WMOD00310

• Title: Cloud Physics Investigations - University of Wyoming - 1977-1981
• Date: 11/1/1982
• State: WY
• Weather Modification - Doc Type: Report

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satisfied in about 50% of the cases, but a substantial portion of

these samples were colder than -8oC and therefore outside the

temperature regime of the Hallett-Mossop process. In the temperature

regime from -3 to _80~, the droplet spectra met the conditions for the

Hallett-Mossop process less than 25% of the time. The average spectra

were relatively narrow; the average dispersion (after correction for

the instrumental broadening described by Cerni, 1982a) was 0.2, and

the average standard deviation in the droplet diameter was near 3 ~m.

The mean diameter was observed to increase with height (Rodi,

198JL and with time (Cooper et al., 1982b, 1982c). The time evolution

was particularly puzzling, and will be discussed further here with

appeal to the evidence from the HIPLEX-1 case studies.

Baker and Latham (1979) proposed that the mixing of cloud parcels

wi th the environment takes place inhomogeneously, at least as long as

the scale of. the mixing process is large enough. Specifically, they

predicted that the mixing process may proceed via complete evaporation

of some regions to a saturated but cloud-free parcel, which could then

mix with other saturated parcels still containing cloud droplets. The

resul t would be a pure dilution effect in the cloud parcels, with

proportionate reductions in the liquid water content and the droplet

concentration but with no change in the shape of the droplet spectrum.

This process would represent the extreme inhomogeneous limit. In

contrast, if the mixing were homogeneous, all droplets would

experience the same undersaturation and the evolution of, the spectrum

would be the reverse of its growth; in this case, the liquid water

content would be reduced much more than the number concentration,

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