Impacts of waves and sea states on air-sea momentum flux in the
Northwest Tropical Atlantic Ocean: parameterization and wave coupled
climate modeling
Abstract
In winter, the Northwest Tropical Atlantic Ocean can be characterized by
various regimes of interactions among ocean current, surface wind, and
wind waves, which are critical for accurately describing surface wind
stress. In this work, coupled wave-ocean-atmosphere model simulations
are conducted using two different wave roughness parameterizations
within COARE3.5, including one that relies solely on wind speed and
another that uses wave age and wave slope as inputs. Comparisons with
the directly measured momentum fluxes during the ATOMIC/EUREC4A
experiments in winter 2020 show that, for sea states dominated by short
wind waves under moderate to strong winds, the wave-based formulation
increases the surface roughness length by 40\% compared
to the wind-speed-based approach. For sea states dominated by remotely
generated swells under moderate to strong wind intensity, the wave-based
formulation predicts significantly lower roughness length and surface
stress (~20%), resulting in increased near-surface wind
speed above the constant flux layer (~5%). Further
investigation of the mixed sea states in the model and data indicates
that the impact of swell on wind stress is over-emphasized in the
COARE3.5 wave-based formulation, especially under moderate wind regimes.
Various approaches are explored to alleviate this deficiency by either
introducing directional alignment between wind and waves or using the
mean wave period instead of the wave period corresponding to the
spectral peak to compute the wave age.