Solar altitude Solar altitude: angle in degrees above horizon Variations in solar altitude and daylength drive seasonality. ☼ 30 degrees

Solar Altitude (con’t.) Solar altitude = 90 – [the number of degrees of latitude that separate place of interest from the declination (subsolar point)] The subsolar point can be determined for the solstices and equinoxes using data already provided, shown here again: Approximate Date Northern Hemisphere Location of the Subsolar Pt. (declination) December 21 December (winter) Solstice 23.5° S latitude (Tropic of Capricorn) March 21 March Equinox Equator (0°) June 21 June (summer) Solstice 23.5° N (Tropic of Cancer) Sept. 22 September equinox

Solar altitude calculation (con’t.) If the date that you need the subsolar point for is not in the previous table, use an analemma. Example: What is the solar altitude for Salem, Oregon on June 21? latitude of place of interest: 45 N latitude of subsolar point: -23.5 N Difference: 21.5 Therefore, solar altitude is calculated as 90 - 21.5 = 68.5 Show animation if time allows

Structure of Atmosphere Layers by temperature, starting at surface: Troposphere: falling temps Stratosphere: rising temps Mesosphere: falling temps Thermosphere: rising temps

Profile of Atmosphere Figure 2.17

Atmospheric Temperature Structure: Troposphere Surface to ~11 mi 90% of mass of atmosphere Global average lapse rate – cools at 3.6 °F/1000 ft. It cools because its greenhouse gasses absorb terrestrial longwave radiation (primary way that the troposphere is heated) and these gasses become less abundant with incr. alt. (also cools because turbulent heat transfer is most effective near ground, less so higher up) Local temp change observed at a particular time (Environmental lapse rate) varies.

Temperature Structure (cont) Stratosphere (11 to 30 mi) Temp. increases w/ elevation because ozone in upper part absorbs shortwave uv radiation from the sun Mesosphere 4-9-18 (30 to 50 mi) Temp. declines w/ elevation, (few gasses here to absorb outgoing longwave radiation or incoming shortwave rad.) Thermosphere (50 mi) outwards Temp. rises w/ elevation, due to solar excitation of individual molecules Aurora borealis caused by charged particles of solar wind colliding with gasses.

Atmospheric Pressure Key concept: atmospheric pressure decreases with increases in height. Figure 2.18

Skip this slide About barometers: http://weather.about.com/od/weatherinstruments/a/barometers.htm

Know in order of abundance: Nitrogen, Oxygen, Argon, Carbon Dioxide Composition of the Homosphere (lowest 50 miles – where the mix of most major gasses is similar throughout) Know in order of abundance: Nitrogen, Oxygen, Argon, Carbon Dioxide Figure 2.19

Earth’s Protective Atmosphere Figure 2.21

Atmospheric Function Much protection from harmful radiation is given in stratosphere, mesosphere, and thermosphere Ozonosphere (part of Stratosphere) Ozone (O3) absorbs UV energy

Natural Factors That Affect Air Pollution Winds can disperse pollution or bring it in from elsewhere Valleys can concentrate pollution Temperature inversions (when temperature in the troposphere increases rather than decreases with height) concentrate pollutants near ground

Temperature Inversion Figure 2.24

Air Pollution Death http://timesofindia. indiatimes

Optional slide Photochemical Smog Figure 2.26

Benefits of the Clean Air Act Compliance costs borne directly by business, consumers, and government entities Benefits enjoyed across all sectors of society, including health, economic, & environmental (ag. forestry, fishing). Net financial benefit (benefits – costs) large Estimated 206,000 fewer deaths by 1990 But still, about 200,000 premature deaths annually in the US come from air pollution http://news.mit.edu/2013/study-air-pollution-causes-200000-early-deaths-each-year-in-the-us-0829 What are leading sources of pollution here?