How was the monthly mean surface stress and fluxes computed?
[12/11/96] The fluxes and stresses are computed in the model during the 6 hour prediction in the assimilation cycle. The reanalysis products are the averages of fluxes and stresses during this 6 hour prediction. The time step of the model is about 15 min. • Does reanalysis use a constant drag coefficient to compute the surface wind stress?[12/11/96] Drag coefficient is a function of bulk Richardson number and is not constant. • How does NCEP/NCAR reanalaysis compute the potential vorticity on isentropic surfaces?[12/06/96] First the static stability N**2=g/T*(dT/dz+g/cp) is computed on model levels. Then the winds, temperature and static stability are interpolated to isentropic surfaces linearly in log(theta). (Outside the model domain, the fields are held constant for now and will later be compressed out of the final product.) Then the absolute vorticity zeta is spectrally computed on the isentropic surfaces, where the shortest wavelength in the spectral domain is about 4 grid lengths
