Chapter 18: Energy Balance in the Atmosphere Lightning Strikes Across the Great Plains. Fig. 18-CO, p.428

Incoming Solar Radiation Almost all surface events are driven by solar energy. Weather: state of the atmosphere at a given place and time Climate: characteristic weather of a region (particularly temp and precipitation) averaged over several decades. Earth receives one two-billionth of the total solar output! Light behaves as a particle (Newton) and wave (Hooke and Huygens) at the same time. Photons travel at the speed of light (through the vacuum of space at 300,000 km/sec) from Sun to Earth (150 million km) in how many minutes?

Figure 18.1 The terms used to describe a light wave are identical to those used for water, sound, and other types of waves. Visible light is a tiny portion of the electromagnetic spectrum. The terms used to describe a light wave are identical to those used for water, sound and other types of waves. Fig. 18-1, p.429

Figure 18. 2 The electromagnetic spectrum Figure 18.2 The electromagnetic spectrum. The wave shown is not to scale. In reality the wavelength varies by a factor of 1022, and this huge difference cannot be shown. Fig. 18-2, p.430

Absorption and Emission: Absorption of a photon causes suntan or sunburn (for example). Emission occurs when the photon hooks up with an electron and falls to a lower energy state. An iron bar (at room temp) emits infrared radiation. If heated it emits red progressing to white: temp of source determines wavelength and color emitted. The Sun (very hot) emits high-energy (low wavelength) radiation…rocks and soil re-emit it as low-energy (invisible) infrared radiation. Figure 18.3 Iron glows red when heated in a forge. If it is heated further, it emits white light. Fig. 18-3, p.431

Albedo: the proportional reflectance of a surface Albedo: the proportional reflectance of a surface. The albedo of common Earth surfaces vary greatly. What would happen to the surface of our planet if glaciers and cloud cover grew? Figure 18.4 The albedos of common Earth surfaces vary greatly. Fig. 18-4, p.431

Figure 18.5 Atmospheric gases, water droplets, and dust scatter incoming solar radiation. When radiation scatters, its direction changes but the wavelength remains constant. Scattering: inversely proportional to the wavelength of light. Short wavelength (blue light) scatters more than long wavelength (red 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 Sun be if viewed above our atmosphere? Fig. 18-5, p.432

Figure 18.6 One half of the incoming solar radiation reaches the Earth’s surface. The atmosphere scatters, reflects, and absorbs the other half. All of the radiation absorbed by the Earth’s surface is re-radiated as long-wavelength heat radiation. The Radiation Balance: one-half of the incoming solar radiation reaches the Earth’s surface. The atmosphere scatters, reflects and absorbs the other half. All of the radiation absorbed by the Earth’s surface is re-radiated as long-wavelength heat radiation. Fig. 18-6, p.432

Greenhouse Effect: 1. rocks, soil and water absorb short-wavelength solar radiation and become warmer. 2. the Earth re-radiates the energy as long-wavelength infrared heat rays. 3. molecules in the atmosphere absorb some of the heat, and the atmosphere becomes warmer. What are the main greenhouse gases? Figure 18.7 The greenhouse effect can be viewed as a three-step process. Step 1: Rocks, soil, and water absorb short-wavelength solar radiation, and become warmer(orange lines). Step 2: The Earth re-radiates the energy as long-wavelength infrared heat rays (red lines). Step 3:Molecules in the atmosphere absorb some of the heat, and the atmosphere becomes warmer. Fig. 18-7, p.433

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

Heat transport by conduction and convection (and advection). Figure 18.8 (A) Convection currents distribute heat throughout a room. (B) Convection also distributes heat through the atmosphere when the Sun heats the Earth’s surface. In this case the ceiling is the boundary between the troposphere and the stratosphere. Fig. 18-8, p.434

Figure 18.8 (A) Convection currents distribute heat throughout a room. Fig. 18-8a, p.434

Figure 18.8 (B) Convection also distributes heat through the atmosphere when the Sun heats the Earth’s surface. In this case the ceiling is the boundary between the troposphere and the stratosphere. Fig. 18-8b, p.434

Figure 18.9 Water releases or absorbs latent heat as it changes among its liquid, solid, and vapor states. (Calories are given per gram at 0_C and 100_C. The values vary with temperature. Red arrows show processes that absorb heat; blue arrows show those that release heat.) Changes of State: at Earth’s surface, water commonly exists in all three states (ice, liquid and water vapor)…Latent heat (stored heat) is the energy released or absorbed when a substance changes from one state to another. Fig. 18-9, p.435

Heat Storage Place a pan of water and a rock outside on a hot summer day, which becomes hotter and why? Specific Heat: amount of energy needed to raise the temperature of 1 gram of material by 1 degree C. Water has very high specific heat…what are the implications? Why are coastal areas are cooler in the summer and warmer in the winter than continental interiors.

How to locate a place on Earth. Temperature changes with latitude and season: Before seasons, do you understand Latitude and Longitude (see Focus On, page 459) How to locate a place on Earth. *Earth has natural points of reference (the North and South geographic poles lie on Earth’s spin axis). *Lines of Latitude form imaginary horizontal rings around the spin axis. Equator at 0 degrees latitude. What about North and South Poles? *Lines of Longitude also in degrees, beginning at Greenwich, England (arbitrarily chosen, 0 degrees longitude). Figure 1 Latitude and longitude allow navigators to identify a location on a spherical Earth. p.436

If light shines directly overhead, the radiation is concentrated on a small area. However, if the light shines at an angle, or if the surface is tilted, the radiant energy is dispersed over a larger area. How does this apply to the Equator and Polar regions of the Earth? Figure 18.10 If a light shines from directly overhead, the radiation is concentrated on a small area. However, if the light shines at an angle, or if the surface is tilted, the radiant energy is dispersed over a larger area. Fig. 18-10, p.437

Where does the most intense solar radiation strike Earth? Equator receives the most concen-trated solar radiation Temps cooler toward poles Figure 18.11 When the Sun shines directly over the equator, the equator receives the most intense solar radiation, and the poles receive little. Fig. 18-11, p.437

Figure 18.12 Weather changes with the seasons because the Earth’s axis is tilted relative to the plane of its orbit around the Sun. As a result, the Northern Hemisphere receives more direct sunlight during summer, but less during winter. Weather changes with the seasons because the Earth’s axis is tilted relative to the plane of its orbit around the Sun. The Northern Hemisphere receives more direct sunlight during summer, but less during winter. Tilt is 23.5 degrees; tropic of Cancer (23.5 degrees north latitude); tropic of Capricorn (23.5 degrees south latitude). Fig. 18-12, p.438

Canadian Arctic, midnight during July…location is 70 degrees north latitude (Beaufort Sea). Figure 18.13 The Sun shines at midnight in July at 70_north latitude in the Canadian Arctic. A small boat sits at anchor near Cape Parry in the Beaufort Sea, Northwest Territories. Fig. 18-13, p.438

During equinoxes (equal nights) all areas on the Earth receive about 12 hours of daylight and darkness. Poles not tilted toward or away from the Sun. In fact, all areas of the Earth receive the same total number of hours of sunlight every year, so why is there such a variation in climates? Table 18-1, p.439

Temperature changes with geography. Lines of avg Temperature changes with geography. Lines of avg. temperature (isotherms) show global temperature distributions in January and July. Changes with altitude. Figure 18.14 Global temperature distributions (A) in January, and (B) in July. Isotherm lines connect places with the same average temperatures. Fig. 18-14, p.440

Figure 18.14 Global temperature distributions (A) in January, and (B) in July. Isotherm lines connect places with the same average temperatures. Fig. 18-14a, p.440

Figure 18.14 Global temperature distributions (A) in January, and (B) in July. Isotherm lines connect places with the same average temperatures. Fig. 18-14b, p.440

Figure 18.15 Continental St. Louis (red line)is colder in winter and warmer in summer than coastal San Francisco(blue line). Ocean Effects: continental St. Louis (red line) is colder in the winter and warmer in the summer than coastal San Francisco. Fig. 18-15, p.441

Figure 18.16 Paris is warmed by the Gulf Stream and the North Atlantic Drift. On the other hand, St. John’s, Newfoundland, is alternately warmed by the Gulf Stream and cooled by the Labrador Current. The cooling effect of the Labrador Current depresses the temperature of St. John’s year round. Paris is warmed by the Gulf Stream and the North Atlantic Drift. St. John’s is alternately warmed by the Gulf Stream and cooled by the Labrador Current. This cooling effect depresses the temperature of St. John’s year round. Fig. 18-16, p.441

Figure 18.17 During the summer, temperatures in Vladivostock, Russia, and Portland, Oregon, are nearly identical. However, frigid Arctic wind from Siberia cools Vladivostock during the winter(red line) so that the temperature is significantly colder than that of Portland (blue line). Wind Direction: during the summer, temperatures in Vladivostok and Portland are nearly the same. In the winter, cold Arctic winds cool Vladivostok to temps much lower than Portland. Fig. 18-17, p.442

Figure 18.18 Clouds cool the Earth’s surface during the day, but warm it during the night. Cloud cover and Albedo. Clouds cool the Earth’s surface during the day, but warm is during the night. Fig. 18-18, p.443

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