Description of a Rain Gauge
A rain gauge is an instrument for measuring the quantity of precipitation. The standard rain gauge is 8 inches in diameter and 24 inches tall. The outer container is called the overflow can, and inside there is a brass or clear plastic measuring tube 2-1/2 inches in diameter and 20 inches deep. On top is a copper or white plastic funnel 8 inches in diameter. Although not part of the rain gauge itself, the measuring stick is essential to accurately measuring of all forms of precipitation, including snow.
Other People Are Reading
-
Measuring Capacity
-
A standard rain gauge accommodates 2 inches of rain in the inner container, which is 2-1/2 inches across and 20 inches high.
When a heavy rainstorm results in water greater than 2 inches, the water flows over the top of the inner container and into the overflow can, which is 4 inches taller than the inner container. The observer measures and records the amount of rain in the inner container and empties the inner container. Then, the observer carefully pours the water from the overflow can into the inner container, measures it and records it. The observer adds the two recorded totals together to obtain a final amount of rainfall.
The Tube
-
The inner container is tall and narrow, but 1 inch in the inner container is only 1/10 inch of rain. This makes it possible to obtain very accurate measurements--to 1/100 of an inch--of the amount of rainfall. The measuring stick used with the rain gauge is calibrated to allow for this apparent distortion of size. The measuring stick also helps account for snowfall depths--snow falling into the rain gauge is measured with the stick; one tenth of an inch of snow on the measuring stick equals 1 inch of snow.
-
Another Rain Gauge
-
A tipping bucket is another type of rain gauge. It uses a specially designed bucket that tips the water on to the ground when the weight of 0.01 inch of rain falls into it. Every time a bucket tips, it trips a switch that sends an electronic signal to a recorder. The recorder has a clock function, so that you can tell how much rain fell in a specified time period by multiplying the number of "tip marks" on the recorder by 0.01.
Homemade Rain Gauge
-
To make your own rain gauge, all you need is a clean jar and ruler. The first step is to put the jar outside, away from buildings and trees or any other overhead obstruction, before the rain begins. After a rainfall, measure how many inches of water are in the jar. Is it accurate? Perhaps not as accurate as one of the official rain gauges described above, but it's close. The difference is that your jar doesn't have the same dimensions. However, it still registers how much rain fell into it.
Correctly Reading a Rain Gauge
-
The surface of the water in the gauge will appear curved, which is called a meniscus. The liquid will be higher where it contacts the inner container because of surface tension. Use the bottom of the curve as the measurement.
The measurements on the side of the inner container are in tenths of an inch, which are designated by the shortest lines on the container's surface and hundredths of an inch, which are designated by the longer lines. The container is designed so that when the inner container is full of water, the water's surface is magnified. This allows you to take a more precise reading.
Never use a ruler to take measurements. A standard ruler isn't calibrated for a rain gauge.
If the inner container is full and rain has spilled into the overflow can, take the measurement from the inner container, record that measurement and empty the water from the inner container. Then, carefully pour the water from the overflow can into the inner container, measure it again and record the amount. Repeat the process until all the water has been measured and poured out. Finally, add up the totals from each measurement for a rainfall total.
-
References
Resources
- Photo Credit Creative Commons - The Weather Observer
More Like This
Comments
-
The image looks nice, but it wouldn't work. A big column (window frame? chimney?) right next to a gauge that is elevated well beyond standard practice would be prone to enormous errors.
