Circulação atmosférica associada aos extremos secos e chuvosos em Uberlândia - MG

Abstract

The occurrence of extreme rainfall events negatively impacts society in social, economical and environmental terms. Therefore, the objective of this study is to detect the patterns of atmospheric circulation linked to the occurrence of dry and rainy extreme events in the city of Uberlandia, MG, from 1980 to 2015, in the summer (December, January and February) and winter (June, July and August) months. The monthly time series of atmospheric and surface samples were obtained from ERA-Interim (ECMWF Data Server), NCEP/NCAR (NOAAESRL) reanalyses and Xavier, King and Scanlon (2017) rainfall dataset. For the determination of dry and rainy extreme events, the percentile procedure was used (10% for dry extremes and 90% for rainy extremes) and for the analysis of atmospheric patterns, the compositions method was used, using the Open GrADs software. The results show that during the dry extreme events in Uberlandia-MG there is the strengthening of the South Atlantic Subtropical Anticyclone (SASA) played a relevant role in all the months analyzed. In the summer months, the Intertropical Convergence Zone (ITCZ) moved northwards is associated with the suppression and/or weakening of the South Atlantic Convergence Zone (SACZ), the weakening of the subtropical jet (January and February) and the weakening of the southern branch and strengthening of the northern branch of the polar jet (December). In the winter months the subtropical jet presents weakening (June and July), associated with a strengthening of the polar jet (June) or strengthening of the northern branch and weakening of the southern branch (July), tripole pattern of the Sea Surface Temperature in the South Atlantic (June), strengthening of the SASA (the whole system in June, west branch in July and northwest branch in August), a weakening of the North Atlantic Subtropical Anticyclone (August), displacement and/or maintenance of the ITCZ to the north (July and August), in agreement with heating in the tropical North Atlantic and the cooling on the tropical South Atlantic (July and August). Concerning the extreme rainy events in Uberlandia-MG, in the summer months the SACZ presents intensification (January and February), associated to the strengthening of the polar jet and the weakening of the subtropical jet, to an anomalous ridge over the South Atlantic located in the south (January) or southwest (February), and to an anomalous ridge over the South region and part of the Southeast and Center-West regions of the country (February). In the winter months, the subtropical jet is strengthened (July and August), associated with a weakening of the polar jet and the SASA (August). Teleconnection patterns associated with the occurrence of extreme rainy events are indicated in practically every month analyzed. It is hopefully that this work could help in the studies of atmospheric circulation patterns that are associated to extreme rainfall events in the Southeast of Brazil. The comprehension about the origin of these events can help in the decision making and planning of institutional/governmental actions in order to mitigate or even to avoid the socio-economical and environmental effects resulting from their occurrence.