Ocean-atmosphere processes and easterly waves in the generation and development of extreme events in the Eastern Northeast of Brazil

Abstract

The coupled ocean-atmosphere wave and sediments transport (COAWST) model was used to simulate periods with intense rainfalls events at the eastern Northeast Brazil (ENEB). The simulations aimed to investigate the ocean-atmospheric interaction under Easterlies Waves Disturbances (EWD) conditions, which lead to intense rainfalls events over the ENEB. In June 2010 the sea surface temperature (SST) was warmer than 28.5 ºC, in the western tropical South Atlantic (WTSA), with persistent anomalies above 1 ºC, characterizing a southern Atlantic warm pool (SAWP). The sensible and latent heat fluxes acted to moisten the lower troposphere and affect the height of trade winds inversion layer (TWIL). The meteorological system, that occurred in low to medium levels during the period, favored the weakening, even to a break of the TWIL. These atmospheric disturbances were associated to convergence, cyclonic vorticity and upward water vapor motion to the medium troposphere levels. The disturbances when reached the ENEB coast, favored the convection and the intense rainfall over the region. The vertical structure of Marine Atmospheric Boundary Layer (MABL) was a key factor to triggering the occurrence of these synoptic activities with a deep convection. The sea-air interaction is important for understanding the climatic variability, due to heat, momentum and moisture exchange. Therefore the SAWP region is an important region to increasing meteorological systems over ENEB leading the variability and intense episodes of rainfall. In this work it was performed experiments with theWeather Research and Forecasting (WRF) and Regional Oceanic Model System (ROMS) in a two-way coupled mode. The goal was verify the improvements of coupled models in forecasting and characterizing the interactions between the ocean-atmosphere dynamics under diferente SAWP conditions which led intense rainfalls at the ENEB. The results evidenced the importance of the application of ocean-atmosphere coupled models in forecasting improvement compared to only atmospheric models, also the SAWP presented direct influence in the ENEB intense rainfall.