[MITgcm-support] Definition of spatial boundary in EXF package

[Martin Losch]

Hi Nicolas,

I think, if your first forcing grid point is a (0,-90) then your second set of parameters is appropriate. 

I understand that the documentation is misleading: What it means is, that field_lon/lat0 is defined at the center of the (forcing) grid cell rather than the corner (we are all caught up in the Finite-Volume C-grid world and the description somehow carries over from the model grid, but is not quite right here).

Martin

On May 1, 2012, at 12:24 PM, Nicolas Bruneau wrote:

> Dear MITgcm support / users,
> 
> I just started to work with the MITgcm model using the EXF package and I would like to have some clarification about the boundary definitions. From the documentation, I can read:
> field_lon0	<Mail Attachment.png>	starting longitude of input
> field_lon_inc	<Mail Attachment.png>	increment in longitude of input
> field_lat0	<Mail Attachment.png>	starting latitude of input
> field_lat_inc	<Mail Attachment.png>	increment in latitude of input
> field_nlon	<Mail Attachment.png>	number of grid points in longitude of input
> field_nlat	<Mail Attachment.png>	number of grid points in longitude of input
> If my external forcing is, for example, a 1.5-degree resolution grid starting at 0 degree in longitude and -90 in latitude, do I need to define the spatial grid in data.exf as:
>  atemp_lon0    = .75  (i.e. 0 + dX / 2)
>  atemp_lon_inc = 1.5
>  atemp_lat0    = -89.25
>  atemp_lat_inc = 120*1.5
>  atemp_nlon    = 240
>  atemp_nlat    = 121
> 
> or do I define it as:
>  atemp_lon0    = 0
>  atemp_lon_inc = 1.5
>  atemp_lat0    = -90
>  atemp_lat_inc = 120*1.5
>  atemp_nlon    = 240
>  atemp_nlat    = 121
> 
> When I'm looking the subroutine exf_interp.F, it looks that the "x_in" variable represents the coordinates of the input and in such a case, I would think the second definition (atemp_lon0 = 0) is the good one but following the documentation, it looks that the first one is the good one. So I imagine, I didn't get something.
> 
> I would be really grateful for some help. Looking forward to hearing from you.
> 
> -- 
> <baslogo1000.gif> 	Dr Nicolas Bruneau 
> British Antarctic Survey 
> High Cross, Madingley Road, Cambridge, CB3 0ET, UK 
> Email: nicbru at bas.ac.uk 
> Phone: +44 (0) 1223 22 13 27
> -- 
> This message (and any attachments) is for the recipient only. NERC 
> is subject to the Freedom of Information Act 2000 and the contents 
> of this email and any reply you make may be disclosed by NERC unless 
> it is exempt from release under the Act. Any material supplied to 
> NERC may be stored in an electronic records management system.
> _______________________________________________
> MITgcm-support mailing list
> MITgcm-support at mitgcm.org
> http://mitgcm.org/mailman/listinfo/mitgcm-support