ENVB 301 Lecture Notes - Lecture 11: Supercooling, Cloud Seeding, Hygroscopy

• School: McGill University
• Department: Environmental Biology
• Course: ENVB 301
• Professor: Ian Strachan

Document Summary

Cloud droplets can form easily with presence of hygroscopic (salt) nuclei, size of drop will not change if it is in equilibrium with surrounding, cloud formation can occur at < 100% rh, clouds form by condensation. This alone is not sufficient to produce precipitation: equilibrium vapour pressure, constant competition between condensation & evaporation, air above droplets has a saturation vapours pressure. In equilibrium with the environment & total # of vapour molecules remains constant. ---> solute effect: solute effect: salt ions bond more tightly with water molecules making evaporation more difficult, reduces equilibrium vapour pressure surrounding the droplet, requires lower rh for equilibrium, as rh increases, condensation>evaporation. Droplet grows: rising rh is countered by growing droplets removing h2o vapour, increase of rh to the point where the rate of h2o vapour removal = rate. How do raindrops form? of availability for condensation. There must be other processes to help!