Tropical Diurnal Cycle of Ocean Surface Winds From CYGNSS Observations

Abstract

The diurnal cycle of ocean surface wind reflects the daily response of air–sea thermal and dynamical processes. Using 1‐hr wind speed data from the Cyclone Global Navigation Satellite System (CYGNSS, 2018–2024), this study refines the characterization of tropical ocean diurnal winds and evaluates their consistency with ERA5 reanalysis. Compared with conventional 6‐hourly satellite records, the hourly sampling of CYGNSS provides sufficient temporal coverage for harmonic fitting, yielding diurnal phase estimates with sub‐hour precision and revealing coherent nighttime wind maxima between 23:00 and 06:00 local time. Both data sets show stronger amplitudes near coasts, straits, and bays, and weaker but detectable signals over open oceans. ERA5 amplitudes are approximately 1.4 times those derived from CYGNSS, with a correlation of 0.75 and a root‐mean‐square phase difference of 1.54 hr. Notably, strong diurnal signals frequently appear in regions lacking buoy observations, highlighting the importance of spaceborne measurements. By providing independent, all‐weather, and high‐frequency observations, CYGNSS offers a unique capability for resolving global diurnal wind variability and validating model‐based reanalysis.