South America Intraseasonal Oscillation: global vs regional indices

Abstract

Abstract The intraseasonal oscillation is a complex non-linear variability that has a significant impact on precipitation. Regional indices have been developed to accurately represent the modulation of the intraseasonal rainfall variability over South America throughout the year. Four univariate indices are obtained by applying Empirical Orthogonal Functions (EOF) and Self-Organizing Maps (SOM) to Outgoing Longwave Radiation (OLR) and precipitation data from the Integrated Multi-satellitE Retrievals for the Global Precipitation Measurement (IMERG). Results demonstrate that the use of regional indices can lead to valuable information concerning the intraseasonal South American rainfall variability, timing, and strength compared to the global indices of the Madden-Julian Oscillation (MJO). Despite being computed using only the South American domain, the regional indices capture the tropical-tropical MJO teleconnection through the zonal wavenumber-1 structure. The diversity in the amplitude and evolution of precipitation, primarily due to the tropical-extratropical teleconnections through the Rossby wave trains, is more evident when using the non-linear SOM index. The regional indices also accurately measure the impacts of the intraseasonal variability on extreme precipitation events over South America. This is illustrated in case studies, such as the 2013/2014 summer drought episode, where a deficient rainy season severely affected the Southeast Region of Brazil, impacting agricultural production and hydroelectric power generation. During this episode, the regional indices show agreement between drought periods and the suppressed precipitation phases, while the global indices show an inactive MJO phase.