El Niño modulation of subdaily air–sea latent heat flux variability in the Hawaiian Islands

An analysis of buoy data from the National Data Buoy Center (NDBC) reveals that El Niño significantly modulates subdaily variations in air–sea latent heat fluxes across the Hawaiian Islands. During El Niño winter months, the mean amplitude (standard deviation) of these variations reached up to 35 W·m −2 —approximately 11 W·m −2 greater than during La Niña winters—representing a 33% increase. To clarify the underlying processes, we examined the drivers of subdaily latent heat flux variability under differing boundary layer stability regimes. Results show that El Niño–Southern Oscillation (ENSO) phases alter the background air–sea humidity difference and wind speed, thereby influencing the amplitude of subdaily flux variations. By analyzing both daily mean and subdaily anomalies of wind speed and humidity difference during El Niño and La Niña events, we quantified their respective contributions. El Niño enhances subdaily flux variability primarily by increasing background humidity differences and wind speeds under near-neutral boundary layer conditions. Under unstable conditions, the elevated humidity difference continues to dominate the variability. During El Niño events, the contributions of background humidity difference and wind speed were 61% and 68%, respectively, under near-neutral stability, and 87% and 36%, respectively, under unstable conditions. These findings highlight the dynamic interplay between large-scale climate variability and high-frequency air–sea interaction processes in the central Pacific.