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



John,

The computational grid spacing of the RUC is 13km, so I agree that 
the rules may need some re-examination on that scale.

I'll await what you determine. I looked quickly at the radar mosaic and
there is a line of pretty impressive convection radiating out of NY
over the 12 hours surrounding your data time, and with the axis of the
short wave tilted over PA, that would appear to be related.I would
probably want to look at a time series of how that feature evolved with
the vertical motions (transverse circulation?).

Steve



> Thanks very much, Steve. I'll look at a few more - there are many
> cases with PV < -0.1 in August '06, at p < 600. We teach our students
> that Avor < 0 circulations are inherently unstable and should not be
> seen, but it is clear that at the resolution available now there are
> transient anticyclones that are strong enough to overcome f. This
> will require more sophistication in my thinking, where I'd planned to
> use the ratio Ozone/PV in a simple way. It is easy to generalize this
> in terms of 'IT', but saying what it means may take some thought. I'll
> let you know when I've looked at other AVOR plots, to confirm that this
> is what I'm seeing on the other dates.      John M.
> 
> Unidata GEMPAK Support wrote:
> 
> > 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
> >
> 
> 


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