Jon Ahlquist 10 2 2006 Chapter 5 Condensation Formation of dew and frost Condensation nuclei Haze Fog radiation advection mixing Cloud classification examples of main types Cloud ceiling Satellite orbits geostationary and polar Condensation nuclei p 109 Small less than 0 2 micrometers Most abundant least effective Large 0 2 to 1 micrometer wavelength of light Giant bigger than 1 micrometer Least abundant most effective Condensation Nuclei cont Some are wettable water spreads out on them as on an unwaxed car Some are not wettable hydrophobic water beads up on them as on a waxed car Some such as salts are hygroscopic they dissolve and allow condensation at 100 relative humidity can be as low as 75 relative humidity p 110 Table salt clumps in salt shaker because of this Rid is a kind of salt sold for drying air in closets Dry haze very small particles Recall that very small particles scatter more blue light than red light If dark background dry haze looks blue Light from elsewhere scattered toward you as blue of sky If light background the light from background travels toward your eyes As it passes through the dry haze more blue light is scattered out so haze looks yellowish just as the sun does Condensation usually forms in air around 100 relative humidity Wet haze example Fig 5 4 p 110 of text Note white haze above water All condensation nuclei in the atmosphere are too small to see well even with a microscope especially small nuclei Consist of dust smoke salt products of chemical reactions etc Haze pp 109 110 Damp Condensation nuclei tiny particles on which condensation can occur Abundant 100 s to 10 000 s in cubic centimeter Wet haze condensation occurred so particles are larger scatter all colors Wet haze looks whitish Forms at relative humidity as low as 75 if salt is in air typically from evaporated sea spray Scatters more light than dry haze Fog pp 110 116 Fog cloud next to ground Fog in city usually thicker than fog over ocean Cities are polluted and have very many condensation particles Ocean fog is made of fewer but larger water droplets Radiation fog ground fog p 111 infrared radiation from ground cools air next to it until condensation occurs The longer the night the more the cooling so radiation fog is most common in late fall and winter Light breeze stirs air bringing more air in contact with cold ground increasing amount of condensation fog Strong wind inhibits fog formation by even greater mixing which brings down drier from above Light winds and clear skies common near center of high pressure so that is where fog often occurs Thickest at sunrise after cooling all night As the sun heats the air the fog evaporates burns off starting at thin edge of fog MET1010 Intro to the Atmosphere 1 Jon Ahlquist Radiation fog fig 5 5 p 111 Drains into in valley Clear above 10 2 2006 Advection Fog pp 112 113 Advection fog warm moist air advects over cold surface Advection means that a wind is required in contrast to radiation fog Occurs along Pacific Coast when warm moist air from Pacific blows over cold ocean current next to California coast Example Fog by San Francisco s Golden Gate Bridge Occurs over Grand Banks when wam moist air from Gulf Stream blows over cold water of Labrador Current In winter occurs along U S Gulf Coast and in England when warm moist air blows onto land cooled by radiation called advection radiation fog Advection fog fig 5 7 p 113 Summary of Radiation and Advection Fog Both radiation fog and advection fog involve warm moist air over cold surface Cold fog drains into low lying areas these cases air is stable warm air has risen cold air has sunk so fog has clearly defined upper surface Radiation and advection fog occur in stable environments covered in chapter 6 Are fairly uniform and featureless in appearance In Upslope Fog pp 112 113 Fog can form when air cools to saturation as it blows up the side of a mountain Recall Air does work as it expands into lower pressure Example Upslope fog on the east side of the Rocky Mountains fig 5 9 p 113 Steam fog also called mixing fog evaporation fog pp 113 116 Water evaporates from warm surface warm moist air rises mixes with cold air above air cools to dewpoint Air in steam fog not stable near surface warm air rises looks wispy with no definite top Occurs over pot of boiling water hence name steam fog heated pool on cold day hot asphalt after summer rain warm lake in mid latitudes when cold air in early fall blows in outdoor MET1010 Intro to the Atmosphere 2 Jon Ahlquist 10 2 2006 How steam fog mixing fog forms Special topic p 115 Imagine two equal sized blobs of air both nearly saturated Recall fig 4 10 p 91 showing saturation vapor pressure versus temperature Midpoint temp vapor pressure for mixed air Initial temperatures vapor pressure for 2 moist blobs of air When the blobs are mixed together their temperatures and dew points are averaged Even if the initial dew points were below saturation the mixed partial can be above saturation If so condensation will result i e mixing fog Fog Review Fog in Florida pp 116 117 Steam fog fig 5 10 p 116 wispy Look at the map on page 116 and explain why coastal California the Appalachians New England and the Gulf Coast are so foggy Cloud classification pp 117 119 Classification proposed in 1803 by English scientist Luke Howard Uses Latin words to describe cloud appearance Stratus http garnet acns fsu edu jelsner fdot OtherRWIS html Florida even gets superfog which is especially dense fog caused by the abundance of condensation nuclei in forest fire smoke For more information do an Internet search on superfog Florida Cloud classification continued Cumulus For more info and great pictures see The Audubon Society Field Guide to North American Weather by David Ludlum c 1991 Cirrus ice clouds Wispy no sharply defined edges High clouds ice halo around sun or moon as low as 10 20 000 ft as high as 26 60 000 ft cirrus layer same root as stratosphere heap root as in accumulate Cirrus lock of hair Nimbus rain cloud Alto prefix used to denote middle clouds just as an alto voice is a middle pitched voice Fog is a problem on Florida highways For info on what other states have done to monitor their highways see cirrostratus cirrocumulus Middle clouds 6500 to 25 000 ft liquid droplets sometimes some ice altostratus altocumulus Low clouds surface to 6500 ft liquid water Clouds of vertical development stratus Fig 5 12 p 119 stratocumulus nimbostratus cumulus cumulus congestus cumulonimbus
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