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 Name Location of the Subsolar Pt. (declination) December 21December (winter) Solstice23.5° S latitude (Tropic of Capricorn) March 21March EquinoxEquator (0°) June 21June (summer) Solstice23.5° N (Tropic of Cancer) Sept. 22September equinoxEquator (0°)

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

About barometers: ments/a/barometers.htmhttp://weather.about.com/od/weatherinstru ments/a/barometers.htm

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

Atmospheric Temperature Structure: Troposphere Surface to ~11 mi 90% of mass of atmosphere Golbal 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 most effective near ground) Environmental lapse rate is variable (local temp change observed at a particular time)

Temperature Structure (cont) Stratosphere –(11 to 30 mi) –Temp. increases w/ elevation because ozone in upper part absorbs shortwave radiation from the sun Mesosphere –(30 to 50 mi) –Temp. declines w/ elevation, as there are few gasses here to absorb outgoing longwave radiation Thermosphere –(50 mi) outwards –Temp. rises w/ elevation, due to solar excitation of individual molecules

Earth’s Protective Atmosphere Figure 2.21

Atmospheric Function (much protection from radiation is given in stratosphere, mesosphere, and thermosphere) Ozonosphere (part of Stratosphere) –Ozone (O 3 ) absorbs UV energy thus temps increase moving into this layer –Chlorine from CFCs destroys O 3

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

Estimated Benefits of the Clean Air Act Total direct cost $523 billion, borne directly by business, consumers, and government entities Direct monetized benefits $5.6 to $49.4 trillion, enjoyed across all sectors of society, including health, economic, & environmental (ag. forestry, fishing). Net financial benefit $21.7 trillion 206,000 fewer deaths in 1990

Optional slide Photochemical Smog Figure 2.26