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1. Introduction
An important question in atmosphere–ocean interaction is how the ocean dynamics, rather than the atmosphere, drive the variability in the sea surface temperature (SST) and air–sea heat exchange. This study characterizes the regime in which oceanic heat advection dominates the mixed layer (ML) heat budget and induces SST anomalies in a semi-idealized framework in the Southern Ocean. The induced SST anomalies subsequently lead to thermal damping by the atmosphere through air–sea heat flux exchange (Liu et al. 1994; Okumura et al. 2001; Small et al. 2008; Kirtman et al. 2012; Bishop et al. 2017; Small et al. 2019). These air–sea heat exchange processes are thus directly linked to oceanic heat advection. This regime corresponds to oceanic mesoscales, which are spatial scales of tens to hundreds of kilometers. Scale at which SST variability transitions from the ocean- to atmosphere-driven regime was found to be around 500 km in Antarctic Circumpolar Current (ACC) region (Bishop et al. 2017; Laurindo et al. 2019; Small et al. 2019). Ma et al. (2016) and Bishop et al. (2020) discussed a thermal damping effect by ocean-driven heat fluxes and demonstrated that underestimating mesoscale air–sea feedback could lead to considerable bias in climate simulations. Since highly variant ML depth (MLD) in the Southern Ocean modulates thermal inertia of the upper ocean, one could expect the MLD to modulate dominant processes in the heat budget as well.
We focus on the Southern Ocean because of its strong currents, strong mesoscale variability, and highly variant MLD. The Southern Ocean has prominent meridional gradients and mostly zonal fronts and currents that extend to considerable depths (Orsi et al. 1995). Mesoscale variability experiences notable changes in zonal direction as well. Mesoscale currents are strong east of the Agulhas region and weak in the Pacific sector. For example, Sallee et al. (2008) showed that eddy diffusivity computed from surface drifters and satellite altimetry observations in the Southern Ocean, peaks in the Agulhas Retroflection current north of the ACC. Therefore, one can expect mesoscale air–sea heat exchange to be stronger in the Indian sector compared to the Pacific sector.
This study links SST anomalies and air–sea heat exchange to three-dimensional heat advection at the ocean mesoscales, while previous efforts have mostly focused on the role of...