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Patrick Squires

A keynote talk given at the American Meteorological Society meeting at the University of Michigan, Ann Arbor, 20th March 1967: some thoughts on trends in cloud physics and weather modification studies.

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James G. Hudson
and
Patrick Squires

Abstract

Systematic spatial variations in CCN concentrations point to a major source near continental surfaces of the same magnitude as the removal rate by precipitation. Various theories of production point to either 1) a source at the surface, or 2) a diffuse source throughout the mixing layer (∼1 km).

The work presented here is an attempt to test the validity of the first hypothesis by using a micrometeorological technique to determine the vertical flux of CCN. A very high degree of precision in measuring CCN and a very high counting rate are required to apply this technique. A pair of continuous flow diffusion cloud chambers (Hudson and Squires, 1976) were developed for this purpose.

The experiment was performed at four different locations in three distinct types of terrain. At all locations the concentrations were consistently greater at higher levels (∼10 m above ground) than at lower levels (∼1 m above ground) indicating surface deposition rather than surface production.

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James G. Hudson
and
Patrick Squires

Abstract

For certain field and laboratory investigations, it would he useful to have apparatus capable of yielding a continuous, instantaneously recorded measurement of the concentration of cloud nuclei. A description of such a device is given, in which some of the problems of static diffusion chambers have, been mitigated. It is shown that clear plateaus exist in the deduced cloud nucleus concentration when plotted against the time the sample spends in the chamber, or against size of droplets detected, or sample flow rate. Transient supersaturations have been eliminated and the sample has been confined to a zone of precisely known supersaturation. It is shown that depletion of supersaturation by growing droplets does not occur for count rates as high as 1500 nuclei sec−1.

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James G. Hudson
and
Patrick Squires

Abstract

A slightly improved version of the continuous flow diffusion cloud chamber which has been described earlier (Hudson and Squires, 1973) has been rotated so that the plates are vertical instead of horizontal, the air flow remaining horizontal. Without other modification, its count agrees with that of the improved horizontal version to within about 1% over the supersaturation range 1.0–0.5%. The vertical mode of operation has certain advantages over even the improved horizontal chamber; in particular, it extends downward the supersaturation range over which reliable results can be obtained. Satisfactory plateaus can be obtained at least down to a supersaturation of about 0.1%. Two vertical chambers have been found to agree to about 1% in the supersaturation range 1.0–0.25%, and to about 10% down to a supersaturation of 0.1%.

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Roscoe R. Braham Jr.
and
Patrick Squires
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