>From: "Jennie L. Moody" <address@hidden> >Organization: UVa >Keywords: 200206270315.g5R3F6u03265 McIDAS GRDCOPY XCD GRID Jennie, I looked into the ETA ABV vs GRDCOPY ABV more after our staff meeting yesterday. You are absolutely correct, the scaling for ABV as decoded by XCD decoders is WRONG by several orders of magnitude. The bottom line is that the XCD decoder scales the ABV, VOR, SHUM, and MIX parameters incorrectly. The problem you are seeing is caused by the exact same problem that Owen ran into some time ago with the SHUM parameter. The "fix" I came up for Owen worked for SHUM because I changed the scaling factor in the XCD GRIB table from 2 to 5 and then changed the output from kg/g to kg/g thus effectively scaling the values by the three orders of magnitude that were in dispute. The same sort of thing can NOT be done for ABV and VOR _unless_ the user always takes into account that the values need to be scaled by 5 orders of magnitude. Instead, I have to modify code to correctly scale those parameters. A comparison between the calculated ABV for ETA U,V fields and the ABV that comes with the model output is, as I believe you already found, pretty good. For the most part, contour plots of the McIDAS calculated vs ETA model fields are indistinguishable. There are regions where there is more detail in the calculated grids, but this is understandable. So, I will implement a fix for the XCD decoders as soon as I chat with SSEC to see if they are in agreement. This, however, does not help you to use the ABV fields that you have in archived datasets -- unless you saved the original GRIB messages. The best approach if you do not have the original GRIB messages is to use GRDCOPY calculated versions of the ABV fields. The other thing that could be done is to write a small routine that would go in and change the scaling factor saved in each GRID header for ABV and VOR. This would fix-up your archive and eliminate the need to calculate ABV/VOR. Sorry I couldn't see the problem sooner... Tom >From address@hidden Fri Jun 28 22:56:56 2002 >Subject: Re: 20020626: McIDAS ETA ABV vs calculated ABV question Tom, Thanks so much, I was pretty swamped and didn't get back to this was feeling harrassed by too many of lifes details. I am glad to be getting away for a couple weeks. I won't be able to work on McIDAS much while I am away, mayge a little when I am at UMBS for a few days. But, what you have told me is very helpful. I will pursue this with great intent when I return. Thanks so much for your help. Jennie
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