Why doesn't snow melt when there is sun out that is kind of hot?
Answers
Sun is powerless to melt clean snow. And when snow does melt, it is not because of the sunlight. Snow does not melt on a spring day because of the sun’s heat. It melts because of the warm air from the sea.
After snow becomes ice, a different problem arises. Clean ice absorbs about two-thirds of the sunlight that hits it – but ice is transparent enough for the light to penetrate quite a long way (10 metres or more) before the absorption takes place.
It is remarkable what profound results follow from this simple property of transparency to sunlight. If, instead of penetrating deeply, the light were absorbed in a shallow surface layer of ice, the summer sun would quickly raise the temperature of the thin surface layer to melting point. And almost immediately, the water would run off.
But when the sunlight penetrates a thick layer of ice before it can be absorbed, it cannot raise the temperature of the ice to melting point quickly enough. When the ice is very cold, the whole summer passes before any melting occurs at all.