Oceanic fronts in the southern Indian Ocean as inferred from the NOAA SST, TOPEX/Poseidon and ERS-2 altimetry data

Abstract

Weekly NODS/MCSST (the NASA Ocean Data System/Multi-Channel Sea Surface Temperature) dataset was used to investigate detailed structure and space-time variability of large-scale fronts in the Southern Indian Ocean (30°60°S and 20°150°E) during the period of 1997-1999. The constructed SST gradient maps for 36 mid-month weeks gave simultaneous viewing of five basic fronts in the whole basin: the North and South Subtropical fronts, the Agulhas Front, the Subantarctic Front, and the Polar Front. Mean location, SST and SST gradients with corresponding standard deviations were calculated for every front at each 10°-spaced longitude. SST gradient maps and charts of sea level anomalies (SLA) based on the combined altimetry data from the TOPEX/Poseidon and ERS-2 satellites, as well as corresponding charts of sea surface dynamic heights (constructed by the superposition of SLA distributions over the climatic dynamic topography), were used to study mesoscale variability related to the fronts. The analysis allowed to distinguish zones of enhanced meandering (eddy formation) with amplitudes of 2°-5° in latitude and wavelength of several degrees in longitude, and their relationship with bottom topography peculiarities. Double structure of fronts and close approach of neighboring fronts appear in different areas of the basin