Tropical Atlantic rainfall variations during boreal summer (June-July-August (JJA)) are quantified by means of a 28-year (1979-2006) monthly precipitation dataset from the Global Precipitation Climatology Project (GPCP). Rainfall variability during boreal spring (March-April-May (MAM)) is also examined for comparison in that the most intense interannual variability is usually observed during this season. Comparable variabilities in the Atlantic maritime intertropical convergence zone (ITCZ) (15 Β°-35 Β°W) strength (P ITCZ ) are found during both seasons. Variations in the ITCZ's latitudinal location (Lat ITCZ ) during JJA, however, are much weaker than during MAM.
P ITCZ and Lat ITCZ are shown to be closely associated with sea surface temperature (SST) anomalies in both the tropical Atlantic and Pacific. Within the tropical Atlantic, the Atlantic NiΓ±o events (Atl3) and SST anomalies in the tropical North Atlantic (TNA) are the two major local factors modulating surface rainfall patterns and variations. Atl3 is significantly correlated with P ITCZ and Lat ITCZ during JJA and MAM. TNA is significantly correlated to P ITCZ during JJA but not to Lat ITCZ . In contrast, TNA is significantly correlated to Lat ITCZ during MAM but its correlation with P ITCZ is weak.
The impact of the El NiΓ±o-Southern Oscillation (ENSO) events (Nino3.4) is observed during both seasons, while the correlation between Nino3.4 and Lat ITCZ is slightly weak. However, with the effects of Atl3 and TNA removed, the ENSO tends to have a quite limited direct impact on the tropical Atlantic, specifically over the open ocean. High second-order partial correlation between Nino3.4 and rainfall is generally confined to the western basin and over the northeastern South America. Therefore, during JJA, the two local SST modes are of dominance for the tropical Atlantic rainfall variability. Nevertheless, the ENSO seems to still play an active role in modulating surface zonal wind anomalies in the western basin and then the Atlantic NiΓ±o mode.