4.1.5 Day 1, 2PM: Temperature profile
To what approximate depth does the sun heat the snowpack at 2PM? In which direction is a thermal gradient created? Select the vector corresponding to the correct strength and direction of the gradient, then click Done. Note that the vectors point from cold to warm, with their widths representing the strength of the gradient (strong vs. weak).
The correct answer is b.
Since we're in late autumn near the winter solstice, the upper snowpack surface will melt relatively slowly. The melting will last a few hours each day if atmospheric conditions remain calm and clear. This means that the thermal gradient is small and is directed upward. Recall that with new snow, solar radiation will warm 15 to 30 cm (6 to 12 in) of the top of the pack.