GEO 203 Notes – 9/16/10Ice to vapor: absorb energy, cool environmentVapor to ice: release energy, heat environmentLatent heat involved in change of stateLatent heat of:L = +- 2.5 x 10^6 J/kgCondensation or evaporationL = +- 0.334 x 10^6 J/kgFreezing or meltingL = +- 2.83 x 10^6 J/kg Deposition or sublimation(J = megajoules)Hurricanes don’t form in lakes, etc. because there is not enough water vapor available for a hurricane to formHeat Transfer in the AtmosphereConduction, convection, radiationConduction of heat energy occurs as warmer molecules transmit vibration (heat) to adjacent cooler moleculesWarm ground surface heats overlying air by conductionConduction requires contactAlways transferred from warmer to colder regionsThe amount of heat transferred by conduction depends on:1. Temperature difference between the two objects2. Their thermal (heat) conductivity—the ability of a substance to conduct heat by molecular motionsLow conductivity: Air, wood, dry soilAir is an extremely poor conductor. Conduction is an efficient process for heattransfer in the atmosphere.High conductivity: Ice, iron, silverConvectionTransfer of heat by the mass movement of a fluid (water, air) moves from one place to another, carrying its heat energy with it.Efficient way to transfer heat in the atmosphere (performed by the sun)Convection always requires motion.Usually associated with vertical movement of the airRate of energy transferred by convection depends on the temperature of the rising air parcel compared to the temperature of its surrounding atmosphereStrong in summer; weak in winterStrong on sunny days; weak on cloudy daysStrong over tropics; weak in polar regionRising and SinkingAs air rises, part of its energy is lost as it expands and cools and when it sinks, it is compressed and the energy of molecules increase causing temperature to increase.Rising air cools because it expandsAs air decreases, higher pressure compresses it, causing it to warm upLECTURE 4: Atmospheric Radiation and Energy Balance (Chapter 2)Conduction only heats a very small portion above the surface it comes in contact withRadiant energy travels in the form of electromagnetic wavesAll objects with a temperature above absolute zero (-273°C; 0 K) emit radiationTypes of radiation by wavelength:AM radio waves: 100mTelevision waves: 1mMicrowaves: 10^-3Infrared waves: 10^-6Visible light: 5 x 10^-7Ultraviolet waves: 10^-7X-rays:
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