# [MITgcm-support] grid question

Menemenlis, Dimitris (3248) Dimitris.Menemenlis at jpl.nasa.gov
Tue Dec 4 17:09:01 EST 2012

```Hi, the (XG,YG) coordinates specify the southwest corner of each grid cell.
So U(i,j) represents the mean velocity between (XG(i,j),YG(i,j)) and (XG(i,j+1),YG(i,j+1))
and V(i,j) represents the mean velocity between (XG(i,j),YG(i,j)) and (XG(i+1,j),YG(i+1,j))
Look at MITgcm/model/inc/GRID.h for detailed description of grid.

On Dec 4, 2012, at 1:24 PM, Yuan Lian wrote:

> The outputs retain on the same grids as in simulations, unless they are specified in the diagnostics, e.g. using the diagnostics package.
>
> Yuan
>
> Jody Klymak <jklymak at uvic.ca> wrote:
>
>> No, I don't believe there is any interpolation.  I'm pretty sure U is on the XG grid, and V on the XC (for example).  Th actual gurus can let us know if I am mistaken.
>>
>> Cheers,   Jody
>>
>> On Dec 4, 2012, at  10:24 AM, Ping Zhai <pingzhai at MIT.EDU> wrote:
>>
>>> Hi Jody,
>>> Thanks for your reply. I know that U, V and  S, T are calculated at different grids. I want to know whether MITgcm keeps these grids in the output or they interpolate the output U, V ...... on a normalized grids. Do you know that?
>>> Best,
>>> Ping
>>>
>>> On 12/4/2012 1:14 PM, Jody Klymak wrote:
>>>> Hi Ping,
>>>>
>>>> Sec 2.11 Spatial discretization of the dynamical equations, of my version of the manual explains xc versus xg. I think in general "g" means boundaries (i.e. u in the x-direction), and "c" means centers (i.e. density).
>>>>
>>>> Cheers,   Jody
>>>>
>>>> On Dec 4, 2012, at  10:02 AM, Ping Zhai <pingzhai at MIT.EDU> wrote:
>>>>
>>>>> Hi,
>>>>> I have a question about the grids of some variables. The grids: XC, XG, YC, YG, RC and RG.
>>>>> My output files are like: U.0000691200.data and U.0000691200.meta
>>>>> What horizontal and vertical grids do these variables (U, V, Eta, S, T, UUtave, UTtave, ......) use?
>>>>> I searched in MITgcm manual, but could not find the information.
>>>>> Best,
>>>>> Ping

```