An enhanced moisture convergence - Evaporation feedback mechanism for MJO air-sea interaction
An enhanced moisture convergence - Evaporation feedback mechanism for MJO air-sea interaction
复制标题
DOI：
10.1175/2007jas2313.1
复制
发表时间：
2008-03
影响因子：
3.1
通讯作者：
A. Marshall;O. Alves;H. Hendon
中科院分区：
文献类型：
--
作者：
A. Marshall;O. Alves;H. Hendon
用观测到的海温气候学强迫大气模式和与海板-海洋模式耦合的大气模式进行了模拟，研究了海-气相互作用对MJO动力学的影响。板条-海洋耦合改善了澳大利亚气象局大气模式中印度-太平洋暖池上的MJO，将其周期从70-100天缩短到45-70天，从而与30-80天的观测振荡显示出更好的一致性。海气耦合通过增加对流层低层的水汽通量来改善MJO，从而促进了主对流中心东侧的对流和降水。这一过程是由MJO对流前海温正异常的地面蒸发增加所触发的，这是由抑制对流区的短波辐射增强所驱动的。这反过来又加强了对该地区的辐合，这支持了在弱背景西风存在的情况下的蒸发-风反馈。随后低层水汽辐合的增加在大气气压降低区域的大规模对流之前进一步滋润了对流层下部。这种不稳定机制被称为增强型水汽辐合-蒸发反馈(EMCEF)，用于理解海-气耦合对观测到的MJO的作用。EMCEF机制还调和了传统上关于第二类摩擦波条件不稳定(CISK)和风蒸发反馈的作用的对立观点。这些结果支持这样的观点，即MJO主要是一种大气现象，海气相互作用改善了它在模式中的存在，但并不是关键的。
Simulations using an atmospheric model forced with observed SST climatology and the same atmospheric model coupled to a slab-ocean model are used to investigate the role of air-sea interaction on the dynamics of the MJO. Slab-ocean coupling improved the MJO in Australia's Bureau of Meteorology atmospheric model over the Indo-Pacific warm pool by reducing its period from 70-100 to 45-70 days, thereby showing better agreement with the 30-80-day observed oscillation. Air-sea coupling improves the MJO by increasing the moisture flux in the lower troposphere prior to the passage of active convection, which acts to promote convection and precipitation on the eastern flank of the main convective center. This process is triggered by an increase in surface evaporation over positive SST anomalies ahead of the MJO convection, which are driven by the enhanced shortwave radiation in the region of suppressed convection. This in turn generates enhanced convergence into the region, which supports evaporation-wind feedback in the presence of weak background westerly winds. A subsequent increase in low-level moisture convergence acts to further moisten the lower troposphere in advance of large-scale convection in a region of reduced atmospheric pressure. This destabilizing mechanism is referred to as enhanced moisture convergaence-evaporation feedback (EMCEF) and is utilized to understand the role of air-sea coupling on the observed MJO. The EMCEF mechanism also reconciles traditionally opposing ideas on the roles of frictional wave-conditional instability of the second kind (CISK) and wind-evaporation feedback. These results support the idea that the MJO is primarily an atmospheric phenomenon, with air-sea interaction improving upon, but not critical for, its existence in the model.