Fronts in the Southern Indian Ocean as inferred from satellite sea surface temperature data

Abstract

Sea surface temperature (SST) derived from the weekly measurements made by the Advanced Very High Resolution Radiometers (AVHRR) of NOAA satellites was used to investigate the 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. Monthly SST gradient maps provided an overall view of five basic fronts: the North and South Subtropical fronts (NSTF and SSTF, respectively), the Agulhas Front (AF), the Subantarctic Front (SAF), and the Polar Front (PF). Mean location of the fronts and associated SST and SST gradients with corresponding standard deviations were calculated at each 10°-spaced longitude. A double structure of the NSTF, SAF, and PF was demonstrated as well as the meandering of all fronts with amplitudes of 2–5° in latitude and wavelength of several degrees in longitude. Convergence and transient interaction between neighboring fronts appear to occur not only in the Crozet and Kerguelen regions, but in other regions as well. The mean locations and SST range of every front are in good agreement with previous work based on hydrographic surveys [J. Geophys. Res. 101 (1996) 3675], although some details are different (in particular, the larger zonal extent of the NSTF and the wider frontal SST ranges than previously observed). A good correspondence of the measurements made during two hydrographic surveys in the Kerguelen region (22 January–3 February 1999) and in the Tasmania region (3–22 March 1998) with satellite SST and SST gradient maps was found.