A Comparison of the Three Upwelling Indices in the South Java Sea Shelf

Abstract

Upwelling plays a crucial role in driving cross-shelf circulation between the continental shelf and boundary currents. It is well known that upwelling results in the exchange of heat, nutrients, fish larvae, and other properties. It controls primary productivity, which promotes higher trophic levels and fisheries. Upwelling can be identified by at least three physical variables: wind, sea surface temperature (SST), and chlorophyll-a (Chl-a). The intensity of upwelling can then be calculated using the Upwelling Index (UI), which is based on these three variables. Wind-based UI (UIET), SST-based UI (UISST), and Chl-a-based UI (UICHL) were calculated using satellite-derived and reanalysis data from 2002 to 2017. Those three UIs were analyzed spatially and temporarily to determine the differences in upwelling strength and duration. The most appropriate UI for explaining the South Java upwelling system in our domain was determined through the correlation analysis. The monthly mean climatology of all UI (UIET, UISST, and UICHL) reveals the seasonal variation, which is high during the southeast (SE) monsoon. The strongest correlation between UISST and Chl-a with the smallest lag times suggested that South Java upwelling in our domain can be identified better using SST-based UI (UISST) than through the Ekman mass transport-based UIET, particularly in the east, relevant to the earlier study.