EAS100 Lecture Notes - Lecture 28: Orographic Lift, Dew Point, Ice

• School: University of Alberta
• Department: Earth and Atmospheric Sciences
• Course: EAS100
• Professor: Korhan Ayranci

Document Summary

Water vapour forms liquid water or ice. Releases energy (latent heat) but first nucleus of new water drop or ice crystal requires energy input. If more than 1 per mm3 , collisions lead to formation of raindrops. High nucleation energy inhibits ice formation down to -9 c. Clouds are mixed water droplets and ice crystals. Water droplets release vapour that condenses on ice crystals. Ice crystals large enough to fall as precipitation are snow. Adiabatic cooling reduces temperature to dew point. Four basic causes that may operate in combination. Density lifting : warm air rises because it expands and therefore has lower density. Frontal lifting : movement of air masses drives warm air over cold. Orographic lifting : mountain range drives air flow upward. Convergence lifting : convergent air creates forces air upward. Flat base (where air reaches dew point), domed top. Typical of rising warm air and density lifting. Form in warm moist air masses, during daytime heating.