热带印度洋偶极子事件期间印度洋大气的变化——大气流函数场和势函数场的分析

大气环流的变异是热带印度洋偶极子（IOD）事件研究中的一个重要问题。本文从风场旋度分量和散度分量角度出发，利用观测资料和大气环流模式，对IOD事件发生时热带印度洋海区上空的大气环流变化进行了分析，揭示出风场不同分量在IOD事件期间的变化特征。研究结果表明，热带印度洋大气环流系统在IOD事件期间，旋度分量和散度分量在垂直方向上呈现明显的一阶斜压形式，而在水平方向上呈现明显的对称分布特征。对低空（850 hPa）来说，无辐散流函数距平场在IOD事件正位相期间表现为关于赤道对称的一对反气旋式环流；无旋度分量在IOD事件正位相期间的响应表现为东印度洋辐散、西印度洋辐合；大气环流的两种分量场均可以在赤道印度洋地区产生距平意义下的纬向东风，正是这种形式的距平东风使得IOD事件依靠海气系统正反馈机制得以维持和发展。而高空（200 hPa）大气环流形式刚好与850 hPa相反。

Variability of Tropical Indian Ocean Atmosphere during Tropical Indian Ocean Dipole Mode Event-The Analysis of the Stream Function and the Potential Velocity of the Wind Field

The atmosphere circulation variability is one of the fundamental problems in the researches on the tropical Indian Ocean Dipole(IOD) mode event.The authors analyze the variability of the wind vorticity field and divergence field during IOD event based on the observation and the numerical model.The result indicates that both the divergent and rotational parts of the wind field present the first order baroclinic pattern in the vertical direction and symmetric pattern in the horizontal direction respectively.In the lower atmosphere,the rotational part shows a pair of symmetric anticyclones around the equator during the positive phase of IOD event and the divergent part shows the divergence in the eastern Indian Ocean and the convergence in the western Indian Ocean.Both the divergent part and the rotational part could generate zonal easterly wind above the equator region in the tropical Indian Ocean,which supports the air-sea positive feedback mechanism.The upper circulation is just reversed with the lower one.