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20040424: Example scripts to create hourly surface objective products.

>From: Michael W Dross <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200404250200.i3P20fCT025076

>
>
>
>
>Hi,
>
>I am looking for example Gempak scripts that create some standard
>convective surface analysis.
>I was able to create some of these products several years ago when I was
>working with McIDAS.
>I am fairly new to Gempak. I am trying to create products similar to LAPS
>or the AFOS ADAP
>application.
>
>For example, calculating & contouring hourly CAPE from observed surface obs
>combined with
>forecast model upper air data, such as the RUC.  I assume this is possible.

Use the OABSFC program to grid surface data to the same projection
as the RUC you have (#211, #236, #252) (CPYFIL allows to
to duplicate the projection information from an existing file
in GDCFIL to create the empty grid file).

STHE is one of the surface parameters that you can plot / grid
from surface data.

The other parameters you can calculate using the grid functions
once you have preformed the objective analysis.

When you grid surface data, the times will be in the form of DATTIM,
while the model data is of the form GDATTIM (eg forecast fxxx).
To mix the 2 sets, you will have to use the inline grid time, level, coordinate
modifiers "^", "@", "%" since you will be accessing surface data with
model data on pressure levels, at forecast times etc.

>
>Also if anyone would be willing share any scripts that compute surface
>theta-e, theta-e advection,
>moisture convergence, LCL level, CAP strength, Lifted Index, etc.

- in OABSFC you can grid STHE, UWND, VWND and compute
theta-e advection with GFUNC = ADV(sthe,wnd)

- in OABSFC you can also grid TMPC, DWPC, PALT to compute other quantities.
For moisture convergence, eg flux divergence of a scalar
GFUNC = SDIV(mixr(dwpc,palt),wnd)

Pressure at LCL
GFUNC = PLCL(palt,tmpc,dwpc)

Other quantities such a lifted index (aside from that already provided
in the model grids), you can compute using your surface grid data
and the model data. For example, to compute lifted index
as the dT at 500mb between a parcel from the surface lifted data
and the 500mb temperature in the RUC_20 grids, then assuming
you have surface temps at 20z in surface.grid
and your 20Z run accesible using the RUC_20 template,
you can compute LI in GDCNTR like:

 GDFILE   = surface.ruc+ruc_20|040428/2000
 GDATTIM  = 2000
 GLEVEL   = 0
 GVCORD   = none
 GFUNC    = sub(tmpk@500%pres^f000+2,tmst(sthe,500))

the above gfunc will use TMPK at 500mb, f000 from the 040428/2000
run of the RUC_20 (eg grid #252) and subtract from this the 
computed parcel temperature at 500mb from the surface STHE value.



You can also use or adapt may of the functions found in the $NMAP_RESTORE 
directory
which are used for the predefined plots in NMAP2 as a starting point for
developing your own functions.


Steve Chiswell

-
>
>Thanks in advance.
>
>Mike
>________________________________________________________
>Michael Dross                             address@hidden
>Duke Power Company                  Meteorologist
>9700 David Taylor Dr.               Voice: 704-594-0341
>Charlotte, NC 28269                       Mobile: 980-722-0756
>
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