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CLASS 16

CLASS 16. HEAT BUDGET OF THE EARTH Basic budget Latitude variations Surface temperatures SEA ICE. Why is the Earth warm?. Why is Mars Colder? (avg. = - 60˚C). " HEAT BUDGET" . Heat comes in..... Heat goes out. " HEAT BUDGET" Where does incoming solar radiation go?.

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CLASS 16

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  1. CLASS16 HEAT BUDGET OF THE EARTH Basic budget Latitude variations Surface temperatures SEA ICE

  2. Why is the Earth warm?

  3. Why is Mars Colder? (avg. = - 60˚C)

  4. "HEAT BUDGET" Heat comes in..... Heat goes out....

  5. "HEAT BUDGET" Where does incoming solar radiation go? • Incoming Solar Energy can be: • Reflected • Absorbed (changed into heat) • Re-radiated out to space • The balance or imbalance of these: • Controls earth surface temperatures • Drives ocean and atmosphere circulation

  6. Reflected light

  7. THE GLOBAL HEAT BUDGET • Of incoming solar radiation how much is.... • Reflected back out to space? • ~ 30% (24% by atmos., 6% by land and sea) • Absorbed? • ~ 70% (23% in atm.; 47% by land & sea) • ABOUT HALFOF THE INCOMING ENERGY IS ABSORBED BY THE LAND AND SEA

  8. 1/3 reflected; ½ absorbed by land and sea

  9. Of the energy absorbed by land & sea (47%), how much is..... 1) Re-radiated (infrared) directly to space?.... 10% 2) Transferred to the atmosphere? ...... 37% MOST OF THE SOLAR RADIATION ABSORBED BY LAND AND SEA IS TRANSFERRED BACK TO THE ATMOSPHERE

  10. Transfer of heat from land and sea to the atmosphere happens in two ways: • 1) Evaporation and condensation of water.... 24% (i.e., 24 out of the original 100 units) • Heat uptake by evaporation -- cools surface • Later…heat released by condensation -- warms atm. • WATER VAPOR VERY IMPORTANT!!!! • 2) Conduction and radiation to atmos. = 13% • Much infrared energy radiated by earth’s surface is absorbed in the atmosphere by "greenhouse gases" • In absence of this greenhouse effect, the earth would be about -10˚C!

  11. Greenhouse effect

  12. This is a Global Average, but....

  13. Solar energy coming in is • max. at Equator • min. at poles

  14. So… at any given latitude, heat input does not match output • low latitudes: solar input > IR output • high latitudes: solar input < IR output

  15. If heat input > output, then temperature should increase constantly • This does not happen…. • What maintains the balance? • Heat transferred from lower latitudes to higher latitudes by oceans and atm. currents • Warm water/air currents: Equator --> poles • Cool water/air currents: poles --> Equator • Convection!!!

  16. Heat is transferred from lower latitudes to higher latitudes by currents in oceans and atmosphere • Warm water/air currents: Equator --> poles • Cool water/air currents: poles --> Equator

  17. These are convection currents • They are driven by temperature differences Warm Cold

  18. Water Vapor Transport => Heat Transport

  19. Temperature Belts Note effects of ocean currents

  20. Temperature variation- Winter vs. Summer

  21. Continents -- large T range • Oceans -- small T range • Reason : Heat capacities, land vs. water Oceans stabilize surface T of Earth

  22. SEA ICE (NOT Icebergs) • Layer of ice that forms annually at high lat. • Near Antarctica; In Arctic Ocean

  23. SEA ICE: Sheets of ice at high latitude • Grow in winter, shrink in summer • Thickness is limited... • < 2 meters (single season) • Ice is a thermal insulator

  24. Sea-ice formation creates high-S water: • Reminder: Ice formation --> high-S water. • This forms the densest and deepest water masses in the oceans.

  25. These are icebergs, not sea ice

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