Synoptic patterns associated with extreme precipitation events over southeastern South America during spring and summer seasons

Abstract

This study focuses on characterizing the diversity of synoptic forcing precursors of extreme precipitation events in southeastern South America (SESA) during the warm season, as well as identifying the differences in the synoptic environment during spring (October-November-December) and summer (January-February-March). The characterization of extreme events was carried out using daily precipitation data from the CPC gridded dataset for the period 1979-2017. Extreme events were defined when the daily precipitation exceeds the 95th percentile of the daily rainy days and covers a minimum area of 100 km 2 . During the spring months extremes are more intense and are preferably located over the central and eastern part of SESA, while during the summer they occur towards the west and south of SESA. The associated synoptic conditions were identified after applying a principal component analysis to the 850 hPa geopotential height for extreme precipitation days using the ERA-Interim reanalysis. Two distinctive patterns for each season were identified. The anomalous intense wind with a northerly component and a negative geopotential height anomaly over northwestern Argentina emerged as the most common features associated with the occurrence of extreme events. Differences between the two patterns emerge in terms of the southward penetration of the northerly wind and the anomalous circulation off the east coast of South America. A high-level jet was detected in both patterns, although a weaker core and located in a position further south is found for the second pattern compared with the first one. Differences in the synoptic forcing features between spring and summer, such as a more intense low-level northerly wind, a deeper northwestern low, a more intense upper-level jet stream and a more extended area of maximum upper-level wind divergence during spring compared with summer, may explain the differences found in the extreme precipitation in SESA for the two seasons.

Influence of Eastern, Central and Mix El Niño on the variability of rainfall in southeastern South America

“…This configuration and the coupling of the subtropical jet and the SALLJ can intensify extratropical cyclones, cold fronts and mesoscale convective systems in the region, as pointed out by Silva Dias (1987) and Tedeschi et al (2013). Furthermore, according to Martinez and Solman (2022), the strengthening of the subtropical jet is associated with extreme precipitation events in southeastern SA, which is consistent with the rainfall patterns found for EP El Niño, especially in spring and summer (Figures 5D, G). Silva and Ambrizzi (2006) emphasize that in strong EN, the SALLJ compounds follow a path slightly positioned south of the climatological circulation, with the maximum jet over northern Argentina, Paraguay and southern Brazil, as can be seen, above all, in SON (0) and D (0) JF (+1) (Figures 6D, G).…”

South American Monsoon Lifecycle Projected by Statistical Downscaling with CMIP6-GCMs

“…The CPC has a daily frequency and horizontal resolution of 0.5 • (available at https://ftp.cpc.ncep.noaa.gov/ precip/CPC_UNI_PRCP/GAUGE_GLB/RT/, accessed on 22 January 2022). It is developed through rain gauge observations and has been applied in several studies in SA [40,[45][46][47]. In this study, the period from 1995 to 2014 is used.…”

The Role of the Subtropical and Extratropical Southern Hemisphere Anomalous Sea Surface Temperature in the Trans‐Seasonal Influence of Southern Annular Mode on Rainfall Over Southeastern South America

“…The southeastern South America (SESA) region, encompassing Uruguay, Paraguay, northwestern Argentina and southern Brazil, has been regarded as one of the few subtropical regions impacted by climate change (Gonzalez et al., 2014). This has been associated with numerous climate‐related disasters, such as bushfires, floods, and drought, that have significant environmental and socio‐economic impacts (Holz et al., 2017; Mariani et al., 2018; Martinez & Solman, 2022; Podestá et al., 2002; Vörösmarty et al., 2013). Additionally, SESA exhibits considerable rainfall variability across different spatial and temporal timescales (Marengo et al., 2012; Vásquez et al., 2018).…”