Chapter 18: Energy Balance in the Chapter 18: Energy Balance in the AtmosphereAtmosphere

Fig. 18-CO, p.428

Incoming Solar RadiationIncoming Solar Radiation Almost all surface events are driven by solar Almost all surface events are driven by solar

energy. energy. WeatherWeather: state of the atmosphere at a given : state of the atmosphere at a given

place and timeplace and time ClimateClimate: characteristic weather of a region : characteristic weather of a region

(particularly temp and precipitation) averaged (particularly temp and precipitation) averaged over several decades. over several decades.

Earth receives one two-billionth of the total Earth receives one two-billionth of the total solar output! Light behaves as a particle solar output! Light behaves as a particle (Newton) and wave (Hooke and Huygens) at the (Newton) and wave (Hooke and Huygens) at the same time. Photons travel at the speed of light same time. Photons travel at the speed of light (through the vacuum of space at 300,000 (through the vacuum of space at 300,000 km/sec) from Sun to Earth (150 million km) in km/sec) from Sun to Earth (150 million km) in how many minutes? how many minutes?

Visible light is a tiny portion of the Visible light is a tiny portion of the electromagnetic spectrum. The terms used to electromagnetic spectrum. The terms used to describe a light wave are identical to those used describe a light wave are identical to those used for water, sound and other types of waves. for water, sound and other types of waves.

Fig. 18-1, p.429

Fig. 18-2, p.430

Absorption and EmissionAbsorption and Emission::

Absorption of a photon causes Absorption of a photon causes suntan or sunburn (for suntan or sunburn (for example).example).

Emission occurs when the Emission occurs when the photon hooks up with an photon hooks up with an electron and falls to a lower electron and falls to a lower energy state. An iron bar (at energy state. An iron bar (at room temp) emits infrared room temp) emits infrared radiation. If heated it emits radiation. If heated it emits red progressing to white: red progressing to white: temp of source determines temp of source determines wavelength and color emitted. wavelength and color emitted.

The Sun (very hot) emits high-The Sun (very hot) emits high-energy (low wavelength) energy (low wavelength) radiation…rocks and soil re-radiation…rocks and soil re-emit it as low-energy emit it as low-energy (invisible) infrared radiation. (invisible) infrared radiation. Fig. 18-3, p.431

AlbedoAlbedo: the : the proportionaproportional l reflectance reflectance of a of a surface. surface. The albedo The albedo of common of common Earth Earth surfaces surfaces vary vary greatly. greatly.

What would What would happen to happen to the surface the surface of our of our planet if planet if glaciers glaciers and cloud and cloud cover cover grew?grew?

Fig. 18-4, p.431

Scattering:Scattering: inversely proportional to the wavelength of light. Short inversely proportional to the wavelength of light. Short wavelength (blue light) scatters more than long wavelength (red wavelength (blue light) scatters more than long wavelength (red light). So, sky is blue…Sun is yellow because this is color of white light). So, sky is blue…Sun is yellow because this is color of white light with most of the blue light removed…what color would the light with most of the blue light removed…what color would the Sun be if viewed above our atmosphere?Sun be if viewed above our atmosphere?

Fig. 18-5, p.432

The Radiation BalanceThe Radiation Balance: one-half of the incoming solar : one-half of the incoming solar radiation reaches the Earth’s surface. The atmosphere radiation reaches the Earth’s surface. The atmosphere scatters, reflects and absorbs the other half. All of the scatters, reflects and absorbs the other half. All of the radiation absorbed by the Earth’s surface is re-radiated radiation absorbed by the Earth’s surface is re-radiated as long-wavelength heat radiation. as long-wavelength heat radiation.

Fig. 18-6, p.432

Greenhouse EffectGreenhouse Effect: 1. : 1. rocks, soil and water rocks, soil and water absorb short-absorb short-wavelength solar wavelength solar radiation and become radiation and become warmer. 2. the Earth warmer. 2. the Earth re-radiates the energy re-radiates the energy as long-wavelength as long-wavelength infrared heat rays. 3. infrared heat rays. 3. molecules in the molecules in the atmosphere absorb atmosphere absorb some of the heat, and some of the heat, and the atmosphere the atmosphere becomes warmer. becomes warmer. What are the main What are the main greenhouse gases?greenhouse gases?

Fig. 18-7, p.433

Energy Storage and TransferEnergy Storage and Transfer: the : the driving mechanisms for weather driving mechanisms for weather

and climateand climate

Heat and TemperatureHeat and Temperature: : temperature is proportional to the temperature is proportional to the avg. speed of atoms or molecules avg. speed of atoms or molecules in a sample (cup of boiling water in a sample (cup of boiling water and bathtub full of ice water)…and bathtub full of ice water)…heat is total energy in a sample heat is total energy in a sample (many more molecules, so total (many more molecules, so total heat energy is greater).heat energy is greater).

Heat transport by conduction and convection Heat transport by conduction and convection (and advection). (and advection).

Fig. 18-8, p.434

Fig. 18-8a, p.434

Fig. 18-8b, p.434

Changes of StateChanges of State: at Earth’s surface, water commonly : at Earth’s surface, water commonly exists in all three states (ice, liquid and water vapor)…exists in all three states (ice, liquid and water vapor)…Latent heat (stored heat) is the energy released or Latent heat (stored heat) is the energy released or absorbed when a substance changes from one state to absorbed when a substance changes from one state to another.another. Fig. 18-9, p.435

Heat StorageHeat Storage

Place a pan of water and a rock outside on a Place a pan of water and a rock outside on a hot summer day, which becomes hotter and hot summer day, which becomes hotter and why?why?

Specific HeatSpecific Heat: amount of energy needed to : amount of energy needed to raise the temperature of 1 gram of material by raise the temperature of 1 gram of material by 1 degree C. Water has very high specific 1 degree C. Water has very high specific heat…what are the implications? heat…what are the implications?

Why are coastal areas are cooler in the Why are coastal areas are cooler in the summer and warmer in the winter than summer and warmer in the winter than continental interiors.continental interiors.

Temperature changes Temperature changes with latitude and season: with latitude and season: Before seasons, do you Before seasons, do you understandunderstandLatitude and LongitudeLatitude and Longitude(see Focus On, page (see Focus On, page 459)459)

How to locate a place on How to locate a place on Earth.Earth.

*Earth has natural points of *Earth has natural points of reference (the North and reference (the North and South geographic poles South geographic poles lie on Earth’s spin axis).lie on Earth’s spin axis).

*Lines of Latitude form *Lines of Latitude form imaginary horizontal imaginary horizontal rings around the spin rings around the spin axis. Equator at 0 axis. Equator at 0 degrees latitude. What degrees latitude. What about North and South about North and South Poles?Poles?

*Lines of Longitude also in *Lines of Longitude also in degrees, beginning at degrees, beginning at Greenwich, England Greenwich, England (arbitrarily chosen, 0 (arbitrarily chosen, 0 degrees longitude).degrees longitude).

p.436

If light shines directly overhead, the radiation is If light shines directly overhead, the radiation is concentrated on a small area. However, if the concentrated on a small area. However, if the light shines at an angle, or if the surface is light shines at an angle, or if the surface is tilted, the radiant energy is dispersed over a tilted, the radiant energy is dispersed over a larger area. How does this apply to the Equator larger area. How does this apply to the Equator and Polar regions of the Earth?and Polar regions of the Earth? Fig. 18-10, p.437

Where does Where does the most the most intense solar intense solar radiation radiation strike Earth? strike Earth?

Equator Equator

receives the receives the most concen-most concen-trated solar trated solar radiationradiation

Temps cooler Temps cooler toward polestoward poles

Fig. 18-11, p.437

Weather changes with the seasons because the Earth’s axis is Weather changes with the seasons because the Earth’s axis is tilted relative to the plane of its orbit around the Sun. The tilted relative to the plane of its orbit around the Sun. The Northern Hemisphere receives more direct sunlight during Northern Hemisphere receives more direct sunlight during summer, but less during winter. Tilt is 23.5 degrees; tropic of summer, but less during winter. Tilt is 23.5 degrees; tropic of Cancer (23.5 degrees north latitude); tropic of Capricorn (23.5 Cancer (23.5 degrees north latitude); tropic of Capricorn (23.5 degrees south latitude). degrees south latitude).

Fig. 18-12, p.438

Canadian Canadian Arctic, Arctic, midnight midnight during July…during July…location is 70 location is 70 degrees degrees north north latitude latitude (Beaufort (Beaufort Sea).Sea).

Fig. 18-13, p.438

Table 18-1, p.439

During equinoxes (equal nights) all areas on the During equinoxes (equal nights) all areas on the Earth receive about 12 hours of daylight and Earth receive about 12 hours of daylight and darkness. Poles not tilted toward or away from the darkness. Poles not tilted toward or away from the Sun. Sun.

In fact, all areas of the Earth receive the same total In fact, all areas of the Earth receive the same total number of hours of sunlight every year, so why is number of hours of sunlight every year, so why is there such a variation in climates?there such a variation in climates?

Temperature Temperature changes with changes with geography. geography. Lines of avg. Lines of avg. temperature temperature (isotherms) (isotherms) show global show global temperature temperature distributions in distributions in January and January and July.July.

Changes with Changes with altitude.altitude.

Fig. 18-14, p.440

Fig. 18-14a, p.440

Fig. 18-14b, p.440

Ocean EffectsOcean Effects: continental St. Louis (red line) is : continental St. Louis (red line) is colder in the winter and warmer in the summer colder in the winter and warmer in the summer than coastal San Francisco. than coastal San Francisco. Fig. 18-15, p.441

Paris is warmed by the Gulf Stream and the North Atlantic Paris is warmed by the Gulf Stream and the North Atlantic Drift. St. John’s is alternately warmed by the Gulf Stream Drift. St. John’s is alternately warmed by the Gulf Stream and cooled by the Labrador Current. This cooling effect and cooled by the Labrador Current. This cooling effect depresses the temperature of St. John’s year round. depresses the temperature of St. John’s year round.

Fig. 18-16, p.441

Wind DirectionWind Direction: during the summer, temperatures in : during the summer, temperatures in Vladivostok and Portland are nearly the same. In the Vladivostok and Portland are nearly the same. In the winter, cold Arctic winds cool Vladivostok to temps much winter, cold Arctic winds cool Vladivostok to temps much lower than Portland. lower than Portland. Fig. 18-17, p.442

Cloud cover and AlbedoCloud cover and Albedo. Clouds cool the . Clouds cool the Earth’s surface during the day, but warm is Earth’s surface during the day, but warm is during the night. during the night.

Fig. 18-18, p.443

p.444