Interannual and Intraseasonal Variations of the Onset and Demise of the Pre-Wet Season and the Wet Season in the Northern Northeast Brazil

Abstract

The Northern Northeast Brazil (NNB) has two rainy periods, namely Pre-Wet Season (PWS) and Wet Season (WES), which are usually treated as one system. The precipitation pattern on NNB is influenced by sea surface temperature (SST) anomalies in the Atlantic and Pacific Ocean on interannual timescales particularly by the Interhemispheric Gradient of SST anomalies (IGS) and El Niño Southern Oscillation (ENSO). On intraseasonal time scales, the MJO is especially important. This study investigates the variability of the PWS/WES. The PWS is largely associated with the development of the South America Monsoon System and South Atlantic Convergence Zone (SAMS/SACZ); the onset is depicted by incursion of the SAMS/SACZ northward. Anomalous atmospheric cyclonic circulation over the southeastern Brazil along with easterlies over the northern Tropical Atlantic marks the early onset of the PWS, while easterlies over the southern Tropical Atlantic are related to late onset episodes. The demise of the PWS is significantly associated with propagation of the MJO, specifically during phases 4-5 of the MJO lifecycle. A Rossby wave train in 200-hPa geopotential height with positive anomalies over central-southern Brazil is depicted during transition between PWS and WES.

Influence of the modes of climate variability in the Tropical Pacific and Atlantic on accumulated rainfall and reservoir water volumes in the Northeast Brazil

“…When the position of this system is shifted abnormally south a few months before the onset of the wet season in the northern NEB, the meridional TSA mode increases moisture transport and rainfall during the wet months (Hounsou‐Gbo et al ., 2015). At the interannual and intraseasonal scales, the influence is associated with the occurrence of El Niño episodes and the Madden‐Julian Oscillation (MJO), respectively (Vasconcelos Junior et al ., 2018). At the intraseasonal time scale, the Southern Semiarid region is influenced by the interaction between the South Atlantic Convergence Zone (SACZ), the Bolivian High (BH) and UTCV.…”

Impacts of the Madden‐Julian Oscillation on the intensity and spatial extent of heavy precipitation events in northern Northeast Brazil

“…Vasconcelos Jr et al (Vasconcelos Junior et al, 2018) showed that the precipitation variability over the NNB varies considerably during the PWS (NDJ) and WES F I G U R E 2 Composites of filtered OLR anomalies during MJO life cycle. Light (dark) grey depicts positive (negative) anomalies.…”

“…Vasconcelos Jr et al (Vasconcelos Junior et al ., 2018) showed that the precipitation variability over the NNB varies considerably during the PWS (NDJ) and WES (FMAM) periods. Figure 5 shows monthly proportions of CEPE occurrences for the two types of thresholds.…”

“…The analysis was performed for the period 1‐Nov May 31, 1979–2010, this period was considered because it presents a greater amount of valid data and density of stations. Based on the study of Vasconcelos Jr et al (Vasconcelos Junior et al ., 2018), the period from November to January refers to PWS, whereas the period from February to May refers to WES.…”

“…The Intertropical Convergence Zone (ITCZ) is the main contributor to this climatic feature (Hastenrath and Lamb, 1978). In addition, a short rainfall period, called the Pre‐Wet Season (PWS), occurs from November to January (Brito and Nobre, 1991; Vasconcelos Junior et al ., 2018). Upper level cyclonic vortices and cold front incursions are the main atmospheric systems controlling the variability of the WES (Kousky, 1979; Kousky and Alonso Gan, 1981).…”