Condensation: Dew, Fog, & Clouds. Chapter 5

Transcription

1 Condensation: Dew, Fog, & Clouds Chapter 5

2 The Formation of Dew & Frost Dew forms on objects near the ground surface when they cool below the dew point temperature. More likely on clear nights due to increased radiative cooling White frost forms when temperature cools below the dew point and the dew point is below 0 C

3 Condensation Nuclei Particles suspended in the air that around which water condenses or freezes. Hygroscopic: water attracted Hydrophobic: water repelling

4 Haze Dry condensation nuclei (above dew point) reflect and scatter sunlight creating blueish haze Wet condensation nuclei (75% relative humidity) reflect and scatter sunlight creating grayish or white haze

5 Fog Saturation reached condensation forms a cloud near the ground Radiation fog: ground cools through conduction and radiation; ground fog Vll Valley fog created tdby cold air drainage High inversion fog

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7 Fog Advection Fog: warm moist fog moves horizontally (advects) over a cool surface. Summer fog on the Pacific coast Observation: Headlands Air converges and rises over headlands d forming fog as compared to lower elevation beaches.

8 Advection Fog in San Francisco

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10 Fog Upslope Fog: moist air flows up an orographic barrier East side of the Rockies Evaporation Fog: Warm moist surface provides enough moisture to saturate a dry air parcel; short lived Steam fog Breath in winter

11 Upslope Fog

12 Example of Evaporation Fog

13 Foggy Weather In general fog not common for most location in the US. However several areas do exist with a high frequency of fog. Two causes: Elevation Ocean currents

14 Average Annual Days of Dense Fog

15 Clouds Classification of clouds: use Latin words to describe height and appearance Factors described Height: low, mid, high, vertical Appearance: shape, density, color

16 Major Cloud Types

17 Cloud Base Heights

18 Basic Cloud Types and Heights

19 Cirrus above 20,000 ft, thin, ice crystals

20 Cirrocumulus

21 Cirrostratus sometimes get halos- often in advance of a storm

22 Altocumulus thunderstorms often develop

23 Altostratus

24 Nimbostratus usually have light to moderate precipitation- darker than altostratus

25 Stratocumulus

26 Stratus

27 Cumulus Also called air weather cumulus or cumulus humilis

28 Cumulus Congestus (well defined top- not fuzzy)-usually summertime

29 Cumulonimbus This has an anvil top from wind shear Usually fuzzy top- thunderstorm clouds From continued growth of cumulus congestus

30 Some Unusual Clouds Not all clouds can be placed into the ten basic cloud forms Unique atmospheric processes and environmental conditions create dramatic and exotic clouds Unusual clouds and weather balloons often cause of UFO reports

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32 Atmospheric Rotors Rotors and Mountain Waves in the lee of the Sierra Nevada Improved understanding and prediction important for aviation safety in complex terrain Forming a strongly coupled system with overlying mountain waves and underlying boundary layer August 7, 2007 Grubisic, AMS 12th Mesoscale Conference, Waterville Valley, NH 32

33 Lenticular

34 More Lenticular Clouds

35 Mammatus Associated with sinking air often with severe weather

36 Cloud Observations Sky conditions: cloud coverage divided into eighths and each amount associated with term such as scattered clouds Observations: cloud ceilings Ceilometer used at airports to determine height from clouds by laser striking clouds and then amount of reflected light recorded Lidar = Light Detection And Ranging

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38 Cloud Observations Satellite Observations Geostationary, polar orbiting Visible light provides a black and white picture of clouds Infrared approximates cloud temperature which infers height Satellites measure many other variables: sea surface temperatures, ozone, upper level features, snow cover, land cover

39 Geostationary Satellite

40 Polar Orbiting Satellites

41 High clouds cold Lower clouds warmer Just cold ground