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Energy: Warming the earth and Atmosphere Chapter 2 Energy, Temperature, & Heat • Energy is the ability to do work (push, pull, lift) on some form of matter. • Potential energy is the potential for work (mass x gravity x height)(PE=mgh) • Kinetic energy is energy of a moving object (half of mass x velocity squared)(KE=1/2mv2) • Temperature is the average speed of atoms and molecules Energy, Temperature, & Heat • Which has more energy? – A lake or a cup of hot tea? • Heat is energy in the process of being transferred from one object to another because of a difference in temperature. • Energy cannot be destroyed or created; First Law of Thermodynamics (Conservation of Energy) Temperature Scales • Kelvin scale – or absolute; 0K = -273°C – Lord Kelvin (1824-1907) • Fahrenheit scale – Water : 32 freeze, 212 boil • Celsius scale – Water : 0 freeze, 100 boil • C=5/9(F-32) or F= 9/5C +32 • K=C+273 Specific Heat • Heat capacity is the heat energy absorbed to raise a substance to a given temperature • Specific heat is the heat capacity divided by mass or the amount of energy required to raise one gram of a substance 1°C • High specific heat equates to slow warming and vice versa Latent Heat (vs sensible heat) Change of state or phase change represents change between solid, gas, and liquid. Latent heat is the energy involved in the change of state. Stepped Art Fig. 2-3, p. 33 Water Phase Changes The hot burner warms the bottom of the pot by conduction. The warm pot, in turn, warms the water in contact with it. The warm water rises, settings up convection currents. The pot, water, burner, and everything else constantly emit radiant energy (orange arrows) in all directions. Heat Transfer in the Atmosphere • Conduction: transfer heat from one molecule to another in a substance – Energy travels from hot to cold – Air is a poor conductor, metal a good conductor • Convection: transfer of heat by the mass movement of a fluid (water or air) • Convection circulation: warm air expands and rises then cools and sinks; thermal cell • Horizontal component – wind • Carries properties – advection • Special Topic: Rising and Sinking Air – As air rises part of its energy is lost as it expands and cools and when the air sinks it is compressed and the energy of molecules increase causing temperature to increase. • Radiant energy from the sun travels through the space and the atmosphere in the form of a wave (electromagnetic waves) and is called radiation. • Units of measure – 1 micrometer (μm) =0.000001 m = 10-6m ects with a temperature greater than 0K radiate energy. Radiant Energy is governed by basic laws Hotter objects radiate more total energy per unit area than do cooler objects (Stefan-Boltzmann Law) The hotter the radiating body, the shorter the wavelength of maximum radiation (Wien’s Displacement Law) Objects that are good absorbers of radiation are good emitters as well (Kirchoff’s Law) Stefan-Boltzmann Law • Hotter objects radiate more total energy per unit area than do cooler objects • The hotter the radiating body, the shorter the wavelength of maximum radiation The hotter sun not only radiates more energy than that of the cooler earth (the area under the curve), but it also radiates the majority of its energy at much shorter wavelengths. (The area under the curves is equal to the total energy emitted, and the scales for the two curves differ by a factor of 100,000.) The sun’s electromagnetic spectrum and some of the descriptive names of each region. The numbers underneath the curve approximate the percent of energy the sun radiates in various regions. – UV index is a weather forecast product that indicates the potential for sun burn due to high energy or short wavelengths emitted by the sun. Balancing Act • If the Earth is radiating energy all the time, why is it not very cold? – – – – Earth is in Radiative Equilibrium Radiative Equilibrium Temperature = 255 K (-18C, 0F) Why is the average surface temperature 288K, 15C, 59F? Our atmosphere absorbs and emits infrared radiation • Does not behave as blackbody – Gases act as Selective Absorbers • GoodSelective absorbers are good emitters at a Absorbers particular wavelength and vice versa. – Kirchoff’s Law The melting of snow outward from the trees causes small depressions to form. The melting is caused mainly by the snow’s absorption of the infrared energy being emitted from the warmer tree and its branches. The trees are warmer because they are better absorbers of sunlight than is the snow. Absorption of radiation by gases in the atmosphere. The shaded area represents the percent of radiation absorbed by each gas. The strongest absorbers of infrared radiation are water vapor and carbon dioxide. The bottom figure represents the percent of radiation absorbed by all of the atmospheric gases. FIGURE 2.13 (a) Near the surface in an atmosphere with little or no greenhouse gases, the earth’s surface would constantly emit infrared (IR) radiation upward, both during the day and at night. Incoming energy from the sun would equal outgoing energy from the surface, but the surface would receive virtually no IR radiation from its lower atmosphere. (No atmospheric greenhouse effect.) The earth’s surface air temperature would be quite low, and small amounts of water found on the planet would be in the form of ice. (b) In an atmosphere with greenhouse gases, the earth’s surface not only receives energy from the sun but also infrared energy from the atmosphere. Incoming energy still equals outgoing energy, but the added IR energy from the greenhouse gases raises the earth’s average surface temperature to a more habitable level. Greenhouse Enhancement • Global warming is occurring due to an increase in greenhouse gases – Carbon dioxide – Methane – Nitrogen Oxide – Chlorofluorocarbons • Positive feedbacks continue the warming trend. – Rising sea temps, increase evaporation add water vapor • Negative feedbacks decrease warming. – Increasing clouds, cooling effect Incoming Solar Radiation (INSOLATION) • Solar constant – about 2c/cm2/min. or 1367 W/m2 • What happens to the INSOLATION? – Scattered – Reflected – Absorbed • The scattering of light by air molecules. Air molecules tend to selectively scatter the shorter (violet, green, and blue) wavelengths of visible white light more effectively than the longer (orange, yellow, and red) wavelengths. Blue skies, red skies, and white clouds – Selective scattering of incoming solar radiation causes reflectance in portion of the electromagnetic spectrum that correspond with the colors our eyes detect. At noon, the sun usually appears a bright white. At sunrise and at sunset, sunlight must pass through a thick portion of the atmosphere. Much of the blue light is scattered out of the beam, causing the sun to appear more red. Cloud droplets scatter all wavelengths of visible white light about equally. This type of scattering by millions of tiny cloud droplets makes clouds appear white. Reflected - energy sent back Albedo - % reflected On the average, of all the solar energy that reaches the earth’s atmosphere annually, about 30 percent (30⁄100) is reflected and scattered back to space, giving the earth and its atmosphere an albedo of 30 percent. Of the remaining solar energy, about 19 percent is absorbed by the atmosphere and clouds, and 51 percent is absorbed at the surface. Stepped Art Fig. 2-17, p. 49 The average annual incoming solar radiation (yellow lines) absorbed by the earth and the atmosphere along with the average annual infrared radiation (red lines) emitted by the earth and the atmosphere Particles and Aurora • Solar wind or plasma - charged particles traveling through space from sun to Earth. • Solar wind interacts with Earth’s magnetosphere and creates auroras – Aurora borealis – Aurora australis The stream of charged particles from the sun—called the solar wind—distorts the earth’s magnetic field into a teardrop shape known as the magnetosphere When an excited atom, ion, or molecule de-excites, it can emit visible light. (a) The electron in its normal orbit becomes excited by a charged particle and (b) jumps into a higher energy level. When the electron returns to its normal orbit, it (c) emits a photon of light. The aurora borealis is a phenomenon that forms as energetic particles from the sun interact with the earth’s atmosphere. The aurora belt (solid red line) represents the region where you would most likely observe the aurora on a clear night. (The numbers represent the average number of nights per year on which you might see an aurora if the sky were clear.) The flag MN denotes the magnetic North Pole, where the earth’s magnetic field lines emerge from the earth. The flag NP denotes the geographic North Pole, about which the earth rotates.