GEMPAK Online Tutorial > GEMPAK Grid Programs
7.0 GEMPAK Grid Data Types
We've already seen a few programs that deal with grid files.
Now we will get a chance to see what lurks deep in these grids.
Here we will look at the programs which display gridded data on
2-D horizontal surfaces at a specified level. Next in the
Graphing Programs we will see programs which
plot vertical profiles and time series using grids.
Gridded data may be obtained from numerical model output,
or by performing objective analysis on surface or sounding
data sets using the OA programs.
For now, we will deal with data that is already in gridded form.
Later we will see what goes in to converting surface and upper air
data into grid files.
Gridded data assumes one of two forms:
- Scalar data - possess only magnitude
- Vector data - comprised of both magnitude and direction
When plotting gridded data, we must know what form the data will assume.
The following programs are used for horizontal data plots:
GDCNTR is used to produce contour plots of data which possess
magnitude. Since vectors possess magnitude, you can contour
the them as well as scalars. GDSTREAM is used to draw
streamlines through a vector field, while GDWIND is used to plot
either barbs or arrows at grid points. GDPLOT2 is a combination
of GDCNTR, GDWIND, GDSTREAM and GDMAP. GDPLOT2 doesn't possess any unique
capabilities, but it can save time in plotting when you
will be plotting both contours and vectors.
In addition to grid fields which are present in the grid file,
GEMPAK possess a robust library
of mathematical and meteorological
functions for manipulating grids. In addition to plotting these
fields, the program GDDIAG
may be used to compute and store derived grids.
GEMPAK Online Tutorial > GEMPAK Grid Programs