8.3 Grids and Grid Files - Creating Grids and Grid Files

In this exercise, you will create a new grid dataset, copy and contour grids,
create advection and divergence grids, and list the grids and grid files.

- Generate a local grid dataset in position 2 of the TEST-GRID dataset
with a maximum of 100 grids, and the description
ADVECTION AND DIVERGENCE GRIDS. Copy in the 12 hour 1000 mb forecast grids
from the first BLIZZARD grid position.
Type: **GRDCOPY BLIZZARD/GRIDS.1 TG.2 DEL=YES LEVEL=1000 FHOUR=12 TITLE='ADVECTION AND DIVERGENCE GRIDS' MAXGRD=100 NUM=ALL**

If you don't specify a maximum number of grids, the grid file is created with space for 1000 grids.

- List the new dataset.
- Type:
**GRDLIST TG.2 NUM=ALL**

- Type:
- Check to see that TG.2 contains the grids required to calculate divergence.
- Type:
**GRDLIST TG.2 DER=DVG**

GRDLIST TG.2 DER=DVG PARAM LEVEL DAY TIME SRC FHOUR FDAY FTIME GRID PRO ----- ------- ------------ -------- ---- ----- ------------ -------- ----- ---- DVG 1000 MB 11 MAR 93070 12:00:00 NGM 12 12 MAR 93071 00:00:00 MATH MERC Number of grids listed = 1 GRDLIST - done

Notice the GRID number is listed as "MATH". This indicates that the component grids required to create a divergence grid all exist within the TG.2 grid file. See the help sections of the individual commands for more information on the common meteorological parameters you can calculate from grids by using the DERIVE keyword.If the grid cannot be created, an error will be produced.

- Type:
- Create a divergence grid from from the grids in the dataset.
- Type:
**GRDCOPY TG.2 TG.2 DER=DVG**

- Type:
- List the contents of the dataset to verify that a divergence grid
was added.
- Type:
**GRDLIST TG.2 NUM=ALL**

Dataset position 2 Directory Title= ADVECTION AND DIVERGENCE GRIDS PARAM LEVEL DAY TIME SRC FHOUR FDAY FTIME GRID PRO ----- ------- ------------ -------- ---- ----- ------------ -------- ------ ---- Z 1000 MB 11 MAR 93070 12:00:00 NGM 12 12 MAR 93071 00:00:00 1 MERC T 1000 MB 11 MAR 93070 12:00:00 NGM 12 12 MAR 93071 00:00:00 2 MERC U 1000 MB 11 MAR 93070 12:00:00 NGM 12 12 MAR 93071 00:00:00 3 MERC V 1000 MB 11 MAR 93070 12:00:00 NGM 12 12 MAR 93071 00:00:00 4 MERC DVG 1000 MB 11 MAR 93070 12:00:00 NGM 12 12 MAR 93071 00:00:00 5 MERC Number of grids listed = 5

Notice that the the DVG grid has now been created, has a grid number, and is listed as a PARAMETER.

- Type:
- List information about the divergence grid:
- Type:
**GRDINFO TG.2 PARAM=DVG**

GRDINFO TG.2 PARAM=DVG Statistics of Parameter: DVG Units: 1/S Level of data: 1000 MB Initial time of data: 120000 UTC Initial day of data: 1993070 Data came from: NGM 12-hour forecast Dataset: TG Minimum: -0.6531000E-04 occurred at [row,col]: [ 33, 26] [lat,lon]: [ 20.00, 77.50] Maximum: 0.3372000E-04 occurred at [row,col]: [ 33, 24] [lat,lon]: [ 20.00, 82.50] Mean: 0.2849890E-07 SD : 0.1168576E-04 Number of points analyzed: 1188 Number of points missing: 282 Row range: 1 to 33 Col range: 1 to 36 GRDINFO Done, Number of grids statistically analyzed=1

- Type:
- Create a temperature advection grid using the U, V and T grids. Use
the formula
TADV = -(u*DDX(T) + v*DDY(T)) . Label the new grid TADV and set the units to K/sec.Type: **GRDCOPY TG.2 TG.2 G1='PARAM T' G2='PARAM U' G3='PARAM V' MATH='-(G2*(DDX(G1))+G3*(DDY(G1)))' NEWPAR=TADV K/S**

*Gn*keywords. See the help sections of the individual commands for more information on the use of these keywords. - List information about the temperature advection grid:
- Type:
**GRDINFO TG.2 PARAM=TADV**

- Type:
- OR, if you would like to get statistical information on a grid created
with a mathematical equation, but won't need to actually display the grid,
you can run the GRDINFO command with the MATH keywords included.
Type: **GRDINFO TG.2 G1='PARAM T' G2='PARAM U' G3='PARAM V' MATH='-(G2*(DDX(G1))+G3*(DDY(G1)))' NEWPAR=TTAD K/S**

In the next lesson, you will display the grids you created using the GRDDISP command.