Why It Snows So Much in the Frozen North
Here’s the conundrum: Snow doesn’t just materialize out of thin air. For those delicate, six-sided crystals of ice to form, they need a nucleus, a speck of dust, where water molecules can cling and order their structure as they freeze. Those ice-forming nuclei are relatively rare. Yet, over the Arctic, where the atmosphere is very clean and the ocean is covered with ice, sometimes it snows interminably. With bazillions of snowflakes crystalizing over dust specks and falling to Earth, why don’t the clouds run out of nuclei? And why doesn’t it quit snowing?
The same question applies to a lesser degree in places like Lake Superior, whose soggy clouds drop countless megatons of snow on the hapless residents of Minnesota, Wisconsin and Michigan.
“Within a few hours, you basically purge the atmosphere of all those particles,” said Shaw, a physicist at Michigan Technological University. “So how can it snow for days on end?”
To answer the question, Shaw and his colleagues, including graduate student Fan Yang, set about developing a model to describe how ice crystals form, grow and fall, and they backed it up using data on arctic clouds, which are very well studied. They hoped that by characterizing just how snow comes into being, they would uncover clues to the puzzle.
What they discovered surprised them. As the number of snow crystals increases, their mass soars by a power of 2.5. “Our first guess would have been that if you triple the number of crystals, you triple the mass,” said Shaw. “It turns out to be a much stronger relationship than that.” For example, if you triple the number of crystals, the mass goes up by a factor of 16. Simply put, the more crystals you have, the bigger they are.
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