| Summary: | The snow environment of the Craigieburn Range is addressed under three major themes: snowfall, snow metamorphism and snow melt. A six year record of alpine climate and three years of snow structure analysis, which form the most extensive and reliable record of alpine snow conditions yet available in New Zealand, act as the data base.
Overall, the results indicate that the Craigieburn Range snowcover is most typical of intermontane or coastal-transition regions. Snow storms and snowpack structure exhibit some characteristics typical of both maritime and continental climates. Snowfalls are usually small magnitude, low intensity events, although on average one extreme event occurs each year. Snow storms often contain periods of rain, and are characterized by temperatures which rarely fall below -6°C. In the absence of strong winds, new snow densities are similar to those for continental regions.
Changes in the density and structure of deposited snow are rapid because of the relatively warm nature of the snowpack. Equi-temperature metamorphism produces density increases of up to 50% per day and is further hastened by frequent melt and rain periods which occur during the main winter period. Indirect climatic evidence suggests temperature gradient metamorphism is unlikely. Field investigations, however, demonstrated that depth hoar crystals occur throughout the snowpack and frequently develop in conjunction with ice crusts, another dominant feature of the snow stratigraphy.
Sensible heat flow is the major source of heat in both winter and spring melt periods. On a daily basis, net radiation is of secondary importance, although during the daylight hours, solar radiation is usually the largest heat supply. The greatest total heat transfer to the snowpack occurs on days with rainfall. For these days, precipitation heat flow is small but the latent heat released by condensation exceeds that from net radiation. Days of high sensible heat transfer, characterized by high winds and warm air temperatures, are related to the occurrence of north-westerly winds. The amount of evaporation during many of these days is equal to high values measured overseas.
The implications of an intermontane classification for the Craigieburn Range is also reviewed relative to two practical considerations, avalanche forecasting and snowmelt hydrology.
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