Easterly Wave Disturbances over Northeast Brazil: An Observational Analysis

Abstract

This paper aims to identify the circulation associated with Easterly Wave Disturbances (EWDs) that propagate toward the Eastern Northeast Brazil (ENEB) and their impact on the rainfall over ENEB during 2006 and 2007 rainy seasons (April–July). The EWDs identification and trajectory are analyzed using an automatic tracking technique (TracKH). The EWDs circulation patterns and their main features were obtained using the composite technique. To evaluate the TracKH efficiency, a validation was done by comparing the EWDs number tracked against observed cases obtained from an observational analysis. The mean characteristics of EWDs are 5.5-day period, propagation speed of ~9.5 m·s−1, and a 4500 km wavelength. A synoptic analysis shows that between days −2 d and 0 d, the low level winds presented cyclonic relative vorticity and convergence anomalies both in 2006 and 2007. The EWDs signals are strongest at low levels. The EWDs propagation is associated with relative humidity and precipitation positive anomalies and OLR and omega negative anomalies. The EWDs tracks are seen over all ENEB and their lysis occurs between the ENEB and marginally inside the continent. The tracking captured 71% of EWDs in all periods, indicating that an objective analysis is a promising method for EWDs detection.

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.…”

Key Climate Oscillation Factors Controlling Precipitation Variability during the Dry Season in Eastern Northeast Brazil: Study Case of Mundaú and Paraíba Do Meio River Basins

“…Global climate phenomena play an important role over the rainy season variability of ENEB [18,19,30,31]. However, this work has also shown that the periodicity modes of precipitation during the dry season in the ENEB, or more specifically in its central parts, is also affected by large-scale climate factors.…”

“…The NEB is exposed to different spatial-temporal rainfall regimes throughout the year. Precipitation at the Northern NEB (NNEB) is characterized by a rainy season from January to May marked by expressive interannual variability [8,16,18,19], and a dry season from June to December characterized by very low amounts of precipitation (near zero). On the other hand, Eastern NEB (ENEB) has the highest annual average precipitation of the NEB, with a wet season from March to August, is also susceptible to annual variations [20,21], but in a different way than the NNEB, while the ENEB dry season might receive substantial amount of precipitation in some years.Many studies have been conducted in order to analyze and characterize such interannual variability of precipitation in NEB, which, however, were predominantly focused on NNEB rainy season [8,10,17,[22][23][24][25][26].…”

“…There is also a growing interest in understanding the dynamics of the precipitation variability over the ENEB [18,20,[27][28][29][30]. However, most of these are focused on the rainy season of the region, its relationship with Atlantic SST patterns and the occurrence of easterly wave disturbance over the tropical Atlantic [18,19,31]. Nevertheless, the dry season in the ENEB may also exhibit high variabilities in terms of volume precipitated, as seen recently (e.g., 96 mm was precipitated in 2016-2017, and more than 400 mm in 2017-2018), and low-rainfall indices during the dry season of this region may directly impact basic economic activities (i.e., mainly rainfed agriculture) and water supply security.The spatio-temporal evolution of drought episodes during the dry season in the ENEB was recently studied by Costa et al [29].…”

Análise de Métodos de Krigagem na Estimativa da Precipitação no Estado do Rio Grande do Norte (Analysis of Kriging Methods in the Estimation of Rainfall on Rio Grande do Norte State)

“…Além da localização geográfica e efeitos locais, a distribuição espacial heterogênea da precipitação sobre as mesorregiões no estado do RN pode ser explicada pela atuação de sistemas meteorológicos distintos. Como é o caso por exemplo, da mesorregião Leste, que registram os maiores acumulados anuais, em virtude, principalmente, da atuação com maior frequência e intensidade dos fenômenos da brisa marítima, que carrega umidade do oceano para o interior do continente, favorecendo o aumento dos movimentos convectivos (Teixeira, 2008) e dos Distúrbios Ondulatórios de Leste (DOL), que são oscilações nos campos de pressão e vento, e é o principal sistema meteorológico responsável por provocar chuvas no litoral do NEB entre os meses de Maio a Julho (Torres e Ferreira, 2011;Gomes et al, 2015).…”