DATA

The plots (gif files) in this directory are generated from the NCEP 1
degree latitude by 1 degree longitude grids taken from the MRF model
runs.  These plots are initialized at 00 GMT each day, and run forward
120 hours.  GSFC acquires the forecasts at about 4AM each morning, and
the analysis at about 2PM each afternoon.

AVAILABLE PLOTS & Naming convention

There are two basic types of plots available.  PV and wind/temperature
charts.  The PV plots all begin with PV*.  The date is attached in the
yymmdd format following PV.  Horizontal plots are then denoted with a
theta value (330K), while cross-sections are denoted with the XSECT
indicator.  If the XSECT indicator is shown, the direction of the cross
secion in indicated next (ENE, N, or WNW).  The 330 K horizontal map is
centered on Ellington, and the cross-sections are all oriented through
Ellington.  The final indicator shows either the data as an analysis
(ANAL) or the forecast hour.  As an example, the gif file
PV_990319_330_48.gif is a PV field on the 330 K isentropic surface
valid at 00 GMT on March 19, 1999 as derived from a 48 hour forecast.
The gif file PV_990316_XSECT_WNW_ANAL.gif is an analysis cross section
oriented in a WNW direction with respect to Ellington field valid at 00
GMT on March 16, 1999.

In a similar way to the PV charts, the comparable gif files showing the
winds and temperatures are shown in the TU*.gif files.  Again, the date
is in the yymmdd format following TU.  Horizontal plots are then
denoted with a pressure value (250 mb), while cross-sections are
denoted with the XSECT indicator.  If the XSECT indicator is shown, the
direction of the cross secion in indicated next (ENE, N, or WNW).  As
with the isentropic maps, the 250 mb map is centered on Ellington. As
another example, the gif file TU_990319_250_48.gif is a Temperature and
wind field on the 250 mb surface valid at 00 GMT on March 19, 1999 as
derived from a 48 hour forecast.

Plot discussion

The horizontal PV map shows Modified PV (the same as Ertel's PV
mulitplied by a constant).  The tropopause is shown as the magenta line
superimposed on the figure, while the Montogomery stream function is
superimposed in white.  The air flow is generally parallel to the
Montgomery stream function, with the speed proportional to the packing
of the contours.  An 1800 km circle is superimposed, showing the
approximate range of the WB57.  Also superimposed are the positions of
the WNW, N, and ENE transect plots.