Tropical Atlantic Contributions to Strong Rainfall Variability Along the Northeast Brazilian Coast

D Veleda,B Bourlès,J Servain,G A Hounsou-Gbo,M Araujo

doi:10.1155/2015/902084

Abstract

Tropical Atlantic (TA) Ocean-atmosphere interactions and their contributions to strong variability of rainfall along the Northeast Brazilian (NEB) coast were investigated for the years 1974–2008. The core rainy seasons of March-April and June-July were identified for Fortaleza (northern NEB; NNEB) and Recife (eastern NEB; ENEB), respectively. Lagged linear regressions between sea surface temperature (SST) and pseudo wind stress (PWS) anomalies over the entire TA and strong rainfall anomalies at Fortaleza and Recife show that the rainfall variability of these regions is differentially influenced by the dynamics of the TA. When the Intertropical Convergence Zone is abnormally displaced southward a few months prior to the NNEB rainy season, the associated meridional mode increases humidity and precipitation during the rainy season. Additionally, this study shows predictive effect of SST, meridional PWS, and barrier layer thickness, in the Northwestern equatorial Atlantic, on the NNEB rainfall. The dynamical influence of the TA on the June-July ENEB rainfall variability shows a northwestward-propagating area of strong, positively correlated SST from the southeastern TA to the southwestern Atlantic warm pool (SAWP) offshore of Brazil. Our results also show predictive effect of SST, zonal PWS, and mixed layer depth, in the SAWP, on the ENEB rainfall.

Highlights

The nearly 60 million inhabitants of Northeast Brazil (NEB) are often affected by long periods of drought or by strong rainy episodes that can induce catastrophic floods
The southwestern Atlantic warm pool (SAWP) does not represent the highest correlation of both SSTA and PWSx anomalies to ENEB rainfall, we considered the SAWP for averaging SSTA and PWSx anomalies to examine the time evolution of the zonal mode in the southern tropical Atlantic
Scientific results suggest the remote influence of El Niño/La Niña events on the variability of sea surface temperature (SST) anomalies in the tropical Atlantic, generating conditions of SST and trade winds that influence the southern migration of the intertropical convergence zone (ITCZ) and rainfall

Summary

Introduction

The nearly 60 million inhabitants of Northeast Brazil (NEB) are often affected by long periods of drought or by strong rainy episodes that can induce catastrophic floods. Crossing the south-equatorial Atlantic basin from West Africa to South America [13, 14], atmospheric easterly waves (EWs) are the third regional component of the seasonal rainfall regime over NEB Excess atmospheric moisture transported westward from Africa to South America generates substantial precipitation in ENEB [4] Remote processes, such as those originating from the equatorial Pacific linked to El Niño or La Niña episodes and those from the midlatitudes in the Atlantic Ocean linked to the North Atlantic Oscillation (NAO), are the final external cause of the rainfall variability in NEB.

Surface Meteorological Data

Subsurface Ocean Data

Results

Summary