High-frequency Intraseasonal Variability of Precipitation in South America and its link with Southern Hemisphere Teleconnection Patterns

Abstract

The long-distance linkage between weather and climate conditions in different regions, i.e., teleconnection patterns, is crucial for understanding and predicting climate variability. In South America (SA), atmospheric Rossby waves originating in the maritime continent play a key role in triggering the South American Monsoon System across different timescales. Current studies have mainly focused on the long-term variability, mostly associated with seasonal, interannual and interdecadal temporal scales. On the contrary, intraseasonal variability has remained underexplored, especially the higher frequency relevant for the under two-week weather prediction. In this research, we investigate the high-frequency intraseasonal variability (HFISV, 8 – 20 days) of precipitation in SA by performing an empirical orthogonal function (EOF) analysis. For this, we use the CPC precipitation data for the summer period between 1979 – 2018. We also track its origin on teleconnection patterns in the Southern Hemisphere (SH) and local processes in SA by using lead and lag regression techniques based on ERA5 reanalysis data and NOAA outgoing longwave radiation. For this analysis, we give particular emphasis on describing active and break rainfall phases over SA. Our results show that HFISV significantly contributes to the total precipitation variability in the region (∼28%). We also found that extreme precipitation events in SA, which can lead to floods and droughts, are closely linked to anomalous high and low-pressure systems over the SH, demonstrating strong connections with Rossby waves in the mid-latitudes originated in the South Pacific Convergence Zone. At a local scale, spatial maps and cross-sectional analysis provided further insights, confirming that local processes feed back and enhance the extreme event, where low-level winds play a critical role in transporting moisture across the region. Local processes are afterwards able to reverse the winds and redistribute the moisture leading to a change in the monsoon phase. Our work highlights that predicting teleconnections, which modulate circulation anomalies and weather patterns, is a potential tool for precipitation subseasonal predictability. This is particularly relevant in arid areas where water is primarily available in the form of seasonal convective storms (e.g., in the Altiplano region), but also in a wider range as continents like Africa, which depend on the SA monsoon.