Abstract
Atmospheric fronts embedded in extratropical cyclones are high-impact
weather phenomena, contributing significantly to midlatitude winter
precipitation. The three vital characteristics of the atmospheric
fronts, high wind speeds, abrupt change in wind direction, and rapid
translation, force the induced surface waves to be misaligned with winds
exclusively behind the cold fronts. The effects of the misaligned waves
on air-sea fluxes remain undocumented. Using the multi-year in situ
near-surface observations and direct covariance flux measurements from
the Pioneer Array off the coast of New England, we find that the
majority of the passing cold fronts generate misaligned waves behind the
cold front. Once generated, the waves remain misaligned, on average, for
about 8 hours. The fully-coupled model simulations indicate that the
misaligned waves significantly increase wave roughness length (300%),
drag coefficient (30%), and momentum flux (20%). The increased surface
drag reduces the wind speeds in the surface layer. The upward turbulent
heat flux is weakly decreased by the misaligned waves because of the
compensating effect between the decrease in temperature and humidity
scaling parameters and the increase in friction velocity. The misaligned
wave effect is not accurately represented in a commonly used wave-based
bulk flux algorithm. Yet, the suggested modification to the current
formulation improves the overall accuracy of parameterized momentum flux
estimates. The results imply that better representing a directional
wind-wave coupling in the bulk formula of the numerical models may help
improve the air-sea interaction simulations under the passing
atmospheric fronts in the midlatitudes.