O-Net 2021

(items 55-60)

Snow, like every thing else, including apple trees, emits and absorbs
radiation. While ultraviolet and visible radiation are strongly reflected (not absorbed) by snow, it is however a strong absorber of infrared radiation. The
battle between the absorption and emission of radiation determines whether
5 there is net warming or cooling of the snow - or neither.
So why would snow under a tree melt faster? At night, snow in the
open absorbs in frared radiation from the ground and the sky which can
be below -30°C when it is clear.
Snow under neath a tree absorbs radiation emitted by the ground and
10 by the tree which is likely to be significantly warmer than the sky
This difference is sufficient to explain why snow under neath a tree
might melt faster than snow of the same depth that is outin the open and
also explains why frost often does notform around trees.
It is also possible that shelter provided by the tree when the snow was
15 falling led to a thinner layer of snow there than in the rest of theimmediate
vicinity.

Snow under a tree melts faster than that in the open because_.

1. there is more snow under a tree than in the open
2. snow under neath a tree takes in less in frared radiation than that on the open ground
3. in frared radiation sent out from the ground underneath a tree is warmer
4. snow under a tree takes in very cold in frared radiation at below -30°C
5. there is not enough infrared radiation underneath a tree to make snow melt

Answer: 3. in frared radiation sent out from the ground underneath a tree is warmer