Tuesday, 24 January 2012: 4:45 PM
Precipitation Gauge Performance During High-Wind/High-Rate Snowfall Events
Room 239 (New Orleans Convention Center )
It is well documented that precipitation gauges elevated above the ground and freely exposed to the wind, will collect less precipitation than gauges protected from the wind (Alter 1937; Goodison et al. 1989; Yang et al. 1998). Wind speeds of only a few meters per second can drastically decrease the amount of precipitation, particularly snow, collected by a gauge. The wind causes hydrometeors to blow over and around the gauge instead of falling into the gauge. Thus, wind speed corrections to precipitation accumulations must be applied to determine the actual precipitation amount. While transfer functions have been developed to correct for these wind errors, most of the data collected for these functions were collected with wind speeds less than ten meters per second. The Research Applications Lab (RAL) at the National Center for Atmospheric Research (NCAR) has maintained a network of precipitation gauges at the Marshall Field Site just outside of Boulder, Colorado for over 15 years. These gauges, primarily GEONOR T-200b gauges, have been installed in various types of gauge shielding including Alter shields, double Alter shields, and Double Fenced Intercomparison Reference (DFIR) shields. Although instances of high precipitation rates (>2 mm/hr) combined with high winds (> 10 m/s) are uncommon, the span of time over which the site has been operational has allowed for data collection during many of these events. A comparison of the gauge accumulations within the various windshields will be presented as well as the derived transfer functions.