Tuesday, 24 January 2012: 4:30 PM
Theoretical Study on the Correlation Between Snowflake Type and Gauge Collection Efficiency
Room 239 (New Orleans Convention Center )
Accurately measuring snowfall amount is challenging for many reasons. In particular, it has been recognized that systematic errors in snowfall measurements are often observed due to the gauge geometry and the associated weather conditions. For example, it common to observe a decrease in the collection efficiency of snow gauge with increasing wind speed. This is due mainly to the deflection of the airflow in the vicinity of the gauge that influences the trajectory of precipitation. The different types of snow crystals, which fall at different terminal velocity, interact differently with the disturbed airflow in the vicinity of the gauge. To address this problem, numerical simulations were carried out and compared with observations collected during the winter 2009-2010. A theoretical study using 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. Theoretical collection efficiencies for different crystal types were computed and compared with observations. The results illustrate the impact of snowflake type on the snow gauge collection efficiency. The numerical simulations were also used to compute a correction factor for the many snowflake types observed. Overall, the type of snowflake helps explain the scatter observed in the collection efficiency for a given wind speed.