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IDV, gridded data, vorticity

Bill,

> I was trying to use the latest version of the IDV to look at contour plan 
> views of vorticity from model gridded data. I tried the NGM and ETA for 
> todays 0 GMT run, with basically the same problems.

>  Absolute vorticity is listed under 3-D grids and under 3-D grids/derived. 
> The former are probably reflect raw grids sent out by NCEP, and the latter 
> are probably computed from u and v grids. But, listing abv in two places is 
> confusing.=20

Yes you are right. The first is supplied by the native grids, the second
computed automaticaly when the grid input selected has the necessary
prerequisites to make an absolute vortivity field.

To avoid confusion, what would you like? We might check for a derived
field and it already exists in the native data, and if so then don't do
the derived grids, for example.


>  Whenever I check the former abv grids, I find very few levels (on 
> motherlode) ?

I see what you mean. Looking at Eta and NGM's absolute vorticity for the
0Z runs of May 11 and May 12 the IDV acts like it creates displays for
all levels, every 50 mb steps from 1000 mb to 100 mb (to 50 mb tops in
the case of NGM output). However I only see an actual display, contours
say, at the 1000 mb level. You can set the "Level" to values other than
1000 mb in the "properties" control, and then nothing appears on screen.
It's like all data at that level is missing. I do not know if this is
due to an IDV problem or if the data really is missing. I will put code
in the IDV to find out, and let you know.

>  Using the latter abv grids, the contours are straight west to east. I wonder 
> if    the relative vorticities are too small and over whelmed by Earth's 
> vorticity ? Deriving relative vortictiy yields contours with the right 
> pattern, but the numbers  are several orders of magnitude larger than the 
> usual ten to minus 5, seconds to  minus one. Are they right ?

Yes the derived computation for the absolute vorticity seems to have
gone off the rails somewhere, and needs to be fixed.

The relative vorticity may actually be right, in a sense. Right click on
the label, click on on "change units." The "unit" shown is 0.001 seconds
minus one. The max value displayed is very roughly 0.1. So that is ten
minus four seconds minus one, which might be what you expect for the max
of relative voticity near the surface.

The IDV used to show the unit on the label line but it was removed.
Which would you prefer?

Be back as soon as I can about the missing absolute vorticity levels. I
hope we can have all this straigtened out in time for  your workshop.

Stu


< Bill Fingerhut, Professor           PHONE: 802-626-6257 >
< Meteorology Dept                    FAX:   802-626-9770 >
< Lyndon State College                                    >
< Lyndonville, Vt 05851                                   >
<                                                         >
< EMAIL:     address@hidden                >
<            address@hidden                  >
< WWW:       http://apollo.lsc.vsc.edu/                   >
<                                                         >
< disclaimer: I know nothing - I only work here.          >

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