Cmos bulletin scmo volume 5 No. April 2017 avril 2017
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- Article: The Nipher Rain Gauge
- The Nipher Rain Gauge
CMOS Bulletin SCMO Vol. 45, No.2
Article: The Nipher Rain Gauge While the “Nipher” used in the Canadian service is classified as a snow gauge, it was originally designed in the nineteenth century as a rain gauge (Abbe, 1888).
In 1769 William Heberden found that an unshielded rain gauge caught less rainfall as it was raised (Heberden, 1769). This was due to the general increase in wind with height. An unshielded receiver will have an additional increase in wind speed over the gauge orifice due to air from below being forced over the top of the orifice. This increase in wind speed would cause some of the rain drops to be deflected away from the receiver orifice. Hence, the rainfall caught by the gauge would be less than the actual rainfall. In 1878, F.E. Nipher developed a rain gauge that was shielded so that the air flow below the orifice top was directed downward (Figure 1), making the gauge height independent. The original Nipher included a receiver surrounded by three interconnected cones that acted as a wind shield. Snowfall is more affected by this wind increase over the receiver orifice than is rainfall. Beginning in the USA this same Nipher shield was applied to a receiver in order to measure snowfall (Figure 2). The original Nipher had the lowest conic section narrowed down to the same diameter as the receiver. The shield would have filled with snow rendering it useless. Brooks opened up the lower end to allow the snow to fall free of the shield. A shielded gauge which appears similar to Brooks’ was field tested in Canada during WWII (Figure 3; Toronto Register No. 300). Further developments by the National Research Council under the direction of Bill Middleton, head (until 1946) of the Instrument Section of Meteorological Service of Canada (MSC), led to a manual snow gauge with an exponentially shaped horn to replace Nipher’s conic sections – a design that was uniquely Canadian (Figure 4). During WWII Bill Middleton and his staff tested a 5" snow gauge similar to the Brooks gauge. Middleton likely also incorporated the curved shield design from M.S. Bastamoff (Bastamoff, 1932 and Abbe, 1888). Eventually a number of tiny models of different types of snow shields were constructed. These were tested in a small wind tunnel at the National Research Council (NRC) in Ottawa, from which the shield with the elliptical curve was selected (Macartney, 1945). The shields, which went into service circa 1953, were made from solid aluminum spun into a flare which was 24" (61 cm) wide at the top (MSC, 1953). During the development of fiberglass Nipher shields for 8" weighing gauges in 1985, a smaller one for the manual 5" gauge was also designed, since the fiberglass units were one third the cost of the aluminum shields (Metcalfe & Goodison, 1985). At that time the curve of the shield was changed from elliptical to spherical with no change in collection efficiency.
Kenneth A. Devine, Meteorological Instrument Consultant Figure 1: Nipher’s Rain Gauge of 1878 (Middleton, 1969). Figure 2: The Brooks Shield, 1938. For 172 daily rainfall events between 1943 and 1945, this 5” Nipher/Brooks snow gauge reported volumes 0.24% higher than the 3.6” standard copper rain gauge (Toronto Register No. 300). But it should be noted that the 3.6” copper gauge measured -5.2% with-respect-to (wrt) a World Meteorological standard pit gauge during a six year rain gauge comparison at Egbert, Ontario (Devine & Mekis, 2008). In general, the gauge which catches the most precipitation, thereby minimizing negative errors, is the better gauge. A later study of the aluminum shielded Canadian Nipher snow gauge at Swift Current from 1961 to 1965 reported that it was -2.9% wrt the 3.6” copper gauge from 137 rainfall days (Pelton, 1965). For 76 days with rainfalls of 2.3 mm or less at Swift Current, the Nipher reported -13.9% wrt the standard copper gauge. A reanalysis of the 1999 to 2005 data for 158 rain days at Egbert, Ontario indicated that the fiberglass shielded Nipher reported -7.4% wrt the pit gauge but -18.2% for those 100 days with less than three millimeters of rainfall. Thus while the Nipher reports similar rainfall values to the older copper manual gauge, for very light rainfalls it has a large negative error. From the Egbert data there was a loss of 0.15 mm per measurement which is mostly due to the retention errors of the large, 52 cm high, copper receiver used in the Nipher (Goodison & Louie, 1985). The evaporative and splash errors have previously been documented (Devine & Mekis, 2008). Figure 3: A similar gauge to the Brooks Shield being tested in Kapsukasing, Ont, in the 1940s. CMOS Bulletin SCMO Vol. 45, No.2
Article: The Nipher Rain Gauge While primarily used a snow gauge in Canada, the Nipher still collects the increasingly frequent winter rainfalls. The Nipher acts as a precipitation gauge throughout the year, whereas the gauges designed only for rainfall such as the Type B manual gauge and TB3 tipping bucket are taken out of service for most of the winter. The present Canadian 5” Nipher snow gauge has proven to be the best system for snowfall measurements in the world next to the Double Fence International Reference (Goodison et al, 1998), and superior to the Tretyakoff shielded gauges used in northern Europe (Strangeways, 2007). This report documents the operational accuracy for rainfall. Since manual gauges remain the best method for determining total rainfall or snowfall, locating Nipher gauges at manned climate stations would be worthwhile since the present snow depths are not an accurate method for measuring snowfall. The Nipher also has the highest precipitation capacities, next to the storage gauges, which may be useful in coastal areas with high rainfall. Both the advantages and shortfalls of the Nipher gauges for rainfall have been shown, and this gauge remains an important source for accurate precipitation measurements in Canada (AES, 1985). “Let us hope that, in time, it will be realized that an accurate knowledge of the amount of rain or snow which falls on a country is as important as many other statistical activities of government.” (Middleton, 1941)
References: Abbe, C., 1888. Meteorological Apparatus and Methods , Government Printing Office, Washington. AES, 1985.
, IB 04-03-01/1, Toronto, October 30 1985. Bastamoff, M.S., 1932. Sur les pluviometers , La Meteorologie, Vol.8. Brooks, C.F., 1938.
, International Association of Hydrology, Bulletin 23, Riga. Devine, K.A. and É. Mekis, 2008. Field accuracy of Canadian rain measurements . Atmosphere-Ocean 46 (2), 213–227. Goodison, B.E., Louie, P.Y.T., 1985.
, WMO Workshop on the Correction of Precipitation Measurements, Zurich, April 1985. Goodison, B.E., Louie, P.Y.T., Lang, D., 1998. WMO Solid Precipitation Measurement Intercomparison , WMO Instruments and Observing Methods Report No.67, WMO/TD-No.872. Geneva. Heberden, W., 1769. Of the different quantities of rain, which appear to fall at different heights, over the same ground ,
Philosophical Transactions of the Royal Society, 59: 359-362. Macartney. L.E., 1945. Wind Tunnel Investigation of Airflow over Snow Gauges , National Research Council of Canada, Report No.MA-168, Ottawa, November 1945. Metcalfe, J.R., Goodison, B.E., 1985. Fiberglass vs Aluminum Nipher Shield – Field Test , Report of the Canadian Climate Centre, AES, Toronto, October 24 1985. Meteorological Service of Canada (MSC), 1953. Snow Gauges , Instrument Circular 54, MSC Circular 2360. Middleton, W.E. Knowles, 1941.
, University of Toronto Press, Toronto. Middleton, W.E. Knowles, 1969.
, John Hopkins Press, Baltimore. Nipher, F.E., 1878.
, American Association for the Advancement of Science, Vol.27. Pelton, W.L., 1965. A Comparison of Three Types of Rain Gauges , Can. J. Plant Sci., Vol.45. Strangeways, I., 2007.
, Cambridge University Press, New York. Toronto Register No. 300, 1946. Climate Archive, Downsview.
Figure 4: The Canadian Nipher Snow Gauge, with dimensions in centimeters. About Ken Ken began his career as an observer and Officer-in-Charge at remote upper air stations. Later he worked three years as a senior electronics technician which included installing the first operational weather stations in Canada. After obtaining his degree and completing the meteorologist training in 1971, he spent four years forecasting on the east coast before moving to headquarters. In Toronto he worked in instrument development, project management, Field Services and finally as Superintendent of Climate Standards. After retiring in 1998 he has been researching and writing articles on the history of meteorological instruments in Canada.
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