Unformatted text preview: Ch. 5 Condensation: Dew, Fog, and Clouds
5.1 Fog 5.2 Clouds Dew and Frost Dew water vapor that condenses upon surface of objects when the temp lowers to the dewpoint If vapor deposits directly to a solid, frost forms 5.1 Fog Fog is formed by either or both: Cooling air is cooled below the dewpoint Adding water vapor via evaporation Fog is maintained by: Formation of new fog droplets via the above processes Radiation Fog Radiation fog is formed by radiational cooling that cools air to dewpoint Typically during clear, calm nights with a shallow layer of moist air near the surface overlaid by dry air Advection Fog Forms when warm air moves (advects) over cold surface, so that the air cool to its dewpoint Example: relatively warm air over farther offshore moving over cold Pacific coast water to form fog rolling over Golden Gate Bridge Upslope Fog Forms when moist air flows upward along a barrier Typically along eastern Rockies in winter and spring Annual Days with Dense Fog Pacific Coast states Appalachian highland region New England Fog can help bring moisture for vegetation Fog is a transportation hazard auto, boat, air 5.2 Clouds High Clouds - Cirrus White, made of ice crystals, thin, high Wispy tails blown by high winds Move from west to east with prevailing winds Not associated with precipitation Low Clouds Stratus Uniform grayish cloud Covers entire sky Resembles a fog that does not reach the ground No heavy precipitation Often found over oceans With quite uniform base Low and dark Low Clouds - Cumulus Looks like cotton Sharp outlines and a flat base Top marks end of upward motion Base may be only 3300 ft and 1 km wide Cumulus have a great deal of blue sky between them Cumulonimbus Clouds with Vertical Development When a towering cumulus continues vertical growth A thunderstorm cloud Can extend from 2000 ft to 40,000 ft or more above ground Lots of latent heat release > 80 mph up- and down-drafts Ice and water (& hail) Sometimes has anvils Hybrid Types of Clouds Cirrocumulus Cirrostratus Stratocumulus Altocumulus Altostratus Summary of Basic Clouds http://eo.ucar.edu/webweather/cloud3.html Summary of Basic Clouds Geostationary Satellites Orbit a fixed spot on the equator at same rate Earth spins Allows continuous monitoring of a specific region Can monitor wind direction and speed in cloudy areas Geostationary Operational Environmental Satellite (GOES) Polar Orbiting Satellites Parallel to earth's meridians (longitude lines) Earth rotates underneath satellites Every point on Earth is observed twice daily Focus on polar regions that are distorted by geostationary satellites Orbit at 850 km providing highly details Cloud Height and Thickness Warm objects radiate more energy than cold objects So we can make high temp regions appear darker, cool temp regions appear lighter Warmer cloud tops are found at lower levels Thus white clouds are higher level clouds, dark clouds are lower level Visible and Infrared Imagery Visible Image Infrared Image Enhanced Infrared Image Water Vapor Imagery It shows regions that become more moist or become more dry It also indicates disturbances in the flow that would otherwise go unseen In clear areas, no clouds provide info on the movement of air So satellites can detect the movement of water vapor in the mid- to uppertroposphere Summary Fog and clouds are formed by water vapor condensing on condensation nuclei. Radiation fog forms when near-surface air cools to dewpoint. Advection fog forms when warmer air is advected (moved) to a colder region. Based on their heights, clouds are divided into high, middle, and low groups. Based on their morphology, clouds are also classified as, cirrus, stratus, and cumulus, nimbus cloud types. Types can be mixed types, i.e., cumulonimbus, stratocumulus. While cirrus is high and cumulus is mostly low, stratus can be middle and low. Clouds are observed by polar-orbiting and geostationary satellites from space on visible and inferred channels. Name Clouds f:\EAS-107\Media_08\Meteorology_Interactive\BlueSkies-Cloud\index.html ...
View Full Document
- Spring '12
- fog, advection fog