modified pressure boundary

Rhydar

Hello anyone.. I am having some difficulties with pressure boundaries, 5000m high. I have an 'open' boundary attempting to model possible in/outflow from the atmosphere. I am using a pressure boundary. I use usrbcs to specifiy variable pressure and temperature at dry adiabatic lapse rate. The pressure however is modified: buoyancy, momentum and eddy viscosity modification (according to the manual). 1)Is this assumption correct? 2)I am not sure of the user fortran for the effective viscosity or the divergence term in the momentum transfer modfication, or the k term in the viscosity modification, has anyone had a similar problem with this kind of boundary? 3)Would they mind spreading some joy my way?