Date of Award:

1984

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Plants, Soils, and Climate

Department name when degree awarded

Biometeorology

Advisor/Chair:

Gene L. Wooldridge

Abstract

Regimes of snow depth, soil temperature, soil matric potential and quasi-friction velocity in a windward site and a lee shelter were examined. The differences were analyzed from a biological perspective to .characterize each location in terms of site favorability to plant growth. The chronology of wind and precipitation events was investigated.

Snow depth was measured with a system of stakes arranged around and in the interior of a rectangular plot encompassing both a windward site and a lee shelter. Soil temperature, soil matric potential and water potential were measured along a transect which originated in the windward site and terminated in the lee shelter. Soil temperature and water potential were measured by thermocouple psychrometer. Mattie potentials was determined by the pressure-plate method. The regimes of quasi-friction velocity at both ends of the transect were determined by the logarithmic profile method, invoking similarity theory. Wind speed and temperature were measured at two heights in each site. A computer program was used to search the wind and precipitation records and ·categorize and sun the precipitation events by wind direction.

The lee shelter exhibited tendencies toward theoretical optima of site favorability. The horizontal distribution of snow maxima was found. to be a function of wind direction at the time of each precipitation event as well as the interaction of wind and the topographical features.

Snow was observed to accumulate to a greater depth in the lee shelter than in the windward site. Mean soil temperature over the study period was 8.5° C in the lee shelter while the windward site was 8.0° C. Soil temperature in the lee shelter was never observed to go below 0° C under a snowpack. The range of soil matric potential in the lee shelter was found to be about 14 atm at a depth of 20 cm and about 17 atm at a depth of 50 cm over the summer season. In the windward site the range of soil matric potential was approximately 30 atm at a depth of 20 cm and about 21 atm at a the 50 cm depth over the same period. The lee shelter exhibited lower (less negative) matric potentials than the windward site. These results were not corroborated by the measurement of water potential by thermocouple psychrometers. In the layer from 1.5 to 4.1 m, the mean quasi-friction velocity in the lee shelter was 39 cm s-1, favoring snow deposition there over the windward site where the mean friction velocity was 21 cm s-l. In the 0 m to 1. 5 m layer, mean friction velocity in the windward site was found to be 55 cm s-1.while the lee shelter mean was 48 cm s-1. These results indicate a distinct seperation of flow downwind of the windward site where the lee shelter resides in the turbulent wake of the windward site.

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