Abstract
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 ∼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°C within a horizontal distance of ∼1.5 km and increases quickly by 0.9°C with a spatial interval of ∼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–2km–1, which is approximately 1.5 times those (1.2 and 59.9 Wm–2km–1) in association with mesoscale eddies. The spectra of LH and SST anomalies show similar peaks at ∼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.
Highlights
The air-sea latent heat flux (LH) is closely associated with sea surface evaporation (E), with a relation of QLH = ρwLeE between them (Yu, 2007), where ρw is the density of seawater and Le is the coefficient for the latent heat of vaporization
LH anomalies with magnitudes of ∼O(10) Wm−2 can be caused by sea surface temperature (SST) anomalies in association with mesoscale eddies
Less attention is devoted to the surface LH anomalies induced by unbalanced submesoscale motions due to the high requirement of spatial and temporal observations
Summary
Where ρa is the air density, cE is the turbulent exchange coefficient, |uz| is the wind speed, and δq = qs − qa represents the air-sea specific humidity difference. Basinscale variations in the LH and analogically air-sea sensible heat flux (SH) can be determined by anomalies in the wind speed and air-sea thermal effects induced by large-scale atmospheric and oceanic oscillations (Cayan, 1992; Yu, 2007; Song and Yu, 2012). High-resolution buoy observations are used to investigate the diurnal variations in the LH over western boundary current systems (Clayson and Edson, 2019), equatorial oceans (Yan et al, 2021) and even coastal seas (Song, 2020), with amplitudes ranging from approximately 10 to 50 Wm−2. The roles of the wind speed (|uz|) and air-sea humidity difference (δq = qs − qa) in contributing to the diurnal variations in the LH depend on the stability of the MABL. Wind (humidity difference) tends to play a predominant role in determining the LH variations under a stable (unstable) MABL
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
