Observations of SST-Induced Wind Perturbations in the Leeuwin Current

Sea surface temperature (SST) perturbations modify low-level winds through the influence of air-sea heat flux across the marine atmospheric boundary layer, mostly observable in the major western boundary current systems. In this study, we investigate the effects of SST on surface winds in a poleward-flowing eastern boundary current system, the Leeuwin Current (LC), using the Advanced Very High-Resolution Radiometer (AVHRR) SST and wind data from Cross-Calibrated Multi-Platform (CCMP) during 2009-2018. There exist robust linear relationships between perturbation SST and perturbation wind speed and their derivatives in the LC. The regression slopes between SST perturbations and wind perturbations appear to be higher in austral summer when the alongshore northward winds are strongly opposing the LC, however, the relationships in winter are statistically more robust when the LC and associated cross-shore SST fronts are the strongest. Consistent with previous studies in the western boundary currents, crosswind perturbation wind speed gradient is the largest for the winds 80 degrees (-100 degrees) to the right (left) of the SST gradient in the LC region. The perturbation wind stress curl induced by the SST signature of the LC causes positive wind stress curl anomalies on the offshore edge of the LC, driving anomalous downwelling and would reduce surface chlorophyll a concentrations along the LC SST front as observed in satellite data, which may have implications in regional biogeochemistry. Plain Language Summary The Leeuwin current (LC) is an eastern boundary current of the southern Indian Ocean that flows poleward off the west coast of Australia. This study focuses on the effects of sea surface temperature (SST) associated with the LC on the surface wind field in the region. Observational data are used to analyze the relationships between SST and wind field. The robust relationships between perturbation SST and perturbation wind and their derivatives have seasonal variations. The feedback of the perturbed wind field to the LC is also discussed, that is, the perturbation wind stress curl induces the anomalous downwelling and reduces surface chlorophyll concentration at the offshore edge of the current.

Automated summary

This study investigates the impact of sea surface temperature (SST) on surface winds in the Leeuwin Current (LC) region, revealing robust linear relationships between perturbation SST and perturbation wind speed with seasonal variations. The feedback of perturbed wind stress curl induced by the SST signature of the LC causes anomalous downwelling and reduces surface chlorophyll concentrations, suggesting potential implications in regional biogeochemistry.