02EnergyBalance

02EnergyBalance - ESM 203 Ear th-Sun energy ESM 203 Ear...

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Unformatted text preview: ESM 203: Ear th-Sun* energy ESM 203: Ear th-Sun* energy balance balance Jeff Dozier & Thomas Dunne Fall 2007 * We will cover terrestrial energy sources later (one-thousandth of the solar flux at the surface, but capable of moving continents and building mountain ranges) 1 2 How Ear th operat es (simplified) How Ear th operat es (simplified) Some fraction (20-30%) is reflected by atmosphere and sur face Remainder (70-80%) is absorbed and emitted at longer wavelengths ◦ Some emitted radiation is absorbed in atmosphere I mbalance between Equator and Poles causes circulation of atmosphere and ocean Heated sur face transfers energy to atmosphere Water at sur face evaporates and moves into atmosphere ◦ … and condenses to fall back to sur face as precipitation 1370 Wm –2 less } and the energy also moves 3 Energy balance pr inciples Energy balance pr inciples Energy is the capacity for doing work (i.e. motivating some change in a system) “Energy” and “heat” are equivalent Energy in – energy out = ∆ energy storage ∆ energy storage ≡ either ◦ ∆ temperature ◦ ∆ “phase” of water (solid, liquid, gas) Temperature (measure of energy storage) “sensible heat” energy in energy out ice water vapor melt freeze condense vaporize gives up energy requires energy (“latent heat”) Methods of energy transfer Methods of energy transfer Radiation: electromagnetic waves propagate through space ◦ all bodies radiate, war mer bodies more ◦ interactions depend on wavelength Conduction: molecule-to- molecule ◦ hot t o cold temperature Convection: mixing in air or water enhances transfer ◦ sensible: temperature difference between war mer and colder f luid ◦ latent: change of phase of wat er dur ing mixing T d day night typical soil temperatures moves heat & vapor 4 Sensible and latent heat Sensible and latent heat Time I nput of energy (heating) Water temperature ( ° C) 100 20 Temperature rising, energy stored in wat er. Sensible heat Temperature steady. Energy converts water to steam, which leaves the pot. Latent heat . 5 Radiation Radiation A body radiates energy when electrons in its atoms receive or generate so much energy that they release a small packet of energy (photon) I f the atoms are receiving or generating a lot of energy (i.e. they are hot) they emit photons in large numbers and frequently. Thus, both the intensity (energy per unit time) and the frequency of emission are high. Since energy ( E ) travels through a vacuum at a constant speed ( c, the speed of light), if the frequency ( ν ) of par ticle (wave) emission is high, the wavelength ( λ ) is shor t: Planck’s law: energy per photon λ ν c = λ ν h h = = h is Planck’s constant 6 There is a There is a spectrum spectrum (range) of wavelengths (range) of wavelengths of electromagnetic radiation of electromagnetic radiation Wavelength ( λ ) For radiation in the climate, we usually use μm (micrometer, 10 –6 m) or nm (nanometer, 10 –9 m) to measure wavelength....
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02EnergyBalance - ESM 203 Ear th-Sun energy ESM 203 Ear...

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