Effects of snowflake characteristics on the collection efficiency of snow gauge

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Monday, 24 January 2011
Effects of snowflake characteristics on the collection efficiency of snow gauge
Washington State Convention Center
Julie M. Theriault, NCAR, Boulder, CO; and K. Ikeda, R. Rasmussen, S. Landolt, S. Ziegler, and A. Jachcik

Poster PDF (2.0 MB)

Accurately measuring snowfall amounts can be critical for a wide variety of studies including snowpack, climate variability and hydrology. It has been recognized that systematic errors in snowfall measurements are often observed due to the gauge geometry and the weather conditions. For example, the higher the wind speed during a snowfall event, the lower the collection efficiency of the snow gauge. Errors in the snow accumulation as high as 30% are often for the same wind speed. The airflow around the gauge varies depending on the wind speed, which influences the trajectory of the falling snowflakes. Since the gauge and the shield are obstacles to the natural airflow pattern, smaller and lighter snowflakes may interact with the gauge and shield differently than larger flakes. To address this, a study was undertaken to determine if different types and sizes of snowflakes fall inside versus outside of a GEONOR snow gauge. Additionally, snowflakes were collected both with and without a shield around the gauge. The collected snowflakes were photographed and the pictures analyzed to determine their characteristics. Finite element modeling was used to simulate the flow around the snow gauge and study the trajectory of various crystal types falling through the atmosphere. The model results were then compared with observations. Preliminary results show that not only the wind speed influences the collection efficiency of snow gauge but the different snow crystal types as well.