Isolating the influence of intraseasonal oscillations on northern South American precipitation

Abstract

Equatorial waves are key drivers of intraseasonal variability in the tropics, exerting a strong influence on convection and rainfall over northern South America. This variability arises from a broad spectrum of quasi-periodic and aperiodic modes operating on synoptic to global scales. Although each wave exhibits distinct dynamics and seasonality, isolating the individual effects of these waves on precipitation remains challenging. Here, we employ a local index to estimate precipitation anomalies associated with the enhancing and inhibiting phases of multiple convectively coupled equatorial waves (CCEWs): easterly waves (EW), Kelvin waves (KW), mixed Rossby–gravity waves (MRG), the Madden–Julian Oscillation (MJO), eastward inertio-gravity waves (EIG), and equatorial Rossby waves (ER). Our results are broadly consistent with previous studies for northern South America and with local indices applied elsewhere, but provide novel evidence of the effects of EIG and ER waves, which had not been previously documented in the region. Positive (negative) precipitation anomalies are systematically associated with enhancing (inhibiting) phases, and their spatial distribution highlights particularly affected areas, including the Andes, the Pacific coast, and the eastern plains. This work presents advances in understanding of the precipitation anomalies during the transit of tropical waves, which is crucial for improving rainfall forecasting systems in the region.