Search Results

You are looking at 1 - 10 of 12 items for

  • Author or Editor: K. J. Heffernan x
  • Refine by Access: All Content x
Clear All Modify Search
E. J. Smith and K. J. Heffernan

Abstract

Full access
J. A. Warburton and K. J. Heffernan

Abstract

Measurements have been made of the time lag which silver iodide particles exhibit in the nucleation of ice crystals at temperatures between −8C and −16C. The time tag is approximately exponential, the decay constants being 3.6 minutes and 1.4 minutes at −8.5C and −15.5C, respectively. The decay constant at −15.5C is less by a factor of 4.5 than that for natural ice nuclei. The observed time lag is in qualitative agreement with Fletcher's theory.

Full access
E. J. Smith and K. J. Heffernan

Abstract

Full access
Earl G. Droessler and K. J. Heffernan

Abstract

A 10-day experiment is described in which simultaneous measurements of ice nucleus concentrations have been made in upslope and downslope wind regimes on the island of Hawaii, near sea level at Hilo airport, at Mauna Loa Observatory (MLO) (elevation 3.4 km), and midway at Kulani (elevation 1.5 km). The main results show: (1) at MLO the downslope flows contain the highest concentrations of ice nuclei, (2) the same downslope flows contain the lowest concentrations of large terrestrial particles, (3) the greatest care must be exercised in using the expansion cold chamber technique to collect data on ice nuclei in the humidity extremes at Hilo and MLO, and (4) no evidence was found In favor of a local terrestrial origin of the ice nuclei, and it is suggested that earlier measurements by Kline and Price and Pales were influenced by instrumental errors.

Full access
E. J. Smith, K. J. Heffernan, and B. K. Seely

Abstract

Finely divided zinc sulfide and freezing nuclei in the form of silver-iodide smoke were released from separate generators at the same time from the same position on the ground. Both were detected simultaneously at distances up to 56 kilometers downwind from the respective generators, by apparatus installed in an aircraft. The comparative concentration was used as a measure of the deterioration in the ice-nucleating properties of the silver iodide. The total number of freezing nuclei, effective at −17C, in silver-iodide smoke from a hydrogen burner, decreased by a factor of ten after eight minutes of exposure in the free atmosphere. The corresponding time with use of a kerosene burner was 50 minutes. The rate of decrease in the number of freezing nuclei was not influenced by the cloud cover.

Full access
Earl G. Droessler, K. J. Heffernan, and E. K. Bigg

Abstract

The feasibility of using the fluorescent properties of zinc sulfide powder to study air motions in the vicinity of jet streams was studied by releasing 230 kg of the substance above the subtropical jet in central Australia and later in Western Australia. Zinc sulfide was detected in some of the air samples obtained at the ground in Australia and New Zealand as far as 7000 km from the source and at various altitudes over eastern Australia.

It is concluded that this tracer could be useful for studying air motions on such a large scale but that transport mechanisms involving clouds may also be important. Very rapid downward transport was a feature of both experiments. A relationship appears to exist between ice nucleus concentrations and the fallout pattern of the zinc sulfide.

Full access
E. K. Bigg, G. T. Miles, and K. J. Heffernan

Abstract

No Abstract Available.

Full access
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.

Full access
E. J. Smith, J. A. Warburton, K. J. Heffernan, and W. J. Thompson

Abstract

The performance of a silver iodide smoke generator, mounted on an aircraft, was measured in flight. The ice-nucleus output was 1014 per gram of silver iodide active at −15C and 1012 at −10C. Considerable variations in the burner configuration and the solution which was burnt had little effect on the performance.

Full access
F. D. Bethwaite, E. J. Smith, J. A. Warburton, and K. J. Heffernan

Abstract

Isolated cumulus clouds with supercooled tops were seeded from an aircraft. Either a large (20 gm), small (0.2 gm) or zero quantity of silver iodide was used, with random choice of treatment. The amount of rain which fell from the cloud was measured at cloud base by means of an impactor on the seeding aircraft.

Clouds with tops −10C or colder which were treated with the larger quantity of silver iodide yielded significantly more rain than similar, untreated clouds. The mean rainfall from clouds seeded with the reduced treatment was also higher than that from the unseeded clouds, but the margin in this case was insufficient to demonstrate the statistical significance of the result.

Full access