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Mike, Assuming: THTA = TMPK * ( 1000 / PRES ) ** RKAPPA then, is is your definition of Wetbulb potential temperature: THTW = TMWK * ( 1000 / PRES ) ** RKAPPA If thats the case, then you can either use the gfunc THTA(tmpc,pres) as thta(sub(tmwk,273),pres) or mul(tmwk,exp(quo(1000,pres),KAPPA)) Steve Chiswell Unidata User Support On Thu, 28 Sep 2000, Michael Brennan wrote: > Steve, > > Thanks for the info. Now that I have that solved, one more question. > Is there any easy way to calculate Wetbulb Potential Temperature in > GEMPAK or GARP? > > Thanks again, > > Mike > > Steve Chiswell wrote: > > > > Michael, > > > > The Garp macro, eg $GARPHOME/fdf/scalar/default/HAS/WetbulbT_C > > is attributed to: > > ! GARP Field Description File (FDF) Template > > ! > > ! Field: Wetbulb Temperature in Celsius. > > ! > > ! Ronald Humble <address@hidden> > > <snip> > > function = sub(sub(TMPK,(mul(sub(quo(MIXR,quo(RELH,100)),MIXR),2490))),273) > > > > The GEMPAK function TMWK (Wet Bulb Temperature in Kelvin) > > is defined in the GEMPAK User Guide, appendix B, and in the > > source code $GEMPAKHOME/source/gemlib/pr/prtmwb.f > > > > C* This function computes wet bulb temperature from the temperature, * > > C* mixing ratio, and pressure. The result is obtained by solving * > > C* for the temperature at which saturation occurs when the latent * > > C* heat required to vaporize the water is provided by a cooling of * > > C* the air. The equation representing the process is * > > C* * > > C* ( TMPK - TMWB ) * CP - ( Rsat (TMWB) - RMIX ) * LVAP = 0 * > > C* * > > C* This implicit equation is solved by Newton's method, since the * > > C* saturation mixing ratio Rsat is a transcendental function of * > > C* TMWB. * > > C* * > > C* The expressions for the heat of vaporization (LVAP) and saturation * > > C* vapor pressure are equations (2) and (10) from Bolton (MWR, 1980). * > > > > Steve Chiswell > > Unidata User Support > > > > On Thu, 28 Sep 2000, Michael Brennan wrote: > > > > > What is the difference between the way GEMPAK calculates TMWK and the > > > GARP macro for Wetbulb Temperature? > > > > > > Thanks, > > > > > > Mike > > > >