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MAPL Grids File Spec
This describes the NetCDF file format that is emitted and understood by the common IO layer used by History/ExtData and any utility that uses the same IO layer. The file metadata consists of two parts, one is grid specific, i.e. a file on say a Lat-Lon grid will have a different metadata than say a Tripolar grid. Some metadata would be consistent however, that being the time and any sort of non-horizontal levels.
A Lat-Lon grid is a 2D dimension grid where the longitude is fixed as the 2nd index of the array varies and the latitude is fixed as the 1st index varies, hence why the coordinates can be 1-D variables.
dimensions:
lon = 180 ;
lat = 91 ;
time = UNLIMITED ; // (1 currently)
variables:
double lon(lon) ;
lon:long_name = "longitude" ;
lon:units = "degrees_east" ;
double lat(lat) ;
lat:long_name = "latitude" ;
lat:units = "degrees_north" ;
int time(time) ;
time:long_name = "time" ;
time:units = "minutes since 2000-04-15 00:00:00" ;
time:time_increment = 60000 ;
time:begin_date = 20000415 ;
float example_variable(time, lat, lon) ;
PS:long_name = "surface_pressure" ;
PS:units = "Pa" ;
PS:_FillValue = 1.e+15f ;
PS:missing_value = 1.e+15f ;
PS:fmissing_value = 1.e+15f ;
PS:scale_factor = 1.f ;
PS:add_offset = 0.f ;
PS:standard_name = "surface_pressure" ;
PS:vmin = -1.e+15f ;
PS:vmax = 1.e+15f ;
PS:valid_range = -1.e+15f, 1.e+15f ;
The latitude and longitude arrays are double precision MONOTONICALLY INCREASING values representing the latitudes or longitudes in degrees that either span the entire globe or can be a regional (non-global lat-long grid).
The tripolar grid is a generic non-global rectilinear grid with a non-pole at the pole. Since the latitude and longitude both vary as either the 1st or 2nd grid index vary the coordinates must be stored as 2D dimensional arrays. We also output the corners of the grid as standard which necessitates an extra 2 dimensions to store the corner values
dimensions:
XCdim = 73 ;
Xdim = 72 ;
YCdim = 37 ;
Ydim = 36 ;
time = UNLIMITED ; // (1 currently)
variables:
double Xdim(Xdim) ;
Xdim:long_name = "Fake Longitude for GrADS Compatibility" ;
Xdim:units = "degrees_east" ;
double Ydim(Ydim) ;
Ydim:long_name = "Fake Latitude for GrADS Compatibility" ;
Ydim:units = "degrees_north" ;
double lons(Ydim, Xdim) ;
lons:long_name = "longitude" ;
lons:units = "degrees_east" ;
double lats(Ydim, Xdim) ;
lats:long_name = "latitude" ;
lats:units = "degrees_north" ;
double corner_lons(YCdim, XCdim) ;
corner_lons:long_name = "longitude" ;
corner_lons:units = "degrees_east" ;
double corner_lats(YCdim, XCdim) ;
corner_lats:long_name = "latitude" ;
corner_lats:units = "degrees_north" ;
float time(time) ;
time:begin_date = 20000416 ;
time:begin_time = 3000 ;
time:long_name = "time" ;
time:time_increment = 10000 ;
time:units = "minutes since 2000-04-16 00:30:00" ;
float AREA(time, Ydim, Xdim) ;
AREA:_FillValue = 1.e+15f ;
AREA:add_offset = 0.f ;
AREA:fmissing_value = 1.e+15f ;
AREA:long_name = "MOM_ocean_area_at_t-points" ;
AREA:missing_value = 1.e+15f ;
AREA:regrid_method = "bilinear" ;
AREA:scale_factor = 1.f ;
AREA:standard_name = "MOM_ocean_area_at_t-points" ;
AREA:units = "m+2" ;
AREA:valid_range = -1.e+15f, 1.e+15f ;
AREA:vmax = 1.e+15f ;
AREA:vmin = -1.e+15f ;