Sub‐Mesoscale Wind‐Front Interactions: The Combined Impact of Thermal and Current Feedback

Abstract

Surface ocean temperature and velocity anomalies at meso‐ and sub‐meso‐scales induce wind stress anomalies. These wind‐front interactions, referred to as thermal (TFB) and current (CFB) feedbacks, respectively, have been studied in isolation at mesoscale, yet they have rarely been considered in tandem. Here, we assess the combined influence of TFB and CFB and their relative impact on surface wind stress derivatives. Analyses are based on output from two regions of the Southern Ocean in a coupled simulation with local ocean resolution of 2 km. Considering both TFB and CFB shows regimes of interference, which remain mostly linear down to the simulation resolution. The jointly‐generated wind stress curl anomalies approach 10−5 N m−3, ∼20 times stronger than at mesoscale. The synergy of both feedbacks improves the ability to reconstruct wind stress curl magnitude and structure from both surface vorticity and SST gradients by 12%–37% on average, compared with using either feedback alone.

Observations Reveal Intense Air‐Sea Exchanges Over Submesoscale Ocean Front

“…From the cold side southward across the front within 5 km, surface air temperature (SAT) increases by 4°C, the upward turbulent heat flux (THF; Text S3 in Supporting Information ) increases by 200 W/m 2 , and surface wind speed changes by 3 m/s (Figure 1b and Figures S2a and S2b in Supporting Information ). The sharp cross‐front change in air‐sea flux and surface atmosphere characteristics is in line with previous studies (Bai et al., 2023; Chen et al., 2022). In contrast to these abrupt changes, SLP decreases gradually by only 3 hPa across the front (Figure S2a in Supporting Information ).…”

“…When integrated over the frontal region (39.8°N-40.2°N), the surface heat and moisture fluxes in MesoF are about 20% smaller than SubMesoF. This enhanced air-sea flux above the submesoscale front, consistent with previous studies (Bai et al, 2023;Chen et al, 2022;Strobach et al, 2022), is mainly associated with a stronger vertical mixing (Figure 2c and Figure S6b in Supporting Information S1). Here we take the surface heat flux as an example to explain the reasons.…”

“…Compared to mesoscale fronts, SST varies more abruptly across submesoscale fronts of spatial scales 1–10 km, and could potentially exert stronger impacts on the air‐sea exchange (Bai et al., 2023; Shao et al., 2019) and atmospheric movement (Chen et al., 2022; Sullivan et al., 2020). However, due to the extremely high resolutions required to resolve submesoscale fronts, only recently have studies started examining the role of submesoscale fronts in regulating the overlying atmospheric activities using observations and idealized models.…”