prize1-2, Exercise 3: The ceiling of weather

Model answer:

Nearly all weather occurs in the troposphere because it holds most of the air and nearly all the water vapour, and because its temperature falls with height, which lets warm air rise and form cloud. The tropopause, the boundary above it, acts like a lid where the air stops cooling with height; a growing thundercloud rises until it reaches this layer and then spreads out sideways in the familiar anvil shape.

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