Climate and Energy Exchange at the Snow Surface in the Alpine Region of the Sierra Nevada 1. Meteorological Measurements and Monitoring

A detailed evaluation of climate conditions in a small alpine watershed, typical of much of the southern Sierra Nevada, is presented for the 1986 water year. Measurements of snowfall, meteorological and snow cover conditions, and snow cover ablation are used to characterize the climate at four locations in the watershed during that snow season. Data from these locations are then combined into two representative sites for the watershed. Measurement approaches and methodologies and the effectiveness of instrumentation used in the study are discussed, and an estimate of the uncertainty of the monitored meteorological parameters is made. The data are integrated into a continuous hourly time series of solar and thermal radiation, air, snow and soil temperature, humidity, and wind at the two representative sites in this remote alpine watershed for an entire snow season. Snow deposition and snow cover depth and density are measured manually at regular intervals throughout the snow season. While problems were encountered monitoring air and snow surface temperature, humidity, and wind, because of the extreme conditions which are likely to occur in an alpine environment, radiation is easily monitored, and the estimated uncertainty of all measured parameters was acceptably low. This effort was required to develop a high quality time series of integrated climate data to evaluate the components of the energy balance of the snow cover during both deposition and ablation conditions.