ERTH 2415 Chapter : Ch 11. summary pt 2.docx
14 Mar 2012
School
Department
Course
Professor
Document Summary
Air temperature drops upward from the ground surface through the troposphere at average rate of 6 c/km. This is a stable rate of decrease in the troposphere. When lapse rate (the actual rate of cooling with height) is greater than 10 c/km, the atmosphere is unstable. Atmosphere instability increases as the temperature differences increase between warm air on the bottom and overlying cool air. Warm, low latitude air is less dense and it wants to rise upward. Air will rise as long as it is less dense than the surrounding air. If bottom air is warm and moist, the warm air may rise enough to pass through the lifting condensation level, allowing condensation of water vapour to begin. This marks the cloud base for a thunderstorm. Individual thunderstorms form on sunny days in late afternoon/early evening when temperature of ground surface and lower troposphere are the highest.
