Chapter 2: The global ledger of radiation and heat

Transcription

1 Chapter 2: The global ledger of radiation and heat

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3 PROPERTIES OF RADIATION Everything radiates at all wavelengths! This includes the Sun, Earth, a candy bar, even us Fortunately, most objects don t radiate a lot of X-rays, gamma rays, etc... However, different objects: Emit different amounts of radiation, and. Emit their maximum radiation at different wavelengths (don t confuse these two differences) So what s the determining factor? TEMPERATURE!

4 PROPERTIES OF RADIATION 2 EASY RULES: 1. The higher the temperature, the more radiation an object will emit (Stephan-Boltzman Law) 2. Higher temperature result in radiation being concentrated at shorter wavelength (Wien s Law)

5 Radiation Energy Transfer by Electromagnetic Waves Electromagnetic Spectrum UV VIOLET RED IR WAVELENGTH FREQUENCY ENERGY

6 PROPERTIES OF RADIATION Sun: 10,000 F (solar, shortwave radiation) 1. lots of radiation; 2. peak radiation in visible range Earth: 60 F (terrestrial, longwave radiation) 1. some (but much less) radiation; 2. peak radiation in infrared range

7 LOWER HIGHER

8 Transparency of the atmosphere by wavelength and atmospheric windows

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10 SOLAR RADIATION & GEOMETRY Not all parts of Earth receive the same amounts of radiation. Why? TILT of our planet, 23.5

11 SOLAR RADIATION AND TILT

12 SOLAR RADIATION AND TILT

13 EARTH S SEASONS

14 LAND OF THE MIDNIGHT SUN

15 Mechanisms of Energy Transfer (Heating): Conduction: Transfer of kinetic or vibrational energy by direct molecular collisions. What could maximize conduction efficiency? Convection: Spontaneous transfer of thermal energy by turbulent mixing in fluids. What conditions might maximize convection? Radiation: Transfer of energy by electromagnetic waves. Only mechanism that doesn t need a medium for transfer. What could prevent radiative transfer? (Heat describes energy flow from hot -> cold, not amount of energy and object has)

16 How does direct radiation from the sun warm a cup of water (PS 2)??

17 Simple Thermodynamic Relationships P( in W) = Power = Energy / time Q(in J)=Total Energy= Power x time x area P A W 2 m incoming solar radiation density (power/are a) Q Q P A mc t T A 1 T P t A m c A 1

18 Assumptions in calculating Temp. warming: No significant net heat lost by conduction, convection, or radiation (this is BS except for rare special circumstances) All incident solar radiation is absorbed Uniform temperature of object Perfect styrofoam insulator Typical Heat Capacities: J/kg/ o C cal/g/ o C Substance or J/kg/K or cal/g/k Water (0 o C to 100 o C) Methyl Alcohol Ice (-10 o C to 0 o C) Steam (100 o C) Benzene Wood (typical) Soil (typical) Air (50 o C) Aluminum Marble Glass (typical) Iron/Steel Copper Silver Mercury Gold Lead

19 EARTH S ENERGY BUDGET Energy from the Sun reaches the top of Earth s atmosphere Does all of it reach the surface? NO For example Ozone (O 3 ) absorbs UV Clouds and gases scatter, absorb, reflect other types of radiation Still, a lot of radiation (energy) reaches the surface of our planet.

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22 NORTH POLE EQUATOR SOUTH POLE Most of the incoming solar radiation is absorbed at the Tropics

23 TERRESTRIAL RADIATION Amount of terrestrial radiation emitted from Earth s surface and atmosphere is dependent on temperature More terrestrial radiation emitted near equator (warmer) Less terrestrial radiation emitted near poles (colder)

24 NORTH POLE EQUATOR SOUTH POLE

25 Earth s Annual Energy Budget

26 EARTH S ENERGY BUDGET Because of the differences in incoming/outgoing radiation on the Earth, we have an energy imbalance between the polar regions and the Tropics. So winds and ocean currents exist to transport heat from the equator to the poles. TO CREATE AN ENERGY BALANCE

27 NORTH POLE EQUATOR SOUTH POLE

28 Average Emitted infrared radiation

29 Incoming solar radiation for August

30 Solar radiation absorbed yesterday

31 August solar radiation absorbed by surface

32 Sea Surface Temperatures

33 Sea Surface Temperature Anomaly

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