Run the following commands to regrid 2-meter temperature data several different ways:

• Regrid to a pre-defined named NCEP Grid 130:

• The default interpolation method is nearest neighbor. Rerun this command using the mean within a 10x10 interpolation box, which applies a large amount of smoothing:

• Next, define the output grid using the path to another gridded data file over the Pacific Northwest of the United States using bilinear interpolation:

• Lastly, manually define a LatLon output domain (latlon Nx Ny lat_ll lon_ll delta_lat delta_lon) using the default nearest neighbor interpolation method:

Run Plot-Data-Plane to visualize the output we generated on the previous page. Use the -plot_range option to keep the color scale fixed across all plots.

• Plot the input data:

• Plot the nearest neighbor G130 output:

• Plot the smoothed G130 output:

• Plot the bilinear Pacific Northwest output:

• Plot the custom lat/lon grid output:

Open each of these PostScript images and compare them to the input ($MET_TUTORIAL_DATA/output/regrid_data_plane/tmp_z2_input.ps).

In this tutorial, we'll run COPYGB several times to do the following:

1. Interpolate to a predefined NCEP grid.
2. Interpolate to a user-defined Lat/Lon grid.
3. Interpolate to a user-defined Lambert Conformal grid.
4. Interpolate to a user-defined Polar Stereographic grid.

Predefined NCEP Grid

First, we'll run the wgrib tool to dump out information about a sample GRIB file:

The -V argument for wgrib dumps out the definition of the grid on which the data resides. This data is on a Lambert Conformal grid with the grid definition parameters listed below:

Lambert Conf: Lat1 12.190000 Lon1 -133.459000 Lov -95.000000
Latin1 25.000000 Latin2 25.000000 LatSP 0.000000 LonSP 0.000000
North Pole (185 x 129) Dx 40.635000 Dy 40.635000 scan 64 mode 8

This data resides on NCEP Grid 212 (image), a 40-km Lambert Conformal grid over the contiguous United States. Now run COPYGB on this file to interpolate this data to NCEP Grid 202 (image), a 190-km Polar Stereographic grid:

In the command above the -x option indicates that we want the data to be extracted and the -g 202 option indicates that the data should be interpolated to NCEP Grid 202. Next, run wgrib on the output and note that the grid definition has changed:

The resulting grid definition parameters are listed below:

polar stereo: Lat1 7.838000 Long1 -141.028000 Orient -105.000000
north pole (65 x 43) Dx 190500 Dy 190500 scan 64 mode 9

For a list of the predefined NCEP grids available, please see:
http://www.nco.ncep.noaa.gov/pmb/docs/on388/tableb.html

For most users of WRF and MET, using the predefined NCEP grids will not suffice. Instead, you will often want to interpolate to the domain on which your model data resides. This is easy to do with COPYGB but will require you to define the grid to be used on the command line. The grid definition arguments to COPYGB differ based on the type of projection used. Listed below are the arguments for user-defined Lat/Lon grids:

copygb -g"255 0 NX NY LAT0 LON0 128 LAT1 LON1 DX DY 64" -x in.grb out.grb

where
	255 0	User-defined Lat/Lon grid
	NX	Number of points on latitude circle
	NY	Number of points on longitude meridian
	LAT0	Latitude of origin * 1000 (lat = -90 ... 90)
	LON0	Longitude of origin * 1000 (lon = -180 ... 180)
	128
	LAT1	Latitude of extreme (last) point * 1000
	LON1	Longitude of extreme (last) point * 1000
	DX	Longitudinal increment in millidegrees
	DY	Latitudinal increment in millidegrees
	64

Please note that all of the grid definition parameters must be integers. All latitude, longitude, and increments values are given in thousandths of a degree.

User-Defined Lat/Lon Grid

Let's define a Lat/Lon grid over the central United States as follows:

• Latitude ranging from 35N to 45N
• Longitude ranging from 105W to 90W
• 0.5 degree grid spacing

Translate this definition to the COPYGB grid specification as follows:

• NX = 30
• NY = 20
• LAT0 = 35000
• LON0 = -105000
• LAT1 = 45000
• LON1 = -90000
• DX = 500
• DY = 500

Plug these numbers into the grid specification and run COPYGB as follows:

Lastly, run wgrib on the COPYGB output and make sure the grid definition matches what you expected:

The COPYGB grid definition parameters for Lambert Conformal grids are listed below:

copygb -g"255 3 NX NY STARTLAT STARTLON 8 CENLON DX DY POLE 64 TRUELAT1 TRUELAT2" -x in.grb out.grb

where
	255 3	User-defined Lambert Conformal grid
	NX	Number of points on latitude circle
	NY	Number of points on longitude meridian
	STARTLAT	Southwest corner latitude * 1000 (lat = -90 ... 90)
	STARTLON	Southwest corner longitude * 1000 (lon = -180 ... 180)
	8
	CENLON	Center longitude * 1000
	DX	Longitudinal increment in meters
	DY	Latitudinal increment in meters
	POLE	Northern (0) or southern (128) hemisphere
	64
	TRUELAT1	First true latitude * 1000
	TRUELAT2	Second true latitude * 1000

Please note that all of the grid definition parameters must be integers. All latitude and longitude values are given in thousandths of a degree. The grid increments are given in meters.

User-Defined Lambert Conformal Grid

Rather than defining a Lambert Conformal manually, we'll use the output of wgrib to define the grid we'd like to use. Let's look again at the wgrib output for NCEP grid 212:

Here is the grid definition:

Lambert Conf: Lat1 12.190000 Lon1 -133.459000 Lov -95.000000
Latin1 25.000000 Latin2 25.000000 LatSP 0.000000 LonSP 0.000000
North Pole (185 x 129) Dx 40.635000 Dy 40.635000 scan 64 mode 8

Translate this definition to the COPYGB grid specification as follows:

• NX = 185
• NY = 129
• STARTLAT = 12190
• STARTLON = -133459
• CENLON = -95000
• DX = 40635
• DY = 40635
• TRUELAT1 = 25000
• TRUELAT2 = 25000

Plug these numbers into the grid specification and run COPYGB follows:

Lastly, run wgrib on the COPYGB output and make sure the grid matches the one listed above:

The COPYGB grid definition parameters for Polar Stereographic grids are listed below:

copygb -g"255 5 NX NY STARTLAT STARTLON 8 CENLON DX DY POLE 64" -x in.grb out.grb

where
	255 5	User-defined Polar Stereographic grid
	NX	Number of points on latitude circle
	NY	Number of points on longitude meridian
	STARTLAT	Southwest corner latitude * 1000 (lat = -90 ... 90)
	STARTLON	Southwest corner longitude * 1000 (lon = -180 ... 180)
	8
	CENLON	Center longitude * 1000
	DX	Longitudinal increment in meters
	DY	Latitudinal increment in meters
	POLE	Northern (0) or southern (128) hemisphere
	64

Please note that all of the grid definition parameters must be integers. All latitude and longitude values are given in thousandths of a degree. The grid increments are given in meters.

User-Defined Polar Stereographic Grid

Again, let's look at the wgrib output for a Polar Stereographic grid and use it to define the grid definition arguments for COPYGB. Run wgrib on a Polar Stereographic dataset:

Here is the grid definition:

polar stereo: Lat1 7.838000 Long1 -141.028000 Orient -105.000000
north pole (65 x 43) Dx 190500 Dy 190500 scan 64 mode 9

Translate this definition to the COPYGB grid specification as follows:

• NX = 65
• NY = 43
• STARTLAT = 7838
• STARTLON = -141028
• CENLON = -105000
• DX = 190500
• DY = 190500
• POLE = 0

Plug these numbers into the grid specification and run COPYGB follows:

Lastly, run wgrib on the COPYGB output and make sure the grid matches the one listed above: