Rain gauges

If basic calculations such as those presented are to be conducted, it is important to collect enough weather parameters to calculate reference evapotranspiration ETf). An on-site weather station should be considered a basic requirement minimum sensor requirements to calculate a Penman equation would include solar radiation, wind speed, relative humidity or actual vapor pressure, and air temperature. An on-site rain gauge is essential but it is also a good idea to have a rain gauge on the weather station even if it is not directly on-site. The most accurate variations of the Penman equation calculate Tq on an hourly basis. However, Penman routines using daily summaries are typically satisfactory for the purpose of calculating soil-water recharge. 

Schwarb M (2000) The alpine precipitation climate. Evaluation of a high-resolution analysis scheme using comprehensive rain-gauge data. Dissertation, Eidgenossisch Technische Hochschule (ETH), Zurich... 

Let us assume for the moment that all raindrops have the same diameter D. The rainfall rate R, the rate at which the depth of water in a rain gauge of constant cross section increases with time, is the product of the total volume of water in a unit volume of air and the terminal velocity Vt(D) of a raindrop ... 

The first tests of this proposed method have been encouraging. On the basis of comparisons between rainfall rates measured with the differential reflectivity technique and with a network of rain gauges, Seliga et al. (1981) concluded that these first measurements of rainfall using the ZDR technique support the theoretical expectations... that rainfall rate measurements with radar can be made with good accuracy. So it may yet be possible to accurately measure rainfall with radar—provided that measurements are made with two orthogonally polarized beams. This exemplifies one of the principal themes of this book scattered polarized radiation contains information that may be put to good use. 

Precipitation can be in the form of rain or snow. Rain is measured by a rain gauge. The amount of snowfall can be measured in two ways ... 

Collecting snow in a rain gauge and allowing it to melt. 

Most measurements of fallout have been made with deposit gauges, which are similar to rain gauges. Unless arrangements are made to expose the gauge only when rain is actually falling, the deposit gauge will also collect dry deposition, that is particles deposited by any of the mechanisms listed above. Table 2.13 shows values of ve for 137Cs and... 

The work reported here represents one aspect of an on-going study into the intra-urban distribution and sources of pollutants in urban precipitation. A dense network of bulk, wet-period and sequential rain samplers, along with intensity rain gauges are operating within the Hamilton area. 

Field Operations. Each si e had four automatic precipitation collectors (Aerochem Metrics) and a Universal Recording Weighing Bucket Rain Gauge (Belfort) with an eight-day spring powered clock and strip chart recorder. An event pen marker was interfaced with the samplers and noted the sampler lid open and close times on the rain gauge strip chart. 

Only events greater than 0.51 mm (0.02 inch) rain gauge depth were included in this study to ensure that sufficient sample was available for analysis. Thus if a week had only small daily events, no corresponding daily and derived weekly data were available however, events greater than 0.51 mm allowed partial analysis and were included. 

Wet deposition was collected on an event basis in polyethylene buckets in Aerochem Metric collectors set to open only during precipitation periods. The precipitation time was determined from a Belfort recording rain-gauge. The precipitation depth (as water equivalent) was determined as the volume of precipitation in the bucket divided by the area of the bucket opening (638 cm2). The precipitation was filtered through 0.4 Aim pore Nuclepore filters to remove particles and was then refrigerated until time for analysis. The ions, N03- and S04--, were analyzed by ion chromatography. 

More recent work has not confirmed the large proportion of stem flow. Work by Franken et al. (1982), carried out in typical Amazon high forest near Manaus, used a system of rain gauges in cleared areas and in the forest canopy, with an extensive series of stem flow collectors. They found that 77.7% of average precipitation reached the soil surface as throughfall, 22% of the rain was intercepted by the canopy, while stem flow only represented 0.3% of the total. 

A rain gauge and a thermometer that registers minimum and maximum temperatures can also provide data that will be useful in making a diagnosis. Position the rain gouge... 

Sediment traps are rain-gauge-like collectors of particles (Fig. 6.9) that have been deployed in the ocean hundreds of times. Although these deplo5mients have revealed a wealth of information about the nature of the sinking particles, it is generally agreed that sediment... 

In each field, a rain-gauge was attached to one monitoring well to collect rainfall and irrigation water. The location of the wells and samplers in Fields 1-7 are shown in Figures 1 and 2. 

The water recharge for the Maui fields was calculated with a simple hydrologic balance for each field using rainfall data from nearby rain gauges. Both fields were non-irrigated. A rainfall-runoff relationship was developed for each field using the USDA-Soil Conservation Service "curve number" approach. The validity of this approach for Hawaii conditions was demonstrated by Cooley and Lane (20). Potential evapotranspiration from pineapple fields was assumed to be one-third of pan evaporation throughout the study period, based on results of Ekern (21). but actual ET was adjusted for the water input for each month (3 ). 

The first network to collect precipitation samples for subsequent chemical analyses all over the United States of America was organized by Junge and Werby (1958). More recently researchers at the National Center for Atmospheric Research4 have published a compilation of data obtained between 1960 and 1966 by means of a network consisting of 33 stations (Lodge et a/., 1968). At the stations, situated mostly in locally non-polluted rural environments, automatic rain gauges were used. 

The first major precipitation chemistry program was initiated by Swedish scientists (see Egner and Eriksson, 1955). The network was extended to the northern and western parts of Europe and for some time chemical data were published in the scientific journal Tellus. At the beginning of the sixties more than one hundred stations were involved in the network. This network is still in operation, and it is now called the European Atmospheric Chemistry Network (Granat, 1978), since not only precipitation chemistry is measured in this program (see Egner et al., 1955). The number of stations at present is about 50. Monthly precipitations samples are collected by open rain gauges. 

Platt ). Monitoring for wet deposition currently is based on collectors such as those shown in Figure 2. The device in Figure 2A consists of two buckets, one of which is open for dry fallout and the other is opened automatically with onset of precipitation. A precipitation sample is collected in a chemically inert vessel which is sealed by the cover after an event. A rain gauge is often used with this device to record the quantity of precipitation. Samples are removed either at regular intervals (which should not exceed 24 hours), or on an... 

Figure 4.4 shows an estimated map of caesium-137 deposition over the UK arising from Chernobyl. Values over the Scottish Highlands and other remote areas are unfortunately somewhat tentative, mainly because of uncertainties in the rainfall in those areas. The map was derived by using surface rain-gauge measurements at nearly 4000 sites across Britain, in conjunction with estimated concentrations of caesium-137 in air during the time of the rain, to yield an estimate of the wet deposition at each site. This was then combined with an estimate of the total dry deposition to yield the total deposition D. The specific formula used is... 

Deposition may be underestimated in the more mountainous areas for two reasons (i) the rain-gauge sites in these areas are often remote and were not read on a daily basis over the weekend and (ii) the sites are usually in valleys and wet deposition would normally be less there than on the neighbouring mountain tops. 

In developing countries, particularly in arid countries, there is a paucity of continuous rain gauge precipitation measurements from which time series analyses can be carried out if required. An attempt is being made to redress this balance, in Kuwait. A technique to resample the monthly TRMM precipitation rate on 0.25° is described for calculating precipitation at any spatial location with limited or no ground control [44], The technique has been cahbrated by testing modeled data... 

The comparison of the satellite precipitation following the bilinear weighted interpolation and the gauge measurement are presented below at eight different spatial locations. The measured data for the rain gauges was not continuous, and at certain times was not recorded due to instrument malfunction and/or calibration errors. However, the TRMM data is continuous (Figs. 32-39). 

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