Intraseasonal Oscillations and hydroclimate of Northern South America, Central America and Mexico (Part I: The identification process)

The contribution of intraseasonal variability (10- 90 days) in OLR data across Northern South America, Central America, and Mexico was studied. This variability is driven by planetary and tropical oscillations, including Kelvin waves, Tropical Easterly Waves, Mixed Rossby-Gravity Waves, and the Madden-Julian Oscillation, which display distinct signals in the wavenumber—frequency power spectra. Using the Wheeler-Kiladis methodology (1999) and the spatial EOF analysis for local activity index and composites by Mounier (2007), our findings reveal that intraseasonal variability accounts for 10% to 35% of the total variance, depending on the specific location, with Kelvin waves being the largest contributors to the OLR variance in the study region. This methodology allows to propose a local index for each coupled convective wave aiming to classify as convection inhibiting (dry) and convection favoring (wet) days events. The annual cycle of these dry and wet events for each wave show interesting patterns like a predominance of Tropical Easterly Waves and Mixed Rossby-Gravity Waves during the boreal summer and major Kelvin waves occurring during May and April.