WMOD00287

• Title: The National Weather Modification Plan
• Prepared For: CAO Subcommittee on Weather Modification
• Prepared By: The Working Group of the CAO Subcommittee on Weather Modification
• Date: 2/13/1981
• Weather Modification - Doc Type: Report

Variability of Precipitation Efficiency Program. These programs are
recommended because they address issues vital to the development of a national
weather modification capability.

(1) Ice Crystal Processes Program. The main purpose of this proposed
NOAA program is to understand cloud ice processes and their roles in
regulating precipitation efficiency. An integrated program of laboratory
experiments, computer lIlOdeling, and field measurements with proven and newly
developed tools is necessary. The results of these basic studies will be used
to formulate more perceptive, adaptable, and testable hypotheses for
purposeful supercooled cloud modification.

The investigations will focus on relatively warm cloud systems (OoC to
-i OoC) and relatively warm portions of deeper, colder systems. Cloud life
cycles rather than steady-state systems will be considered. Knowledge of the
evolution of hydrometeor populations is of ucmost importance, although some
studies of growth of a few or individual ice particles may be fruitful.
Limited cloud seeding will be conducted, not to alter precipitation but to
investigate specific aspects of the ice processes.

Specific problems of ice particle development are to be addressed within
the framework of three factors:

o Factor A: The origin, timing, rate, relative order of development,
and interaction of the various individual ice processes, in relation
to optimum precipitation efficiency, especially in terms of
hydrometeor populations.

o Factor B: Cloud physical, thermodynamic, and dynamic structure, and
its evolution, including cloud energetics and dynamics as they
specifically influence and interact with the ice processes,
particularly in relatively warm cloud systems (Le., at T )-lOoC);
the consequent spatial and temporal distributions or liquid water
and ice in selected types of clouds; and nonuniformities in spatial
and temporal concentration and dispersion of hydrometeors. Emphasis
is on the microscale, although some interactive ~soscale phenomena
must be considered.

o Factor C: Cloud modification requirements, such as recognition or
potential windows or triggering mechanisms for cloud modification,
recognition or naturally efficient cloud systems, and specification
of the concentrations of ice crystals required for optimal
precipitation efficiencies.

Overlap or observational, laboratory, and modeling components of the
research program is ~~pected and encouraged, in order to establish necessary
linkages. The laboratory work will focus primarily on details of individual
processes. The modeling will address the interaction of microphysical
processes in the context of realistic evolution of cloud thermodynamics and
dynamics--all with attention to cloud water budget and precipitation
efficiency. ~'fodeling allows specific processes to be simulated independently

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