model horizontal velocities error

General scientific issues regarding ROMS

Moderators: arango, robertson

Post Reply
Message
Author
isabelmonteiro
Posts: 38
Joined: Wed Feb 18, 2004 3:50 pm
Location: Instituto de Meteorologia

model horizontal velocities error

#1 Post by isabelmonteiro » Tue May 04, 2010 9:12 am

I'm running a ROMS upwelling configuration for north-eastern off Iberia. To check if the model grid and other grid parameters are OK I setup a Run with no forcing, summer stratified configuration and a realistic smothed batymetry. I was exepcting to get a near-steday flow with near zero horizontal velocities.
In fact I did obtain velocities ~0.0001 m/s that seems to be quite large (see att). Can you tell me the expected model velocities error (with no forcing) :?:
Attachments
VH_02_smth_23dias.jpg
VH_02_smth_23dias.jpg (34.49 KiB) Viewed 2376 times

User avatar
kate
Posts: 3782
Joined: Wed Jul 02, 2003 5:29 pm
Location: CFOS/UAF, USA

Re: model horizontal velocities error

#2 Post by kate » Wed May 05, 2010 1:42 am

I would expect something like what you are seeing.

lanerolle
Posts: 157
Joined: Mon Apr 28, 2003 5:12 pm
Location: NOAA

Re: model horizontal velocities error

#3 Post by lanerolle » Wed May 05, 2010 3:47 am

What velocities do you get if you do a simple geostropic balance using your T, S vertical stratification? The rho that you need for it can be calculated using the expressions in ROMS/Nonlinear/rho_eos.F (which you may need to code up in a separte routine in C++, Matlab or Fortran).

User avatar
jivica
Posts: 136
Joined: Mon May 05, 2003 2:41 pm
Location: The University of Western Australia, Perth, Australia

Re: model horizontal velocities error

#4 Post by jivica » Thu May 06, 2010 1:11 am

I should say that this is really good to do at the begining :wink: ,
just to make sure you have all setup right (!) and can explain "ghost currents" if you have them :roll:

What I do is run model similar like you but with analitical (for my region specific) vertical T & S; just to be sure that there are no horizontal gradient introduced in the initial phase. Than after some time (depending on the grid/region), say 2 weeks, you could notice that you have growing velocities at the bottom. This should represent mayor contribution from HPGE (Horizontal Pressure Gradient Error) because of imperfect vertical coordinate. Those regions with higher bottom velocities should correspond with regions characterised with higher values of rx1 -> (in a fact you can compute it and plot it)
If this is not acceptable for you reconsider to smooth bahtymetry more or change vertical structure (less vertical levels, higher theta_s ...)
Cheers
Ivica

isabelmonteiro
Posts: 38
Joined: Wed Feb 18, 2004 3:50 pm
Location: Instituto de Meteorologia

Re: model horizontal velocities error

#5 Post by isabelmonteiro » Mon May 31, 2010 7:46 am

I'm still getting horizontal velocities ~0.001 m/s with no forcing with bathymetry smoothing,the slope parameter maximum value is r = grad(h)/h = 0.2.

What is "no motion" with ROMS? What do you consider acceptable horizontal velocities with no forcing ?

Isabel

Post Reply