Surface Heat Flux Induced by Mesoscale Eddies Cools the Kuroshio-Oyashio Extension Region
Published in Geophysical Research Letter, 03 January 2020
Sea surface temperature (SST) is a key player in the air‐sea interaction, influencing storm tracks, atmospheric circulation, and climate modes. Although prevailing theories attribute variations of large‐scale 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 upper‐ocean heat budget in the Kuroshio‐Oyashio extension region. Despite making nearly no contribution to the net heat exchange at the air‐sea interface, the eddy‐induced 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 eddy‐induced heat flux anomalies. This makes the conversion of eddy potential energy to eddy kinetic energy significantly reduced, corresponding to a weaker eddy‐induced restratification flux. The finding complements the existing theories on large‐scale SST dynamics and has important implications for understanding extratropical climate variability.
Plain Language Summary
Sea surface temperature (SST) plays a fundamental role in the air‐sea 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 ocean‐driven 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 mesoscale‐atmosphere (OME‐A) interactions have a significant influence on the large‐scale SST in the Kuroshio‐Oyashio extension region, complementing the existing views on the large‐scale SST dynamics. This is because the eddy‐induced 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 OME‐A 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 −T′Q′|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 Kuroshio‐Oyashio extension region. Geophysical Research Letters, 47, e2019GL086050. https://doi.org/10.1029/2019GL086050