Trend and interannual variability of Walker, monsoon and Hadley circulations defined by velocity potential in the upper troposphere
Trend and interannual variability of Walker, monsoon and Hadley circulations defined by velocity potential in the upper troposphere
复制标题
DOI：
10.3402/tellusa.v56i3.14410
复制
发表时间：
2004-01
期刊：
影响因子：
--
通讯作者：
Hitoshi Tanaka;N. Ishizaki;A. Kitoh
中科院分区：
文献类型：
--
作者：
Hitoshi Tanaka;N. Ishizaki;A. Kitoh
在本文中，我们尝试利用200 hpa水平的月平均速度势场，在Hadley、Walker和季风环流的贡献下划分对流层上层的全球发散场。首先，分析了速度势的纬向平均值，以代表哈德利环流。然后将与纬向平均的偏差分为年平均和季节周期部分，分别代表沃克环流和季风环流。每个循环的强度是通过它们在每个分量中分离的速度势场中的峰值来测量的。根据这种分离，1月Walker、季风和Hadley环流的平均强度分别为120:60:40 （× 105 m2 s-1）和120:90:45 （× 105 m2 s-1）。基于这个简单的定义，然后使用国家环境预测中心/国家大气研究中心（NCEP/NCAR）再分析定量地检查每个环流的年际变化。Walker环流强度的时间序列与南方涛动指数（SOI）一致，且近几十年来强度有所减弱。哈德利环流在北方冬季有增强的趋势。最后，将同样的分析应用于气象研究所（MRI）耦合大气-海洋环流模式（CGCM1）的模式大气，该模式大气中CO2以1% - 1年的复合速率逐渐增加，持续150年。结果表明，当全球变暖发生一个世纪后，北方夏季Hadley环流增强40%，季风环流减弱20%。结果表明，提出的简单分离Walker、季风和Hadley分量的热带环流是有用的，尽管它不是严格的，对于模式对全球变暖的响应的初步评估。
In this paper, we attempt to divide the global divergent field at the upper troposphere in contributions from the Hadley, Walker and monsoon circulations, using a monthly mean velocity potential field at 200-hPa level. First, the zonal mean of the velocity potential is analysed to represent the Hadley circulation. The deviation from the zonal mean is then divided into its annual mean and the seasonal cycle parts, which are considered to represent the Walker and monsoon circulations, respectively. The intensities of each circulation are measured by their peaks in the velocity potential field separated in each component. According to this separation, the mean intensities of the Walker, monsoon and Hadley circulations appear to be 120: 60: 40 (× 105 m2 s—1) in January and 120: 90: 45 (× 105 m2 s—1) in July, respectively. Based on this simple definition, interannual variabilities of each circulation are then examined quantitatively using the National Center for Environmental Prediction/National Center for Atmospheric Research (NCEP/NCAR) reanalysis. The time series of the intensity of the Walker circulation coincides with the Southern Oscillation index (SOI), and the intensity has weakened in recent decades. That of the Hadley circulation indicates intensifying trend in boreal winter. Finally, the same analysis is applied for the model atmosphere by the Meteorological Research Institute (MRI) coupled atmosphere’ocean general circulation model (CGCM1) with a gradual increase in CO2 at a compound rate of 1% yr—1 for 150 yr. It is shown that the Hadley circulation intensifies by 40% and the monsoon circulation decays by 20% in boreal summer when the global warming has occurred in a century later. The result demonstrates that the proposed simple separation of the tropical circulation in the Walker, monsoon and Hadley components is useful, although it is not rigorous, for the initial assessment of the model response to the global warming.