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.

The main idea of this passage is that_.

1. different kinds of radiation affect the way snow melts and cools
2. in winter, it snows only when the temperature is below 30°C
3. snow of the same depth will melt at the same rate
4. snow in the open does not last as long as that underneath a tree
5. a thinner layer of snow usually occurs in the area under a tree

Answer: 1. different kinds of radiation affect the way snow melts and cools