Energy: Warming the Earth & the Atmosphere

1. Energy: Warming the Earth & the Atmosphere • This chapter discusses: • The role of solar energy (e.g. short wave radiation) in generating temperature & heat • Earth's processes for heat transfer in the atmosphere, including long wave radiation, to maintain an energy balance

2. Energy & Temperature Figure 2.1 • When solar radiation collides with atmospheric gas molecules, they move. • This produces: • temperature, defined as the moving molecules average speed • kinetic energy • Total energy increases with greater molecule volumes.

3. Temperature Scales Thermometers detect the movement of molecules to register temperature. Fahrenheit and Celsius scales are calibrated to freezing and boiling water, but the Celsius range is 1.8 times more compact. Figure 2.2

4. Latent & Sensible Heat Figure 2.3 Heat energy, which is a measure of molecular motion, moves between water's vapor, liquid, and ice phases. As water moves toward vapor it absorbs latent (e.g. not sensed) heat to keep the molecules in rapid motion.

5. Heat Energy for Storms Figure 2.4 Latent heat released from the billions of vapor droplets during condensation and cloud formation fuels storm energy needs, warms the air, and encourages taller cloud growth.

6. Conduction - Heat Transfer Conduction of heat energy occurs as warmer molecules transmit vibration, and hence heat, to adjacent cooler molecules. Warm ground surfaces heat overlying air by conduction. Figure 2.5

7. Convection - Heat Transfer Figure 2.6 Convection is heat energy moving as a fluid from hotter to cooler areas. Warm air at the ground surface rises as a thermal bubble, expends energy to expand, and hence cools.

8. Radiation - Heat Transfer Radiation travels as waves of photons that release energy when absorbed. All objects above 0° K release radiation, and its heat energy value increases to the 4th power of its temperature. Figure 2.7

9. Longwave & Shortwave Radiation The hot sun radiates at shorter wavelengths that carry more energy, and the fraction absorbed by the cooler earth is then re-radiated at longer wavelengths, as predicted by Wein's law. Figure 2.8

10. Electromagnetic Spectrum Figure 2.9 Solar radiation has peak intensities in the shorter wavelengths, dominant in the region we know as visible, but extends at low intensity into longwave regions.

11. Absorption & Emission Figure 2.10 Solar radiation is selectively absorbed by earth's surface cover. Darker objects absorb shortwave and emit longwave with high efficiency (e.g. Kirchoff's law). In a forest, this longwave energy melts snow.

12. Atmospheric Absorption Solar radiation passes rather freely through earth's atmosphere, but earth's re-emitted longwave energy either fits through a narrow window or is absorbed by greenhouse gases and re-radiated toward earth. Figure 2.11

13. Greenhouse Effect Figure 2.12B Figure 2.12A Earth's energy balance requires that absorbed solar radiation is emitted to maintain a constant temperature. Without natural levels of greenhouse gases absorbing and emitting, this surface temperature would be 33°C cooler than the observed temperature.

14. Warming Earth's Atmosphere Figure 2.13 Solar radiation passes first through the upper atmosphere, but only after absorption by earth's surface does it generate sensible heat to warm the ground and generate longwave energy. This heat and energy at the surface then warms the atmosphere from below.

15. Scattered Light Solar radiation passing through earth's atmosphere is scattered by gases, aerosols, and dust. At the horizon sunlight passes through more scatterers, leaving longer wavelengths and redder colors revealed. Figure 2.14

16. Incoming Solar Radiation Figure 2.15 Solar radiation is scattered and reflected by the atmosphere, clouds, and earth's surface, creating an average albedo of 30%. Atmospheric gases and clouds absorb another 19 units, leaving 51 units of shortwave absorbed by the earth's surface.

17. Earth-Atmosphere Energy Balance Figure 2.16 Earth's surface absorbs the 51 units of shortwave and 96 more of longwave energy units from atmospheric gases and clouds. These 147 units gained by earth are due to shortwave and longwave greenhouse gas absorption and emittance. Earth's surface loses these 147 units through conduction, evaporation, and radiation.

18. Earth's Magnetic Field Figure 2.17 Earth's molten metal core creates a magnetic field that covers earth from the south to north pole.

19. Solar Wind High energy plasma is blown from the sun in a dangerous solar wind, and the magnetosphere deflects this wind to shield the earth. Figure 2.18

20. Ions & Aurora Belts Solar winds entering the magnetosphere excite atmospheric gas electrons. When the electron de-excites it emits visible radiation. Figure 2.19A The aurora is created by these solar winds and de-exciting ions, and has belts of expected occurrence at both poles. Figure 2.20