[Mitgcm-support] Bottom drag coefficients

[mitgcm-support at dev.mitgcm.org]

Stephanie,

According to Haidvogel & Beckmann (book, sect 5.6.6) a typical
resistance coefficient is  r_b = 0.0002 m/s . This corresponds
to bottomDragLinear in the code.

For the quadratic term, the non-dimensional drag coefficent
is typically  C_d = 0.001 - 0.003 (no units).  This corresponds
to bottomDragQuadratic.

I had once asked Chris Edwards if these stress parameterization
should have density units included but since the convention is
as above and we'll stick to it.

Alistair.

Chris Edwards wrote:
> Quadratic:
> -(u'w')@bottom = tau_b = Cd rho |u| u
> Cd, the quadratic drag coeff, is non-dimensional.
> Units:
> tau_b ~ N/m^2 = kg /ms^2
> rho |u|u ~ kg/m^3 m/s m/s ~ kg/m s^2 
> 
> Linear:
> -(u'w')@bottom = tau_b = r rho u
> r, the linear drag coeff, is in units m/s.
> r rho u ~ m/s kg/m^3 m/s ~ kg/m s^2
> 
> For shallow water flow, the divergence of the stresses should lead to
> du/dt ... = ... - ru/H -Cd|u|u/H
> which shows an equivalent check for r (m/s) and Cd (nd).