Conceptual Model of RadNud Boundary Condition

[cflanary]

I'm searching for a good conceptual description of the RadNud boundary condition, specifically for tracers and 3-D momentum. I understand the nudging inflow timescales set in the *.in file and how the boundary is updated.

I'm having trouble with the concept of radiating out of the boundary and the outflow timescales. I think it's an open boundary and tracers and 3-D momentum can advect out of these boundaries freely, but that doesn't explain why there is an outflow timescale.

For my example, I have tracers nudged at 1 day and outflow at 28 days and 3-D momentum nudged at 4 days and the outflow at 112 days.

TNUDG == 28.0d0
ZNUDG == 0.0d0
M2NUDG == 0.0d0
M3NUDG == 112.0d0

OBCFAC == 28.0d0

Thank you

[dcherian]

RadNud means there's a nudging term added to the radiation condition. The timescale refers to the timescale of this nudging which is (generally) longer if the phase speed (determined for the radiation condition) is directed outward and shorter if it is inward.

The reference is this paper: http://www.sciencedirect.com/science/ar ... 0300000135