Adjusting Wind Speed Measured over Variable Height Alfalfa for Use in the ASCE Standardized Penman-Monteith Equation

摘要

The ASCE Standardized Reference Evapotranspiration Equation expects the weatherstation wind speed data to represent that occurring at a height of 2 m over anddownwind of a smooth measurement surface such as clipped grass. The TaskCommittee on the Standardized Equation provided guidance for adjusting wind speedmeasured at height other than 2 m, or, for situations when the wind speed is measuredover and downwind of 0.5 m alfalfa. The latter adjustment attempts to account forthe effects of both grass and alfalfa crop characteristics (height, roughness) on thewind profile. A more physically representative approach to adjust wind speeds atvarious heights and various weather measurement surface conditions to equivalentwind speed at 2 m height over clipped grass is tested. Wind speeds weresimultaneously measured during the 2008 growing season at 2-m and 3-m heightsabove ground surface over variable height alfalfa at two Colorado AgriculturalMeteorological Network (CoAgMet) electronic weather stations and at the researchalfalfa lysimeter installation at the Colorado State University Arkansas ValleyResearch Center. These wind speed measurements were adjusted to estimated windspeed at 2 m over grass, and compared.