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Surface Energy Balance (1)

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Surface Energy Balance (1)

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  1. Surface Energy Balance (1)

  2. Review of last lecture • The mission of meteorology is to understand and predict weather- and climate-related disasters (e.g. tornados, hurricanes, El Nino and global warming). • The modern climatology (meteorology) was born in the 1940s (a very young science!), but has been growing very fast! Now we have a global observational network with many satellites, ships, radars and surface stations, as well as very comprehensive prediction models running on the world’s largest computers. • The current status of weather and climate predictions: (1) weather prediction good to 10 days, (2) tropical cyclone prediction good in track but not in intensity, (3) climate prediction good to two seasons, (4) climate change projections have a 3-fold difference in magnitude. • The main reasons of the difficulties: (1) Teleconnection problem, (2) Feedback problem, and (3) Subgrid-scale problem. • Importance of the ABL: (1) interface between atmosphere and ocean/land/ice - flux transfer and feedback, (2) the human beings are living in the ABL and change the environment, (3) a basic subgrid-scale process

  3. Energy basics • Energy: the ability to do work • Many forms: electrical, mechanical, thermal, chemical, nuclear, … • Joule (J): standard unit of energy (1 J= 0.239 calories) • Watt (W): rate of energy flow (W = 1 J/s)

  4. Methods of Energy Transfer • Conduction • Molecule to molecule transfer • Heat flow: warm to cold • e.g. leather seats in a car • Convection • transferred by vertical movement • physical mixing • e.g. boiling water • Radiation • propagated without medium (i.e. vacuum) • solar radiation provides nearly all energy • The rest of this chapter deals with radiation

  5. Radiation • Everything continually emits radiation • Transfers energy in waves • Waves are both electrical and magnetic, hence electromagnetic radiation

  6. Radiation Quantity and Quality • Quantity: how much? wave height • (amplitude). Hotter bodies emit more energy than colder bodies • Quality: what kind?  wavelength: distance • btw. crest and crest (or trough and trough). generally reported in μm (microns)- one millionth of a meter.Hotter objects radiate at shorter wavelengths • Travels at the speed of light (300,000 km/s). It takes 8 minutes for light from the Sun to reach Earth, and 4.3 years for light from the next nearest star, Proxima Centauri to reach us.

  7. The Electromagnetic Spectrum The limitations of the human eye!

  8. A man detected by different instruments Infred device Bare eyes X-ray Microscope

  9. Wavelength of Sun and Earth Radiation Sun = “shortwave” (0.4-0.7 μm) Peak 0.5 μm (green) Sun Earth = “longwave” (4-100 μm) Peak 10 μm (infrared)

  10. Satellite Measurements of the Earth’s Radiation Budget NASA’s Earth Radiation Budget Satellite (ERBS) 1985-1989

  11. Earth’s energy budget (averaged over the whole globe and over a long time) Yellow: shortwave Red: longwave • At the top of the atmosphere: Incoming shortwave = Reflected Shortwave+ Emitted longwave • At the surface: Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Subsurface Diffusion Sensible heat 7% Net Longwave 21% Latent heat 23%

  12. Net Radiation • At the top of the atmosphere, radiation is balanced, i.e. (SW + LW = Net = 0) • At the surface, on the contrary, radiation is not balanced, i.e., (SW + LW = Net Radiation).

  13. Latitudinal Variations in Net Radiation • tropic-to-tropic – energy surplus • poles – energy deficits • ~ 38o N/S – balance • imbalance of net radiation at surface  • Equator/Tropics vs. high latitudes • drives global circulation • agents: wind, ocean currents, • weather systems

  14. Seasonal and diurnal variations in net radiation • Seasonal variation • Summer: energy surplus • Winter: energy deficits • Diurnal variation • Day: energy surplus • Night: energy deficits

  15. Seasonal variation of surface radiation

  16. Earth’s energy budget (averaged over the whole globe and over a long time) Yellow: shortwave Red: longwave Sensible heat 7% Net Longwave 21% Latent heat 23% • At the top of the atmosphere: Incoming shortwave = Reflected Shortwave+ Emitted longwave • At the surface: Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux

  17. Summary • What is energy? 3 methods of energy transfer • The names of the 6 wavelength categories in the electromagnetic radiation spectrum. The wavelength range of Sun (shortwave) and Earth (longwave) radition • Earth’s energy balance at the top of the atmosphere. Incoming shortwave = Reflected Shortwave+ Emitted longwave • Earth’s energy balance at the surface. Incoming shortwave + Incoming longwave = Reflected shortwave + Emitted longwave + Latent heat flux + Sensible heat flux + Subsurface conduction