Hands-on project teaches students the challenges of measuring precipitation

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.

“We sprayed our rain gauge with a water-resistant coating, which would make the water bead right off of the container,” said Kwasnik, a graduating senior in meteorology.

The group’s results were inconclusive, but not necessarily because of wetting loss.

“When it came to snow, our gauge reported less than the National Weather Service rain gauge on Walker Building, and this could be because of wind or because we used a different location,” explained Kwasnik.

The impact of wind on measurement was the focus of Campbell’s group, which experimented with a new windshield for the rain gauge.

“The National Weather Service typically uses a wind shield with metal spokes that form a ring around the gauge to protect it from wind, but we tried a windshield made of fabric,” said Campbell, a junior. “This dispersed the wind, allowing some to go through and some to go over it.”

Campbell’s project produced results similar to Kwasnik’s group, collecting less precipitation than the National Weather Service’s gauge while also dealing with leaking issues.

Learning how to write scientific reports

However, not all of the students in the class will be measuring rainfall during their careers. The broader benefit is that students hone their technical writing skills.

“The focus of the class is to take the experiment’s results and write about them clearly and effectively,” said Huff. “The class prepares students for whatever trajectory they take in meteorology. Possessing effective written communication skills will be invaluable regardless of their career.”

Kwasnik and Campbell found this part of the course to be challenging at times, but they acknowledged the benefits it will have for their future careers.

“The writing was difficult at times for me, but I found that I improved with things like conciseness as the semester went on,” said Campbell, who hopes to find a job studying space weather after she finishes her undergraduate studies. “This will be helpful in any job that I get.”

As a member of Penn State’s ROTC program, Kwasnik will spend several years as a pilot for the U.S. Navy before exploring other careers in meteorology, but the skills he acquired from this course will serve him immediately.

“As a pilot, you need to have technical writing skills to explain potential situations to maintenance crews,” he said. “It’s important to be able to communicate efficiently with good technical details to save time when diagnosing problems in the air.”