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Chapter 18: Energy Balance in the Atmosphere 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? 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 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 highenergy (low wavelength) radiation…rocks and soil re-emit it as low-energy (invisible) infrared radiation. Fig. 18-3, p.431 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? Fig. 18-4, p.431 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 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 longwavelength infrared heat rays. 3. molecules in the atmosphere absorb some of the heat, and the atmosphere becomes warmer. What are the main greenhouse gases? 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). Fig. 18-8, p.434 Fig. 18-8a, p.434 Fig. 18-8b, p.434 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. 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). 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? Fig. 18-10, p.437 Where does the most intense solar radiation strike Earth? Equator receives the most concentrated solar radiation Temps cooler toward poles Fig. 18-11, p.437 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). 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 (isotherms) show global temperature distributions in January and July. Changes with altitude. Fig. 18-14, p.440 Fig. 18-14a, p.440 Fig. 18-14b, p.440 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 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 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 Fig. 18-17, p.442 Portland. Cloud cover and Albedo. Clouds cool the Earth’s surface during the day, but warm is during the night. Fig. 18-18, p.443 p.444