Current WRP Projects: Project 37

Instrumentation for Improved Precipitation Measurement in Wintertime Snowstorms

  • Project Number:  37
  • PI:  Jefferson Snider, Professor, (307 766 2637)
  • Status:  Ongoing
  • Period:  03/01/2011 - 02/28/2013


It is widely recognized that precipitation measurements (rain and snow) can be biased by wind-induced errors. Measurement of snowfall is especially confounded by wind occurring at forested measurement sites. Negative bias occurs if a precipitation gauge is shadowed by trees, and positive bias occurs if a secondary flux occurs due to wind resuspension of antecedent snowfall. In addition, a negative wind-induced bias occurs because the downward vertical speed of a snow particle is decreased by the airflow distortion near a precipitation gauge. Because the fall speed of a rain drop is much larger than that of a snow particle the flow distortion bias is largest for the snow particle. Fall speeds for these two particle types are about 1 m/s (snow) and 10 m/s (drop) assuming a 4 milligram particle mass (liquid equivalent particle diameter = 2 mm).

These complications are evident in many studies of snowfall, even when using a wind shield to slow down the horizontal air velocity (and thus the vertical velocity distortion) near a gauge orifice. We propose to use a new type of precipitation sensor (the “hotplate”) in an intercomparison with conventional gauges. Both the hotplate and the conventional gauges will be deployed at a wintertime cloud seeding target site. The primary objective of the work is the development of a correction for the hotplate’s report of the precipitation rate. One M.S. student will be supported by the project and a hotplate snow sensor will be upgraded with visible and infrared radiometers reporting measurements necessary for the correction. It is anticipated that the research will advance the hotplate as a device superior to conventional gauges for measurement of snowfall.

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