Wind increase above warm Agulhas Current eddies

Abstract

Sea surface temperature estimated from the Advanced Microwave Scanning Radiometer E onboard the Aqua satellite and altimetry derived sea level anomalies are used south of the Agulhas Current to identify warm mesoscale eddies presenting a distinct SST perturbation superior to 1 °C to the surrounding ocean. The analysis of 2500 instantaneous charts of equivalent stability neutral wind speed estimates from the SeaWinds scatterometer onboard the QuikScat satellite collocated with sea surface temperature and sea level anomaly show stronger wind speed above warm eddies than surrounding water at all wind directions in about 800 of the 2500 cases. For those cases where the wind is stronger above warm eddies, we do not find any relationship between the increase in surface wind speed and the sea surface temperature perturbation. Sea surface temperature perturbations that we consider range from 1 to 5.5 °C. Sizes of eddies range from 100 to 250 km diameter. Mean background wind speed is about 11 m s−1 with a mean increase above the eddy of 2 m s−1. Wind speed increase of 4 to 7 m s−1 above warm eddies is not uncommon.