MJO modulating the activity of the leading mode of intraseasonal variability in South America

Abstract

Intraseasonal (IS) variability in South America is efficiently described through the first empirical orthogonal function of filtered precipitation or outgoing longwave radiation (OLR) anomalies. In the 30-90-day band, the leading OLR pattern between October and April is a dipole with centers of action in the South Atlantic Convergence Zone (SACZ) and southeastern South America (SESA). The Madden Julian Oscillation (MJO) was shown to have an impact on the rainfall in South America, with greater influence during the austral warm season. The aim of this study is therefore to assess the modulation of the MJO in the activity of the leading pattern of variability in South America, named the 3090-Seasonal-Intraseasonal (SIS) pattern. It was found that the most intense periods of activity of the SIS pattern appear to be related to intense MJO events with coherent eastward propagation. Furthermore, positive 3090-SIS phases, associated with enhanced (inhibited) convection over the SESA (SACZ) region generally occur during MJO progression from the eastern Indian Ocean to the Western Pacific (i.e., Maritime Continent sector). On the contrary, negative 3090-SIS phases, associated with enhanced (inhibited) convection over SACZ (SESA) are observed when the MJO active phase locates between the Western Pacific and the western Indian Ocean (African sector). The 3090-SIS pattern modulation by the MJO opens the opportunity to develop skillful subseasonal prediction tools in South America.