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Simple Elegance - The Rain Gauge


Consider the rain gauge used in GLOBE, CoCoRaHS, and other citizen science programs. Just four pieces plus 2 mounting screws – an inner graduated cylinder, an outer cylinder, a cap/funnel, and a mounting bracket. The area of the outer tube is exactly 10 times the areas of the inner tube and the cap/funnel, so the graduations on the inner cylinder can be spaced ten times further apart. Thus, 0.2 mm of rain fills the inner tube to a depth of 2.0 mm, which one can read.

In addition, if heavy rainfall fills the inner cylinder, the rest of the rainfall overflows into the outer cylinder, which has a volume almost ten times the volume of the inner cylinder. The total rainfall can be measured by repeatedly filling the inner cylinder from the outer cylinder and adding up the amounts.

The cap/funnel greatly reduces the area through which water can evaporate. Once rain is in the inner or outer cylinder, little water can be lost before a reading is taken. The cap also helps keep larger debris from being caught in the rain gauge.

When the weather is at or below freezing, the inner cylinder needs to be removed so water expanding as it freezes won’t crack it, but the outer tube without the cap/funnel can still collect precipitation that may be a mix of rain and frozen precipitation. For snow measurements, the outer cylinder offers an excellent way to collect samples from a snow board. When samples melt, the inner cylinder still serves as a graduated cylinder to measure the liquid equivalent of the snow.

With care to mount the rain gauge vertically and in a place where all the rain can fall into the gauge and no extra water can get into it, a few seemingly simple pieces of Plexiglas are transformed into a robust research instrument. Of course, these pieces are simple but elegant in their design, enabling excellent, affordable possibilities for citizen science, and through GLOBE, for student learning and contributions to environmental understanding.

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