When it doesn’t show signs of stopping, most of us just
mumble a few choice words and get out the snow shovel. Scientists, however,
wonder where all that snow is coming from, particularly in pristine places like
the Arctic. Raymond Shaw and his colleagues may have found an answer.
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?