18 Nebraskaland • December 2020
IN THE FIELD
Snow cover provides a wealth of opportunities for outdoor
enthusiasts. It insulates the ground during cold spells, helps
replenish soil moisture reserves as meltwater percolates and
unfortunately, helps to increase flood risk under the right
conditions. As snow melts, we witness fluxes of energy.
While probably not the phrase you were expecting, a transfer
of energy is ultimately what causes solid crystals to morph
into liquid fortunes.
Energy we receive from the sun, called shortwave radiation,
is one factor that produces snowmelt. The most obvious,
but not the most powerful, is through direct absorption of
sunlight by the snow.
Snow is a great reflector of those solar rays; a lot of energy
— sometimes up to 95 percent — simply bounces off, so to
speak.
However, when this shortwave energy is absorbed by
any object not covered by snow, such as tree trunks, fence
posts or grasses, that's when the magic happens. These
darker objects absorb sunlight — 80 percent more than
snow — and transform solar into thermal radiation, which
warms the surrounding air. Melt circles start to form around
these objects, and the bright white blanket slowly darkens.
As more ground is exposed, more sunlight is absorbed by
the darker landscape, which heats the surface and the air,
speeding up the melting process.
Other fluxes of energy result in snowmelt also. A warm
ground can transfer heat to the snowpack, nudging the
melting process. Water vapor in the atmosphere can land on
the snow causing melt through condensational warming. In
fact, this has been shown to produce significant melt during
warm spells in the winter when sun angles are low.
Finally, rain on snow is a rapid, but sometime destructive,
way to cause snowmelt; just think of March 2019 as an
example.
Here's hoping you can enjoy the snow before energy fluxes
transform the white canvas back to familiar hues.
By Martha D. Shulski
CIRCLES IN THE SNOW
PHOTO
BY
CHRIS
HELZER
