Summer dry events on synoptic and intraseasonal timescales in the Southeast Region of Brazil

Abstract

Dry events occurring in the Southeast Region of Brazil (SEB) during the summer (rainfall season) have been in evidence in the last years, mainly due to previous extreme events in the 2013/14 and 2014/15 seasons. Drought analyses are usually carried out with monthly data. Here our methodology addresses the issue with daily data in order to generate a thorough analysis. Dry events were evaluated for different homogeneous precipitation sub-regions within the SEB, over 37 December-February (DJF) seasons and with two different timescales of duration: synoptic (5-9 days) and intraseasonal (≥10 days). Two main distinct dynamic patterns were found for dry events in southern and central-northern parts of SEB, respectively, but no major differences were identified for the different timescales of occurrence. Southern events were characterized by a stationary ridge acting over the whole southern South America, making the transient systems approximation to southern SEB difficult. At the same time, this pattern showed a northern-shifted South Atlantic Convergence Zone (SACZ) configuration. In the central-northern events, a high pressure centered between the South and Southeast regions of Brazil was associated with the dryness conditions. An anomalous southward shift of meteorological systems characteristic of the South American summer was also verified for these events. Over the South Atlantic, an opposite SST anomaly configuration was identified between southern and central-northern events.