Fog/Foggy Weather

Overview

• Types of fog – Advection fog – Radiation fog – Upslope fog – Evaporation (mixing) fog – Steam fog • Fog formation (1) by cooling… air is cooled below its saturation (2) by evaporation and mixing

Condensation: review

• Important concept in fog and cloud formation • Evaporation vs. Condensation

Radiation fog

• Produced by the earth’s radiational cooling • Forms best on clear nights + shallow moist air near the ground + light winds • Common over land in fall and winter • Also called valley fog or Tule fog (e.g., central valley) • Valley fog can persist for weeks unless cold air moves in aloft or strong winds mix it up.

http://www.cabrillo.edu/~crsmith/tule.html

Reference: wikipedia

Advection fog

• Forms by condensation of warm, moist air carried by winds over the cold coastal water • common along summertime West Coast – Water near the coast is much colder than offshore water (see upwelling in Ch.8) + onshore winds • Fog disappear as it is pushed inland by onshore winds (due to evaporation)

Burn off (of fog)

• Refers to dissipation of fog • Sunlight warms the ground → enhances evaporation of fog and mixing of air

Summary & additional info

• http://www.geog.ucsb.edu/~joel/g110_w08/ lecture_notes/california_fog/california_fog.

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