Topographically channeled ocean-atmosphere coupling in the southern Caribbean and summer climate variability

Abstract

This research links global climate to regional weather by considering Caribbean trade wind strength in the context of the large-scale Walker circulation across the Pacific-Atlantic basins, and localized processes involving air-sea interactions between freshwater flux, the ocean mixed-layer depth, and topographic channeling of airflow north of Colombia. Trade wind driven coastal upwelling in the southern Caribbean is enhanced by the Andes Mountains, and creates a focal point for summer climate variability. This emerges in empirical orthogonal function (EOF) analysis of June-July surface zonal winds in the period 1979-2022. Highest EOF loading occurs at 12° N, 75° W northwest of Colombia. Point-to-field correlations with the EOF time score reflect a Pacific-Atlantic thermal dipole and Walker circulation linked with the El Niño-Southern Oscillation (ENSO). As southern Caribbean trade winds weaken, run-off increases, the upper ocean becomes buoyant, and westward currents slacken. Composite differences show that slow trade-wind conditions in June-July induce a counter-current that spreads warm fresh water northeastward from Colombia. This plume disperses toward the Antilles Islands with sufficient memory to triple the number of tropical cyclones in August-September. A slow trade-wind case study in June 2011 emphasizes key air-sea interactions. Channeling of the large-scale airflow north of the Andes Mountains creates a narrow atmospheric bridge for transmission of ENSO signals.