THE TROPOSPHERE The troposphere is the name given collectively to the lower layers of the atmosphere extending from the ground to a height of approximately io km., and is a region characterized by a decrease in temperature with increasing height—the temperature lapse.
Air is relatively transparent to the short-wave radiation of sunlight which therefore heats the air very little as it penetrates the lower layers of the atmosphere. On a sunny day, solar radiation falling on the Earth's surface is in part temporarily absorbed, and in part reflected back as a radiation of longer wave-length that is more readily absorbed by air. This reflected radiation now heats the layer of air near the ground and the heat later becomes diffused through the lower layers of the atmosphere from below upwards. Air temperature is thus highest near the ground and decreases with increasing height, unless a `temperature inversion' is formed under conditions described below. The normal temperature decrease (or `lapse rate') is about o•6°C. per ioo metres. At the top of the troposphere is the tropopause—the boundary between troposphere and stratosphere.
The troposphere comprises the five following layers.