GEMPAK Online Tutorial
24 VERTICAL COORDINATES
GEMPAK supports the following known vertical coordinates:
- NONE - Surface Data
- PRES - Pressure
- HGHT - Height
- THTA - Potential Temperature
- SGMA - Sigma
- PAGL - Pressure Above Ground
- HAGL - Height Above Ground
Other vertical coordinates that GEMPAK doesn't know about can
be handled as long as they are 4 letter representations,
such as ETAL.
Interpolation and Transformation
Occasionally, the vertical coordinate on which
data are available in there native format is not the
optimum coordinate for performing analysis. Similarly,
it is possible that data may not be provided at
the desired level for analysis.
GEMPAK provides for interpolating to alternate levels
and coordinates through the program
GDVINT. Additionally, the grid area may be subsetted to
a new grid file using GDVINT. If the output file does not currently
exist, it will be created.
- GVCORD specifies the input and output vertical coordinates
separated by a slash (ie input/output).
- When SGMA is specified, the pressure on SGMA=0 is
given following a semicolon. For example, if the
pressure at SGMA=0 is 50 mb, the specification in
GVCORD is SGMA:50.
- VCOORD specifies a list of GEMPAK coordinate names found in the
input file to be converted to the output coordinate.
Here's one for practice:
- Convert the current ETA analysis to a THTA vertical coordinate.
- Construct a plot of Montgomery Stream Function (PSYM)
on the 300K Theta surface for F000.
- Overlay pressure contours on your Montgomery Stream Function
analysis to show vertical motion for air parcels.
GEMPAK Online Tutorial
