Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download 4 October
Document related concepts
Transcript
Readings Mon. (Precipitation) with Keri Bean Chapter 7 (175-190) Wednesday 10/6, Exam 2 Chapters 4-7 Lectures 9/20 – 10/4 Same format as Exam 1, study guide to be updated tonight Today Forms of precipitation Snow Rain Sleet Freezing rain Graupel Hail Precipitation Processes Topic: Freezing of Cloud Droplets Spontaneous or homogeneous freezing Ice embryo Precipitation Processes Cloud Seeding Inject cloud with small particles that act as ice condensation nuclei, starting the precipitation process. NEED CLOUDS: seeding does not generate clouds Cold clouds with a low seed ration best Dry ice, silver iodide Stepped Art Fig. 7-12, p. 174 Precipitation in Clouds Starts quickly Most Precipitation formed through ice crystal growth & accretion Many times rain starts as ice Precipitation Types Rain: falling drop of liquid water Drizzle: less than 0.5 mm Virga Cloudburst Snow: frozen water falling from sky (crystal or flake) Most precipitation starts as snow Forms of Precipitation Snow Growth • Bergeron process • Riming • Aggregation Lake effect snows • Lake supplies moisture & warmth – Both destabilize air • Land slows wind, forces uplift Topographic influences Forms of Precipitation Rain • Rainshowers – Large and small drops fall at same time – Large drops fall faster, hit ground first – (unless they break up) • Raindrop shape Rainfall: source of water Precipitation Types Sleet: air below freezing, then travels through a layer of air above freezing, begins to melt and then falls through a layer of air below freezing just above the ground surface. Freezing Rain: ground surface is freezing as rain hits the surface it freezes. Forms of Precipitation Sleet Ice crystals melt in an inversion then refreeze near surface • Sleet requires warm layer for melting Freezing Rain 0 degree liquid freezes on contact with frozen ground Sleet formation Freezing rain Forms of Precipitation Precipitation Types Snow Grains: solid equivalent of drizzle, no bounce or shatter Snow Pellets: larger than grains, bounce, break, crunch underfoot Graupel: ice particle accumulation with rime Hail: graupel act as embryo in intense thunderstorm, grow through aggregation as pushed up by updraft. Forms of Precipitation Graupel Extensively rimed ice crystals • Hail nucleus Forms of Precipitation Hail Concentric layers of ice around graupel • Up and downdraft interactions in thunderstorms • New layer for each refreezing Great Plains = highest frequency Stepped Art Fig. 7-29, p. 185 Hail Formation Fig. 7-30a, p. 186 Annual hail frequency
