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Heat and Energy Transport in the Atmosphere

Heat and Energy Transport in the Atmosphere. RECAP: Energy, Temperature and Heat. Energy Kinetic Potential, e.g. gravitational Temperature scales Absolute temperature: K Fahrenheit scale: F Celsius scale: C Freezing point: 273K<->0C<->32F Boiling point: 373K<->100C<->212F

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Heat and Energy Transport in the Atmosphere

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  1. Heat and Energy Transport in the Atmosphere

  2. RECAP: Energy, Temperature and Heat • Energy • Kinetic • Potential, e.g. gravitational • Temperature scales • Absolute temperature: K • Fahrenheit scale: F • Celsius scale: C • Freezing point: 273K<->0C<->32F • Boiling point: 373K<->100C<->212F • Heat capacity and specific heat capacity • Large heat capacity: the object requires more energy/heat (and it takes longer) to warm up to a certain degree. • Alternatively: given the same amount of heat, the object with the largest heat capacity warms up to the lowest T • C(water) > C(soil) > C(air)

  3. Heat Capacity • Heat capacity: the amount of heat energy that is required to change the temperature of a body by 1 K. • Heat capacity= Heat energy/Temperature change • It depends on the material and on the mass of the body • Specific heat capacity: the amount of energy that is required to change the temperature of 1 gram of substance by 1 degree C. • It does not depend on the mass of the body. • It depends only on the material of the body. > > = >

  4. Table 2-1, p. 30

  5. Thermal inertia • Bodies with a large heat capacity cool and/or heat up very slowly. • Analogy with a heavy body (a big truck) • Water has a high heat capacity (large thermal inertia) 1cal/gram/degree • Regions near large bodies of water (rivers, lakes, oceans) do not experience sharp temperature changes. Their climate is mild. • Air and land have smaller specific heats than water. Figure 3.23

  6. Phase Changes

  7. Phase transitions (1 gram of water) Sensible heat 600 cal 100C Temperature C Latent heat 100 cal 80 cal 0C vapor water boiling ICE melting HEAT IN

  8. Latent heat • Latent heat: the heat required to change a substance from one state to another (phase change) • Evaporation/Melting (cools the environment) • Condensation/Freezing (heats the environment)

  9. The importance of latent heat

  10. Heat: Q • Heat is energy in the process of being transferred from one object to another. • The amount of heat is equal to the change of energy that results from the process of energy transfer. • Processes of heat transfer: • Conduction; • Convection; • Radiation.

  11. Heat Conduction • Description: • Transfer of kinetic energy from one molecule to another • Objects are in physical contact • Necessary conditions: • Heat is conducted whenever there is a T difference. • The energy flow is from the body of higher T towards the body with lower T • Conducting materials: • Good conductors: metals • Insulators (poor conductors): water, air, wood. • Conduction is NOT an efficient way to transport energy in the atmosphere. • The heat transport through conduction near the ground is relevant only for a thin layer a few cm thick.

  12. Table 2-2, p. 33

  13. Convection • Description: • Transfer of heat by mass movements of a fluid. • Rising air cools and sinking air warms!!! • Convection is a very efficient way to transport energy in fluids (gas, liquid). • Advection: the horizontal movement of a parcel of fluid.

  14. Development of a thermal Fig. 2-6, p. 34

  15. Radiation • Description: • Energy carried by electromagnetic waves. • They are NOT mechanical waves!!! • Characteristics: • Wavelength l: the distance between two adjacent peaks. • Units: 1 mm (micron)= 10-6 m • May propagate through vacuum and “transparent” materials. • Visible: 0.4-0.7 mm

  16. Radiation and Temperature • All bodies with T>0K emit radiation (electromagnetic energy). • The origin of the emission is the transition of the atoms (molecules) from one energy state to another. • The wavelength and the amount of energy emitted by the body depend on its temperature. • Higher T -> larger internal energy -> atoms vibrate faster -> the radiation has shorter wavelength and higher energy. The Sun’s electromagnetic spectrum

  17. Black body radiation Stefan-Boltzmann Law: Wien’s Law: • Black body: it emits and absorbs at all wavelengths.

  18. Temperature and Emitted Energy Energy The Sun emits ~(6000/288)4~188,000 times more energy than the Earth!!!

  19. Sun/Earth radiation • Sun • T=6000 K • lmax=0.5 mm • Maximum in visible • Earth • T=288 K = 15 C • lmax=10 mm • Maximum in IR The Sun emits (6000/288)4~188,000 times more energy than the Earth!!!

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