Heavy Rainfall Episodes in the Eastern Northeast Brazil Linked to Large-Scale Ocean-Atmosphere Conditions in the Tropical Atlantic

Abstract

Relationships between simultaneous occurrences of distinctive atmospheric easterly wave (EW) signatures that cross the south-equatorial Atlantic, intense mesoscale convective systems (lifespan > 2 hour) that propagate westward over the western south-equatorial Atlantic, and subsequent strong rainfall episodes (anomaly > 10 mm·day−1) that occur in eastern Northeast Brazil (ENEB) are investigated. Using a simple diagnostic analysis, twelve cases with EW lifespan ranging between 3 and 8 days and a mean velocity of 8 m·s−1were selected and documented during each rainy season of 2004, 2005, and 2006. These cases, which represent 50% of the total number of strong rainfall episodes and 60% of the rainfall amount over the ENEB, were concomitant with an acceleration of the trade winds over the south-equatorial Atlantic, an excess of moisture transported westward from Africa to America, and a strengthening of the convective activity in the oceanic region close to Brazil. Most of these episodes occurred during positive sea surface temperature anomaly patterns over the entire south-equatorial Atlantic and low-frequency warm conditions within the oceanic mixing layer. A real-time monitoring and the simulation of this ocean-atmosphere relationship could help in forecasting such dramatic rainfall events.

A further analysis of the tropical Atlantic SST modes and their relations to north‐eastern Brazil rainfall during different phases of Atlantic Multidecadal Oscillation

“…Rainfall variability due to the other systems such as the easterly wave disturbances (EWs) and upper tropospheric cyclonic vortices (TCVs) is out of the scope of the present analysis. The EWs affect eastern NEB during austral winter (Yamazaki and Rao, 1977;Kouadio et al, 2012;Hounsou-Gbo et al, 2015) and the TCVs are more common during austral summer and affect most of NEB (Kousky and Gan, 1981).…”

Impacts of the Madden‐Julian oscillation on intraseasonal precipitation over Northeast Brazil

“…When these disturbances propagate toward the eastern NEB they can generate large rainfall amounts specially over the eastern coastal areas (e.g. Gomes et al, 2015;Hounsou-gbo et al, 2015;Kouadio et al, 2012). Rao et al (1993) found that the seasonal variation of the intensity and position of the subtropical high in the South Atlantic Ocean modulates coastal winds during the fall and winter.…”

Dynamical downscaling of the precipitation in Northeast Brazil with a regional climate model during contrasting years

“…The convection activity is most intense in the equatorial western Atlantic region (near eastern coastland of Brazil) in autumn 1999. The convection activity associated with disturbances formed in the west African coastland reached eastern Brazil owing to the intensification of easterly trade winds, as suggested by recent observational studies (Kouadio et al , ). On the other hand, the convection activity is located in the tropical eastern Atlantic region in autumn 1998 (Figure (a)).…”