[MITgcm-support] Lock exchange problem with the MITgcm

[Flavien Gouillon]

*Dear all,*

*I am starting with the MITgcm but have experience with ROMS and HYCOM. 
I am running a similar simulation of the well known lock exchange 
problem by Haidvogel and Beckmann (and more recently Burchard and 
Rennau, 2009). In a closed flat 2D (x-z) basin (20m depth), I have 2 
initial densities, 5kg/m3 difference (salinity is passive), separated by 
a vertical wall that I removed at t=0. I turn off all explicit mixing 
and diffusion, lateral and bottom free-slip. I have the latest version 
of the MITgcm and run in a hydrostatic fashion. Resolution is 500m (cst) 
in dx (128pts total points) and 40 levels (dz=0.5m, cst). It seems to 
work well but I have few questions since I am quite unfamiliar with this 
model:*

* *- *It seems that, for any advection scheme I choose, the MITgcm is 
quite “dispersive” (by dispersive I mean that oscillations appear at the 
interface of the 2 densities) if I do not prescribe high enough 
viscosity (1e-3 for viscA[hz] and 1e4 for viscA4). I did not notice this 
using ROMS. Is there any documentation on this that I could read or 
anybody has some info to give me? I have attached 2 figures (run with 
the 1st order upwind) for the case of no viscosity (all viscosity terms 
at 0) and viscosity at 1e-3 as well as my data file.*

* *- *The other question is: when running with the 3^rd order upwind 
advection scheme, my density profile has, in some places, a persistent 
non-monotic (lighter to denser) feature (unstable conditions, denser 
water above a lighter one). I thought that running with a hydrostatic 
model would prevent such thing and will not allow any ‘overturning’ (by 
quickly mixing any unstable profile) or will blow-up. Is the MITgcm 
capable of handling such thing even running with the hydrostatic option 
and without any mixing?*

* *- *If anybody tried to reproduce the lock exchange problem from 
Haidvogel and Beckmann (or any other lock exchange prob) I would greatly 
appreciate any advices/info/etc...!*

*I hope I was clear enough, please don't hesitate to ask me if I need to 
provide more info, Thanks in advance for all your help, *

*Flavien *

-- 
_______________________
Flavien Gouillon
GRA, Physical Oceanography
COAPS/FSU
www.coaps.fsu.edu/~gouillon

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