Anomalous patterns of SST and moisture sources in the South Atlantic Ocean associated with dry events in southeastern Brazil

Abstract

This paper examines the distributions of anomalies of sea surface temperature (SST) and of the moisture sources in the South Atlantic Ocean during extreme dry events in southeastern Brazil in the austral autumn, winter and spring for the period 1982-2009. The extreme dry events were identified based on a combination in which consecutive dry days and variable percentiles were considered in five homogeneous regions in terms of precipitation in southeastern Brazil, as defined through cluster analysis. Composites of anomalies of SST and moisture sources for the dry events selected for the different homogeneous regions show specific characteristics for each region, but some similarities were apparent for the southern and northern parts of southeast Brazil. During spring in all regions, and during autumn and winter in the southern regions, a tripole pattern of SST anomalies was found (negative, positive and negative), together with an anomalous anticyclonic circulation in the Atlantic Ocean transporting moisture to southern Brazil associated with positive SST anomalies. A decrease in the climatological moisture sources in the south of Brazil then ensues, and dry conditions prevail in the regions of interest. In winter and autumn in the northern regions, the same tripole pattern of SST anomalies was also found, but shifted northwards. An anomalous cyclone is associated with the negative SST anomalies, and the climatological moisture sources to the northeast of Brazil reduce their contribution to the region of interest, where negative precipitation anomalies are registered. It seems that the events selected show the results of reductions both in terms of the availability of moisture and in atmospheric instability.

The Atmospheric Branch of the Hydrological Cycle over the Negro and Madeira River Basins in the Amazon Region

“…Figure 9 shows that the dry conditions simultaneously affected both basins after 2014 and hence the time coincidence of the May 2015-March 2016 and August 2015-July 2016 episodes in the NRB and MRB. Pampuch et al [108] examined the distributions of anomalies of SST and of the moisture sources in the South Atlantic Ocean during extreme dry events in southeastern Brazil. However, these authors did not quantify the anomalies in the moisture contribution to the target regions.…”

Contribution of water-limited ecoregions to their own supply of rainfall

“…The Lagrangian particle dispersion model FLEXPART v9.0 (Stohl et al 1998, Seibert andFrank 2004) is used to trace water vapour trajectories and quantify moisture sources. FLEXPART is here constrained by wind and specific humidity data from ERA-Interim, as in recent applications of the model dedicated to investigate water vapour trajectories , Pampuch et al 2016. The atmosphere is divided into two million air particles that are moved by 3D winds.…”

“…Figure 4(d) uses reanalysis data (Dee et al 2011) of 500 hPa vertical wind velocity anomalies (ω′) to investigate mean synoptic stability-see e.g. Pampuch et al (2016), Gimeno et al (2010b)-and anomalies in CAPE to investigate mean convective stability-see e.g. Taylor and Ellis (2006), Johnson and Xie (2010).…”

Climatology and Trend of Severe Drought Events in the State of Sao Paulo, Brazil, during the 20th Century

“…The study of long-term drought variability and the atmospheric patterns that lead to a lack of precipitation may depend on atmospheric and oceanic reanalyses. Studying droughts over a long time span is important to identify the low frequency atmospheric variability associated with these phenomena in a complex subtropical region [22] and also to assess trends, which determines regional impacts of climatic changes [23].…”