UNIVERSITY PARK, Pa. — Do you ever wonder how much rain or snow falls during a storm? Measuring a storm’s total precipitation is a very challenging task, and, each year, a group of meteorology students gets to learn just how many factors are involved through a hands-on project that lets them design and build their own rain gauges.
Paige Campbell and Mike Kwasnik, both undergraduates studying meteorology in the College of Earth and Mineral Sciences, explored these variables in METEO 440W, an upper-level meteorology course that combines lab experiments with learning how to write scientific reports. The course features a semester-long project focused on designing and building rain gauges, and then measuring the precipitation that’s collected.
A rain gauge typically consists of two key parts — a wide cylinder that collects the precipitation and a narrow cylinder that allows for an accurate measurement.
“The idea behind the standard rain gauge, such as the one that the National Weather Service (NWS) uses, is that the wider cylinder maximizes the collection accuracy of the precipitation, which is then funneled into the narrow cylinder for accurate measurement,” said Amy Huff, assistant professor of meteorology. “The standard NWS gauge has a 10-to-1 ratio of areas of the cylinders, which means that one-tenth inch of collected rain corresponds to one inch of water in the measurement cylinder. The measurement cylinder is calibrated to account for the 10-to-1 ratio.”
Mitigating uncertainty while measuring precipitation
There is often uncertainty when measuring precipitation; variables like wind and location can skew final tallies.
“Precipitation measurements are point measurements, which means that one measurement represents an entire area, such as State College,” explained Huff.
State College’s measurement comes from a rain gauge on top of Walker Building on the University Park campus. However, if a thunderstorm strikes a different part of State College, for example, it is likely that the rain gauge on Walker Building would report a lower amount of precipitation than if someone measured the rainfall where the storm hit.
Each group in the class designed and built a rain gauge and then placed it either next to the one on Walker Building or in another chosen location in State College. The rain gauges collected data for 14 days in February.
Kwasnik’s group placed its 5-gallon rain gauge in an open field and sought to reduce wetting loss, or the loss of water during measurement because either the water evaporates or fails to funnel through to the narrow cylinder.