Air-Sea Latent Heat Flux Anomalies Induced by Oceanic Submesoscale Processes: An Observational Case Study

The classical theory predicts that a geostrophically balanced mesoscale eddy can cause a sea surface temperature (SST) anomaly related to Ekman pumping. Previous studies show that an eddy-induced SST anomaly can result in a sea surface latent heat flux (LH) anomaly at a maximum magnitude of similar to O(10) Wm(-2), decaying radially outward from the center to the margin. In this study, we investigate the LH anomalies associated with submesoscale processes within a cyclonic eddy for the first time using recent satellite-ship-coordinated air-sea observations in the South China Sea. Unbalanced submesoscale features can be identified as submesoscale SST fronts. Along the ship track, the SST strikingly decreases by 0.5 degrees C within a horizontal distance of similar to 1.5 km and increases quickly by 0.9 degrees C with a spatial interval of similar to 3.6 km. The along-track SST is decomposed into three parts: large-scale south-north fronts and anomalies induced by mesoscale and submesoscale motions. Our analysis shows that the amplitude of the LH anomaly induced by the mesoscale SST anomaly is 12.3 Wm(-2), while it is 14.3 Wm(-2) by unbalanced submesoscale motions. The mean (maximum) spatial gradient of the submesoscale LH anomalies is 1.7 (75.7) Wm(-2)km(-1), which is approximately 1.5 times those (1.2 and 59.9 Wm(-2)km(-1)) in association with mesoscale eddies. The spectra of LH and SST anomalies show similar peaks at similar to 15 km before sloping down with a power law between k(-2) and k(-3), indicating the underlying relationship between the LH variance and submesoscale processes.

Automated summary

This study investigates the latent heat flux (LH) anomalies associated with submesoscale processes in a cyclonic eddy using recent satellite-ship-coordinated air-sea observations. Unbalanced submesoscale features are identified as submesoscale SST fronts. The results show that these submesoscale fronts induce larger LH anomalies than mesoscale eddies and have a higher spatial gradient.