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  • Author or Editor: R. E. Ruskin x
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W. A. Hoppel
,
J. E. Dinger
, and
R. E. Ruskin

Abstract

Measurements of the number density, volatility and supersaturation spectra of CCN during aircraft soundings to about 15,000 ft MSL over Arizona, Central Pacific, Alaska, and in a convective region over Florida, and on five flights to an altitude of 35,000 ft off the cast and west coasts of the United States are presented. The results show that generally over continental areas away from strong anthropogenic sources the number of CCN is about ten times as great as in marine air masses and as found over snow-packed polar regions. Over continental areas the count decreases with altitude; whereas in the oceanic environments and polar regions the count sometimes increases above the inversion such that at higher altitudes there are no systematic differences between oceanic and continental environments. On several occasions, over the Pacific, anomalously high counts of several thousand CCN cm−3 have been encountered. Five soundings to 35,000 ft indicate no systematic increase or decrease in CCN with altitude above 20,000 ft. Above the inversion about 60% of the total aerosol population are CCN active at a supersaturation of 0.7%, the nuclei having an average radius <2.6×10−6 cm.

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S. C. Mossop
,
R. E. Ruskin
, and
K. J. Heffernan

Abstract

A long-lived cumulus cloud off the southern coast of Australia was found to contain ice crystals, even though the coldest temperature in it was about −4C. Two instrumented aircraft made successive passes through the cloud and continuous samplers were used to replicate cloud particles. It was found that columnar crystals were present in concentrations up to 100 liter−1. This was at least three orders of magnitude greater than the expected concentration of active ice nuclei as determined by cloud chamber measurements made under the base of the same cloud. It appears that some ice crystal multiplication mechanism was at work, though the exact nature of the process cannot be decided on available evidence.

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