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

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.

Anomalously large latent heat fluxes in low to moderate wind conditions within the eddy-rich zone of the Northwestern Pacific

“…In relation to air-sea fluxes of TCs over mesoscale eddy feature, Shay and Uhlhorn (2008) report that the ocean heat content (OHC) in the loop current exceeds 100 kJ cm -2 , while, estimated surface enthalpy flux at Isidore's eyewall was 1.8 kW m -2 , where the maximum observed wind was 49 m s -1 , while the maximum estimated surface enthalpy flux during hurricane Lili was 1.4 kW m -2 , associated with peak surface winds of 51 m s -1 . These show that a high surface enthalpy flux over 1 kW m -2 could easily happen during TCs, while a large spatial gradient of LHF anomaly up to 75.7 Wm −2 km −1 was reported due to the submesoscale processes (Song et al, 2022).…”

Observational energy transfers of a spiral cold filament within an anticyclonic eddy

“…After calibration, the accuracies of temperature and conductivity are 0.003°C and 0.003 mS/cm, respectively. As a successful underway measurement, the MVP300 has captured submesoscale processes in many previous studies (e.g., Taylor et al, 2018;Shao et al, 2019;Song et al, 2022).…”

“…These filaments have an enhanced vertical velocity (O (10 -100) m/day; Capet et al, 2008;Ruiz et al, 2019), introduce nutrient-rich deeper water into the surface mixed layer (SML), and influence the primary production (Lehahn et al, 2007) and sea surface temperature through vertical heat transport (Su et al, 2020). Consequently, within cold or warm filaments, the submesoscale process modulates the air-sea heat fluxes (Song et al, 2022), influencing climate variability (Wang et al, 2022).…”

Morphological and optical properties of carbonaceous aerosol particles from ship emissions and biomass burning during a summer cruise measurement in the South China Sea

“…The measurements of solar radiation (SR), temperature (T ), pressure (P ), relative humidity (RH), relative wind direction (RWD), and relative wind speed (RWS) were provided by the automatic weather station (AWS430, Vaisala Inc., Finland) (Song et al, 2022) located on the front deck of the research vessel. This station comprises a range of integrated sensors, including a wind speed and direction sensor (model WMT702), a temperature and humidity sensor (model HMP155), and an atmospheric pressure sensor (model BARO-1).…”