Inclusion of Non-stationarity of the Wind and Wave Fields in the Bulk Formula for Surface Fluxes: A New Direction
Abstract
Non-stationarity of the wind field disrupts the equilibrium between the wind, stress, and wave fields. We examined the effect of non-stationarity of the wind field on the stress by analyzing six years of turbulent flux data from the Oestergarnsholm tower in the Baltic coastal zone. On average, the impact of the non-stationarity on the stress and drag coefficient becomes important for wind speeds less than about 6m/s. The drag coefficient is augmented during the initial stages of acceleration and during the later stages of deceleration. The underestimation of the sea-surface stress due to the stress divergence between the surface and the 10-m level was investigated. The magnitude of the stress divergence increases modestly with decreasing wave age, increases with increasing stability, and decreases with increasing instability, due partly to the impact of stability on the boundary-layer depth. We also analyzed heat flux measurements at two levels along with profiles of air temperature, and multiple measurements of the water temperature. We examined simple relationships of the heat flux to the wind speed and stratification and the potential influences of fetch and temperature advection. For a given wind direction sector, the transfer coefficient varies only slowly with increasing instability, but decreases significantly with increasing stability.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 04, 2022
- Accession Number
- AD1176291
Entities
People
- L. Mahrt
Organizations
- Northwest Research Associates