keseimbangan energi di bumi
TRANSCRIPT
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Copyright © 2011 by John Wiley & Sons, Inc.
Alan Strahler
Introducing
Physical
Geography
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Slide
Chapter 2 The Earth’s Global Energy Balance
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The Earth’s Global Energy
Balance
Chapter 2 Return
to Main Slide 2
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Return
Chapter Outline 1. Electromagnetic Radiation Ozone Layer
2. Insolation over the Globe 3. Composition of the Atmosphere 4. Sensible Heat & Latent Heat Transfer
5. The Global Energy System
Energy Balance Click Section
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contentSlide 3
CERES – Clouds & Earth’s Radiant Energy Systems
6. Net Radiation, Latitude, &
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1. Electromagnetic Radiation RADIATION AND TEMPERATURE SOLAR RADIATION CHARACTERISTICS OF SOLAR ENERGY LONGWAVE RADIATION FROM THE EARTH THE GLOBAL RADIATION BALANCE Return
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1. Electromagnetic Radiation All surfaces emit radiation. •Hot objects - radiation in the form of light •Cooler objects - emit heat radiation. Earth emits exactly as much energy as it absorbs from the sun - energy balance Electromagnetic Radiation - collection of waves, wide range of wavelengths, travel away from the surface of an object. Wavelength is the distance separating one wave crest from the next wave crest
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1. Electromagnetic Radiation Gamma rays and X rays – short wavelength, high energies, hazardous to health. Ultraviolet - 10 nm to 0.4 μm. Can damage living tissues. Visible light - 0.4 to 0.7 μm. from violet blue, green, yellow, orange, to red. Near-infrared - 0.7 to 1.2 μm. Similar to visible light. From the Sun. Cannot be seen because eyes not sensitive to radiation beyond 0.7 μm. Shortwave infrared - 1.2 and 3.0 μm. From the sun Middle-infrared - 3.0 μm to 6 μm. From Sun or hot sources on Earth (forest fires, gas well flames) Thermal infrared – 6 μm to 300 μm. Given off by bodies at temperatures found at the Earth’s surface.
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1. Electromagnetic Radiation Return
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RADIATION AND TEMPERATURE Hot objects radiate more energy that cool Hotter object, shorter wavelength Suburban scene at night. Black and violet tones - lower temperatures Yellow and red tones – higher temperatures. Ground and sky - coldest, windows of the heated homes warmest. Return
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SOLAR RADIATION Sun - ball of constantly churning gases heated by continuous nuclear reactions (hydrogen to helium at high temperatures
to Main Slide 1. Electromagnetic Radiation 9
Intensity of solar radiation is greatest in the visible portion of the spectrum. Most of the solar radiation in the visible spectrum penetrates the Earth’s atmosphere to reach the surface.
and pressures) •Surface temperature 6000°C (11,000°F) •Rays of solar radiation spread apart as they move away from the Sun •Rate of incoming energy, solar constant about 1367 W/m2
•Intensity of received (or emitted) radiation = power of the radiation and the surface area being hit by (or giving off) energy Return
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CHARACTERISTICS OF SOLAR ENERGY Sun emits shortwave radiation (ultraviolet, visible and shortwave infrared) Earth emits longwave radiation (infrared) - much is absorbed by the Earth’s atmosphere before it leaves (e.g. by carbon dioxide) Radiation intensity is shown on a logarithmic scale. Return
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LONGWAVE RADIATION FROM THE EARTH Earth radiates less energy that the sun •Energy radiated by Earth is Longwave •Wavelengths are absorbed by gases in the atmosphere, such as water vapor and carbon dioxide Return
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THE GLOBAL RADIATION BALANCE Shortwave radiation from the Sun transmitted through space, intercepted by the Earth. Absorbed radiation is then emitted as Longwave radiation to
outer space. 1. Return
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THE GLOBAL RADIATION BALANCE Incoming solar radiation is either: • reflected (scattered) back to space, or • absorbed by the atmosphere or surface Return
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to Main Slide 1. Electromagnetic Radiation
THE GLOBAL RADIATION BALANCE Absorption of shortwave radiation by the Earth and atmosphere provides energy that the Earth – atmosphere system radiates away in all directions. Return
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2. Insolation over the Globe DAILY INSOLATION THROUGH THE YEAR ANNUAL INSOLATION BY LATITUDE WORLD LATITUDE ZONES Return
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2. Insolation over the Globe Insolation – the flow rate of incoming solar radiation. It is high when the Sun is high in the sky. • Angle of the solar beam striking the Earth varies with latitude • Insolation is strongest near the equator and weakest near the poles. • The intensity of the solar beam depends on the angle between the beam and the surface. Return
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2. Insolation over the Globe
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• Most intense when the beam is vertical. • Beam at an angle of 45° covers a larger surface, less intense. • At 30° beam covers greater surface, even weaker. 17
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DAILY INSOLATION THROUGH THE YEAR Daily insolation depends on: 1) Angle that the sun’s rays strike 2) How long a place is exposed to those rays Midlatitude, mid summer – days are long, sun’s position is high – maximum heating Return
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DAILY INSOLATION THROUGH THE YEAR Return
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DAILY INSOLATION THROUGH THE YEAR Equator - Sun’s path across the sky varies in position and height above the horizon. Sun is always in the sky for 12 hours, but its noon angle varies through the year. Return
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DAILY INSOLATION THROUGH THE YEAR North Pole Sun moves in a circle in the sky at an elevation that changes with the seasons. Return
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DAILY INSOLATION THROUGH THE YEAR Tropic of Capricorn - the Sun is in the sky longest and reaches its highest elevations at the December solstice. Return
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ANNUAL INSOLATION BY LATITUDE
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Tilted Axis • Annual insolation varies smoothly from equator to pole • Insolation greater at lower latitudes • High latitudes receive flow of solar Energy • Insolation at poles 40 percent of equator.
Axis Perpendicular
• No seasons
• Annual insolation high
at the Equator, Sun
directly overhead at
noon every day
throughout year
• Annual insolation zero at the poles, • Sun’s below horizon. Tilt redistributes significant portion of insolation from equator to poles. Return
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WORLD LATITUDE ZONES Globe divided into broad latitude zones based on the seasonal patterns of daily insolation observed globally Return
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3. Composition of the Atmosphere Constant gases in the Troposphere Nitrogen 78% (converted by bacteria into a useful form in soils) Oxygen 21% (produced by green
plants in
photosynthesis and
used in respiration) Return
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4. Sensible Heat & Latent Heat Transfer Sensible heat – the quantity of heat held by an object that can be sensed by touching or feeling Latent heat - heat that is used and stored when a substance changes state from a solid to liquid (or directly to a gas) or liquid to gas (e.g. evaporation of water) Latent heat transfer – the transfer of heat from an evaporating surface to the atmosphere Return
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4. Sensible Heat & Latent Heat Transfer Sensible heat transfer refers to the flow of heat between the Earth’s surface and the atmosphere by conduction or convection. Latent heat transfer refers to the flow of heat carried by changes of state of water. Return
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5. The Global Energy System SOLAR ENERGY LOSSES IN THE ATMOSPHERE ALBEDO COUNTERRADIATION AND THE GREENHOUSE EFFECT GLOBAL ENERGY BUDGETS OF THE ATMOSPHERE AND SURFACE CLIMATE AND GLOBAL CHANGE Return
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SOLAR ENERGY LOSSES IN THE ATMOSPHERE Clear Sky 80% of insolation reaches Earth’s surface
20% of insolation reflected back to space (3% by scatter, 17% by molecules and dust) Cloudy Sky 30 to 60% reflected by clouds 5 to 20% absorbed in Clouds 45 to 10% reaches Earth’s surface Return
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ALBEDO Albedo - percentage of solar radiation reflected Snow and Ice – 0.45-0.85 (also expressed as 45 to 85%) Black Pavement – 0.03
Water - 0.02 Fields, forests, bare ground - 0.03 to 0.25. Earth and atmosphere system - 0.29 and 0.34. Planet sends back to space slightly less than one-third Return
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ALBEDO Fresh snow has a high albedo, reflecting most of the sunlight it receives. Only a small portion is absorbed Return
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ALBEDO Asphalt paving reflects little light, so it appears dark or black and has a low albedo. It absorbs nearly all of the solar radiation it receives. Return
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ALBEDO Water absorbs solar radiation and has a low albedo unless the radiation strikes the water surface at a low angle. In that case, Sun glint raises the albedo. Return
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COUNTERRADIATION AND THE GREENHOUSE EFFECT
Shortwave radiation passes through atmosphere, absorbed and warms surface.
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Surface emits longwave radiation which goes (A) directly to space, or, (B) absorbed by atmosphere Return
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COUNTERRADIATION AND THE GREENHOUSE EFFECT Atmosphere radiates longwave energy back to the surface and also to space as counterradiation (C & D) Counterradiation produces the greenhouse effect. Return
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COUNTERRADIATION AND THE GREENHOUSE EFFECT Water vapor and carbon dioxide act like glass allowing shortwave radiation through but absorbing and radiating longwave radiation. Return
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GLOBAL ENERGY BUDGETS OF THE ATMOSPHERE AND SURFACE Return
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6. Net Radiation, Latitude, & Energy Balance Net radiation - difference between incoming and outgoing radiation At high latitudes there is an energy deficit Poleward - heat transfer moves surplus energy from low to high latitudes Return
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Ozone Layer – Shield to Life Ozone Layer
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Ozone – form of oxygen with 3 oxygen atoms (O3) • Shelters Earth's surface from ultraviolet radiation • Attacked by synthetic chemical components – Chlorine, fluorine and carbons – Chlorofluorocarbons (CFC’s) • 1980’s hole in ozone discovered over Antarctica • Ozone layer thins during the spring in the Southern Hemisphere (September, October) • 1987 – 23 nations signed treaty to cut CFC’s Return
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Ozone Layer – Shield to Life Ozone Layer
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The Antarctic ozone hole of 2006 was the largest on record - 29.5 million square miles. •Low values of ozone –purple, ranging through blue, green, and yellow. •Ozone concentration is measured in Dobson units Return
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CERES – Clouds & Earth’s Radiant Energy Systems
CERES – Clouds & Earth’s Radiant Energy Systems NASA study of the Earth’s radiation budget from space for 20 years •NASA Experiment—Clouds and the Earth’s Radiant Energy (CERES) •New generation of instruments in space that scan the Earth and measure the amount of shortwave and longwave radiation leaving the Earth at the top of the atmosphere. •Continuous monitoring of the Earth’s radiant energy flows
•Small, long-term human or natural changes can be detected 42
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CERES – Clouds & Earth’s Radiant Energy Systems
CERES – Clouds & Earth’s Radiant Energy Systems Average Shortwave Flux - 0 to
210 W/m2, March 2000 •Equator - thick clouds reflect solar radiation back to space. •Midlatitudes - cloudiness shows up as light tones. •Tropical deserts - bright. •Snow and ice is reflective, amount of radiation at poles low – so do not appear bright. •Oceans - absorb solar radiation so low shortwave fluxes.
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CERES – Clouds & Earth’s Radiant Energy Systems
CERES – Clouds & Earth’s Radiant Energy Systems Average Longwave Flux -
100 to 320 W/m2, March 2000 •Equator – low values due to blanketing of thick clouds trapping longwave radiation •Tropical oceans - clear sky emits high longwave flux •Poles - surface and atmospheric temperatures drop, longwave energy
emission Low
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Chapter Review 1. Water in the Environment 2. Humidity
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3. The Adiabatic Process 4. Clouds 5. Precipitation 6. Types of Precipitation 7. Thunderstorms 8. Tornadoes 9. Air Quality
Acid Deposition Observing Clouds from GOES
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