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Subsections


aaksetr.F


subroutine aaksetr

Description

Sets the eddy viscosity and eddy diffusivity from a a Richardson number fromulation.

Numerical Equations

It has a mixing length scale l to be assumed to be a fraction of the water depth in this case l = 0.05H and the richardson number is:

\begin{displaymath}
R_i = \frac{\partial b}{\partial z}\frac{1}{\left( {\frac{\p...
...\right)^2 + \left( {\frac{\partial v}{\partial z}}
\right)^2}
\end{displaymath}

A basic value of aa or ak resulting from surface or bed stress is assumed to be given by $u_\ast$, where $u_\ast$ is the appropiate friction velocity. Then this is reduced liniearly until a cut-off value (Ri = 0.23) is reached. Hence for the bed stress contribution to aa
\begin{displaymath}
A(z_1) = min( A_1(z)) \quad \mbox{where} \quad z \leq z_1
\end{displaymath} (36)


\begin{displaymath}
\begin{array}{ll}
A_1 (z) & = u_\ast l\frac{\left( {0.23 - ...
...\quad \quad \quad \quad \quad for Ri \ge 0.23 \\
\end{array}\end{displaymath}

with similar formulation for the surface stress contribution, which decreases monotonically from the surface downwards.The contributions from surface and bed stress are then added together. A minimum value 0.002 m$^2$s$^{-1}$ is assumed for $u_\ast$ due to surface stress, and a minimum value of 10$^{-4}$ is used for aa and ak.

Subroutine Arguments

none

Local variables

ff Fraction of $u_\ast$
i,icg,ipn,j,jcg,k,ki Grid indeces.
tagb,tagu,tagv,tagfb,tagfs,taggb,taggs Message passing taggs.
alb,als Length scale for surface and bed stress.
ustb,usts,ustl $u_\ast$ for bottom and surface and $u_\ast$
wsp3 Wind speed cubed.
ri,rif Richardson number and Richardson number function.
ab,as bottom and surface contributions for aa or ak

Global variables changed

aa Eddy viscosity
ak Eddy diffusivity

Logical units

none

Order of Things

  1. Exhanges variables needed between processors.
  2. Calculates Ri at u points and makes sure that is positive.
  3. Calculates rif.
  4. Calculates $u_\ast$ for bottom and surface.
  5. Calculates the mixing length for surface and bottom.
  6. Calculates aa due to bed stress decreasing upwards.
  7. Calculates aa due to surface stress decreasing downwards.
  8. Combine the surface stress and bottom stress contribution of aa.
  9. Calculates Ri at b points and makes sure that is positive.
  10. Calculates rif.
  11. Calculates $u_\ast$ for bottom and surface.
  12. Calculates the mixing length for surface and bottom.
  13. Calculates ak due to bed stress decreasing upwards.
  14. Calculates ak due to surface stress decreasing downwards.
  15. Combine the surface stress and bottom stress contribution of ak.

Calls

Exch3DS,Exch3DR

Called By

b3drun.F

Options - Logical

none

Options - Compiler

none

Known Issues

Not complitely parallelised


next up previous
Next: advdif_spm.F Up: The Proudman Oceanographic Laboratory Previous: Subroutines
The AMMP Project 2005-04-20