geography test 2

geography test 2 - CONDENSATION EVENTS FORMATION TYPES...

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CONDENSATION EVENTS: FORMATION & TYPES ** Clouds, Fog, and Dew all have 2 properties in common: 1) they must form from saturated or nearly saturated air RH (relative humidity) = 100% dew point T = air T 2) They must have a surface upon which the water vapor can condense * dew : the ground, vegetation, a car, or similar surface * clouds & fog ---- need condensation nuclei (figure 7.21, page 195) -- microscopic particles of dust, salt, smoke, etc -- hygroscopic nuclei: very absorbent condensation nuclei, usually of sulfate and nitrate crystals *** CLOUDS : a form of condensation best described as a dense, visible aggregation of minute droplets of water or tiny crystals of ice. p. 195 * How do they form? a parcel of moist air reaches the point of saturation where the water vapor is changed to liquid water droplets. either by cooling the air T or the dewpoint T. OR by adding more water vapor. cooling the air T is the most common method ** Cloud Classification : table 7.2 page 196 * 2 criteria for classifying clouds 1) Height of cloud base above the surface. * 3 categories: 1. strato clouds (lower) 2. alto (middle) 3. cirro (upper) 2) Degree of vertical development . figure 7.23 page 198 * 2 main categories: 1. stratus : “layer”, horizontal development
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2. cumulus : “heap”, or ‘cotton balls”; vertical development * some other common names used -- Cirrus: “curl of hair”, the clouds found the highest up in the atmosphere & composed of ice crystals Nimbus : “violent rain”, cumulonimbus = thunderstorms, nimbostratus = stratus clouds which are producing rain/snow (fig 7.24 page 200) *** FOG : basically a cloud at ground level * condensation can occur in some instances where the RH is as low as 75-80% (most cases are 90%) * as the water droplets get bigger they become visible, this decreases visibility (being able to look through the droplets). If visibility is reduced to 1 km, the haze or cloud is categorized as fog . *** 4 main categories of fog: Radiation fog : produced over land when radiational cooling decreases air T° to the d.p.T° (fig 7.28 page 201) * also called ground fog or valley fog if it forms in low lying areas from cold, heavy air draining downhill ( cold air drainage ) figure 7.27 page 201 * forms best on calm, clear nights in late fall & winter * forms from the ground upward and usually is deepest around sunrise Advection fog : occurs when warm, moist air moves over a cold surface & the air cools to below its d.p.T° * advection = horizontal movement of air (wind)
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EX: west coast of U.S.(San Francisco Bay area), Midwest U.S. in winter, some desert areas (Atacama in South America) Upslope fog : created when warm, moist air flows up along an elevated plain, hill, or mountain * air temp. reaches dew point temp. by adiabatic cooling as it rises EX: western Great Plains of the U.S. & eastern side of the Rocky Mts. Evaporation fog : when the air reaches saturation primarily by adding water vapor and not lowering the air T° (figure 7.26 page 201) * water evaporates into the parcel of air * 2 main types: 1) Steam fog: forms when cold air moves over warm water; the warmer water evaportes into the unsaturated colder air causing saturation, condensation and fog formation EX: over a heated swimming pool (esp. in fall or winter),
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