Observed sub-daily variations in air–sea turbulent heat fluxes under different marine atmospheric boundary layer stability conditions in the Gulf Stream

Abstract Based on data collected from 14 buoys in the Gulf Stream, this study examines how hourly air–sea turbulent heat fluxes vary on sub-daily timescales under different boundary layer stability conditions. The annual mean magnitudes of the sub-daily variations in latent and sensible heat fluxes at all stations are 40 and 15 W·m−2, respectively. Under near-neutral conditions, hourly fluctuations in air–sea humidity and temperature differences are the major drivers of sub-daily variations in latent and sensible heat fluxes, respectively. When the boundary layer is stable, on the other hand, wind anomalies play a dominant role in shaping the sub-daily variations in latent and sensible heat fluxes. In the context of a convectively unstable boundary layer, wind anomalies exert a strong controlling influence on sub-daily variations in latent heat fluxes, whereas sub-daily variations in sensible heat fluxes are equally determined by air–sea temperature difference and wind anomalies. The relative contributions by all physical quantities that affect sub-daily variations in turbulent heat fluxes are further documented. For near-neutral and unstable boundary layers, the sub-daily contributions are О(2) and О(1) W·m−2 for latent and sensible heat fluxes, respectively, and they are less than О(1) W·m−2 for turbulent heat fluxes under stable conditions.