Timescales of Atmosphere-Ocean Interaction in the Southern Ocean

Abstract:

The Southern Ocean is an important region of the global ocean, exerting a strong influence on carbon uptake, global overturning formation, and heat exchange. Improving our understanding of the effects that upper ocean processes have on the overlying atmosphere will enhance our predictive understanding of climate variability and change. Recent studies have focused on the space-scale dependence of the lagged correlation between sea surface temperature (SST) and turbulent heat flux (Q). We focus here on the time-scale dependence in different dynamical regions of the Southern Ocean.

We perform an analysis of satellite data from 1993-2019 with one-degree spatial resolution and varying temporal resolution. We examine the observed lagged-correlation relationships between SST or SSH (sea surface height) and Q on monthly, interannual, and seasonal timescales to determine which process drives air-sea heat exchange. Variations in SSH are used as a proxy for upper ocean heat content variations. From these correlations we define SST-Q feedback and SSH-Q feedback, which estimate the strength of atmospheric feedback to SST anomalies and to upper ocean heat content, respectively. We also define an effective depth of air-sea interaction (H) as the ratio of SSH-Q and SST-Q feedbacks scaled by the thermal expansion coefficient. A comparison of H to the maximum mixed-layer depth demonstrates the relative role of oceanic and atmospheric processes in renewing upper ocean heat content variations. When comparing the frequency spectra of SSH and SST, we find that SSH exhibits a steeper high-frequency falloff than SST, and find strong coherence between the two fields at a frequency of one year. We combine these two analyses to investigate the time-scale dependence of H in different dynamical regimes in the Southern Ocean.