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Why snow reflects less light after it settles, and other questions you can help answer

  • The map from Nov. 27, 2017, shows a week's worth of measurements of albedo (light reflection) off snow on the ground in New Hampshire. Courtesy—CoCoRaHS



Monitor staff
Tuesday, November 28, 2017

Perhaps because I grew up in Virginia, I can never shake the feeling that snow is almost too weird to be real.

Each time it snows, I am surprised anew that such a wispy substance can fall from on high, trap you in your home for a week, create the most beautiful scenes in nature as if to apologize, then disappear like nothing ever happened.

Weird. But also very interesting.

Here’s something else interesting about snow: It reflects less light after it sits on the ground for a while, but not because of all the twigs and dirt that land on it as the days go by.

The decline in albedo, a measure of how much light gets reflected, is mostly caused by change in the size of snow “grains” as flakes are compressed together as the snowpack settles. Bigger grains increase the likelihood that any given photon from sunshine will be absorbed rather than bounced back into the air: hence, lower albedo.

Is that neat or what? Even better, I learned about it from a citizen-science project that you – yes, you! – can be part of. It’s called the CoCoRaHS Albedo Project at UNH.

That clunky name reflects that it’s a subset of the national Community Collaborative Rain Hail Snow network, a group of volunteers who measure precipitation every morning at their homes. About 50 people in New Hampshire, including me for the past eight years, take CoCoRaHS measurements at their homes each day.

We upload the results to a national database that reflects microclimate variability and aids in forecasting floods and improving climate models. It’s an oddly satisfying task, even when it sends me outside in freezing rain wearing slippers to read the gauge.

The albedo project began in 2011 with the idea of piggybacking on CoCoRaHS to fill in data gaps.

“We don’t have a lot of measurements on the ground for snow albedo,” said Elizabeth Burakowski, an assistant professor at UNH’s Institute for the Study of Earth, Oceans and Space and a founder of this project. “This seemed like a good way to get them.”

“We’re now starting our seventh season. We’ve got retired engineers, weather nuts, high schools and middle schools,” she said, running through a mental list of volunteers.

You can check out results on the CoCoRaHS online map (cocorahs-albedo.org/map). There are only a dozen sites around the state, mostly because measurements must be taken close to local noon, to better calibrate the light. That removes any CoCoRaHS volunteers who don’t work at home, which is a lot of us.

Each day that snow is on the ground, volunteers measure its depth and density at a specific site in their yard by collecting snow in a calibrated tube and weighing it. They then use a pyranometer, a sort of light meter that measures solar radiation, to measure light from the sky and light from the ground.

More than 5,500 readings have been made so far, allowing an ever-better understanding of the relationship between snowfall, snowpack and light reflection. The goal, Burakowski said, is to help perfect and design models on how the climate is changing and will change down the road.

Snow albedo matters in this because the amount of sunlight that is reflected upward, rather than absorbed by the ground or plants, is a factor is understanding how much the planet will heat up.

Snow albedo is part of a positive-feedback loop, one of several that make climate change alarming: Warming weather means less snow on the ground, which means lower global albedo levels, which means more heat is absorbed, which means warming increases further, etc.

If we want to understand what we’re doing to the planet so we can better respond to the changes – and we most certainly do –then figuring out snow albedo is important.

The work isn’t too hard to do after a little bit of equipment training, but Burakowski would like to make it easier.

“We’re trying to simplify it, using smartphones to measure radiation. There is an app, but it’s not particularly good – results of plus or minus 20 percent – so we’re trying to design a new app that will reduce that window quite a bit,” Burakowski said.

Want to be part of the process? Send Burakowski an email (Elizabeth.Burakowski@unh.edu) and she’ll see if you fit the bill. Remember, you’ve got to be available at the same location around noon every day during winter.

In the meantime, please join me in my annual Early Winter Snow Dance, designed to entice the weather gods to dump on us plenty of what TV meteorologists love to call “the white stuff.”

Snow might be weird, yes, but it’s also awesome. Bring it on!

(David Brooks can be reached at 369-3313 or dbrooks@cmonitor.com or on Twitter @GraniteGeek.)