Test 2 Study Guide MET1010 Chapter 4 Humidity Condensation and Clouds Saturated Air Saturated air has no net loss of liquid or water vapor molecules Wind enhances evaporation Warm water evaporates faster than cold water because the molecules move faster in warm water more likely to break water tension Clouds form from slow moving cold molecules forming on condensation nuclei Condensation occurs primarily when the air is cooled Warmer air molecules are moving fast thus cool air attach to nuclei easier Humidity Vapor Pressure 1 000mb inside parcel 78 Nitrogen 780mb 21 Oxygen 210mb 1 Water Vapor 10mb Actual Vapor Pressure Saturation Vapor Pressure The amount of water vapor that is necessary to make the air saturated at any given temperature The number of molecules escaping is increased thus the rate at which it condenses also increases Thus at higher temperatures it takes more water vapor to saturate the air Saturated vapor pressure rises with temperature and vice versa Test 2 Study Guide MET1010 Relative Humidity The ratio of the air s water vapor content to its capacity RH Water Vapor Content Water Vapor Capacity RH Actual VP SaturationVP x 100 Relative Humidity increases with water vapor content Relative Humidity is highest early in the morning coolest part of day because saturation temperature is lowest at cold temperatures Dew point Temperature to which air must be cooled for saturation to occur High dew points indicate high water vapor content Low dew points indicate low water vapor content When air temperatures and dew point are far apart relative humidity is low When air temperature and dew point are close relative humidity is high When equal air is saturated relative humidity is 100 Relative humidity tells how close the air is to being saturated Dry air can have a high relative humidity In polar air the dew point temperature is low and the air is considered dry But the air temperature is close to the dew point and so relative humidity is high Human Discomfort When the air temp and RH are high body moisture doesn t readily evaporate Wet bulb temperature Lowest temp reached by evaporating water in air Test 2 Study Guide MET1010 Evaporation requires 600cal g of energy Psychrometer Instrument two thermometers that obtains dew point and relative humidity Hygrometer Instrument that measures humidity Dew and Frost Dew When water vapor condenses on objects and water beads form More likely to form close to the ground because it is colder More likely to form on calm clear nights opposed to cloudy windy nights Forms only when warmer than 32 F Frost Temperatures way past dew point below 32 F Water vapor changes directly into ice this process is also known as deposition Has a tree like branching pattern Haze Layer of particles dispersed through portion of atmosphere Water collects on nuclei as relative humidity rises and scatters light Fog Cloud resting near the ground was at one point haze As relative humidity increases so does the density of water on the nuclei Radiation Fog Fog produced by radiational cooling of Earth Forms best on clear nights or slight breeze Cold heavy air sinks to valleys thus seen in low lying areas Advection Fog When warm moist air moves over a colder surface moist air cools to saturation point Pacific coast warm air moves west over cold shore waters Always involved with the movement of air Radiation Fog vs Advection Fog Calm conditions vs Windy conditions Test 2 Study Guide MET1010 Upslope Fog Fog that forms as moist air flows up along an elevated surface Eastern side of Rockies Cold air moves from low to high becomes colder and if moist fog forms Evaporation Fog Mixing of two unsaturated masses of air Evaporation initially enriches the air with water vapor Example taking a warm breath on a cold day hot tub on a cold day Condensation nuclei have an affinity for water they are hygroscopic Clouds A visible aggregate of tiny water droplets or ice crystals suspended in air High Clouds Generally form above 20 00ft Almost exclusively ice crystals and are thin Usually white can appear red orange or yellow during sunrise sunset Cirrus Thin wispy clouds Most commonly seen Cirrocumulus Small rounded white puffs in long rows Rarely seen Cirrostratus Thin sheet like Form a halo because they are so thin Used to predict rain or snow Middle Clouds Test 2 Study Guide MET1010 Generally have bases around 6 500ft to 23 000ft Composed mostly of water droplets can be ice crystals Altocumulus Gray puffy masses Rolling parallel waves Usually has dark part and light part Indicate storms on humid days Altostratus Gray or blue gray cloud Covers entire sky Thinner sections sun or moon can be dimly visible Can predict prolonged periods of precipitation Low Clouds Nimbostratus Bases lying below 6 500ft to surface Almost always composed of water droplets Dark gray wet looking cloud layer Cannot see sun or moon through nimbostratus Light or moderate rain shower Contain very low small clouds called stratus fractus scud Stratocumulus Rows or patches of rounded masses with clue sky visible behind Appear near sunsets Can be light to dark gray Similar to altocumulus but stratocumulus is closer to the ground Stratus Uniform grayish cloud Covers entire sky Resembles fog that doesn t reach the ground Accompanied by light drizzle mist Vertical Development Cumulus Variety of shapes Big puffy cotton balls with flat base White to light gray Very scattered lots of clue sky in between Usually fair weather Cumulonimbus Thunderstorm cloud Can start at 2 000ft and rise to 39 000ft Violent up and down drafts Winds can make it look like an anvil All forms of precipitation come from cumulonimbus Test 2 Study Guide MET1010 Unusual Clouds Lenticular Clouds Stack on top of each other Has a lens shape Pileus Cap Cloud Mammatus Clouds Looks like a scarf topping a cumulus cloud Form from sinking air Bag like sacks hang beneath cloud Looks like cow s utter Contrail Nacreous Clouds Noctilucent Clouds Condensed water vapor that forms behind jets Found in stratosphere over 100 000ft high Found in mesosphere Luminous night clouds composed of tiny ice crystals Chapter 4 Vocab Actual Vapor Pressure The pressure exerted by the water vapor molecules in a given volume of air Advection Fog Occurs when warm moist air moves over a cold surface and the air cools to below its dew point Test 2 Study Guide MET1010 Altocumulus Clouds A middle cloud usually white or gray Often occurs in layers or patches with wavy rounded masses or
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