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19990701: stability from model grid

Matt,

I interpreted your previous question as how to calculate a
sfc to 5km stability (eg a single layer).

The problem you have is that the ETA grids have temperature 
all the way down to 1000mb, even if that level is below ground.
From your statement below, you only want to see stab(tmpc) values
where the layer is above ground.

Actually, this is something that gdcross does in a cross section,
but since you want to output the values at a singe grid point-
you are presumably using GDPROF which plots a profile at a
single gridpoint/time and outputs the data values it calculates.
This is quite easy with:
gvcord=pres
gfunc = stab(tmpc)

however, the output will extend below the surface level when the model
levels include tmpc below the surface.

GDPROF requires two conditions for not extending below the surface
by following the grid levels all the way down:

1) The surface pressure grid should be available on the same gvcord
as the gfunc is calculated on.

2) The gfunc should not be a layer quantity

What needs to be done is 1) copy the pres@0%none grid to
pres@0%pres, and 2) compute stab(tmpc) and output the grid to
a single level rather than a layer.

Attatched is a quick script that will compute STBC at the midpoint of
each 50mb model level, for each forecast time, and copy the
surface pressure grid. After running the script, you can use
GDPROF like:

 GPOINT   = den
 GDATTIM  = f048
 GVCORD   = pres
 GFUNC    = stbc
 GVECT    = 
 GDFILE   = $HDS/1999070112_eta_grid211.gem
 LINE     = 5
 MARKER   = 0
 BORDER   = 1
 PTYPE    = log
 SCALE    = 0
 XAXIS    = 
 YAXIS    = 1000/100
 WIND     = an6
 REFVEC   = 
 WINPOS   = 1
 FILTER   = 0
 TITLE    = 5/-1
 PANEL    = 0
 CLEAR    = y
 TEXT     = 1/22/1
 DEVICE   = xw
 OUTPUT   = t
 THTALN   = 
 THTELN   = 
 MIXRLN   = 
 GEMPAK-GDPROF>r
 GDPROF PARAMETERS

 Grid file:                 $HDS/1999070112_eta_grid211.gem
 Grid function:             stbc
 Grid vector function:      
 X,Y grid point:             42.49   32.21
 Lat/lon:                    39.87 -104.67
 Number of levels:           14
 Data range:                 -8.68   -1.49
 Scaling factor:             10** 0
 Wind display:            an6                                                   
                  
Enter <cr> to accept parameters or type EXIT:




                                    PROFILE



       990703/1200V048  STBC   DEN


       LATITUDE, LONGITUDE = (  39.87, -104.67 )




                  PRES                  STBC
                 775.00               -6.944
                 725.00               -7.588
                 675.00               -7.652
                 625.00               -6.594
                 575.00               -6.560
                 525.00               -8.220
                 475.00               -8.401
                 425.00               -8.681
                 375.00               -7.787
                 325.00               -7.250
                 275.00               -7.777
                 225.00               -6.437
                 175.00               -4.356
                 125.00               -1.485
 Parameters requested: GPOINT,GDATTIM,GVCORD,GFUNC,GVECT,GDFILE,LINE,MARKER,
 BORDER,PTYPE,SCALE,XAXIS,YAXIS,WIND,REFVEC,WINPOS,FILTER,TITLE,PANEL,CLEAR,
 TEXT,DEVICE,OUTPUT,THTALN,THTELN,MIXRLN.
 GEMPAK-GDPROF>

In the above run, the surface pressure for DEN is 817 mb, so the first
layer that stability is above the ground level for the ETA model is the
800:750 layer. STBC is output as valid at 775mb, and so on up to the top..

Let me know if you need further assistance.

Steve Chiswell
Unidata User Support

--------------------------------------------------------------
#!/bin/csh -f
# set the eta model file name appropriately!
set GDFILE=$HDS/1999070112_eta_grid211.gem

set FHRS=("f000" "f006" "f012" "f018" "f024" "f030" "f036" "f042" "f048")

# loop for each forecast time
foreach FHR ($FHRS)

# copy the surface pressure grid to gvcord=pres
gddiag << EOF1        
   GDFILE = $GDFILE
   GDOUTF = $GDFILE
   GDATTIM  = $FHR
   gfunc = pres
   glevel = 0
   gvcord = none
   grdnam = pres@0%pres
   r

   e
EOF1

# compute stab(tmpc) for 1000:950 layer and output to STBC@975
# repeat up through 150:100 mb layer.
set GLEV1=1000
while($GLEV1 > 100)
   @ GLEV2 = $GLEV1 - 50
   @ GLEVA = $GLEV1 + $GLEV2
   @ GLEVA = $GLEVA / 2

   gddiag << EOF2
   GDFILE = $GDFILE
   GDOUTF = $GDFILE
   GFUNC    = stab(tmpc)
   GDATTIM  = $FHR
   GLEVEL   = ${GLEV1}:${GLEV2}
   GVCORD   = pres
   grdnam = stbc@${GLEVA}
   r

   e
EOF2
@ GLEV1 = $GLEV1 - 50

end # end while GLEV

end # foreach FHR










>From: Matt Fearon <address@hidden>
>Organization: .
>Keywords: 199907010105.TAA27142

>Your previous reply was very helpful, but I think I may not
>of explained my question enough. I am using the eta model.
>I would like to calculate the stability or lapse rate in layer
>sections from the surface up to 500mb. I am looking to
>locate stable and unstable layers from the surface up to 500mb.
>I need these calculations at individual grid points for each
>forecast hour.
>
>Performing a calculation of dT/dZ from the surface to 500mb didn't
>provide me with the ability to locate individual stability regions. Sorry to
>be bothersome. Any advice would be extremely helpful.
>
>Thank you,
>Matt Fearon
>address@hidden
>
>Unidata Support wrote:
>
>> >From: Matt Fearon <address@hidden>
>> >Organization: .
>> >Keywords: 199906302250.QAA24636
>>
>> >I am a fairly new user of gempak software, but I know how to tinker
>> >around
>> >pretty well.
>> >
>> >I am trying to extract stab(tmpc) for layers above ground level to
>> >achieve a temperature lapse rate at individual grid points (from the
>> >surface
>> >to about 5km). I have been using the gdlist program, however the region
>> >I am
>> >concerned with is California. Therefore I have to deal with elevation
>> >issues.
>> >I have been trying to use hagl instead of pres for the vertical
>> >coordinates, but I
>> >have been unsuccessful.
>> >
>> >If someone knows a good method for extracting stab(tmpc) to establish a
>> >lapse rate
>> >at individual grid points considering elevation, I would greatly
>> >appreciate all advice.
>> >
>> >Thank you,
>> >Matt Fearon
>> >address@hidden
>> >
>>
>> Matt,
>>
>> >From your question, you apparently want to calculate:
>>
>> T(~5km) - T(surface)
>> -------------------
>> Z(~5km) - Z(surface)
>>
>> If you are using the ETA 211 grid from the IDD for instance,
>> you have  T@2m, T@500mb, Z@surface, Z@500mb.
>>
>> So, assuming that either 500mb or 550mb is adequate in approximating
>> ~5km, you can do:
>>
>> gvcord = pres
>> glevel = 500
>> gfunc = quo(sub(tmpc,tmpc@2%hagl),sub(hght,hght@0%none^f000))
>>
>> The Height grid is only given at F000 (since the ground doesn't advect with 
> time),
>> hence the ^f000 specification).
>>
>> Actually, since the above temperature is at 2m, while the height is at 0m HA
> GL,
>> you could add 2m to the height subtraction around the last "sub"
>> to get something like: quo(sub(,),sub(hght,add(hght@0%none^f000,2)))
>>
>> The point is, depending on what model grid you have, you may have to
>> determine if you have temp at 2m , and height at 0m etc.
>> The best way to do this is to use gdinfo to inspect your grids
>> to determine what parameters they give you to work with.
>> Steve Chiswell
>> Unidata User Support
>> ****************************************************************************
>> Unidata User Support                                    UCAR Unidata Program
>> (303)497-8644                                                  P.O. Box 3000
>> address@hidden                                   Boulder, CO 80307
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>