The Convection Connection: How Ocean Feedbacks Affect Tropical Mean Moisture and MJO Propagation
The Convection Connection: How Ocean Feedbacks Affect Tropical Mean Moisture and MJO Propagation
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DOI：
10.1029/2019jd031015
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发表时间：
2019-11
期刊：
影响因子：
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通讯作者：
C. DeMott;N. Klingaman;W. Tseng;M. Burt;Yingxia Gao;D. Randall
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文献类型：
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作者：
C. DeMott;N. Klingaman;W. Tseng;M. Burt;Yingxia Gao;D. Randall
通过四个大气环流模型 (GCM) 的耦合和非耦合模拟，研究了马登-朱利安振荡 (MJO) 对海洋反馈的响应。每个耦合模型的月平均海面温度 (SST) 都指定给其各自的非耦合模拟，以确保模拟对之间具有相同的 SST 平均状态和低频变化。与之前的研究一致，耦合提高了每个模型将 MJO 对流传播到海洋大陆以外的能力。对 MJO 湿静态能量收支的分析表明，所有四个耦合模型中 MJO 向东传播的改善都是由于柱状水汽 (CWV) 的经向平流增强所致。尽管每个耦合和非耦合模拟对中的平均态海温相同，但耦合会增加赤道附近的平均态 CWV，从而锐化赤道方向的水分梯度并增强经向水分平流和 MJO 传播。 MJO 和非 MJO 期间的 CWV 复合材料表明，MJO 本身不会导致水分梯度增强。相反，对降雨率（R）和海温异常条件下的低层次网格尺度湿润的分析表明，耦合增强了 R> 5 mm day−1 的低层对流湿润；这种增强在赤道附近最为明显。四个模型的低层湿润过程各不相同，我们根据海洋模型配置、积云参数化和对流对柱相对湿度的敏感性来解释它们。
The response of the Madden‐Julian oscillation (MJO) to ocean feedbacks is studied with coupled and uncoupled simulations of four general circulation models (GCMs). Monthly mean sea surface temperature (SST) from each coupled model is prescribed to its respective uncoupled simulation, to ensure identical SST mean‐state and low‐frequency variability between simulation pairs. Consistent with previous studies, coupling improves each model's ability to propagate MJO convection beyond the Maritime Continent. Analysis of the MJO moist static energy budget reveals that improved MJO eastward propagation in all four coupled models arises from enhanced meridional advection of column water vapor (CWV). Despite the identical mean‐state SST in each coupled and uncoupled simulation pair, coupling increases mean‐state CWV near the equator, sharpening equatorward moisture gradients and enhancing meridional moisture advection and MJO propagation. CWV composites during MJO and non‐MJO periods demonstrate that the MJO itself does not cause enhanced moisture gradients. Instead, analysis of low‐level subgrid‐scale moistening conditioned by rainfall rate (R) and SST anomaly reveals that coupling enhances low‐level convective moistening for R> 5 mm day−1; this enhancement is most prominent near the equator. The low‐level moistening process varies among the four models, which we interpret in terms of their ocean model configurations, cumulus parameterizations, and sensitivities of convection to column relative humidity.