ATM OCN (Meteorology) 100
FORMATION OF CLOUDS, FOG, DEW & FROST
Lecture #8 Scheduled for:
25 JUN 2004 (R)
Recommended Readings from Moran (2002):
pages 122-126; 128-130; 139-142
Today's Lecture Objectives:
- To list the mechanisms involved in cooling air to saturation.
- To compare and contrast the physical characteristics of dew and frost.
- To explain how dew and frost form.
- To compare and contrast the physical characteristics of fog and clouds.
- To describe the various processes that result in fog development.
- To explain the types of cloud formation processes.
- To describe the condensation processes within a cloud, explaining the role of condensation nuclei.
- To distinguish between cloud condensation nuclei and ice forming (or freezing) nuclei.
- What is a cloud?
- Why are clouds important
- Background: Cloud, Fog, Dew and Frost
B. REQUIREMENTS FOR FORMING DROPLETS
- Statement of the Practical Problems
- The Need for Saturation Conditions
- The Role of the Condensation Process at the Earth's Surface
- The Role of the Condensation in the Free Atmosphere
C. LOW LEVEL SATURATION PROCESSES & PHENOMENA
- Dew and Frost
- Formation Mechanisms
- Comparison and Contrasts
D. CLOUD (FOG) FORMATION REQUIREMENTS
- Special Problems
- Cloud Condensation Nuclei
E. MECHANISMS FOR CLOUD (FOG) FORMATION
- Formation Options
- Evaporation Mechanisms
- Cooling Mechanisms
- Expansional Cooling
- Evaporative Cooling
- Advection Cooling - Horizontal Transport
- Radiative Cooling
- Expansional Cooling Specifics
- Review of adiabatic processes
- Dry adiabatic lapse rate
- No phase change of water or R.H. less than 100%
- Rate is 10 Celsius degrees per 1000 m (or 5.5 Fahrenheit degrees per 1000 ft)
- Saturation (moist) adiabatic lapse rate
- Phase change of water or R.H. = 100%
- Rate is 6 to 7 Celsius degrees per 1000 m (or 3 Fahrenheit degrees per 1000 ft)
- Ways to lift for Expansional Cooling
- Dynamic Lifting --
- In surface low pressure systems
- Along fronts
- Lifting by Convection -- Localized heating
- Mechanical Lifting -- Over mountain barriers (orographic lifting)
- Comparison between clouds and fog
- Fog Formation Mechanisms
- Cooling to Saturation
- Addition of moisture
- Types of Fog
- Fog Types Classification by temperature:
- Warm fog
- Cold fog
- Ice fog (or ice crystal fog)
- Fog Type Classification by formation process:
- Radiation fog
- Upslope fog (or mountain fog)
- Frontal fog
- Advection fog
- Steam fog (also known as sea smoke)
- Rain fog
Links to Other References:
Latest revision: 7 July 2004 (2240 UTC)
Produced by Edward J. Hopkins, Ph.D.
Department of Atmospheric and Oceanic Sciences
University of Wisconsin-Madison Madison, WI 53706