气候变化领域集成服务门户(CCPortal): Impact of the Benguela coastal low-level jet on the southeast tropical Atlantic SST bias in a regional ocean model

CCPortal

DOI	10.1007/s00382-020-05616-5
	Impact of the Benguela coastal low-level jet on the southeast tropical Atlantic SST bias in a regional ocean model
	Kurian J.; Li P.; Chang P.; Patricola C.M.; Small J.
发表日期	2021
ISSN	0930-7575
起始页码	727
结束页码	748
卷号	56 期号:2021-09-10
英文摘要	The current generation of coupled ocean–atmosphere climate models, which are widely used for studying the dynamics of the climate system and to make projections of future climate, suffers from erroneously warm (exceeding 5 °C) sea surface temperature (SST) simulation in the eastern boundary upwelling systems (EBUS) in the Atlantic and Pacific oceans. While recent improvements in the horizontal resolution of coupled model components helped to alleviate this issue in the North and South Pacific and North Atlantic oceans, the warm bias in the Southeast Tropical Atlantic (SETA) region still remains above 5 °C. Recent studies have highlighted the importance of inaccuracies in the near-coastal winds, especially in the Benguela low-level coastal jet (BLLCJ), in the formation of this warm SST bias. In addition, unique ocean circulation features like the poleward flowing coastal current and the presence of a strong coastal SST front were argued to contribute to the complexity in simulating realistic SST in the SETA region. In this study, we investigate how ocean model resolution and the spatial structure and strength of the BLLCJ affect the SST warm bias in the SETA. We conducted a suite of ocean model experiments with varying horizontal resolutions (81–3 km) and different atmospheric forcing products. We found that the accuracy in the magnitude of BLLCJ’s alongshore component and in the spatial structure of BLLCJ are the primary factors in reducing the warm SST bias in SETA and the ocean model horizontal resolution is of only secondary importance. A weaker alongshore component of the BLLCJ leads to a weaker upwelling through Ekman transport and fails to generate a downwind equatorward surface jet in the ocean. When the core of the BLLCJ is too far offshore, the broad wind stress curl zone gives rise to anomalous poleward depth integrated flow through Sverdrup balance and weakens the wind stress curl induced Ekman pumping near the coast. Both the presence of a poleward current, which can transport warm equatorial waters farther south, and the absence of the equatorward surface jet contributes to the warm SST bias. Heat budget analysis shows that the contribution from the anomalous poleward flow is a bigger contributor to the warm bias than the weak upwelling. With more realistic, high-resolution winds, an ocean model resolution increase from 27 to 9 km slightly reduces the extent and magnitude of SST bias. However, no such improvement occurs with coarse resolution less realistic winds. Sensitivity experiments using atmospheric forcing fields from different sources confirm that the major contribution to the warm SST bias is in fact from the erroneous winds rather than other atmospheric forcing fields like net shortwave and downward longwave radiation. Further studies are needed to understand whether eddy heat advection or mean flow heat advection primarily cause the warm SST bias. © 2021, The Author(s), under exclusive licence to Springer-Verlag GmbH, DE part of Springer Nature.
英文关键词	Angola-Benguela front; Benguela low-level jet; Coupled model SST bias; Ekman pumping and divergence; Sverdrup balance; Upwelling
来源期刊	Climate Dynamics
文献类型	期刊论文
条目标识符	http://gcip.llas.ac.cn/handle/2XKMVOVA/183284
作者单位	Department of Oceanography, Texas A&M University, College Station, TX, United States; International Laboratory for High-Resolution Earth System Prediction, Texas A&M University, College Station, TX, United States; Department of Atmospheric Sciences, Texas A&M University, College Station, TX, United States; Climate and Ecosystem Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA, United States; Climate and Global Dynamics Division, National Center for Atmospheric Research, Boulder, CO, United States
推荐引用方式 GB/T 7714	Kurian J.,Li P.,Chang P.,et al. Impact of the Benguela coastal low-level jet on the southeast tropical Atlantic SST bias in a regional ocean model[J],2021,56(2021-09-10).
APA	Kurian J.,Li P.,Chang P.,Patricola C.M.,&Small J..(2021).Impact of the Benguela coastal low-level jet on the southeast tropical Atlantic SST bias in a regional ocean model.Climate Dynamics,56(2021-09-10).
MLA	Kurian J.,et al."Impact of the Benguela coastal low-level jet on the southeast tropical Atlantic SST bias in a regional ocean model".Climate Dynamics 56.2021-09-10(2021).