Intraseasonal SST-precipitation relationship and its spatial variability over the tropical summer monsoon region
Intraseasonal SST-precipitation relationship and its spatial variability over the tropical summer monsoon region
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DOI：
10.1007/s00382-012-1547-1
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发表时间：
2013-07
期刊：
影响因子：
4.6
通讯作者：
M. Roxy;Y. Tanimoto;Y. Tanimoto;B. Preethi;P. Terray;R. Krishnan
中科院分区：
文献类型：
--
作者：
M. Roxy;Y. Tanimoto;Y. Tanimoto;B. Preethi;P. Terray;R. Krishnan
本文利用最近的高质量卫星数据和最先进的耦合模式——气候预报系统第2版（CFSv2）的模拟，研究了亚洲季风区季节内变率（ISV）中的海温-降水关系。CFSv2在再现观测到的气候平均夏季风降水的空间分布及其年际变率方面表现出很高的能力，这一任务一直是许多最近气候耦合模式的难题。该模式在模拟向北传播的季风季内异常（包括海温和降水）方面也表现出合理的能力，这些异常与观测到的ISV特征基本一致。观测和模式的结果表明，在季节内时间尺度上，亚洲季风区大气对流对海温异常的响应存在空间变异。阿拉伯海响应快，降水滞后海温约5天；而在孟加拉湾和南海上空则较慢，滞后约12天。季节内海温异常导致整个盆地的类似大气响应，这包括大气柱底部的不稳定，从地表附近的等效位势温度异常可以观察到。然而，由于强烈的海温纬向梯度的存在加速了潮湿空气的上升运动，阿拉伯海上空存在一个相对强烈的地面辐合，导致阿拉伯海局地降水异常的响应相对于孟加拉湾和南海要快。在观测数据方面，该模式较好地模拟了海洋-大气耦合，但对季节内海温异常的估计过高，导致海温-降水关系被夸大。一项详细的研究指出，海洋模型的混合层厚度存在系统性偏差，需要加以纠正。太浅（深）的混合层增强（抑制）了季内海温异常的幅度，从而放大（减弱）了模式中的ISV和季风的活动中断期。
The SST-precipitation relationship in the intraseasonal variability (ISV) over the Asian monsoon region is examined using recent high quality satellite data and simulations from a state of the art coupled model, the climate forecast system version 2 (CFSv2). CFSv2 demonstrates high skill in reproducing the spatial distribution of the observed climatological mean summer monsoon precipitation along with its interannual variability, a task which has been a conundrum for many recent climate coupled models. The model also exhibits reasonable skill in simulating coherent northward propagating monsoon intraseasonal anomalies including SST and precipitation, which are generally consistent with observed ISV characteristics. Results from the observations and the model establish the existence of spatial variability in the atmospheric convective response to SST anomalies, over the Asian monsoon domain on intraseasonal timescales. The response is fast over the Arabian Sea, where precipitation lags SST by ~5 days; whereas it is slow over the Bay of Bengal and South China Sea, with a lag of ~12 days. The intraseasonal SST anomalies result in a similar atmospheric response across the basins, which consists of a destabilization of the bottom of the atmospheric column, as observed from the equivalent potential temperature anomalies near the surface. However, the presence of a relatively strong surface convergence over the Arabian Sea, due to the presence of a strong zonal gradient in SST, which accelerates the upward motion of the moist air, results in a relatively faster response in terms of the local precipitation anomalies over the Arabian Sea than over the Bay of Bengal and South China Sea. With respect to the observations, the ocean–atmosphere coupling is well simulated in the model, though with an overestimation of the intraseasonal SST anomalies, leading to an exaggerated SST-precipitation relationship. A detailed examination points to a systematic bias in the thickness of the mixed layer of the ocean model, which needs to be rectified. A too shallow (deep) mixed layer enhances (suppress) the amplitude of the intraseasonal SST anomalies, thereby amplifying (lessening) the ISV and the active-break phases of the monsoon in the model.