Mesoscale Surface Wind‐SST Coupling in a High‐Resolution CESM Over the KE and ARC Regions

Abstract

A strong positive correlation exists between mesoscale sea surface temperature (SST) and surface wind stress perturbations in the extratropical oceans, which is revealed by high‐resolution satellite but is difficult to be accurately simulated in low‐resolution coupled ocean‐atmosphere models. The extent to which the mesoscale coupling is captured in a high‐resolution Community Earth System Model (CESM‐HR) is assessed in this study, with a focus on two regions, the Kuroshio Extensions (KE) and Agulhas Return Current (ARC), respectively. Compared with satellite observations, it is found that the CESM‐HR can well depict the characteristics of the mesoscale air‐sea coupling, with its strength being comparable to that observed; but in the KE region, the simulated strength is only half of the observed during summer. Mechanisms for the atmospheric responses to mesoscale SST perturbations through the pressure adjustment (PA) and the downward momentum transport (DMT) are analyzed. The results highlight different mechanisms for controlling the atmospheric responses over the KE and ARC regions, which are regionally and seasonally dependent. In the ARC region, pronounced dipole patterns of sea surface pressure (SLP) and vertical velocity perturbation responses indicate that the DMT exerts a dominant effect in both winter and summer. In the KE region, monopole patterns show the main role played by the PA mechanism for the atmospheric adjustment in summer, while dipole patterns indicate the main role played by the DMT mechanism in winter. The weak coupling strength in summer over the KE is closely related to the inadequate parameterization of vertical heat mixing.

The Northern Hemisphere Wintertime Storm Track Simulated in the High‐Resolution Community Earth System Model

“…As shown in the Introduction, changes in absolute SST and SST gradients can significantly affect both the strength and location of storm tracks. Thus, it may be expected that alterations in SST and related air‐sea interactions would be related to the changes in storm tracks (Bryan et al., 2010; Feng et al., 2019), since frontal‐scale and mesoscale ocean‐atmosphere interactions are better represented in HR (Chang et al., 2020; Tang et al., 2021). Note that the observed SST is from ERA5, which is a combination of the UKMet.…”

“…The HR model permits tropical cyclones and ocean mesoscale eddies and presents an improved performance in terms of the mean climate state and interannual variability simulations (Chang et al., 2020). Furthermore, HR can portray well the features of mesoscale air‐sea coupling (Tang et al., 2021). HR and LR simulations make it possible to investigate the impact and benefit of increasing horizontal resolution on the NH storm tracks in CESM.…”

Toward Earth system modeling with resolved clouds and ocean submesoscales on heterogeneous many-core HPCs

“…Previously, we developed the 25 (10) km atmosphere (ocean) HR-ESM (referred to as CESM-HR_sw1.0) based on CESM1.3 on the Sunway TaihuLight HPC system with updates of some dynamic-core and parallelism modules [ 10 , 11 ], which exhibits substantially improved capability in reproducing climate extremes such as marine heatwaves [ 82 ], the Atlantic overturning circulation [ 83 ] and middle-high latitude air–sea interactions [ 84 ]. Making full use of such experiences and the substantially powerful capability of the new Sunway HPC system, we develop the kilometer-level HR coupled model based on CESM version 2 (CESM2) (see Text S2 ).…”

Modulating effect of the divergent and rotational wind induced by mesoscale sea surface temperature perturbations in the Kuroshio Extension

“…Mesoscale coupled sea surface temperature (SST) and wind stress perturbations are observed in the Kuroshio Extension and other areas of western boundary current extension (Chelton et al, 2004; Maloney & Chelton, 2006; Xie, 2004). SST perturbations influenced atmospheric perturbations by means of downward momentum transport and horizontal pressure adjustment (e.g., Chelton, 2013; Frenger et al, 2013; Gao et al, 2019; Lindzen & Nigam, 1987; Minobe et al, 2008; Tang et al, 2021; Wallace et al, 1989; Xie, 2004). The induced wind stress perturbations then have a feedback effect on the ocean by influencing air–sea heat and momentum fluxes (e.g., Wei et al, 2017).…”