Transient Response of the Southern Ocean to Idealized Wind and Thermal Forcing across Different Model Resolutions

The Southern Ocean has undergone significant climate-related changes over recent decades, including intensified westerly winds and increased radiative heating. The interplay between wind-driven cooling and radiative warming of the ocean is complex and remains unresolved. In this study, idealized wind and thermal perturbations are analyzed in a global ocean-sea ice model at two horizontal resolutions: nominally, 1 degrees and 0.1 degrees. The sea surface temperature (SST) response shows a clear transition from a wind-driven cooling phase to a warming phase. This warming transition is largely attributed to meridional and vertical Ekman heat advection, which are both sensitive to model resolution due to the model-dependent components of temperature gradients. At higher model resolution, due to a more accurate representation of near-surface vertical temperature inversion and upward Ekman heat advection around Antarctica, the anomalous SST warming is stronger and develops earlier. The mixed layer depth at midlatitudes initially increases due to a wind-driven increase in Ekman transport of cold dense surface water northward, but then decreases when the thermal forcing drives enhanced surface stratification; both responses are more sensitive at lower model resolution. With the wind intensification, the residual overturning circulation increases less in the 0.1 degrees case because of the adequately resolved eddy compensation. Ocean heat subduction penetrates along more tilted isopycnals in the 1 degrees case, but it orients to follow isopycnal layers in the 0.1 degrees case. These findings have implications for understanding the ocean response to the combined effects of Southern Hemisphere westerly wind changes and anthropogenic warming.

Automated summary

This study analyzed the impact of wind and thermal perturbations in the Southern Ocean, finding that higher resolution models are better at predicting anomalous sea surface temperature warming. Additionally, wind intensification leads to less increase in residual overturning circulation in the higher resolution case, and changes in mixed layer depth due to thermal forcing are more sensitive in lower resolution models.