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
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DOI：
10.1111/j.1600-0870.2004.00049.x
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发表时间：
2004-05-01
影响因子：
2
通讯作者：
Kitoh, A
中科院分区：
文献类型：
--
作者：
Tanaka, HL;Ishizaki, N;Kitoh, A
本文利用200 hPa月平均速度位场，将对流层高层全球辐散场分为Hadley环流、步行者环流和季风环流的贡献。首先，分析速度势的纬向平均值来代表Hadley环流。对纬向平均值的偏离被分为年平均和季节循环两部分，分别代表步行者和季风环流。每个循环的强度由它们在每个分量中分离的速度势场中的峰值来测量。根据这种分离，步行者、季风和Hadley环流的平均强度在1月为120：60：40（x 10（5）m（2）s（-1）），在1月为120：90：10（x 10（5）m（2）s（-1））。45（x 10（5）m（2）s（-1））。根据这个简单的定义，然后利用国家环境预报中心/国家大气研究中心（NCEP/NCAR）再分析定量地检验了每个环流的年际变化。步行者环流强度的时间序列与南方涛动指数（SOI）相吻合，近几十年来强度有所减弱。最后，利用美国气象研究所（MRI）耦合的大气-海洋环流模式（CGCM 1）对模式大气进行了同样的分析，模拟大气中CO2浓度以1%（-1）的复合速率逐渐增加，持续150年。结果表明，当全球变暖发生后的世纪，北半球夏季Hadley环流增强40%，季风环流减弱20%。结果表明，所提出的简单分离步行者、季风和Hadley分量的热带环流的方法虽然不严格，但对模式对全球变暖响应的初步评估是有用的。
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 (x 10(5) m(2) s(-1)) in January and 120: 90: 45 (x 10(5) m(2) 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.