Relative dominance of wind stress curl and Ekman transport on coastal upwelling during summer monsoon in the southeastern Arabian Sea

Abstract

Coastal upwelling in the south eastern Arabian Sea (SEAS) that occurs and intensifies during the summer monsoon season (June–September) is assessed in terms of alongshore wind stress and its curl using ECMWF reanalysis (ERA 5) winds for the period 2016–2020. Critical role of wind stress curl and its spatio-temporal variability, with advancing monsoon in modulating upwelling along the coast, is studied using Ekman pumping and vertical velocities integrated from coast to offshore boundary of positive curl. From the analysis it is observed that the Ekman transport dominates the southern part of the region while Ekman pumping is stronger for the northern section of the study area. This study also helps to delineate the offshore extent of upwelling throughout the monsoon season with a strong yet narrow zone hugging the coast during July/August (peak monsoon) while a broad and diffused upwelling zone for the rest of the season. This spatio-temporal variability in coastal upwelling is dominated by wind stress curl and its significance was not yet explored well for the SEAS region. From the analysis, 2016 was observed to be strong upwelling, while 2019 was the weakest upwelling season as inferred from data on wind, sea surface temperature, sea level anomaly and chlorophyll-a concentration.