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[GEMPAK #DHJ-627451]: PV from RUC fields in GEMPAK

John,

I downloaded the RUC grid in question from the NOMADS server.

I believe the source of your negative numbers is the AVOR(VLAV(wnd))
in the layer from 200 to 300 mb (you can plot the vertical profile in gdprof
and watch see the graph go negative there).

I plotted up the AVOR(VLAV(WND)) term for GLEVEL=250:300 and overlaid the 275 mb
winds and hght field in this gif:
http://www.unidata.ucar.edu/staff/chiz/gifs/avor_06073001f000.gif

The center of the upper level wind circulation is in SE PA with that
negative vorticity to the NW.

The sign or the vorticity remains negative simply using AVOR(wnd), so
its not an artifact of the VLAV() function. Even though the winds aren't that
strong, it is a tight closed circulation.

Chiz




> Hello, Steve:
> Here are things I am looking at to figure out what's up with PV < 0
> in this set. I'm tabulating the date/time and p range for PV < -0.05
> (scaled by 10**6) over a month. This is an arbitrarily-selected cutoff
> for "significant" negativeness. I'd looked at 12, one hour periods
> before, and I want to know whether this is a common or transient
> occurrence.
> Your focus on the LDF term reminds me that PV is a ratio, and that
> eeither N or D could be negative - even though I don't see missing
> levels it is certain that these have opposite signs. So I'll be prepared
> to run gdprof again, looking at N and D separately for the troublesome
> times. Any suggestions you may have over and above this are welcome.
> John M.
> 
> Unidata GEMPAK Support wrote:
> 
> > John,
> >
> > If you can give me a gpoint/time/run (and GEMPAK version) I can take a look.
> > It is most likely that the LDF(THTA) would be negative in the lower layers,
> > but since you are seeing these values well up into the atmosphere, that 
> > shouldn't
> > be the case....but if you are missing a large number of levels, then the
> > LDF calculation could be way off.
> >
> > Steve Chiswell
> > Unidata User Support
> >
> >
> >>Hello, Steve:
> >>We've been working with RUC fields from the Conduit feed,
> >>and recently have been using gdprof to list the vertical
> >>profile of variables at a site. In looking at pvor(thta,
> >>wnd) I quite often see PV < 0. When the magnitudes are small
> >>I can be undistressed, but when I see this, I am flummoxed,
> >>(p, pvor*10**6):
> >>412.31                0.382
> >>387.30                0.314
> >>362.28                0.259
> >>337.27                0.095
> >>312.25               -0.118
> >>287.23               -0.247
> >>262.20               -0.305
> >>237.17               -0.323
> >>212.13               -0.230
> >>187.08                0.070
> >>162.02                1.852
> >>136.93                6.565
> >>111.80                8.240
> >>
> >>I have not yet inspected the fields for this day and
> >>time, but can do so of course. Is this something you've
> >>noted before?       John M.
> >>
> >>
> >
> >
> >
> > Ticket Details
> > ===================
> > Ticket ID: DHJ-627451
> > Department: Support GEMPAK
> > Priority: Normal
> > Status: Closed
> >
> 
> 


Ticket Details
===================
Ticket ID: DHJ-627451
Department: Support GEMPAK
Priority: Normal
Status: Closed