric origin intruding into the troposphere return toward the original levels to the east side of the cyclone. In spite of the return motion, they eventually descend and merge in the troposphere, since the net downward movement of air particles for a long time is induced by dynamical effects of the cyclone. On the other hand, the model shows the quasi-horizontal outflow of the stratospheric air through the tropopause gap in the subtropics does not take place. Possible general circulation of air particles was discussed and presented in the model. It will be referred to as Lagrangian general circulation of the atmosphere. Its structure shows one cell over a hemisphere with downward and upward branches in higher and lower latitudes, respectively, and coincides with the so-called Brewer-Dobson circulation in the lower stratosphere. Therefore, it may be considered that the individual short-range and statistical long-range mechanisms of Stratospheric-Tropospheric mass exchange are the preferential descending motion in the rear of the cyclone and the Brewer-Dobson type meridional circulation, respectively. The experiment shows that Lagrangian general circulation has the vertical downward velocity of about 100 mb/month at a level of the mid-latitude tropopause, indicating that the magnitude of the residence time needed for the stratospheric air to be completely replaced is of the order half a year. However, since there are some reasons to consider that this value is underestimated by a factor of 2~3, it may be inferred that its magnitude is of the order 1~2 years in the real atmosphere, being in agreement with the results of observational studies.