METEOROLOGICAL INFLUENCES ON “sr CONCENTRATIONS
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deposition by precipitation. Since then, study has been made of other
precipitation-producing systems. For evaluation of the relative importance of the several meteorological parameters involved inthe
rainout removal of radioactive debris from the atmosphere, examination has been made of several different types of weather systems, each
of which is characterized by its own precipitation-causing processes.
The parameters important in determining the nuclear-debris concentra-
tion vary for each of these weather systems, For example, rapidly
changing cloud tops and entrainment from the surroundings are im-
portant parameters for convective cells, whereas the vast volumes of
the atmosphere involved in extratropical cyclones suggest that trajectories in complex circulation may be the controlling parameter in
determining nuclear-debris concentrations at a given location,
Precipitation-formation processes, such as all water or water—ice,
affect the concentration of nuclear debris in ground-level precipitation through the different processes of nucleation and raindrop growth.
Evaporation below cloud bases is alsoimportant. Finally, the availability
of nuclear debris in the atmosphere for rainout processes is time and
location dependent.
The following meteorological parameters that we believe to be
important in the determination of nuclear-debris deposition in precipitation were studied:
Maximums along troughs and fronts
Precipitation growth mechanisms
Height of rain-generation levels
Proximity of jet streams and tropopause
Stratification of debris across inversions
Evaporation of raindrops
The weather systems studied and their respective collection sites
were as follows:
Weather system
Extratropical cyclones
Showers and thunderstorms
Orographiclifting
Fog and stratus
Collection site
Central Pennsylvania and the west
coast of the United States
Oklahoma and central Pennsylvania
Hawaii
California
A study of orographic lifting is being made in conjunction with an
analysis of the effect of the trade-wind inversion on the vertical
transport of nuclear debris. The Sr concentration in samples of air
and precipitation taken during two short periods in 1963 indicated a
dependence of concentration upon the inversion strength. A more extensive collection and atmospheric-analysis program was completed
during August 1964; the preparation of the data from this program is
underway. Some sampling of drizzle and fog has been made along the