The Impact of Indian Ocean Mean-State Biases in Climate Models on the Representation of the East African Short Rains
The Impact of Indian Ocean Mean-State Biases in Climate Models on the Representation of the East African Short Rains
复制标题
DOI：
10.1175/jcli-d-17-0804.1
复制
发表时间：
2018-07
影响因子：
4.9
通讯作者：
L. Hirons;A. Turner
中科院分区：
文献类型：
--
作者：
L. Hirons;A. Turner
印度洋偶极子（IOD）在控制东非短雨，从10月至12月的年际变化的作用，检查在国家的最先进的模式，并详细在一个特定的气候模式。在观测中，湿短雨季与IOD的正相位和赤道印度洋的异常东风低空气流有关。一个模型捕捉到正IOD遥相关的能力与它对平均状态的表示密切相关。在短雨季，在赤道印度洋观测到的低空风是西风。然而，分析的模型中有一半在整个流域表现出平均状态的东风。具体而言，这些模型表现出平均状态低层赤道东风在印度洋，而不是观察到的西风，是无法捕捉到的纬度结构的水分平流到东非在积极的IOD。此外，相关的异常东风表面风应力导致东印度洋的上升流。这种上升流吸引了冷的次表层沃茨，增强了东西之间的纬向海面温度梯度，加强了正IOD型，进一步放大了东风应力。这种积极的Bjerknes耦合反馈是强东风平均状态模型，导致在这些模型中的一个潮湿的东非短雨降水偏差。
The role of the Indian Ocean dipole (IOD) in controlling interannual variability in the East African short rains, from October to December, is examined in state-of-the-art models and in detail in one particular climate model. In observations, a wet short-rainy season is associated with the positive phase of the IOD and anomalous easterly low-level flow across the equatorial Indian Ocean. A model’s ability to capture the teleconnection to the positive IOD is closely related to its representation of the mean state. During the short-rains season, the observed low-level wind in the equatorial Indian Ocean is westerly. However, half of the models analyzed exhibit mean-state easterlies across the entire basin. Specifically, those models that exhibit mean-state low-level equatorial easterlies in the Indian Ocean, rather than the observed westerlies, are unable to capture the latitudinal structure of moisture advection into East Africa during a positive IOD. Furthermore, the associated anomalous easterly surface wind stress causes upwelling in the eastern Indian Ocean. This upwelling draws up cool subsurface waters, enhancing the zonal sea surface temperature gradient between west and east and strengthening the positive IOD pattern, further amplifying the easterly wind stress. This positive Bjerknes coupled feedback is stronger in easterly mean-state models, resulting in a wetter East African short-rain precipitation bias in those models.