Standard Rain Gauge Research Articles

Rain and Snow Gauge Comparisons

The performance of four types of rain gauges and three methods of measuring snow-fall were compared over a 10 year period. Under the conditions of the test the United States Weather Bureau's (now National Weather Service, NOAA) standard precipitation gauge proved most reliable for measuring rain at all intensities, whereas the Meteorological Service of Canada's (now Atmospheric Environment Service of Canada) Nipher gauge was superior to other snow gauges for measuring snowfall.The Atmospheric Environment Service of Canada's standard rain gauge sometimes seriously undercaught in times of intense rain. Wind velocity did not seem to be the cause, but rather the intensity of the rain itself.Under blizzard conditions both the snow board and the United States National Weather Service's Alter shielded gauge proved unsuitable for measuring snowfall.

Effects of Fertilization of a Black Spruce Stand on Nitrogen Contents of Stemflow, Throughfall, and Litterfall

The nitrogen (N) contents of stemflow, throughfall, litter, and rain were investigated in a black spruce stand with 95% crown closure treated with three levels each of nitrogen and phosphorus fertilizers in a factorial design. Throughfall and rain were collected in standard rain gauges. Stemflow was collected using lead collars coated with an inert plastic and fixed on the tree trunks. Litter samples were collected with fiberglass screens. In all samples, NH4+-N and total-N were determined.During this study, 18–20% of the rainfall was lost through interception and evaporation, 80% was throughfall, and less than 0.5% reached the ground as stemflow. Average concentrations of NH4+-N for all fertilized plots in stemflow, throughfall, and rain were 0.15, 0.23, and 0.09 p.p.m. N, respectively, and the total-N in these samples was 1.69, 0.63, and 0.37 p.p.m. N in the same sequence. Quantities of nitrogen in the throughfall were highest in the fertilized plots, i.e. fertilization increased the concentration of NH4+-N and total-N in throughfall but not in stemflow. In both stemflow and throughfall, highest concentrations of nitrogen were recorded in June. The estimated nitrogen returned to the ground by litterfall, throughfall, stemflow, and unintercepted rain was 16.00, 4.33, 0.04, and 2.62 kg N/ha/year.

Rain gage catch variation due to airflow disturbances around a standard rain gage

Although the spatial position has an important influence on the performance of a rain gage, the physical presence of the gage itself must be considered a hindrance to its operation. An obstruction to airflow in the vicinity of the gage, owing to the presence of the gage, results in disturbances in the local precipitation pattern in which the rainfall measurement is made. The airflow pattern data obtained in a study of a wind tunnel model and aerodynamic drag characteristics of water drops are used to perform a computer simulation on the movements of the drops as they approach the gage. These drop paths are analyzed to establish the effectiveness of the gage in measuring precipitation. If we use drop sizes of 1–5 mm in diameter, we find that the gage catches from 103 to 11% of the drops as the free stream velocity increases from 10 to 50 feet per second. In general, the decrease in catch is less pronounced as the drop size is increased.

Rainfall Excesses in the United Kingdom

Rainfall has been recorded in the United Kingdom in a systematic fashion for over Ioo years. Information about the incidence of heavy rain is of particular interest to the hydrologist for use in flood prediction, but the data need to be classified. Bilham devised one method of classifying and predicting the frequency of heavy rain, but another more satisfactory approach is through the use of a Gumbel-type extreme value analysis, as this allows magnitude frequency relations to be determined at a point. The problems of transforming point values into areal assessments are described and a method for calculating the probable maximum precipitation is put forward. The low intensities of British maxima are significant in relation to the development and maintenance of the typical British upland scene. THE BRITISH weather and climate are supposedly free from the extremes experienced in other parts of the world. Yet unexpected snowfall throws the transport system into confusion, hurricane force winds cause considerable damage in urban areas and floods occur at a time of the year when a heat wave might be expected. The cost of these and similar events must amount to millions of pounds each year while, in addition, there is sometimes loss of life. Heavy rain is the usual cause of river floods, although rapid snow-melt is an important but rarer factor. Information about the amount and distribution of rainfall in the United Kingdom has been collected systematically for more than 1oo years, and now the network consists of some 6500 standard rain gauges, many read daily by volunteers. By comparison with other countries, this is one of the best national rain-gauge networks,1 in terms of the number of gauges and the lengths of records, although there are reasons to suspect the efficacy of the standard gauge.2 Unfortunately, the network of rain recorders is much more limited, both in number of gauges and length of records. Hence knowledge of the relationships between the intensity, frequency and duration of rainfall is somewhat limited for periods other than the rainfall day. The occurrence of exceptionally heavy daily falls of rain for the period 1863 to I960 has been described by A. Bleasdale.3 From that study and the map (Fig. I) it is evident that a rainfall of Ioo mm4 has been surpassed on some occasion in almost every part of the country. As might be expected, the heaviest falls have occurred in those parts of the north and west where the largest annual totals are recorded. On the other hand, it is noteworthy that there have been events of a similar magnitude in some of the regions of low rainfall, particularly near to the east coast and across the neck of the South-West Peninsula. This part of the West Country seems especially susceptible to heavy rain, possibly because convectional storms are reinforced by the effects of orography. Within the last 50 years it has experienced at least five storms which produced daily falls in excess of 50o mm, the most recent occurrence being on Io July 1968. On that day, amounts of up to I70 mm were registered to the north of the Mendip Hills and there were widespread falls of over Ioo mm. The outstanding example, however, was the storm of July 1955 when 280 mm was recorded at Martinstown, Dorset-the largest amount ever caught in one day at any United Kingdom station. Of course, limitations of the rain-gauge network, particularly in the mountainous areas, may have led to many other excessive falls not being recorded. There is also the fact that the probability of rain falling at 0900 hours (the time of observation) increases towards the north 49 This content downloaded from 157.55.39.45 on Tue, 19 Jul 2016 05:46:16 UTC All use subject to http://about.jstor.org/terms

Seasonal variation in rain gage catch

In northern Ohio 8‐inch standard rain gages consistently caught more precipitation in summer and less in winter than adjacent digital punch gages although average annual totals were almost identical. A similar seasonal pattern was found in a comparison of precipitation catch by weighing lysimeters and adjacent weighing type recording rain gages in Ohio and in a comparison of standard and recording rain gage catch in Nebraska. Some reasons for the differences in their implications are discussed.

An Accurate Small Orifice Rain Gage

An accurate, inexpensive, small‐orifice rain gage (modified Victor‐rain gage) with an orifice diameter of 29.2 mm was developed for use in rainfall networks and in agrometeorological and hydrological studies. It has a large capacity and can be installed and read easily. Comparison with standard rain gages showed good agreement under various conditions of exposure and with different observation techniques. Small amounts of rainfall are likely to be overestimated, owing to a film of water adhering to the glass water container of the gage, whereas hail tends to be underestimated. If the gage is intended for storage, the funnel tube has to reach nearly to the bottom of the inner vessel.

Direct Interception of Cloud Water on Lanaihale, Hawaii

AbstractLanai, a relatively dry island, lies in the trade wind flow downstream from Maui and Molokai and is peculiarly adapted to a demonstration of the amount of water that can be gathered by direct interception from clouds. An observation station was established at the 2,750‐foot level on Lanaihale in July 1955, and maintained for 3 years. The water collected over the 3 years by a network of rain gauges set beneath a Norfolk Island pine tree averaged 391 inches while rainfall in the open was only 149 inches. Since the tree also intercepted some rainfall, a net of 30 inches is suggested as the annual gain from cloud water interception. A wire harp kept oriented into the wind by a vane gathered 1,706 inches of water while rainfall alone was 97 inches. The harp had a vertical silhouette 27.5 times the area of the standard rain gauge in which the catch was measured. A 15‐ to 20‐inch gain per unit vertical area exposed is suggested as the annual direct cloud interception by the harp. Identical catchers of aluminum louver mounted at several elevations up to 30 feet above the ground gave an increased catch greater than the increase of wind with elevation.

A Modification of the Standard Weather Bureau Rain Gage for Summer and Winter Use 1

This article describes a modified collection unit for the standard Weather Bureau-type rain gage. The described unit, consisting of a polyethylene bottle, rubber stopper, vent tube and adapter funnel, replaces the metal collection tube of the standard gage. In a laboratory test, evaporation from the modified system was not great enough in a 30-day period to measure with a standard measuring tube. Field tests showed the described unit superior to the standard collection unit and equal to the standard unit with a 0.20-inch oil film in the reduction of evaporation. The described unit, which eliminates recharging with oil or antifreeze after each reading, has been in field use for two years without damage from freezing.

A Report on the Difference Between the Precipitation Records as Taken on the Standard Canadian and United States Rain-gauges

Synopsis This describes a comparison of rainfall observations as taken at the Victoria College on the Canadian standard rain gauge of 3.57 inch diameter, and the standard U. S. 8 inch gauge, and a similar comparison made at Seattle Weather Bureau. The results appear to show that the small gauge records more rainfall than the larger gauge, but the difference is less during windy weather. No cause for this difference is given at the present time. It is also pointed out that the cedar stick causes a displacement of .01 inch per inch in the 8 inch gauge.

IMPROVED GAGES FOR PRECIPITATION

Abstract SYNOPSIS An improved recording gage for precipitation.—This instrument records the weight of rain, snow, etc., falling into a suitable receiver supported by a spring balance. The original instrument of this pattern was designed by the author in 1888, the present improvements consisting of a more compact balance mechanism, whereby the movement of the receiver is more nearly rectilinear, and a device for obtaining two or more traverses of the record sheet by the pen; improved accuracy and greater capacity are secured in this way without increasing the dimensions of instrument. The record sheets require changing only after each rain, whether of one or several days duration, and the accuracy of registration can be checked by measuring the amount of rain in the standard raingage. The instrument is of simple, rugged construction in order that it may function properly under severe conditions and can be exposed in any place suitable for the standard raingage. A new registering raingage for isolated stati...