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Earth’s Climate System (part 2) revisiting the radiation budget heat capacity heat transfer

Earth’s Climate System (part 2) revisiting the radiation budget heat capacity heat transfer circulation of atmosphere (winds) Coriolis Effect circulation of oceans (currents). From last time:. Earth’s climate system climate driven by “solar energy”

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Earth’s Climate System (part 2) revisiting the radiation budget heat capacity heat transfer

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  1. Earth’s Climate System (part 2) • revisiting the radiation budget • heat capacity • heat transfer • circulation of atmosphere (winds) • Coriolis Effect • circulation of oceans (currents)

  2. From last time: • Earth’s climate system • climate driven by “solar energy” • climate operates to distribute solar energy • across surface

  3. Revisiting the radiation budget energy in = energy used for warming + energy radiated back to space Unequal distribution across Earth

  4. Energy input & output averaged over year

  5. Earth’s spin axis is inclined, so we get seasons 23.5o

  6. Energy input by latitude & month

  7. Radiation budget energy in = energy used for warming + energy radiated back to space Energy transferred to Earth: Raises temperature, drives winds, ocean currents

  8. Energy input & output averaged over year: Excess heat in equatorial areas, heat deficit in polar areas

  9. Average surface temperatures: Higher in equatorial than polar areas

  10. Response to seasonal forcing: temperature changes Northern hemisphere

  11. Response to seasonal forcing: average surface temperature changes over year

  12. Response to seasonal forcing: albedo changes (temperature-albedo feedback)

  13. Ocean Land Northern hemisphere Why does land temperature undergo bigger temperature changes, and change more rapidly, than ocean temperature? Because of differences in “heat capacity”.

  14. Heat capacity -- quantity that measures the ability of a substance to absorb heat heat capacity = density x specific heat cal / cm3 g / cm3 cal / g

  15. Heat capacity • water has higher heat capacity than rock • water has a greater ability to store heat • (it is a good “heat sink”) • it takes more energy to raise temperature of water • than rock

  16. Heat capacity Heat capacity = Density x Specific Heat (cal/cm3) (g/cm3) (cal/g) For water: 1 g/cm3 1 cal/g Ratios of heat capacities: water : ice : air : land = 60 : 5 : 2 :1 so water has a capacity to absorb heat that is 60 times that of the land’s capacity fo absorb heat

  17. On average, surface heats up more at equator than at poles • drives winds • in atmosphere • drives ocean • currents • strongly affects • climate (& weather)

  18. Heat transfer • heat flows from hot to cold • heat transfer by various means • -- conduction • -- convection • -- radiation • should get flow of heat from equator to poles • heat imbalances drive winds, precipitation • patterns & ocean currents

  19. Circulation of atmosphere (winds) We get flow of air & heat from ground upwards. “Warm air rises, cold sinks”. Why?

  20. “Warm air rises, cold sinks”. • Because: • most heating at • surface • warm air has lower • pressure & density • than cold air • lower density air • moves up, higher • density air moves • down

  21. Wind Uneven heating of atmosphere causes it to move vertically & horizontally across the ground. Air that moves across surface is called “wind”. We get systematic wind patterns on planets.

  22. Venus: (1) rotation rate very slow (243 Earth days) (2) get simple wind circulation pattern (northern and southern Hadley Cells) Hadley Cells

  23. Earth: (1) rotation rate fast (2) get complex wind circulation pattern owing to Hadley Cells + Coriolis Effect

  24. Coriolis Effect • apparent deflection of moving objects (e.g. air • masses, ocean currents) on planet caused by planetary rotation • deflection to right in northern hemisphere, • to left in southern hemisphere

  25. In red: apparent path of objects moving towards or away from equator

  26. westerlies easterlies

  27. Flow of heat in atmosphere also determines precipitation patterns. “It rains most at the equator, and least in the tropics (+- 30o latitude) and poles”. Why?

  28. “It rains most at the equator, and least in the subtropics (+- 30o latitude) and poles”. • Because: • Warm air can hold • more water vapor • than cold air • When warm air rises, • it cools • Equator has lots of • warm, wet, rising air • Subtropics & poles • have dry, sinking air

  29. desert belt rain belt desert belt

  30. Circulation of oceans (currents)

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