Does regional air–sea coupling improve the simulation of the summer monsoon over the western North Pacific in the WRF4 model?

ABSTRACT

A new regional coupled ocean–atmosphere model, WRF4-LICOM, was used to investigate the impacts of regional air–sea coupling on the simulation of the western North Pacific summer monsoon (WNPSM), with a focus on the normal WNPSM year 2005. Compared to WRF4, WRF4-LICOM improved the simulation of the summer mean monsoon rainfall, circulations, sea surface net heat fluxes, and propagations of the daily rainband over the WNP. The major differences between the models were found over the northern South China Sea and east of the Philippines. The warmer SST reduced the gross moist stability of the atmosphere and increased the upward latent heat flux, and then drove local ascending anomalies, which led to the increase of rainfall in WRF4-LICOM. The resultant enhanced atmospheric heating drove a low-level anomalous cyclone to its northwest, which reduced the simulated circulation biases in the stand-alone WRF4 model. The local observed daily SST over the WNP was a response to the overlying summer monsoon. In the WRF4 model, the modeled atmosphere exhibited passive response to the underlying daily SST anomalies. With the inclusion of regional air–sea coupling, the simulated daily SST–rainfall relationship was significantly improved. WRF4-LICOM is recommended for future dynamical downscaling of simulations and projections over this region.

Graphical abstract

摘要

利用新的区域海气耦合模式WRF4-LICOM研究了海气耦合过程对西北太平洋夏季风模拟的影响。研究表明, 耦合模式改进了非耦合模式模拟的西北太平洋夏季平均降水, 环流, 海表净热通量和夏季雨带的南北移动。耦合与非耦合模式的差异主要在南海北部及菲律宾岛以东地区。耦合模式里更暖的海温减弱了大气的总体湿稳定度, 增强了向上的潜热通量, 导致局地异常上升运动, 使得局地降水增加。进一步分析表明, 海气耦合过程明显改进了日平均SST-降水的相关关系。因此, 未来针对该区域气候变化模拟和预估动力降尺度建议采用区域耦合模式。

KEYWORDS:

• Regional coupled ocean–atmosphere model
• regional climate model
• western North Pacific summer monsoon
• regional air–sea interactions

关键词:

• 区域海气耦合模式
• 区域气候模式
• 西北太平洋夏季风
• 海气耦合过程

Acknowledgments

The comments from the two anonymous reviewers are greatly appreciated.

Disclosure statement

No potential conflict of interest was reported by the author.

Supplementary material

Supplemental data for this article can be accessed here.

Additional information

Funding

This work was jointly supported by the National Natural Science Foundation of China [grant number 41875132] and The National Key Research and Development Program of China [grant number 2018YFA0606003].