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Hi Randy- > Can IDV interpolate the staggered variables to the > non-staggered or mass points (like w and the > geopotential). Yes, but it's memory intensive and not out of the box. Whenever we do math or combine grids, the grids are resampled to a common domain which is essentially the domain of the first grid in the equation. So for calculating wind speed from u and v, we resample v to the u grid and then do the calculation (sqrt(u*u+v*v)). The resulting grid has the domain of u. There is a formula under the Grids category called Resample Grid. So, you could use this and take the T grid which is unstaggered, and resample the other grids to that, then use those in formulas to calculate the quantities you want. Don > thanks, > randy > > --- Unidata IDV Support <address@hidden> > wrote: > > > Hi Randy- > > > > > we have WRF output in netcdf that we are reading > > into > > > IDV (actually its Mcidas-V). We have been trying > > to > > > display the 2D terrain as a surface. Then, we want > > to > > > display a cross section (east-west) as a function > > of > > > height of let's say u-component of the wind. This > > also > > > works, however, the bottom few model levels are > > > displayed "below" the terrain surface. The wrf > > output > > > is on a sigma level coordinate system and the > > terrain > > > is in meters above sealevel. We believe IDV is > > > plotting the data wrong because it is incorrectly > > > calculating the heights of the sigma-levels. We > > know > > > this because when we do an independent calculation > > > outside of IDV the lowest layer in the model > > matches > > > the terrain height. You will also notice that some > > of > > > the data does not plot correctly east of the > > mountains > > > that when displayed in matlab plots correctly. > > > I am enclosing a image of the display rotated to > > show > > > both the sub-terrain plotting and the missing > > stripe > > > of data on the right side. > > > > > > > The staggered WRF grids are problematic in many ways > > - > > there is a lot of overhead in resampling from one > > staggering > > to another, it uses a lot more memory because we > > have to > > keep both the staggered grids and the normalized > > grids in > > memory, etc. We recommend that people use the > > WRF-Post options > > to convert their data to pressure coordinates and > > calculate > > the most commonly used met variables. But we also > > realize that > > some need to have the staggered coordinates so we > > allow for that. > > > > For variables like U which are on a vertical > > Pressure coordinate, the height > > is determined through a transformation of pressure > > to height. The default > > is to use the standard atmophere, but you can change > > to use a logarithmic > > transform (Vis5D) in the Formats & Data section of > > the User Preferences. > > > > The formula we use for calculating the height for > > the variables (e.g. W) on > > the staggered Z (height) coordinate is: > > > > height(x,y,z) = (PH(x,y,z)+ PHB(x,y,z)) / 9.81 > > > > > > So, for comparison of the first 10 values in your > > file that are calculated vs HGT > > we get: > > > > HGT: > > 1575.897, 1580.329, 1584.752, 1590.211, 1596.429, > > 1602.936, 1609.786, > > 1616.844, 1624.55, 1633.135 > > > > (W) (PH(x,y,z)+ PHB(x,y,z)) / 9.81: > > > > 1575.897, 1580.3292, 1584.7522, 1590.2109, > > 1596.4291, 1602.9358, 1609.7863 > > 1616.8439, 1624.5498, 1633.1349 > > > > (U) Pa -> m using standard atmosphere: > > > > 1524.0593, 1528.1156, 1532.2056, 1536.9418, > > 1542.4225, 1548.4596, 1554.9199, > > 1561.5878, 1568.6985, 1576.4624 > > > > So, for the variables with a pressure vertical > > coordinate, you will see > > some differences. Plotting a cross section of W > > lines up pretty nicely > > with the terrain. > > > > The blank line is a function of the sampling that we > > have to do between > > the native coordinates and the calculated > > lat/lon/alt values. I don't > > have a good solution for that. > > > > Don Murray > > > > > > Ticket Details > > =================== > > Ticket ID: YRR-987022 > > Department: Support IDV > > Priority: Normal > > Status: Open > > > > > > > > ____________________________________________________________________________________ > Be a better friend, newshound, and > know-it-all with Yahoo! Mobile. Try it now. > http://mobile.yahoo.com/;_ylt=Ahu06i62sR8HDtDypao8Wcj9tAcJ > > Ticket Details =================== Ticket ID: YRR-987022 Department: Support IDV Priority: Normal Status: Open