19991020: LCL calculations

>From: Matt Fearon <address@hidden>
>Organization: Desert Research Institute
>Keywords: 199910210034.SAA10372

>Steve,
>
>I was wondering if it is possible to calculate the LCL
>(lifting condensation level) for the entire grid for a particular
>forecast period? I have tried using plcl, to get the
>pressure level of the LCL, but that does not seem to work.
>I am trying to use gdlist so I can output to a text file.
>The process I have been trying is below,
>
>$GEMEXE/gdlist <<EOF
>   GDATTIM = f00
>   GLEVEL  = 1000
>   GVCORD  = pres
>   GFUNC   = plcl
>   GDFILE  = /data1/gempak/grids/99101800_eta.gem
>   GAREA   = grid
>   PROJ    = mer
>   SCALE   = 0
>   OUTPUT  = f/dum
>   r
>
>When you have a chance, your suggestions would be
>greatly appreciated.
>
>Thank you,
>Matt Fearon
>address@hidden
>

Matt,

plcl isn't a defined parameter in the gparms, so that is probably the source of
your trouble.

You can compute Tlcl and Plcl using available formulas in many text books.
For example:

Tlcl =                2840
          --------------------------  + 55
          3.5ln(T) - ln(A) - 7.108

   
    A =     P * r
         ----------
          .622 + r         


Plcl = P *  (Tlcl) 
            -----  **3.5
             (T)

Where P is in kPA, T in Kelvin, r is mixing ratio. The other factors come from 
their conversion of Log and Ln and pa to kPa.

So, it can be done with gddiag.....its just not readily available as a gfunc.

Steve Chiswell

            ( T  )