Satellite-based observations of surface turbulent stress during severe weather

Vector surface turbulent stresses are estimated from vector winds determined from space-borne scatterometers. Scatterometer vector winds differ subtly from in situ observations of vector winds. These differences are exaggerated for severe storm conditions, which is advantageous for determining surface stress. A physically based model for surface stress is developed to link surface turbulent stress to near-surface winds, and to explain the observed qualitative differences between in situ and scatterometer winds. The improvements of this model compared to previous formulations are in the near-surface boundary conditions on wind speed and a vertical offset (i.e., displacement height) of the log-wind profile, due to wave modification of the surface. The boundary condition on wind speed implies that there must be a vertical offset, and it can be used to derive the displacement height. This formulation represents a first estimate of the dependence of displacement height on wave characteristics. One advantage of this approach is that it removes sea state dependency from Charnock’s constant. Strengths and weaknesses are discussed for this model and for its application in determining scatterometer-based vector surface turbulent stress.