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rain gauge
RAIN GAUGE
Many residents have various
types of instruments to gather and measure the rain. Rain gauges come in a variety
of shapes and sizes, but all are used to accurately measure the amount of fallen
precipitation. The typical home rain gauge consists of a plastic tube or wedge
with measurement increments on its side. One just reads the water level on the
side of the rain gauge.
The most common rain gauge
found at weather offices is the standard 8 inch rain gauge and has been used
over 100 years. It consists of a large cylinder with a funnel and a smaller
measuring tube inside of it. The dimensions of this instrument are very specific
so water that collects in the measuring tube has exactly one-tenth the cross
sectional area of the top of the funnel. The reason for the smaller measuring
tube is so that more precise rainfall measurements can be made due to the exaggeration
of the height of water in the tube. For example, one-tenth of an inch of rainfall
would actually fill an inch of the measuring tube. A special measuring stick
inserted into the measuring tube takes into account the vertical scale exaggeration.
The tipping bucket rain
gauge is an alternative to the standard rain gauge for measuring rainfall. It
uses gravity. Two specially designed buckets tip when the weight of .01 inches
of rain falls into them. When one bucket tips, the other bucket quickly moves
into place to catch the rain. Each time a bucket tips, an electronic signal
is sent to a recorder. To calculate the rainfall for a certain time period,
simply multiply the number of marks on the recorder by .01 inches. The tipping
bucket rain gauge is especially good at measuring drizzle and very light rainfall
events, unfortunately it has a difficult time keeping up with heavy rain from
a thunderstorm.
The weighing rain gauge
is another type of rain gauge. It is composed of container sitting upon a scale.
The scale is adjusted for the container and measures the weight of the collected
rain water. The measurement is traced out on a rain chart for a permanent rain
record.
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