From: Janet Roseli <Janet.Brockett@noaa.gov>
Date: December 3, 2007 9:58:23 AM MST
To: Robert Luke <Robert.Luke@noaa.gov>
Subject: Dew Point



double DlgMeterolDataLb::dewpt(double DryBulb, double WetBulb)
{                 //  Will return a (float) dew point when passed a drybulb and
           //  a wetbulb temperature in Degrees C.
           //  Returns 999 if the dew point can not be computed
                       //   dew point based on casio program  code
           //   coefficients for saturation vapor pressure
           //   with respect to ice,    with respect to water
                       double coef[7][2] = {6.109177956,       6.107799961,
                 5.03469897E-1,     4.436518521E-1,
                 1.886013408E-2,    1.428945805E-2,
                 4.176223716E-4,    2.650648471E-4,
                 5.824720280E-6,    3.031240396E-6,
                 4.838803174E-8,    2.034080948E-8,
                 1.838826904E-10,   6.136820929E-11};
                       double p,q,w,dif,deweq;
           int i;
           int ice;
           //int ihold;
           CString cshold;
                       if(WetBulb <= 0)
              ice = true;
           else
               ice = false;
                                   w=WetBulb;
           dif=DryBulb - WetBulb;
           if (dif < 0.0)
           {
               return 999.;
           }
           i=1;
           if(ice)i=0;
                             p=coef[0][i]+w*(coef[1][i]+w*(coef[2][i]+w*(coef[3][i]+w*(coef[4][
           i]+ w*(coef[5][i]+w*coef[6][i])))));
                       // use standard atmosphere of 29.92 inches of mercury
                      p=p-(1013.20789*dif*(0.00066*(1.+w* 0.00115)));
          if(p >= 0.0)
          {
              q=log(p);
              deweq= (243.5*q-440.8)/(19.48-q);
              //ihold = int(deweq);
                              return deweq;
          }
          else
            return 999.;
           }