Monday, 15 January 2007
Three-dimensional airflow analysis inside snow gauge shielding to determine snow gauge collection efficiencies
Exhibit Hall C (Henry B. Gonzalez Convention Center)
It is well documented that the collection efficiency of unshielded precipitation gauges decreases with increasing wind speeds. Various wind shields have been designed to help increase the collection efficiency of snow gauges. The Double Fence Intercomparison Reference (DFIR) shield is the World Meteorological Organization (WMO) standard shield for snow gauge measurements. In an attempt to understand why the DFIR shield provides a higher collection efficiency than other shields, a study was undertaken using three-dimensional sonic anemometers to measure both the horizontal and vertical winds in the DFIR shield. Sonic anemometers were also placed in an Alter shield with 16-inch slats, an Alter shield with 18-inch slats and a double Alter shield with 16-inch slats. Additionally, a sonic was placed in an 18-inch Alter shield with a GEONOR casing positioned just below the sonic to determine the effects the gauge-casing can have on both winds and the collection efficiency. Comparisons of the wind patterns between shields during rain and snow events are presented.