Natural Snowfall Research Articles

A FIELD TEST FOR ASSESSING THE WINTER HARDINESS OF ALFALFA IN NORTHWESTERN CANADA

A procedure is described for separating differences in winter hardiness among alfalfa (Medicago sativa L.) cultivars under field conditions. The procedure depends upon two factors associated with winterkill in northern Alberta during the 1977–1978 winter, namely, low food reserves in the crowns resulting from improper cutting management plus cold stress due to lack of snow in early winter. To induce these conditions we recommend that year-old plants be clipped in mid-June, late July and early September and that snow be removed once from the plot during early winter on the first day that air temperatures below −30 °C are forecasted. Natural snow fall can protect the plot for the remainder of the winter. If soil temperatures do not drop close to the range of the LT50 of the control cultivars, snow cover may be removed again provided air temperatures are below −30 °C. Cultivar rankings for winter hardiness following severe stress induced by snow removal were significantly correlated (r = 0.944**) with the mean survival observed at five locations following natural winter stresses in this region. Although additional work is warranted, the induced stress procedure has real merit in screening winter-hardy genotypes in the field and in assessing management techniques to reduce the effects of stressful winter environments on alfalfa production in northwestern Canada.Key words: Alfalfa, winter hardiness, field test, snow removal, frequent clipping

On the growth mechanism of polycrystalline snow crystals with a specific grain boundary

Observed frequently in a natural snowfall at temperatures lower than -20°C, the crossed-plate crystal is an assemblage of two to four thin basal plates, each plate extending along a CSL grain boundary with a relation of 70.3°/[11 2 0]. A possible growth mechanism is proposed to account for the characteristics growth in the direction of the axis [11 2 0]. If two or more grain boundary dislocation (GBD) structures are contained at a CSL grain boundary, growth layers will overflow alternately on the (10 1 0) planes of each component crystal at the intersection of these planes. Thus, the distinctive structure of the CSL grain boundary, like the feature of a screw dislocation step, will induce the preferential growth in this direction.

The spectra of charging events due to the collision of natural ice particles with an ice surface

AbstractA sensitive, solid state electrometer has been built which is capable of measuring the individual charges acquired by an ice surface exposed to precipitation or cloud particles. Measurements made in natural snowfall show that the individual charges fluctuate widely both in sign and magnitude. Individual charges ranging from ‐10−2 e.s.u. to 10−2 e.s.u. have been recorded within an interval of a few seconds. In most cases the ice surface received a net positive charge, and the median charge per collision was about 2 × 10−4 e.s.u. The charging spectra commonly followed a log‐normal distribution.It is suggested that two important mechanisms for the charging were the direct transfer to the ice surface of some of the charge residing on the ice particles in the air and the fragmentation of the ice particles as they collided with the ice surface.

FACTORS AFFECTING THE ELECTRIC CHARGE ACQUIRED BY AN ICE SPHERE MOVING THROUGH NATURAL SNOWFALL1

Abstract The factors affecting the electric charge acquired by an ice sphere moving through natural snowfall have been investigated experimentally. When graupel particles were in the air the sphere always received a positive charge. If graupel was not present the sign of the charge appeared to be related to the direction of the atmospheric electric field. When the field was directed downwards the ice sphere received negative charge, and when the field was directed upwards the sphere received positive charge. The results are explained in terms of the direct transfer to the ice sphere of some of the net charge on the ice particles in the air making a glancing contact with the ice sphere. The charges that an ice sphere received by this mechanism appeared to be much larger than any charges that might have been generated by asymmetrical rubbing between the ice particles in the air and the surface of the ice sphere.

Interaction between a natural snowfall and a cooling tower plume: An experimental study with a millimetric Doppler radar

A precipitation band, about 30 km long and 2 km wide, downwind of a nuclear power plant was observed with a millimetric Doppler radar. The three-dimensional radar analysis showed that this band resulted from the growth, by a seeder-feeder process, of a natural snowfall falling in the moist plume produced by the exhaust of the nuclear plant. At the exit from the 0.6 km deep plume, the mean snow precipitation rate was approximately enhanced by a factor of two. This corresponds to an extraction rate of water in the plume by snow scavenging of 600 kg s −1, that is about one third of the water injection rate into the atmosphere by the cooling towers.