20031202: Gempak - Red Hat Linux - various gfunc and gvect questions

>From: "Allison Hoggarth" <address@hidden>
>Organization: UCAR/Unidata
>Keywords: 200312022223.hB2MNZ42011345

>Institution: North Carolina State University
>Package Version: 5.6
>Operating System: Red Hat Linux
>Hardware Information: Dell
>Inquiry: I am trying to plot a number of variables in GEMPAK, but I
>have been rather unsuccessful.  First of all, I am trying to plot a
>couple of different versions of the Rossby number that differ from the
>given Rossby number within gfunc, but I cannot figure out what needs to
>go into the gfunc.  The first Rossby number is calculated as | dV/dt |
>/ f |V| , where V is the observed wind.  The second Rossby number is
>calculated as |Vag| / |V|, where Vag is the component of the
>ageostrophic winds normal to the flow.

Allison,

since WND is the Gempak observed wind, and CORL is the coriolis
parameter, you can calculate the various terms:
| dV/dt | =  mag(vsub(wnd^f012,wnd^f000))
| V | = mag(WND)
| Vag | = mag(AGE)



>
>The second set of variables that I am trying to plot are four
>components of the divergence equation, and then their sum as well: (1)
>f*zeta; (2) 2*J(u,v), where J is the Jacobian, u is the u-wind, and v
>is the v-wind; (3) Laplacian (geo hght); (4) Beta*u-wind.  The scale of
>each of these 4 components is near 10^-8 or so.   I think I got the
>Laplacian to work out, but I am having troubles with the other three.

Knowing that CORL is f, and Beta is ddy(corl), the rest should fall out.
If you are still having trouble, can you give me specifics of what
your problem is?

>
>The third variable that I am trying to plot is the 300mb Isallobaric
>wind.  I know that to get the Isallobaric wind it is isal(s), but I
>don't know what needs to be used for the 's' and then whether it is
>plotted under gfunc or gvect.

From the GPARM online help:
      Standard vector grids are:
  
        WND     Total wind
        GEO     Geostrophic wind
        AGE     Ageostrophic wind
        ISAL    Isallobaric wind
        THRM    Thermal wind

These vectors will be computed automatically if possible, otherwise 
you can use the ISAL(s) where "s" is most typically HGHT
on pressure coordinates (eg ISAL is equivalent to specifying ISAL(hght) 
for your 300mb plot ). 

Since ISAL is a time difference quantity, your GDATTIM should be
a time range, such as GDATTIM=f012:f000. For example, in gdplot2,
plotting the f000 and f012 300mb hght field and the f012:f000 ISAL
field:
 GDFILE   = eta
 GDATTIM  = f000 ! f012 ! f012:f000
 GLEVEL   = 300
 GVCORD   = pres
 PANEL    = 0
 SKIP     = 0
 SCALE    = 0
 GDPFUN   = hght ! hght ! isal
 TYPE     = c ! c ! s
 CONTUR   = 21
 CINT     = 120
 LINE     = 5 ! 6 ! 3
etc.


You can plot the vectors using TYPE as arrows, barbs, or streamlines,
or transform to a scalar using MAG(isal).


Steve Chiswell




>
>I greatly appreciate any help or insight that you can provide.  Thanks!
>
>
>