The external pressure-gradient


   subroutine extpressure(method,nlev)

This subroutine calculates the external pressure-gradient. Two methods are implemented here, relating either to the velocity vector at a given height above bed prescribed or to the vector for the vertical mean velocity. In the first case, dpdx and dpdy are $ x$- and $ y$-components of the prescribed velocity vector at the height h_press above the bed. The velocity profile will in this routive be shifted by a vertically constant vector such that the resulting profile has an (interpolated) velocity at h_press which is identical to the prescribed value. In the second case, dpdx and dpdy are $ x$- and $ y$-components of the prescribed vertical mean velocity vector, and h_press is not used. Here the velocity profile is shifted in such a way that the resulting mean velocty vector is identical to dpdx and dpdy.

For both cases, this is a recalculation of the external pressure gradient, since at all points the same acceleration has been applied in this operator split method.

If the external pressure-gradient is prescribed by the surface slope, then it is directly inserted in (12) and (14).

For details of this method, see Burchard (1999).


   use meanflow,     only: u,v,h
   use observations, only: dpdx,dpdy,h_press
   method to compute external
   pressure gradient
   integer, intent(in)                 :: method
   number of vertical layers
   integer, intent(in)                 :: nlev
   Original author(s): Hans Burchard & Karsten Bolding

Karsten Bolding 2012-12-28