INTERANNUAL RAINFALL VARIABILITY IN NORTHEAST BRAZIL - OBSERVATION AND MODEL SIMULATION

The relationship between interannual variability of rainfall in north- east Brazil and tropical sea-surface temperature is studied using obse rvations and model simulations. The simulated precipitation is the ave rage of seven independent realizations performed using the Laboratoire de Meteorologie Dynamique atmospheric general model forced by the 197 0-1988 observed sea-surface temperature. The model reproduces very wel l the rainfall anomalies (correlation of 0 . 91 between observed and m odelled anomalies). The study confirms that precipitation in north-eas t Brazil is highly correlated to the sea-surface temperature in the tr opical Atlantic and Pacific oceans. Using the singular value decomposi tion method we find that Nordeste rainfall is modulated by two indepen dent oscillations, both governed by the Atlantic dipole, but one invol ving only the Pacific, the other one having a period of about 10 years . Correlations between precipitation in north-east Brazil during Febru ary-May and the sea-surface temperature 6 months earlier indicate that both modes are essential to estimate the quality of the rainy season.