Dave-
A couple of other notes on this. If you use the Transect Display,
you can confirm your results by overlaying the vertical
cross section of (u,v,omega) on top of a color filled
display of omega. You can also create a simple formula
that would multiply omega by a constant if you wanted
to increase the effect of the vertical motion. The
formula would be:
float(user_constant)*field
which would prompt you for your constant. Use this formula
instead of Negate a Field and put in a positive or negative constant
when you are prompted (e.g. -5), then select the field to
act on.
Don
Don Murray wrote:
Hi Dave-
Dave Dempsey wrote:
I wanted to plot a vertical cross section of streamlines, but that
capability doesn't seem to be present in the IDV v2.0, unless I'm
missing something. Could this be another programming project for IDV
users comfortable with Jython? (I'm not there yet.)
The underlying VisAD system does not support 3D streamlines
(i.e. a cross section) at this time. Perhaps one of the
streamline experts could comment on this.
As an alternative, I figured out how to use the existing system
formula "Make flow vectors from u, v, and w data" to plot a vertical
cross section of flow vectors. The formula requires u, v, and w fields
as input. However, the NAM and GFS model output files contain pressure
vertical velocity (omega) fields rather than w fields. Does this mean
that the formula will get the sign of the vertical component reversed?
(It certainly doesn't seem capable of converting omega fields to w
fields, given that that would seem to require the geopotential height
field at multiple times and the temperature field, but if it got the
sign right then there'd still be useful qualitative info in the vector
computed from omega and horizontal velocity.)
I'm not an object-oriented programmer so I got lost trying to trace
the code that renders the 3-D flow vectors to see how it treats the
sign of the vertical velocity. The formula invokes the
ucar.unidata.data.grid.DerivedGridFactory class, which invokes the
createFlowVectors method, which invokes the visad class FieldImpl,
which invokes ....
Can anyone comment on what the "Make flow vectors from u, v, and w
data" formula does with u, v, and omega fields?
The formula expects that the 3 fields (u,v,w) are in units of m/s
(or something compatible) and as you note, the models have
omega, not w. Apparently, the IDV does plot omega for
w, but the display will only be qualitative as you note. If you want
to reverse the sign, then when you select the "w" parameter, instead of
selecting omega, select the formula System->Negate a field
which will then prompt you for what you want to negate. At
that point, select your omega field.
No programming necessary. ;-)
Don
*************************************************************
Don Murray UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx P.O. Box 3000
(303) 497-8628 Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
*************************************************************
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*************************************************************
Don Murray UCAR Unidata Program
dmurray@xxxxxxxxxxxxxxxx P.O. Box 3000
(303) 497-8628 Boulder, CO 80307
http://www.unidata.ucar.edu/staff/donm
*************************************************************
