This directory contains

   pe_icon_out.nc.gz          - A compressed output file from a 30 day
                                simulation initialized at 12:00gmt on
                                August 1, 2000
   pe_icon_out.header         - A dump of the header information of
                                pe_icon_out.nc created by the ncdump utility
   ReadMe.txt                 - This file.
   grids_AOSN2_med_sasm.nc.gz - A compressed grid file.

The relevent information for extracting velocity data is given by the following
dimensions and variables:

dimensions:
	vlat = 84 ;
	vlon = 53 ;
	outlev = 20 ;
	vector = 2 ;
	time = UNLIMITED ; // (61 currently)
	axis3 = 3 ;

variables:
	float vgrid3(vlat, vlon, outlev, axis3) ;
		vgrid3:long_name = "3D grid positions at velocity points" ;
		vgrid3:axis = "1: longitude, 2: latitude, 3: depth" ;
		vgrid3:units = "degrees_east, degrees_north, meter" ;

	float time(time) ;
		time:long_name = "time since initialization" ;
		time:units = "seconds" ;
		time:field = "time, scalar, series" ;

	float vtot(time, vlat, vlon, outlev, vector) ;
		vtot:long_name = "total velocity" ;
		vtot:units = "centimeter second-1" ;
		vtot:field = "total velocity, vector, series" ;
		vtot:positions = "vgrid3" ;
		vtot:_FillValue = 1.e+35f ;
		vtot:missing_value = 1.e+35f ;

To get the positions of every velocity point on the HOPS sigma-coordinate
system:

   longitude = vgrid3(:,:,1,1)
   latitude  = vgrid3(:,:,1,2)
   depth     = vgrid3(:,:,:,1)

Notice that only the top level LAT/LON data is necessary.  These values
don't change with depth.

The navigation of the total velocity ("vtot") is indicated by the
positions attribute.

One thing to beware of:  the velocity is oriented along the model grid
   vtot(:,:,:,:,1) is roughly across isobaths
   vtot(:,:,:,:,2) is roughly along isobaths
To rotate back to lat/lon orientation, extract the variable "lrotang" from
the grids file and use the formula

   phi(i,j) = lrotang(i,j)*pi/180
   ulon(n,j,i,k) = vtot(n,j,i,k,1)*cos(phi(i,j)) - vtot(n,j,i,k,2)*sin(phi(i,j))
   vlat(n,j,i,k) = vtot(n,j,i,k,1)*sin(phi(i,j)) + vtot(n,j,i,k,2)*cos(phi(i,j))

One other pointer, the last slab of velocity data
   vtot(:,vlat,:,:,:)
is filler and just contains the fill values
		vtot:_FillValue = 1.e+35f ;
If you're working in Matlab, it's usually a good idea to check for these
fill values when the data is first read in, and replace them with NaN's.