Anomalies in the atmospheric circulation associated with the rainfall excess or deficit in the Pampa Region in Argentina

Abstract

[1] We have investigated the relationship between extreme anomalies in the monthly precipitation of the Pampa Region (PR), Argentina, and large-scale circulation anomalies over the South American continent and the neighboring oceans. The composite maps of the extreme rainfall anomalies reveal that this atypical behavior extends beyond the PR and that comparable anomalies simultaneously take place in the center and south of Chile and in the western South Atlantic Ocean. We have analyzed the anomalies in the water vapor flux and in the circulation of the lower and upper levels of the troposphere that occurred in 85 months with extreme rainfall anomalies between 1955 and 1998. The study combines the use of a complete set of observed precipitation data and several atmospheric variables from the National Centers for Environmental Prediction Reanalysis. We have found well-defined anomalous circulation patterns that embrace the south of the continent and the vicinity of the Pacific and Atlantic Oceans, which are very similar but of opposite signs for both rainfall extremes. The interaction between these anomalies in the high-level flow and the subtropical jet stream generates the necessary conditions for vorticity advection and flow divergence, which is consistent with the expected vertical motions. The principal component analysis was applied to the pressure anomaly fields to distinguish those aspects of the large-scale patterns that are more directly related with the rainfall extremes. The amplitudes of some of the dominant PC are significantly correlated with the precipitation anomalies, and they highlight the mechanisms leading to rainfall extremes during El Niño-Southern Oscillation, and neutral periods.

Low‐level circulation and precipitation simulated by CMIP5 GCMS over southeastern South America

“…Water vapour sources for southeastern South America rainfall only comes either from the tropical humid continent or from the Atlantic Ocean (Labraga et al, ; Barros et al, ; Saurral et al, ). Moist air from the Pacific Ocean cannot reach this region because of the Andes barrier that from 40°S to the north is higher than the 700 hPa level.…”

Burrowing activity by armadillos in agroecosystems of central Argentina: Biogeography, land use, and rainfall effects

“…Annual rainfall decreases from 1000 mm in the NE to 800 mm in the SW (see Fig. 1C), although inter-annual variability of rainfall is quite frequent in the Pampas with extensive rainfall or drought (Labraga et al, 2002;Scian et al, 2006). According to data provided by the Servicio Meteorológico Nacional of Argentina (SMN, Exp_144540), the first year of our study was considered as a normal period (%800-900 mm, see Fig.…”

Comparison between winter precipitation in southeastern South America during each ENSO phase

“…This area, hereinafter referred as the north region (N), covers the north part of Cuenca del Plata [e.g., Berbery and Collini , 2000]. EN events are also significant rainier than NEU cases in the sector limited by 34°S–39°S and 57°W–63°W, which is a region of very important agricultural and cattle raising production [e.g., Labraga et al , 2002], hereinafter referred as south region (S).…”