Energy Balance Chapter 18

Solar Energy Electromagnetic (EM) radiation Energy waves with different properties depending on wavelength, frequency Longwave (low frequency): heat, radio waves Shortwave (high frequency) Visible: light Invisible: Ultraviolet, x rays, etc Electromagnetic spectrum – shows EM wavelengths by frequency and wavelength

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 radiation – electrons of absorbing material are “excited” by increase in energy Increase in temperature; physical/chemical change Examples: sunburn, cancer Emission of radiation – excited electrons return to original state; radiation emitted as light or heat Example: earth emits radiation in the form of heat after absorption of solar energy (light)

Reflection and Albedo Reflection –electromagnetic radiation bouncing of from a surface without absorption or emission Albedo – proportional reflectance of a surface a perfect mirror would have an albedo of 100% Glaciers & snowfields approach 80-90% Clouds – 50-55% Pavement and some buildings – only 10-15% Scattering – gases and water droplets scatter light in all directions short “blue” wavelengths scatter more, so skies are blue

Figure 18.4 The albedos of common Earth surfaces vary greatly. Fig. 18-4, p.431

the Radiation Balance Sun emits EM radiation of all wavelengths, but primarily shortwave (i.e. light). Earth’s surface absorbs this energy Most is re-emitted, as heat (longwave) Greenhouse Effect “greenhouse gases” let shortwave energy (light) pass through, but absorb and emit longwave energy radiated by the Earth, keeping it the atmosphere

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. Fig. 18-6, p.432

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 & transfer Temperature – is proportional to the average speed of atoms or molecules in a sample. Hot water molecules move faster than cold water molecules Hot cup of tea has higher temperature than bathtub of ice Energy: increases the speed of atoms/molecules average energy per molecule X number of molecules E.g.: bathtub of ice has more energy than a cup of tea When energy flows from hotter substance to colder substance, we call that heat transfer (manifested by either temperature change or phase change)

Energy Storage and Transfer Conduction – Heat flow from hotter object to cooler object due to direct contact (water is in contact with flame). Convection – heat flow due to currents of liquid or gas (when warm air rises, transfers energy to the surrounding air)

Energy storage & transfer – climate’s driving mechanism Specific heat – the amount of energy required to change the temperature of 1 gram of something by 1oC Water has a high specific heat; need a large energy transfer to change it’s temperature

Energy storage & transfer – climate’s driving mechanism Change of state – change from solid to liquid, or liquid to gas Latent heat – heat absorbed or released during a change of phase without temperature change E.g.: we put heat into water to create steam Around 540 calories The change from ice to water only requires 80 calories When water vapor condenses, it releases that heat

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.) Fig. 18-9, p.435

Figure 1 Latitude and longitude allow navigators to identify a location on a spherical Earth.

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. Fig. 18-12, p.438

Figure 18.15 Continental St. Louis (red line)is colder in winter and warmer in summer than coastal San Francisco(blue line). 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. 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). Fig. 18-17, p.442

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 18.18 Clouds cool the Earth’s surface during the day, but warm it during the night. Fig. 18-18, p.443