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  • Author or Editor: L. B. MaChattie x
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L. B. MaChattie

Abstract

Application of temperature observations depends on assessment of the difference in temperature between points of observation and points of application. As an aid to estimating temperature variations in valleys, particularly in Rocky Mountain forest land, summer season observations in 1960 from 21 thermohygrographs were analyzed. Daily maximum and minimum temperatures were the main variables considered.

Temperature differences between successive 20-day periods were generally greater than those due to elevation, aspect or crown cover within a period. A nocturnal inversion of 9F in the first 300 ft above valley bottom occurred on the average clear summer night, with a nearly isothermal layer 500 ft or more thick above that. Literature reports indicate that nocturnal inversions in other valleys on clear nights usually differ by less than a factor of 2 from the Kananaskis data. An inversion of 3F in daily maximum temperature was also found in the first 300 ft above valley bottom; this is attributed, with reason, to a difference in evapo-transpiration between slope and valley bottom.

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L. B. MacHattie

Abstract

Anemograph charts from three stations in a north-south valley were analyzed to find the degree to which average diurnal variations were explainable on the basis of valley wind theory and local topography. Prominent diurnal cycles of the cross-valley component were found in the monthly averages at each station. At one station it was a morning-evening slope-wind cycle; at the other two, a day-night cycle up and down a sub-valley. The component along the main valley showed greater complexity, which is partially attributed to gradient wind interference in the afternoon when convective activity is greatest. The diurnal patterns for a group of selected clear days were similar to, but slightly sharper than, those of the monthly average charts.

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G. A. Isaac, R. S. Schemenauer, C. L. Crozier, A. J. Chisholm, J. I. MacPherson, N. R. Bobbitt, and L. B. MacHattie

Abstract

A cloud seeding technique is proposed which has the objective of stimulating rainfall from cumulus clouds drifting over forest fires. Preliminary tests of the ice crystal production capability of the cloud seeding technique were conducted on five cumulus clouds near Yellowknife, N.W.T., Canada, during July 1975. These clouds were over forest but not near forest fires. A T-33 turbulence research aircraft performed the seeding by burning wing-mounted TB1 AgI flares while flying through the clouds at the −5 to −10°C level. The T-33 turbulence measurements enabled estimates to be made of the rate of dispersion of the AgI. Microphysical measurements were made before and after seeding by an instrumented DHC-6 Twin Otter aircraft flying at the seeding level, and these were compared with measurements in six untreated cumulus clouds. High concentrations of ice crystals appeared after seeding in four of the five seeded cumulus clouds, and on two occasions precipitation-sized particles appeared at the seeding level. The evidence indicates that the AgI aerosol produced large quantities of ice crystals.

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