# Ocean Modeling Discussion

ROMS/TOMS

Search for:
 It is currently Wed May 22, 2019 4:59 pm

 Page 1 of 1 [ 4 posts ]
 All times are UTC
Author Message
 Post subject: Left side of the upwelling examplePosted: Thu May 15, 2008 11:12 pm

Joined: Tue Jun 19, 2007 3:32 pm
Posts: 35
Location: National Center for Atmospheric Research
I have plotted the flow vectors in a cross section of the upwelling example. Everything looks fine except for the left (south) side of the channel. Recall that the wind here is into the page and the Coriolis force is to the left (southern hemisphere). Here is the entire section:

As you can see, there is some complexity on the left side. Here is the detail:

Is that Kelvin-Helmholtz instability over there? Induced by the vertical shear between the surface current and the return bottom current in the shallows? Or do I have some numerical error in my Python code:

http://acd.ucar.edu/~drews/plotSection.py

Carl

Top

 Post subject: Posted: Fri May 16, 2008 5:10 pm

Joined: Wed Jul 02, 2003 5:29 pm
Posts: 3559
Location: IMS/UAF, USA
Hi Carl,

It's likely that there is some alternating up and down flow. You can check for sure by plotting vertical velocity with contours. Now, there's the question of direction on vectors. Ideally, if the flow is along the sloping bottom, you would want your vectors to be parallel to the sloping bottom. You have some shooting out of the bottom in the big picture, then lifting up off the bottom in the zoom in. They can't both be right.

Top

 Post subject: Posted: Sat May 17, 2008 2:48 pm

Joined: Sun Jul 27, 2003 6:49 pm
Posts: 85
Location: UNH, USA
Carl-

The upwelling code is define to use a constant value of vertical mixing, as you can tell from this code in upwelling.h

Quote:
#if defined GLS_MIXING || defined MY25_MIXING
# define KANTHA_CLAYSON
# define N2S2_HORAVG
#else
# define ANA_VMIX
#endif

and by noting that neither GLS_MIXING or MY25_MIXING are enabled earlier in the file. Furthermore, on the side of the "upwelling" model case in which there is downwelling, the left side in your plot, light water is being forced under denser water. This leads to a static instability in the water column. With a low and constant viscosity, this leads to convection in the model.

Unfortunately, in a relatively coarsely resolved hydrostatic model, this convection is poorly represented as 2 Delta X upwelling cells, as you see in your plot. To model the convection properly, you would need a horizontal resolution that is small compared to the water depth (!!) and a non-hydrostatic model. This will tend to be computationally unfeasible if you want to use the model to resolve any reasonably large area. Thus you must parameterize convection. MY25_MIXING will do an ok-ish job of doing this by cranking up the eddy viscosity. See Austin & Lentz's paper on the inner shelf for a discription of how the inner shelf will develop in a case like that shown in the "upwelling" model case.

P.s. how well developed is your python plotting code for ROMS output -- is it good enough to share?

Cheers,
Jamie Pringle
University of New Hampshire

Top

 Post subject: That Python codePosted: Mon May 19, 2008 3:21 pm

Joined: Tue Jun 19, 2007 3:32 pm
Posts: 35
Location: National Center for Atmospheric Research
Jamie -

Thanks for the information about mixing and convection. Your comments will be useful to me, since my research involves shallow water.

That Python code is a quick-and-dirty script that I put together to produce a plot. I posted it in case someone needs to review my processing to answer my question. The code contains too many hard-wired numbers and too much debugging. It's okay to share for someone who is new to Python, or who wants to see how to read NetCDF and put up a basic plot, but I would not consider it to be well-engineered code. "No warranty implied." But it might be useful to those who are learning.

Carl

Top

 Display posts from previous: All posts1 day7 days2 weeks1 month3 months6 months1 year Sort by AuthorPost timeSubject AscendingDescending
 Page 1 of 1 [ 4 posts ]

 All times are UTC

#### Who is online

Users browsing this forum: No registered users and 1 guest

 You cannot post new topics in this forumYou cannot reply to topics in this forumYou cannot edit your posts in this forumYou cannot delete your posts in this forumYou cannot post attachments in this forum

Search for:
 Jump to:  Select a forum ------------------ News, Events & Job Opportunities    Meetings/Workshops    Job Opportunities    Ocean News ROMS/TOMS    ROMS Adjoint    ROMS Benchmarks    ROMS Bugs    ROMS Discussion    ROMS Documentation    ROMS Ecosystem    ROMS FAQ    ROMS Ice    ROMS Information    ROMS Installation    ROMS Known Problems    ROMS Messages    ROMS Problems    ROMS Releases    ROMS Results    ROMS Sediment    ROMS Source    ROMS Tips    ROMS Tools and Techniques    ROMS Trivia    ROMS Usage    ROMS Webinar    ROMS Wish List ROMS/TOMS Applications    User Applications    Adriatic Sea Ocean Modeling    Ocean Modeling FAQ