4.1.7 Day 1, 6PM: IR cooling

In the early evening, radiative cooling quickly takes over and the top of the snowpack cools very quickly. In contrast to solar absorption, the vast majority of radiative loss happens within a few millimeters of the top of the snowpack. In our case, since the outgoing radiative loss is much larger than the daily solar radiative gain, nighttime temperatures at the top of the snowpack are much lower now.

Schematic of radiational cooling at night for the snowpack.

What happens to the very top portion of the snowpack, which melted earlier in the day? Select the correct answer, then click Done.

The correct answer is b.

Melting will stop because the surface temperature of the snowpack falls well below freezing after sunset. Crusting (the freezing of the snowpack surface) occurs quickly around sunset.