Sea ice concentration variability over the Southern Ocean and its impact on precipitation in southeastern South America

Abstract

This paper quantifies the relationship between sea ice cover (SIC) on the Southern Ocean precipitation and river discharges over southeastern and eastern South America. The period of analysis covers from 1981 to 2008 and includes monthly mean data of SIC over the Ross, Amundsen-Bellingshausen and Weddell Seas, atmospheric variables and discharges of selected river in eastern South America. To isolate the effect of known modes of climate variability on SIC, the signals of El Nino-Southern Oscillation and the Southern Annual Mode are removed from all time series through regression analysis. Composites of precipitation differences over South America reveal a pattern of enhanced rainfall activity over the South Atlantic Convergence Zone (SACZ) in summer (JFM) when SIC is above average particularly over the Weddell Sea area, while winter (ASO) SIC anomalies show negative and significant correlations with rainfall over much of South America. Moisture fluxes patterns in summer reveal increased moisture transport towards the SACZ region and decreased low-level jet activity (and precipitation) over northern Argentina. In particular a large dry bias over southeastern South America associated to positive SIC anomalies on the Weddell Sea in September is shown to impact the discharges of the Uruguay and Iguazu Rivers, with the largest effects found two months after the SIC anomaly (November). Although less robust, a relationship with the Parana River is also found. These results suggest that increased SIC over the Weddell Sea during September can help to forecast drier conditions particularly on the Uruguay basin and somewhat wetter conditions in the SACZ region within the following season.