92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Monday, 23 January 2012
Indian Ocean Response to South Tropical Atlantic Teleconnection
Hall E (New Orleans Convention Center )
Rondrotiana Barimalala, Earth System Physics Section, Trieste, Italy; and A. Bracco, F. Kucharski, and A. Crise

The goal of this work is to investigate the effect of the South Tropical Atlantic (STA) teleconnection on the Indian Ocean (IO) interannual variability. A series of recent studies showed that not only the El Nino Southern Oscillation and Indian Ocean Dipole affect the IO variability but also Sea Surface Temperature (SST) anomalies in the STA region modulate the interannual variability of the African and Indian monsoon rainfall, as well as the IO SST. Physically, such teleconnection can be explained by a simple Gill-Matsuno mechanism. Here, with a regional ocean model coupled with the NPZD (Nutrient-Phytoplankton-Zooplankton-Detritus) ecosystem model we analyze the effect of the tropical Atlantic teleconnection on IO circulation and ecosystem variability. Cold (warm) SST anomalies in the tropical Atlantic area trigger strengthening (weakening) of the Somali jet and therefore cold (warm) SST anomalies in the northern IO during boreal summer. Changes in thermocline depth due to upwelling/downwelling favorable winds are found to be the primary causes of SST anomalies in the Findlater jet area, whereas anomalies in surface heat fluxes cause the changes in the eastern Arabian Sea and Bay of Bengal. The shoaling (deepening) of the thermocline is accompanied by an increase (decrease) in phytoplankton concentration by approximately 10 to 25 % of the annual variance that propagates in the surrounding regions through horizontal advection. Overall the physical and biological responses found in this work shows that the STA impact onto the Indian basin, identified in several atmospherical fields in previous in studies using observational data, idealized experiments with atmospheric General Circulation Models and coupled models, extends to the IO circulation and its primary productivity.

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