I. Axial Tilt and Orbit around Sun— A. Earth tilts 23.5o to orbit around Sun B. Latitudes of Sun incidence 1. polar circles—Arctic, Antarctic 2. tropical circles—Cancer, Capricorn 3. equator C. Days corresponding to Sun incide nce 1. solstice—overhead Sun at tropical circle—June 22, December 22 2. equinox—overhead Sun at equator—March 22, September 22 D. Day length varies with latitude and season, due to circle of illumination 1. longest/shortest at solstice, at high latitudes 2. equinox—equal day and night all over the world II. Heating A. Greater heating capability with higher Sun angle 1. latitude controls on Sun energy 2. seasonal controls on Sun energy B. Low latitudes have high Sun angle year round C. Incoming Solar Radiation 1. Temperature Variation greater in areas closer to poles 2. Temperature Distribution—affected by land‐water relation as well as latitude III. Heat— A. Thermal energy, transferred from warm substances to cooler ones B. Methods of heat transfer 1. conduction— a. through matter by molecular activity b. air is poor conductor of heat energy 2. convection—heat rises a. transfer of heat by circulation within fluid b. caused by expansion of heated fluid reduces density c. lower atmosphere heated by Earth’s surface 3. radiation—through empty space a. Solar radiation is source of energy for weather and climate 1) Electromagn etic radiation from radio waves to gamma waves 2) Visible light small segment between infra‐red and ultraviolet a) Infrared is heat b) Ultraviolet causes sunburn, etc. 3) microwaves and x rays bracket ir and uv b. all objects emit radiant energy 1) hotter object emit more, and at shorter wavelengths 2) the better absorber of radiation, the better ability to emit energy a) Earth is excellent absorber and emitter b) Atmospheric gases selective absorbers of longer wave radiation IV. Incoming solar radiation A. Absorbed, transmitted, redirected (reflected or scattered) B. Distribution 1. about 50% is transmitted to surface and absorbed by Earth 2. about 30% is reflected back to space 3. about 20% absorbed by atmospheric gases and clouds C. reflection and scattering 1. reflection— a. changing direction of light without reducing intensity b. Albedo—fraction of radiation reflected by a surface 1) Affected by length of travel through a tmosphere 2) Affected by angle of incidence upon water 2. scattering— a. disperses light into many weaker rays in many directions b. accomplished by dust, gas molecules c. diffuses light to make shadows have light D. absorption 1. nitrogen poor absorber of radiation 2. oxygen and ozone absorb most of uv radiation high in atmosphere 3. most atmospheric gases do not absorb visible wavelengths—transmit V. Atmosphere is mixture of gases, with varying proportions with respect to location and timing A. Nitrogen and Oxygen make up 99% of clean, dry air up to 80 km B. Minor components include argon (0.93%), and carbon dioxide (0.037%) C. Variable components affect weather and climate 1. water vapor a. varies from almost none to up to 4% of atmosphere b. source of all clouds and precipitation c. absorbs heat from Earth and Sun d. change of water’s phase captures or releases ‘latent heat’ 2. aerosols and dust a. remain suspended for extended period of time b. sources include sea salt, blown soil, fires, pollen, volcanic eruptions c. act as surfaces for water vapor to begin condensation d. reflect and scatter incoming solar energy 3. ozone a. molecular oxygen with three atoms has properties distinct from O2 1) damages tissue of organisms 2) can be created near surface by reactions in smog b. concentrated 10 to 50 km above surface in stratosphere 1) Sun’s radiation breaks O2 into O and O in stratosphere 2) O collides with O2 and forms O3 at this altitude 3) Lightning makes O3 in troposphere c. Ozone important absorber of UV radiation VI. Height and structure of atmosphere A. Pressure is weight of overlying air 1. about 1000 millibars, 1 kg/cm2, 14.7 lbs./in2 2. half of all atmosphere is below 5.6 km from surface (Mt. McKinley~6.2) 3. beyond 16 km, less than 10% of atmosphere remains 4. traces exist above 100 km, less than one millionth of it B. temperature variation with height 1. troposphere—mixed zone includes most weather phenomenon a. temperature decreases with height in troposphere b. average temperature change is 6.5o C/km 1) normal ‘environmental lapse rate’ 2) not consta nt, monitored by weather equipment c. average height of tropopause: 12 km 1) height varies with location and temperature 2) end of troposphere called ‘tropopause’ d. temperature and humidity can be transferred in troposphere by turbulence and mixing 2. Stratosphere a. Stratosphere lacks mixing of troposphere b. Constant temperature to about 20 km c. Gradually increases to about 50 km, at the ‘stratopause’ 1) Ozone concentrated in stratosphere absorbs UV energy 2) This absorbed energy creates the increased temperatures 3. Mesosphere a. Temperatures in mesosphere decrease with height to ~80 km b. Decreases to about ‐90o C at ‘mesopause’ 4. Thermosphere beyond mesopause a. Tiny fraction of atmosphere b. Subject to direct radiation from Sun c. Temperature increases to “1000o C”, but described by speed of molecules, not feeling of warmth, due to extremely low density VII. Sun energy heats atmosphere A. Mostly between Tropical circles, where direct rays fall 1. solstice when direct rays most poleward—June 21 and December 21 2. equinox when direct rays at equator—March 21 and September 21 3. day length varies between extre mes at solstices, equal on equinox B. seasonal variations in Sun energy from constant axial tilt toward Polaris C. additional causes of local temperature other than day length and Sun angle D. Distribution of temperatures 1. Cooler in polar areas 2. Warmest at tropics in continental areas 3. Warmness follows the direct rays of Sun: as it travels from tropic to tropic throughout year 4. Oceanic currents warm western side of ocean basins, and the continents adjacent to them 5. Oceanic currents cool eastern side of ocean basins and the continents adjacent to them. E. Heating of Atmosphere—greenhouse effect 1. Atmosphere transmits about 50% of energy received to Earth’s surface 2. Absorbed energy by Earth’s surface re‐emitted as
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