Observation‐Based Estimates of Vertical Velocity in the Tropical Upper Oceans

Abstract Equatorial upwelling plays a crucial role in regulating regional climate variability and biological productivity from seasonal to interannual time scales. Typically, sea surface temperature or surface chlorophyll anomalies are used as proxies for upwelling because of the challenges in directly measuring vertical velocities. Here, we show that using a synthesis product of surface drifter observations, reanalysis winds, and satellite altimetry to infer vertical velocity in the equatorial band (±3°; w eq ) improves the representation of the spatiotemporal characteristics of w eq compared to estimates from other commonly used products. We focus on the annual mean, seasonal cycle, interannual variations, and long‐term trends of vertical velocity estimates, derived by applying the continuity equation to horizontal current divergence in the upper 30 m across the tropical Pacific, Atlantic, and Indian Oceans. Mean w eq values of 0.6 ± 0.2, 0.3 ± 0.2 and 0.1 ± 0.2 m day −1 are observed in the Pacific (150°W–90°W), Atlantic (20°W–0°), and Indian Ocean (60°E–90°E), respectively. Vertical transport across 30 m is 46 ± 14 Sv in the Pacific and 8 ± 4 Sv in the Atlantic. Interannual variations in w eq are primarily driven by climate modes specific to each basin and are up to ±0.4 m day −1 in the Pacific, ±0.1 m day −1 in the Atlantic, and up to ±0.6 m day −1 in the Indian Ocean. From 1993 to 2022, Pacific w eq significantly increased by 24 ± 13% (0.14 ± 0.07 m day −1 ). This increase in Pacific equatorial upwelling aligns with stronger trade winds and intensified upper‐ocean currents.