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Mark, Mixing ratio is scaled by 1000 for display as g/kg when plotting the known variables MIXR, MIXS, SMXR, SMXS since that is a traditional (non-MKS) display quantity, though in MKS units, it is calculated in g/g. Your computation of MAGGRADSMXR is not interpreted as mixing ratio any longer (as the resulting name of the computed field is no longer a form of mixing ratio). So, your estimated value of 1.3 g/kg/10km would be 1.3x10^-7 g/g/m or 130x10^-9 (or around the upper end of the range you mentioned in your email). If it is more convenient to display, as g/kg, you can add a mul(x,1000) for g/kg or even scale up to "per 100km" instead of meters as some publications use. Steve -------------------------------------------------------------------------- Dr. Steve Chiswell Uniadta User Support On Fri, 2004-09-24 at 10:37, Mark Conder wrote: > Hi Mr. Chiswell > > I have a question regarding the GRAD function on gridded data in > GEMPAK? > > I have a grid of sfc mixing ratios. > If is use MAG(GRAD(SMXR)) I get values on the order of 10-100 with a > 10**9 scale factor. > > My grid spacing is approx. 30 km. > For my dryline case I can manually see a E-W gradient of say about 4 > g/kg/30 km or 1.3/10 km (for example on successive E-W grid points the > smxr goes from 4 to 8 to 12) > > It looks as though the GRAD function does a d(smxr)/dx and a d > (smxr)/dy for the gradient. But even with the minimal observed > gradient in the y-dir I can't understand the resulting small values. > > I guess I am wondering if the values are scaled down quite a bit. I > guess from km to m would scale it down by 1000, but that seems to > still leave about a 10^4 or 10^5 unknown factor. > > Thanks, > Mark > > > ________________________________________ > Mark Conder > National Weather Service Forecast Office > Lubbock, TX > >