|MadSci Network: Earth Sciences|
The layers of the atmosphere go in this way: • From the ground up to about 12 km is the troposphere. In this region the temperature goes lower as you go higher. So there is cooler air lying on top of warmer air; warmer air is less dense, so it rises, while the denser, heavier air moves downward. This results in an unstable situation, where the atmosphere is constantly turning over in a turbulent fashion. We see this turbulence as winds and weather systems. "troposphere" comes from a Greek word "tropos" which has a meaning of "turning over" or "turbulent" • Between about 12 and 50 km altitude the temperature rises again as you go higher. This region has much gentler circulation. There is only slow vertical mixing because warmer air overlies cooler. "stratosphere" comes from a Greek word "stratos" which has a meaning of "layer" • From 50 km altitude up to 85 km the air is very thin and there is a lot of chemical reaction going on. It gets cooler as you go higher. "mesosphere" comes from a Greek word meaning "middle" • From 80 km altitude up to about 300 km, a lot of very high energy processes are happening. This is the region where high energy particles emitted from the sun first encounter a significant amount of the earth's atmosphere. Temperatures increase as you go higher in this region, and get very hot indeed above about 150 km. "thermosphere" comes from a Greek word "thermos" meaning "hot" or "temperature" • Above 300 km, the outer part of the atmosphere gradually blends into the same chemical composition and properties as the extremely thin gas of interplanetary space. We sometimes refer to this region as "exosphere", which comes from a Greek word meaning "outside" •• And finally, the region above 80 km altitude is also sometimes known as the "ionosphere", because it contains large quantities of electrically charged particles, or "ions"
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