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Following four types are the most widely used recording rain gauges:
Type # 1. Symon’s Rain Gauge:
The Indian Meteorological Department has adopted Symon’s rain gauge (Fig. 2.3). A glass bottle and funnel with brass rim are put in a metallic cylinder such that the top of the cylinder is 30.5 cm above the ground level.
Rain water falls into the glass bottle through the funnel. The water collected in the bottle is measured with the help of a standard measuring glass jar which is supplied with the rain gauge. The jar measures rainfall in millimeters.
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At each station, rainfall observations are taken twice daily at 8.30 am and 5.30 pm. Recording rain gauges automatically record the intensity of rainfall and the time of its occurrence in the form of a trace (or graph) marked on a graph paper wrapped round a revolving drum.
Type # 2. Tipping Bucket Rain Gauge:
A 300 mm diameter funnel collects rain water and conducts it to one of the two small buckets (Fig. 2.4) which are so designed that when 0.25 mm of rainfall is collected in a bucket it tilts and empties its water into a bigger storage tank and simultaneously moves the other bucket below the funnel. When any of the two buckets tilts, it actuates an electric circuit causing a pen to make a mark on a revolving drum.
The recording equipment can be remotely located in a building away from the rain gauge. At a scheduled time, the rain water collected in the storage tank can be measured to yield total rainfall in the measuring duration. The rainfall intensity (and also the total rainfall) can be estimated by studying the record sheet on which each mark indicates 0.25 mm of rain in the duration elapsed between the two adjacent marks.
Type # 3. Weighing Bucket Rain Gauge:
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This gauge (Fig. 2.5) has a system by which the rain that falls into a bucket set on a platform is weighed by a weighing device suitably attached to the platform. The increasing weight of rain water in the bucket moves the platform. This movement is suitably transmitted to a pen which makes a trace of accumulated amount of rainfall on a suitably graduated chart wrapped round a clock-driven revolving drum.
The rainfall record of this gauge is in the form of a mass curve of rainfall (Fig. 2.6). The slope of this curve at any given time gives the intensity of rainfall at that time.
Type # 4. Siphon Rain Gauge:
This gauge (Fig. 2.7) is also called float type rain gauge as this gauge has a chamber which contains a light and hollow float. The vertical movement of float on account of rise in the water level in the chamber (due to rain water falling in it) is transmitted by a suitable mechanism to move a pen on a clock-driven revolving chart. The record of rainfall is in the form of a mass curve of rainfall and, hence, the slope of the curve gives the intensity of rainfall.
