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>From: "Matthew G. Fearon" <address@hidden> >Organization: Desert Research Institute >Keywords: 200003092327.QAA01340 >Steve, > >I was wondering the methodology or scheme that is used within >the gdvint program to interpolate from one vertical coord. to the >other. For example, say I want to convert from pressure to sigma >and I use the following specification with the gdvint program > > glevel = 8000-4500-500;10000-8050-50 > gvcord = pres/sgma:1 > >this will give me back sgma levels of 10000, 9950, 9900, 9850, >9800 etc.. to 8000 and levels of 8000, 7500, 7000 etc.. to 4500 > >I realize sigma is p/psfc but there are only so may pressure levels >available in model output, e.g. 1000 950 900 etc every 50mb, to >use for interpolation of the sigma levels. I was wondering kind >of vertical interpolation method is being used besides p/psfc. Is it >linear or is some other scheme being used ? > >Sorry my question is a bit wordy. Hopefully you know what >I am getting at. Please reply when it is convenient. > >Thank you, >Matt Fearon >address@hidden > > Matt, The interpolation routines are called from: $GEMPAKHOME/source/programs/gd.gdvint/vivint.f (calls to vc_quad, vc_lnin) Where possible, the quadratic interpolation using log pressure are performed, otherwise, a linear interpolation using lon pressure is performed. Steve Chiswell