Annual intensification of the Somali jet in a quasi-equilibrium framework: Observational composites
Annual intensification of the Somali jet in a quasi-equilibrium framework: Observational composites
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DOI：
10.1002/qj.388
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发表时间：
2009-01-01
影响因子：
8.9
通讯作者：
Emanuel, Kerry A.
中科院分区：
文献类型：
--
作者：
Boos, William R.;Emanuel, Kerry A.
与季节日照强迫的演变相比，伴随着印度夏季风开始的索马里喷气机的年度增强是迅速的。利用基于观测的数据集，介绍了该喷流开始时的动力学和热力学变化。在东非高地以东约1000公里的海面上出现了急流的突变分量，并伴随着近赤道的阿拉伯海上空的深对流和斜压流的增加。这些突变与位于东非高地附近的跨赤道急流的核心分离得很好。然后在对流准平衡框架中考察索马里急流和相关季风的开始。这种框架与夏季的平均状态是一致的，因为在孟加拉湾北部和邻近沿海地区，对流层自由温度的峰值几乎与亚云层熵的峰值同时出现。急流的开始伴随着阿拉伯海上空表面焓通量的大增加（0 {100 W m(-2)}），这几乎与对流层深部上升的同时增加同时发生，并与之线性相关。与此同时，最高的云下熵从孟加拉湾略微向内陆移动，自由对流层温度最高的区域向极地扩展。讨论了所有这些变化与风蒸发反馈的一致性以及季风突变发生的其他几种假设机制。版权所有(C) 2009皇家气象学会
The annual intensification of the Somali jet, which accompanies the onset of the Indian summer monsoon, is rapid compared to the evolution of the seasonal insolation forcing. Using observationally-based data sets, the dynamic and thermodynamic changes accompanying the onset of this jet are presented. The abrupt component of jet onset is shown to occur over ocean about 1000km east of the East African highlands, and is accompanied by increases in both deep convection and baroclinic flow over the off-equatorial Arabian Sea. These abrupt changes are well separated from the core of the cross-equatorial jet, which is located over land adjacent to the East African highlands.The onset of the Somali jet and the associated monsoon are then examined in a convective quasi-equilibrium framework. Such a framework is consistent with the mean summer state, in that peak free-tropospheric temperatures are nearly collocated with peak subcloud layer entropies over the northern Bay of Bengal and adjacent coastal regions. Jet onset is accompanied by a large (O{100 W m(-2)}) increase in surface enthalpy flux over the Arabian Sea that is nearly collocated with, and linearly related to, the concurrent increase in deep tropospheric ascent. At the same time, the highest subcloud entropies shift inland slightly from the Bay of Bengal, and the region of warmest free-tropospheric temperatures expands poleward. The consistency of all of these changes with a wind-evaporation feedback and several other hypothesized mechanisms of abrupt monsoon onset is discussed. Copyright (C) 2009 Royal Meteorological Society