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Unformatted text preview: Condensation: Dew, Fog, and Clouds Condensation: This chapter discusses: 1. How dew, frost, haze, fog, and clouds form from 1. atmospheric moisture atmospheric 2. Classification of fog and cloud types from 2. observation observation Formation of Dew & Frost Formation Figure 6.1 Figure 6.2 As air cools to its saturation, or dew point, vapor molecules slow As down and can adhere as dew on the ground surface or as frost when air temperature drops below freezing. when Daily temperature lows often occur by radiational cooling, Daily forming dew at night or early morning. forming Haze & Water Seeking Nuclei Haze Figure 6.3 Above the ground surface, cooling and slowing water vapor instead Above condenses upon condensation nuclei. condenses Hygroscopic particles such as salt or dust seek condensing vapor, Hygroscopic and can form a wet white haze when relative humidity is above 75%, or a dry blue haze when drier. 75%, Ground Based Radiation Fog Ground Figure 6.4 Fog is condensed vapor droplets at a density that severely restricts Fog visibility. visibility. It may form by radiation fog, which occurs at the ground when dew It point temperature is reached by radiational cooling. point Acid fog threatens humans health because the droplets combine Acid with gaseous pollutants. with Advection Fog Advection Figure 6.5 Warm moist air that moves, or advects, above a cold surface may Warm become cooled to its dew point temperature, creating an advection fog. fog. This fog often forms above the ocean due to mixing currents, or This when warm ocean air rolls into the cooler waters at the Pacific Coastline. Coastline. Condensation & Moisture Sources Condensation
Fog that is Fog filtered by tree branches, or condensation of vapor directly onto vegetation or the ground surface, provides an important water source for ecological processes. processes. Figure 6.6 Evaporation or Mixing Fog Evaporation
Fog can form by Fog mixing warm unsaturated air with cool unsaturated air, which can occur during evaporation. during Steam fog is on Steam example of this mixing process and occurs when warm pools of water are a source for vapor that condense into the cooler air above. the Figure 6.7 Fog & Human Safety Fog
Foggy days in the US Foggy have a predictable distribution due to ocean and mountain influences. influences. Fog can help crop Fog growth in California, but can also cause severe automobile, airplane, and boating accidents. accidents.
Figure 6.8 As a result, there are As several fog dispersal experiments. experiments. Cloud Groups & Types Cloud Clouds are water droplets suspended in the Clouds atmosphere. atmosphere. Clouds are grouped by their elevation as high, middle, Clouds low, and those that vertically stretch across many altitudes. altitudes. There are several cloud types in these 4 groups. Cirrus Clouds Cirrus High clouds (above 6000 m in middle High latitudes) that are thin and wispy and comprised mostly of ice crystals. and Figure 6.9 Cirrocumulus Clouds Cirrocumulus High clouds High that are rounded puffs, possibly in rows, are less common than cirrus. than
Figure 6.10 Cirrostratus Clouds Cirrostratus
High clouds High that thinly cover the entire sky with ice crystals. crystals. Light Light passing through these crystals may form a halo. form Figure 6.11 Altocumulus Clouds Altocumulus
Middle clouds Middle (between 2000 and 7000m in middle latitudes) that are puffy masses of white with gray edges. with With your hand With overhead, they are about the size of your fingernail. fingernail. Figure 6.12 Altostratus Clouds Altostratus Middle Middle clouds that cover the entire sky and may create a dimly visible or watery sun and diminish formation of shadows. shadows.
Figure 6.13 Nimbostratus Cloud Nimbostratus Low clouds Low (below 2000m) with precipitation that reaches the ground. ground. Shredded parts Shredded of these clouds are called stratus fractus or scud. or Figure 6.14 Stratocumulus Clouds Stratocumulus Figure 6.15 Low clouds with rounded patches that range in color from light to Low dark gray. dark With your hand extended overhead, they are about the size of your With palm. palm. Stratus Clouds Stratus Figure 6.16 Low clouds that resembles a fog, but does not reach the ground, and Low can generate a light mist or drizzle. can Cumulus Humilis Clouds Cumulus Figure 6.17 Clouds with vertical development that take a variety of shapes, Clouds separated by sinking air and blue sky. separated Shredded sections are called cumulus fractus. Cumulus Congestus Clouds Cumulus Figure 6.18 Clouds with vertical development that become larger in height, with Clouds tops taking a ragged shape similar to cauliflower. tops Cumulonimbus Cloud Cumulonimbus Figure 6.18 Clouds with vertical development that have grown into a towering Clouds thunderstorm cloud with a variety of key features, including the anvil top. anvil Summary of Cloud Types Summary Figure 6.20 Lenticular Clouds Lenticular An unusual An cloud that has a lens shape and forms in the crest of a wave. wave. Figure 6.21 Banner Cloud Banner Figure 6.22 A lenticular cloud that forms downwind of a mountain peak and is lenticular regularly replenished by condensing water vapor. regularly Pileus Cloud Pileus An unusual An cloud that forms above a building cumulus by deflected moist winds. moist Figure 6.23 Mammatus Clouds Mammatus Figure 6.24 An unusual cloud that hang like sacks, formed by sinking air with a An high water content. high Jet Contrails Jet Jet engine Jet exhaust provides vapor and nuclei for condensation trails (contrails), which evaporate quickly in dry air, but linger with higher relative humidities. humidities.
Figure 6.25 Nacreous Clouds Nacreous Figure 6.26 An unusual cloud best viewed at winter in the poles and forms in the An stratosphere. stratosphere. Noctilucent Clouds Noctilucent Figure 6.27 An unusual wavy cloud that is best viewed at the poles and forms in An the upper mesosphere. the Ground based Viewing of Clouds Ground Figure 6.28 Clouds directly overhead will appear to be less densely packed than Clouds clouds at the horizon due to viewing angles. clouds Satellite Observation of Clouds Satellite Figure 6.29 Geostationary satellites are able to view clouds from above. As they move in synchronicity with earth's rotation, they can As provide regular coverage for a region and help in forecasting. provide Polar Orbiting Satellites Polar Figure 6.30 Satellites can detect more than clouds, and polar orbits allow for Satellites lower altitudes and more image resolution. lower These satellites take multiple passes of the earth before returning to These the same location. the Satellite Imaging Options Satellite Sensors on board the satellite are Sensors able to detect visible and other electromagnetic signals, such as infrared, to determine cloud heat and infer its height. and Figure 6.33 Visible & Infrared Images Visible Visible imagery captures all clouds as white, but infrared Visible imagery can distinguish differences. imagery Figure 6.32A Figure 6.32B Computer Image Enhancement Computer Infrared imagery can be evaluated Infrared and enhanced by a computer program that highlights changes in temperature and cloud types. temperature Figure 6.33 False Color Imagery False Figure 6.34 Satellite images can be viewed in false color to more clearly Satellite distinguish areas of importance, such as green coolest cirrus clouds and darker gray areas of drier air. and ...
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This note was uploaded on 03/15/2010 for the course ATOC ATOC 250 taught by Professor Gyakum during the Spring '09 term at McGill.
- Spring '09