[MITgcm-support] numerical stability criteria

[David Wang]

Hello all,

I was checking the numerical stability of my setup against the criteria 
given in the chapter 3.10.2.1 and found these calculations in the manual 
don't seem to be all correct.

1. for the stability parameter to the horizontal Laplacian friction Sl = 
4*Ah*deltaTmom/delX^2,
for this particular 4x4 gloal ocean example run described in the manual, 
it's calculated to be 4*5E5*(40*60)/(77,000^2) = 0.81, which is above 
the 0.3 upper limit. In verification/global_ocean.90x40x15/input/data 
namelist, deltaTmom is 1200, which however still gives Sl as large as 
0.4, not 0.16 in the manual.

2. for the stability parameter to the vertical Laplacian dissipation Sl 
= 4*Az*deltaTmom/delZ^2 = 4*1E-3*(40*60)/(50^2) = 0.004, not 0.015. 
Also, what its upper stability limit should be? It's not given in the text.

3. the numerical stability for inertial oscillations Si = 
f^2*deltaTmom^2 = (1.43E-4)^2 * (2400)^2 = 0.12, not 0.24

I don't doubt the formulae, so what else could be wrong?

Thanks,
- D.W.

-- 
Daiwei (David) Wang	Graduate Student
Lamont-Doherty Earth Observatory of 
Columbia University
Voice: (845) 365-8694
Email: dwang<AT>ldeo.columbia.edu