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Precipitation

Precipitation. Objectives: To understand how precipitation is formed. To describe three types of rain – frontal, orographic and convectional. What are the six types of precipitation?. Rain Drizzle Snow Sleet Hail Dew.

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Precipitation

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  1. Precipitation Objectives: To understand how precipitation is formed. To describe three types of rain – frontal, orographic and convectional.

  2. What are the six types of precipitation? • Rain • Drizzle • Snow • Sleet • Hail • Dew

  3. Condensation produces minute water droplets, less than 0.5mm in diameter (or ice crystals if temperature is below freezing). • They are so small they are kept buoyant by the rising air that creates them. • So, although condensation produces clouds, clouds do not always mean precipitation.

  4. But… • These water droplets (or ice crystals) become large enough to overcome the lifting mechanism and fall to the floor. • There are two theories…

  5. 1. Bergeron-Findeisen Mechanism • Through adiabatic cooling of air as it rises the upper parts of clouds are below freezing point. • Even at the equator upper cloud may be as cold as -65°C. • Freezing nuclei (salt and fine soil particles) attract super-cooled water droplets and increase in mass. • At critical mass they fall towards the surface, either melting or remaining frozen.

  6. 2. Collision & Coalescence Process • Water droplets are constantly moving within a cloud. • They collide, fuse and increase in mass until they reach critical mass and fall.

  7. Marketplace • Design a poster to teach others about one type of rainfall: • Frontal • Orographic • Convectional • Sources of information: • Essential AS Geography p200-201 • Advanced Geography p158 • Waugh p219-220 • Geog.2 p27

  8. Objectives: To name two types of fog. To explain how these types of fog are formed. Fog

  9. Chinese tourist spot hidden in early morning fog Haar fog off East coast Advection Fog Golden Gate Bridge San Francisco – 105 foggy days a year Advection fog near a river – horizontal movement of air over colder surface Salt provides an ideal hygroscopic nuclei to help form this haar fog off California

  10. Radiation Fog Thick fog makes travelling very difficult & dangerous Pollution gets trapped under a temperature inversion producing the orange smog over LA

  11. Summary

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