Comparison of precipitation gage catches with a modified alter and a rigid alter type windshield

Abstract

Gage catch from two standard weighing recording rain gages (Belfort model 5-780), one with a modified Alter windshield and one with a rigid Alter type windshield, were compared for 89 storms with wind speeds ranging from 4 to 32 mph (6.4 to 51.5 km/h) and temperatures ranging from 14 ø to 69øF (-10 ø to 21 øC). The differences between gage catches were statistically significant at the 1% level for wind speeds of 12 to 16 mph (19.3 to 25.7 km/h) and for temperatures of 23øF (-5øC) or less. Since on the average the windshields do not produce significantly different catches, either windshield can be used to compute actual precipitation by using the Hamon dual gage approach.

Reynolds Creek Experimental Watershed and Critical Zone Observatory

“…Snow monitoring was initiated at the very start of the RCEW project, as the importance of snow in the overall hydrologic cycle was recognized from the outset. In the early years, snow courses were established, the snow pillow, now used throughout the United States, was developed (Johnson and Marks, 2004; Marks et al, 2002), and methods for estimating wind‐affected precipitation were established (Hanson et al, 1979; Rawls et al, 1975). It was quickly discovered that the amount of snow falling was only part of the knowledge required to understand snow accumulation and melt dynamics.…”

Precipitation

“…A ratio of snow catch in gages with a rigid shield (Nipher) to gages with a flexible shield (Alter) showed an exponential decrease from 1.0 at no wind to 0.5 at winds near 20 m/s. At high wind speeds, free swinging Alter shields were observed to loop, which created more turbulence than they removed (Rawls et al, 1975). Gages with a rigid Alter shield and a flexible Alter shield had essentially the same catch, so both variations are currently in use.…”

EVALUATING THE ACCURACY OF RAINFALL CATCH BY THREE DIFFERENT GAGES1

“…There are many studies that have been conducted to improve precipitation measurements. Techniques suggested for improvement may include proper site selection (Leonard and Reinhart, 1963;Chang and Lee, 1975;Golubev, 1985;Sevruk and Zahlavova, 1992), shielded gages (Nipher, 1878;Alter, 1937;Warnick, 1953;Lapin and Samaj, 1989), tilted gages (Hamilton and Reimann, 1958), pit gages (Koschmieder, 1934;De Bruin, 1985), dual gages (Hamon, 1971;Larson, 1972;Rawls et al, 1975), wind corrections (Chang and Lee, 1974;Chang and Lee, 1975;Allerup, 1985;Gronowski, 1989), lysimeters (McGuiness, 1966;Morgan and Lourence, 1969), and vectopluviometers (Hamilton, 1954). However, all these techniques and methods have weaknesses with wind still being a major concern in precipitation studies (Larson and Peck, 1974;Sevruk and Zahiavova, The U.S. standard nonrecording, weighing gage, and the standard gage fitted with an Alter windshield are the three most common raingages used for precipitation measurements in the United States.…”