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Integrated Science—Ch 17 Notes—The Weather The Atmosphere -relatively thin shell of gases that surround the solid Earth -more gas molecules found near the surface -atmosphere thins rapidly as the altitude/height increases -Composition of the Atmosphere -composed mostly of 3 gases -Nitrogen—78% -Oxygen—21% -Argon—1% -contains varying amounts of water vapor -enters by evaporation and leaves as precipitation -N, O, Ar, and water vapor make up about 99.97% of the volume -remaining gases mostly CO2and traces of inert gases -Carbon dioxide--.03% -in addition to gases the atmosphere also contains particles of dust,smoke,salt crystals, and tiny solid or liquid particles called aerosols -larger particles are not suspended as the aerosols are and settle out of the atmosphere as dust or soot -Atmospheric Pressure -pressure decreases as altitude increases -equalize pressure via the eustachian tube -measured using a barometer -Warming the Atmosphere -radiation from sun must pass through the atmosphere -atmosphere filters, absorbs, and reflects incoming radiation -on average Earth reflects about 30% of the total radiation back to space -about 2/3 due to clouds -only about ½ of incoming radiation reaches Earth’s surface -reflection and selective filtering by atmosphere allow global average of 240 watts per square meter to reach surface -wide variations occur with latitude and season -radiation that reaches surface is absorbed -rocks, soil, water and ground become warmer -emit absorbed solar energy as infrared radiation (wavelengths longer than visible light spectrum) -infrared absorbed by water vapor and Carbon dioxide causing increased kinetic energy of molecules causing increased temperature -the more CO2 in the atmosphere the more energy that will be redirected back to Earth increasing the temp. near the surface -Greenhouse Effect--process of heating the atmosphere by absorption of solar radiation and reemission of infrared radiation -Structure of the Atmosphere -temperature decreases as altitude increases -an average temperature decrease of 6.5 C for every 1 km increase in height -applies only to air not rising or sinking -Inversion--layer where temperature increases with height -often occur on calm winter days after arrival of cold front -stagnant mass of cold air may settle over an area -also occur on calm,clear , and cool nights when surface rapidly loses radiant energy to space -results in a “cap” of cooler more dense air overlying the warmer air beneath -often leads to increased air pollution because it prevents dispersion of pollutants -temperature decreases with height until about 11 km (6.7 miles) -Troposphere--layer from surface to where temperature stops decreasing -almost all weather occurs here -Stratosphere--2nd layer above troposphere -temperature increases with height -less turbulent than troposphere—better for planes -temperature gradually increases to about 48 km (30 miles) http://www.foxnews.com/science/2013/10/23/antarctic-ozone-hole-hits -Ionosphere--outermost layer -where molecules merge with vacuum of space -electrons and ions here responsible for reflecting radio waves around Earth and for the northern lights -The Winds -Troposphere heated from the bottom up as surface of Earth absorbs sunlight -Uneven heating of Earth’s surface sets stage for convection -As local region of air becomes heated it expands and becomes less dense -less dense air is pushed upward by nearby cooler more dense air -Results in 3 general motions of air 1. Upward movement of air over a region of greater heating 2. The sinking of air over a cooler region 3. Horizontal movement of air is wind -direction is defined as the direction from which it blows -air in troposphere rises, moves as wind, and sinks -all 3 movements related and all occur at the same time over regions of the landscape -during a day with gentle breezes on the surface, the individual fluffy clouds form over areas where the air is moving upward -the clear are between the clouds is over areas where the air is moving downward -Local Wind Patterns -2 factors important for understanding local wind patterns 1. The relationship between air temperature and air density -cool air has a greater density than a warm air mass -warm air is buoyed up by cool air -results in upward,downward, and horizontal movement of air called a convection cell 2. The relationship between air pressure and the movement of air -upward movement of air produces a “lifting” effect on the surface results in an area of lower pressure -downward movement produces a “piling up” effect on the surface resulting in an area of higher pressure -air generally moves from an area of high pressure to an area of low pressure -Local wind patterns where land is next to water -land and water have different heating rates and may have different surface temperatures -3 principle reasons for difference 1. The specific heat of water is greater than that of soil -equal masses of soil and water exposed to sunlight—soil heats about 1 C while water heats about ½ C 2. Water is a transparent fluid that is easily mixed and spreads out the heating effect -sunlight warms a relatively thin layer of soil concentrating the heating effect 3. Water is cooled by evaporation, which helps keep the body of water at a lower temp. -results in warm air mass over land and a cooler air mass over water -cool air moves in from the ocean to the land -Sea Breeze -at night land cools more rapidly and the wind direction reverses blowing out toward sea -Local wind pattern due to Mountains -mountain slope heated more than the valley because it receives more direct sunlight -cooler air from valley blows up the mountain slope -Cold dense air can collect in valleys -a weather disturbance or front can disturb accumulation of cold air and cause it to pour out of its resting place through canyons and lower valleys -air moving from high altitude to lower altitude becomes compressed increasing its kinetic energy and thus its temperature -Chinook wind—common to mountainous regions—has sharp temp. increases that can melt snow in a day Global Wind Patterns -apparent when records analyzed for long period of time -Temperature imbalances drive global circulation of the Atmosphere -Earth receives more direct sunlight at equitorial regions than at Higher latitudes -temps. Of lower troposphere generally higher at equitorial region and lower with latitude toward both poles -the lower troposphere from 10 degrees N to 10 degrees S of The equator is heated,expands, and becomes less dense -hot air rises in this belt around the equator -Intertropical Convergence Zone -rising air cools resulting in heavy average precipitation -Tropical rainforests here -the now dry, rising air reaches upper parts of the troposphere and spreads north and south sinking back towards the surface -descending air reaches the surface to form a high pressure belt that is centered about 30 N and 30 S of the equator -air moving away from this high pressure belt produces the prevailing northeast trade winds and the prevailing westerly winds of the Northern hemisphere -great deserts of Earth also located in this high-pressure belt of descending dry air -Poleward of the belt of high pressure the atmosphere circulation is controlled by a powerful belt of wind near the top of the troposphere called the jet stream -Jet Stream--sinuous, meandering loops of winds that tend to extend all the way around the Earth, moving generally from the west in both hemispheres at speeds up to 100 mi/h (160 km/h) or more -may occur as a single belt, or loop, of wind but may divide into 2 or more parts -develops North and South loops of waves much like waves on a long rope -waves vary in size -waves bulge toward the poles(crests) or toward the equator(troughs) -warm air masses move toward poles ahead of a trough and cool air masses move toward the equator behind a trough as it moves eastward -the Intertropical Convergence Zone, the 30 degree belt of high pressure, and the meandering jet stream all shift toward or away from the equator during different seasons of the year