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Surface Heat Flux Induced by Mesoscale Eddies Cools the Kuroshio-Oyashio Extension Region
January 30,2020

Published in Geophysical Research Letter, 03 January 2020

Sea surface temperature (SST) is a key player in the airsea interaction, influencing storm tracks, atmospheric circulation, and climate modes. Although prevailing theories attribute variations of largescale SST to atmosphere forcing and ocean internal dynamics, we find that sea surface heat flux anomalies induced by mesoscale eddies exert significant influences on the upperocean heat budget in the KuroshioOyashio extension region. Despite making nearly no contribution to the net heat exchange at the airsea interface, the eddyinduced heat flux anomalies weaken the thermal stratification in the upper ocean and result in pronounced sea surface cooling. The underlying dynamics is the efficient dissipation of eddy potential energy by eddyinduced heat flux anomalies. This makes the conversion of eddy potential energy to eddy kinetic energy significantly reduced, corresponding to a weaker eddyinduced restratification flux. The finding complements the existing theories on largescale SST dynamics and has important implications for understanding extratropical climate variability.

Plain Language Summary

Sea surface temperature (SST) plays a fundamental role in the airsea interactions. At large scales (~1,000 km), it is traditionally thought that the atmospheric forcing drives the midlatitude SST variability. At mesoscales (~100 km), it is an oceandriven scenario where pronounced SST anomalies carried by ocean eddies exert an imprint on the atmospheric boundary layer. In this study, we find that such ocean mesoscaleatmosphere (OMEA) interactions have a significant influence on the largescale SST in the KuroshioOyashio extension region, complementing the existing views on the largescale SST dynamics. This is because the eddyinduced heat flux anomalies damp the SST anomalies and thus available potential energy of eddies. Correspondingly, the conversion of eddy available potential energy to kinetic energy is significantly reduced in presence of OMEA interactions, resulting in less heat transported from the subsurface to the surface region.

Fig. SST difference in CTRL and FILT simulations. (a) Time‐mean SST in CTRL minus that in FILT; (b) time‐mean OME‐A EPE feedback measured by TQ|z = 0 (Q is defined positive upward) in CTRL; time‐mean (c) temperature profiles and (d) thermal stratification profiles in CTRL and FILT in the KOE region (denoted by the black boxes in (a) and (b), 36–44°N, 147.5–162°E); time series of (e) temperature and (f) thermal stratification in CTRL minus those in FILT. All values shown here are the ensemble mean and only the values in the last 90‐day model integration are used for the computation of time mean.

Shan, X., Jing, Z., Gan, B., Wu, L., Chang, P., Ma, X., et al. ( 2020). Surface heat flux induced by mesoscale eddies cools the KuroshioOyashio extension region. Geophysical Research Letters, 47, e2019GL086050. https://doi.org/10.1029/2019GL086050


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