GLBy0.08/expt 93 lat and lon

[Dantonio Corrado]

Hi everyone,

I use the url"https://ncss.hycom.org/thredds/ncss/GLBy0.08/expt_93.0/uv3z?var=water_u&north=44&west=136&east=164&south=28&horizStride=1&time_start=2022-01-04T00%3A00%3A00Z&time_end=2022-01-04T09%3A00%3A00Z&timeStride=1&vertCoord=15&accept=netcdf" to download data. And I didn't chose to add lat and lon variables in, however the data I downloaded contains latitude and longitude. Why?

Dan

[Dantonio Corrado]

And I compared the latitude and longitude before and after whether or not I chose to include the latitude and longitude variables, which are the same. So can I use the latitude and longitude in the data which I didn't  chose to include the latitude and longitude variables?

Dan

[Alan Wallcraft]

When the grid is rectilinear, like GLBy0.08, the coordinate variables (x and y axis) are longitude and latitude.  So you get these by default.

For curvi-linear grids, the coordinate variable isn't lon,lat because the axis has to be 1-d and lon,lat are 2-d.  In this case you would have to ask separately for lon,lat.

Alan

[Dantonio Corrado]

Dear Alan

Thanks for replying to my question, can you give me an example of which ones are  curvi-linear grids?

Dan

[Alan Wallcraft]

The original model is on a curvi-linear grid, see for example regional_depth_11.nc, but all our "distribution" grids are recti-linear.

COAPS 28> ncdump -h regional_depth_11.nc
netcdf regional_depth_11 {
dimensions:
MT = UNLIMITED ; // (1 currently)
Y = 3298 ;
X = 4500 ;
variables:
double MT(MT) ;
MT:long_name = "model time" ;
MT:units = "days since 0001-01-16 00:00:00" ;
MT:calendar = "360_day" ;
MT:axis = "T" ;
double Date(MT) ;
Date:long_name = "date" ;
Date:units = "day as %Y%m%d.%f" ;
Date:C_format = "%13.4f" ;
Date:FORTRAN_format = "(f13.4)" ;
int Y(Y) ;
Y:point_spacing = "even" ;
Y:axis = "Y" ;
int X(X) ;
X:point_spacing = "even" ;
X:axis = "X" ;
float Latitude(Y, X) ;
Latitude:standard_name = "latitude" ;
Latitude:units = "degrees_north" ;
float Longitude(Y, X) ;
Longitude:standard_name = "longitude" ;
Longitude:units = "degrees_east" ;
Longitude:modulo = "360 degrees" ;

float depth(MT, Y, X) ;
depth:coordinates = "Longitude Latitude Date" ;
depth:units = "m" ;
depth:_FillValue = 1.267651e+30f ;
depth:valid_range = 5.f, 7199.98f ;
depth:long_name = "depth" ;

// global attributes:
:Conventions = "CF-1.0" ;
:title = "HYCOM GLBb0.08" ;
:institution = "Naval Research Laboratory" ;
:source = "HYCOM archive file" ;
:experiment = "37.1" ;
:history = "field2ncdf" ;
}

Alan.