A parameterization model for calculation of vertical fluxes of momentum due to terrain induced gravity waves.

Type: Report
Series: RMK 5
Author: Collins, W.G.


Various sources of information indicate vertical fluxes of mountain induced wave momentum to be on the order of several tenths of a Pascal over mountaineous terrain. The implied wind tendencies in layers of wave absorption in typical situations are several meters per second per day. On the basis of the size of this probable effect, a parameterization model has been developed to calculate the momentum fluxes within the framework of a largescale numerical weather prediction model. The calculation model assumes a continuous linear wind profile as well as constant stability within each layer. The hydrostatic assumption is made for the total motion. The vertical velocities
and resultant vertical momenturn fluxes are caused by the
air being forced over the topography . For this mode l , the
individual spectral elements of the terrain height are
not important . Rather , an integral over the elements is
used as the forcing function which determines the momenturn
flux magnitude . This forcing function must be determine-
d as a function of horizontal direction for each largescale
grid box . Sample calculations are given which illustrate
the results possible from the parameterization
model .