1Solar Radiation - initial source of energy to the Earth. It can be absorbed, reflected and reradiated. The redistribution of this energy controls the structure and dynamics of the Atmosphere and Oceans.Chapter 8 Circulation of the AtmosphereThe Atmosphere Is Composed Mainly of Nitrogen, The Atmosphere Is Composed Mainly of Nitrogen, Oxygen, and Water VaporOxygen, and Water VaporWhat are some properties of the atmosphere?•The lower atmosphere is a fairly homogeneous mixture of gases. •Water vapor occupies up to 4% of the volume of the atmosphere.•The density of air is influenced by temperature and water content.Ascending air cools as it expands. Cooler air can hold less water, so water vapor condenses into tiny droplets - clouds. Descending air warms as it compresses –the droplets (clouds) evaporate.Greenhouse GasesGases: permanent and variable Permanent = present in constant relative % of total volume Variable = concentration changes with time and locationSuspended microscopic particlesWater dropletsThe Atmosphere Moves in Response to Uneven The Atmosphere Moves in Response to Uneven Solar Heating and EarthSolar Heating and Earth’’s Rotations RotationAn estimate of the heat budget for Earth. On an average day, about half of the solar energy arriving at the upper atmosphere is absorbed at Earth’s surface. Light (short-wave) energy absorbed at the surface is converted into heat. Heat leaves Earth as infrared (long-wave) radiation. Since input equals output over long periods of time, the heat budget is balanced.• Heat budget• Solar input must balance solar output• Temperature increases/decreases if input is greater/less than output• Average Earth Temperature is 16oC• Solar Energy is reradiated from the surface as a long wave.• Surface of Earth (including oceans) is heated from above• Atmosphere is heated from below2O3absorbs UV Solar Radiation, heats Atm.Vertical (thermal) structure of the atmosphere• Troposphere: lowest layer 0-12 km, temperature decreases with altitude• Tropopause: minimum temperature zone between the troposphere and stratosphere• Stratosphere: layer above tropopause 12-50 km, temperature increases with altitude• Mesosphere: layer above stratosphere 50-90 km, temperature decreases with height• Thermosphere: layer above mesosphere >90 km, extends out to space The AtmosphereDensity of air depends on temperature, water vapor and altitude•Temperature decrease = density increase•Water vapor increase = density decrease•Altitude increase = density decreaseThe Solar Heating of Earth Varies with The Solar Heating of Earth Varies with LatitudeLatitudeHow solar energy input varies with latitude.Equal amounts of sunlight are spread over a greater surface area near the poles than in the tropics.Ice near the poles reflects much of the energy that reaches the surface there.The atmosphere reflects, scatters and absorbs solar radiation. At high latitudes solar radiation travels a longer path through atmosphere.The Solar Heating of Earth Varies with LatitudeThe Solar Heating of Earth Varies with LatitudeEarth as a whole is in thermal equilibrium, but different latitudes are not.The average annual incoming solar radiation (red line) absorbed by Earth and the average annual infrared radiation (blue line) emitted by Earth. Polar latitudes lose more heat to space than they gain, and tropical latitudes gain more heat than they lose. The amount of radiation received equal the amount lost at about 38°N and S. The area of heat gained (orange area) equals the area of heat lost (blue areas) so Earth’s total heat budget is balanced.What factors govern the global circulation of air?• Uneven solar heating• The Coriolis effectWarm equatorial water flows to higher latitudesCool Polar water flow to lower latitudesRe-distribution of heat• Heat gained at Equatorial latitudes• Heat lost at higher latitudes• Winds and ocean currents redistribute heat around the EarthOceans do not boil away near the equator or freeze solid near the poles because heat is transferred by winds and ocean currents from equatorial to polar regions.The Seasons: solar heating varies with seasonsThe Seasons: solar heating varies with seasonsDuring the Northern Hemisphere winter, the Southern Hemisphere is tilted toward the sun and the Northern Hemisphere receives less light and heat. During the Northern Hemisphere summer, the situation is reversed.* Earth revolves around the Sun (365 days) * Earth rotates about its own axis (1 day) * angle (‘tilt’) that axis of rotation makes with plane that contains trajectory around the Sun is 23½°and it remains that way (same orientation) as the Earth revolves around Sun Winter (Northern Hemisphere tilts away from sun)Spring (sun aims directly at equator)Summer (Northern Hemisphere tilts toward sun)Fall (sun aims directly at equator)23½°To PolarisThe tilt (23½° inclination) causes the seasons3EarthEarth’’s Uneven Solar Heating Results in Larges Uneven Solar Heating Results in Large--Scale Thermal Cell type of Atmospheric CirculationScale Thermal Cell type of Atmospheric CirculationA convection current forms in a room when air flows from a hot radiator to a cold window and back.Air warms, expands, becomes less dense, and rises over the radiator. Air cools, contracts, becomes more dense, and falls near the cold glass window.A convection cell is driven by density differencesEnters Co!EarthEarth’’s Uneven Solar Heating Results in Larges Uneven Solar Heating Results in Large--Scale Atmospheric CirculationScale Atmospheric CirculationThe Coriolis effect is the observed deflection of a moving object, caused by the moving frame of reference on the spinning Earth.How does this apply to the atmosphere?As air warms, expands, and rises at the equator, it moves toward the pole, but instead of traveling in a straight path, the air is deflected eastward.In the Northern Hemisphere air turns to the right.In the Southern Hemisphere air turns to the left.What factors govern the global circulation of air?• Uneven solar heating• The Coriolis effectThe The CoriolisCoriolisEffect Deflects the Path of Moving Effect Deflects the Path of Moving ObjectsObjectsSketch of the thought experiment in the text, showing that Buffalo travels a shorter path on the rotating Earth each day then Quito does.A continuation of the thought experiment. A look at Earth from above the North Pole shows that Buffalo and Quito move at different