WMOD00307

• Title: A Proposal for Cooperative Weather Research Between the Santa Barbara County Water Agency and the US Department of Interior Bureau of Reclaimation in the Context of the Weather Damage Modification Program through the State of CA 2002-2003 Winter Season
• Date: 10/17/2002
• State: CA
• Weather Modification - Doc Type: Report

Weather Damage Modification Program 32

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detailed terrain to be modeled. The grid spacing is thus limited by the available computer
resources and how quickly an output product is needed. The horizontal grid spacing is typically
3 km on a 51 X 51 grid point array. There are seven vertical layers or channels.

Plume spread is governed by the Gaussian assumption, wherein the horizontal spread of the
seeding plume is assumed to have a normal or Gaussian distribution, parameterized by the
Pasquill-Gifford neutral class (Turner 1969). This results in a maximum concentration of
seeding material at the center of the plume, and decreasing concentrations tapering off on each
side, cross wind. As downwind distance from the source increases, so does the spread of the
plume. Plume width is expressed as (]Y' a parameter graphed by Turner. The concentration of the
plume, Cplume, spreading horizontally in the Gaussian model is then expressed by:

[-i]
C"'_ = (v,,~,DJ 2'; (2)

where D is a shorthand notation for vertical dispersion with a unit length, Q is the source strength
in mass per time, V is the wind speed, and y is the cross-wind distance. Equation (2) shows that
as (]y (and downwind distance) increases, the plume spreads, decreasing the concentration. The
width of the plume can be graphically represented by plotting circles whose radii are a function
of (]y.

The model programming is in C/C++, and the model can be run under any MS WINDOWS or
LINUX (UNIX) operating system. Graphical display is presently being done through
GRAPHER (Golden Software) that has been configured to automatically produce images by
clicking on the respective icon for each of the model outputs. The microprocessor run-time to
produce Fig. 1 was under one minute on a Pentium ill machine. Model output is to hard-wired
file names and their names are passed to the user on the display as each task is completed. Some
of the output files are automatically accessed in the graphics stage. Each of the graphics displays
has an icon on the desktop display that is a shortcut to starting the GRAPHER program. When
selected, GRAPHER automatically retrieves these data plus geographical data and titles, to draw
the respective display. If a hard copy is needed, the picture can be sent to a printer by pulling
down on File and selecting Print.

Prior to the field program, the Santa Barbara area terrain must be processed into a format
readable by the model. Digital elevation data are available from the U.S. Geological Survey
(USGS) via the Internet.

The sounding data must be decoded and input as well. The Vaisala system proposed provides
the data in the WMO standard TT AA, TTBB and PPBB format, so input will pose no
difficulties. In addition, other soundings from nearby locations (e.g. Vandenberg AFB) can also
be used if desired. Test runs will be made with all anticipated data formats prior to entering the
field, to ensure that everything functions properly.