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

Abstract

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.