Characterization of Changing Precipitation Regimes
John Hallett, DRI, Reno, NV; and R. Rasmussen
Precipitation regimes may be characterized by the amount of precipitation which falls at a given rate, with a degree of perception improving at high resolution but limited by the statistics of collection of individual falling elements. An electrically and mechanically robust instrument (the hot plate total precipitation gauge) has been developed for measurement of precipitation as rain, snow or mixed phase at time resolution down to 1/2 minute, capable of providing measurements from <1/100 to > 2 - 4 inches water equivalent per hour having a sensor area of 265 cm2. Precipitation rates are measured by the power requirement (converted from latent heat of evaporation) to maintain a horizontal exposed sensor maintained at constant temperature, qualified by a local wind speed and air temperature reference; falling and blowing snow may be separated by two sensors at different heights, as may a changing snow surface height and vertical momentum transfer during precipitation events. Particle phase may be deduced from an independent sensor element or inferred from ambient temperature for complete evaluation of the processes.
Direct output provides precipitation rate and amount between selected times; it also provides probability rate and time distribution functions for short individual shower system times or on a seasonal or longer basis. The probability functions are interpreted in terms of changing cloud precipitation processes and the time variability in terms of seasonal (or longer term) changing time series of convective or stratiform precipitation having different time scales of evolution. Thus a warming climate with input of more water vapor from evaporation leads to higher temperature cloud bases to encourage higher precipitation rates from enhanced rate processes.
Extended Abstract (1.6M)
Session 4, Observed Climate Change in the Atmosphere and Oceans: Part 2
Tuesday, 31 January 2006, 1:45 PM-5:30 PM, A314
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