Fog Flashcards
What is Fog? What are the conditions needed for formation?
Fog is a cloudline on the ground.
cooling - down to saturation/dewpoint
adding of water vapour - relative humidity to 100%
mixing of air masses with high humities
condensation - latent heat released.
What is radition fog? What conditions needed?
nightime terrestrial radiation cools the ground, which cools the air mass by conduction.
upto 1000ft
Conditions: - Night Clear Skies No wind HIgh humidty stable conditions
Dissapation: - Will take same amount of time as formation Increased insolation Re-evaporation of water droplets Increase in winds and/or cloud cover Advection
What is Advection fog? What conditions?
Warm moist air flows over a cold surface, air cooled by conduction.
Can occur anytime of day, anywhere. (often coastal areas)
Conditions
Low wind (approx 15-20 kts)
High humidity
cold surface must be cooler than dewpoint of airmass
Dissapation
Increase and wind
change of wind direction
change in airmass (means change in humidity)
What is Steaming fog/Artic Sea Smoke? Conditions?
Forms over warm water (autumn, early winter)
Adding of water vapour
Can form anytime
Conditions: - Very stable conditions High Humidity High Latitude Weak winds warm water!
Dissapation: -
Stronger winds or direction
What is Orographic Fog? Conditions?
Adiabatic coolinf or airmass up a hillside.
Forms on the upwind side
Conditions: - Orographic lighting Stable conditions Only over land Any time of day.
Dissapation: -
Change of wind direction (means different mass/humidity)
Lifting stops
What is Frontal Fog? Conditions needed?
When two fronts meet - can extend across surface for 200nm - precipitartion saturations colder airmass underneath and thus fog forms. Doesn’t last long and mostly in wintertime.
Conditions: - warm front mosit cold air can form over land or sea anytime of day
Dissapation: -
Will move with front
What is freezing fog?
Supercooled water droplets which will freeze on contact.
What is the definition of mist?
suspended water droplets, visability over 1km and less than 5km.
What is Haze?
Solid particles in the air. between 1km to 5km.
