When meteorologists tell us that so many inches of rain have fallen, how wide is the collecting tube?

Question

Obviously 6 inches depth of water in a test tube is lower in volume than 6 inches in a bucket....

Answer 1

An inch of rain is just what it sounds like - one inch of water. If you had a sraight-sided cylinder, then there would be one inch of water in the bottom. Since a one-inch rainfall is a lot and pretty unusual, most of the time we are interested in amounts less than an inch. Rain gauges are usually designed with the collecting part at the top (where the rain enters) having a larger cross section than the straight-sided measuring part at the bottom. Picture a wide funnel feeding into a narrower cylinder.

As an example, consider a rain guage with a collecting area at the top of 2 square inches funnelling down to a measuring part of only one square inch. In this case, every one inch of water in the bottom would represent 1/2 inch collected at the top:

2 sq in top collection area x 1/2 in of rain = 1 sq in of measuring part area x 1 in of water in the bottom.

The ratio of the amount of rain to the height of the water in the bottom is the same as the ratio of the measuring part (bottom) area to the collection (top) area. Because the amount of water standing in the measuring part is related to the actual rain amount by this ratio, the calibration marks on the measuring part have to be "stretched" by the same ratio to convert from the height of water in the bottom to the actual rainfall collected by the larger collection (top) part.

The reason this is done is that it allows us to accurately measure smaller, more common amounts of rain. If we had to measure directly, we could never measure rainfalls like 0.05 inches. However, if our collection part area/measuring partarea ratio is 20:1, that 0.05 inches will result in one inch of water (0.05 inches x ratio of 20 = 1 inch) standing in the bottom measuring part - an easily measured amount.

Answer 2

It doesn't matter. What does matter is the radius (area) of the funnel used to collect the rain. The wider the funnel, the more rain collected. So all you have to do is divide the volume of rain in the tube by the area of the funnel, and you have the actual depth.

For a wider funnel, more water would be collected proportionately, and the actual depth would be the same, even though the tube depth of water is higher.

Answer 3

The collecting tube can have any area.If we say there was two inches of rain it simply means that water will stand to a height of two inches at that place if it is not either obsorbed by earth or drained away from the area over which it has fallen.

Answer 4

it doesnt matter. that is thy rain is measured in deapth, NOT volume

Answer 5

hahahah

i love ya dude, that question totally made my day! :)