Opened 7 years ago

Closed 7 years ago

#1021 closed help (fixed)

Info required on latitude/longitude grids

Reported by: jcrook Owned by: willie
Component: UM Model Keywords: grid, STASH, Arakawa
Cc: Platform: HECToR
UM Version: 6.6.3

Description

Is there some documentation on the different latitude/longitude grids used within HadGEM2? Within STASH you can get some variables out on different grids, eg B, C, P, U/V grid. I want to know what these mean. For many variables it doesn't specify what the grid is. I also want to know if the associated latitude and longitude with a variable are defining the centre of the grid cell or some edge of the grid cell. I'm particularly uncertain about latitude as it often goes from -90 to 90 and 90 cannot be at the centre as there is nothing beyond 90.

Change History (4)

comment:1 Changed 7 years ago by willie

  • Owner changed from um_support to willie
  • Status changed from new to accepted

Hi Julia,

Grids are discussed in UM documentation paper 15, chapter 4.

I hope that helps.

Regards,

Willie

comment:2 Changed 7 years ago by jcrook

Thanks. The documentation is helpful. I am interested in the variables output by STASH along with their latitude and longitudes. I can see u and v are on one set of grids and temperature is on another which is staggered (actually halfway between the u and v grids). I think from the documentation the latitude and longitude given with the STASH variables are the centre point for the particular variable so I can calculate the north and south and east and west boundaries of that grid cell assuming cells meet halfway. However, at the poles I think those cells that have a latitude of 90N must be half the height of the next cell down because I can't go further north than 90N. This is not so clear from the documentation. I need to know the north and south boundaries to find the surface area of the cell. I can't use a cos(lat) weighting for area because the latitudes are not evenly spaced in the ocean model. I need to use sin(lat_top)-sin(lat_bot) weighting.

comment:3 Changed 7 years ago by willie

Hi Julia,

There is some description of the various grids at http://en.wikipedia.org/wiki/Arakawa_grids, including some scientific references.

In the STASH master or user file, there is a grid code that is described in UM document C4.

Regards,

Willie

comment:4 Changed 7 years ago by willie

  • Keywords grid, STASH, Arakawa added
  • Resolution set to fixed
  • Status changed from accepted to closed
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