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Simon Fraser University
GEOG 214
Owen Hertzman

Lecture Notes GEOG 214 Lecture 1 Lecture 1: The Earth’s Atmosphere Objectives: 1. Define concepts of meteorology, weather and climate 2. Identify major permanent and variable gases in the Earth’s present-day atmosphere, and identify major sources and sinks of these gases. 3. Describe the evolution of Earth’s atmosphere 4. Describe the average vertical structure of density, pressure, and temperature in the atmosphere 5. Identify and describe the four atmospheric layers defined by temperature structure 6. Describe the ionosphere and its significance to radio communication 1.0 Weather and Climate • Meteorology is the study of the atmosphere and its phenomena ▯ From Greek meteoros, meaning “high in the atmosphere” • Weather defined as condition of atmosphere at a particular place at a particular time ▯ Weather comprised of following elements: air temperature, air pressure, humidity, clouds, precipitation, visibility, winds • Climate defined as atmospheric condition at a particular place averaged over a specific period of time (typically > 1 year) 1.1 Earth’s Atmosphere Today • Average radius of Earth ~ 6400 km • 99% of the Earth’s atmosphere lies within 30 km of the Earth’s surface. ▯ The atmosphere is a thin layer around the solid earth, with horizontal scales much greater than vertical scales. • There’s no upper limit to the atmosphere; it becomes thinner and thinner, eventually merging with empty space. 1.1.1 Composition of the Atmosphere • Local composition of atmosphere determined by local production (sources) and destruction (sinks) of atmospheric gases, as well as transport and diffusion. • Permanent gas concentrations vary only over geological timescales (i.e. timescales > 100,000 years). Most abundant permanent gases: nitrogen (N ; 78%)2and oxygen (O 2 21%). • Variable gases vary in space and time. • Variable gases are: water vapour (H O)2 carbon dioxide (CO ), m2thane (CH ), 4 nitrous oxide (N O), ozone (O ), particles (e.g. dust, soot), chlorofluorocarbons 2 3 (CFCs). • Concentration of carbon dioxide, methane, nitrous oxide, chlorofluorocarbons small (< 0.1%) ▯ trace gases • Important class of variable gases are atmospheric pollutants, defined as substances harmful to humans, animals and/or plants; pollutants are introduced into the air by anthropogenic (human-produced) and natural processes (e.g. volcanoes, forest fires) ▯ 1 Lecture Notes GEOG 214 Lecture 1 • Water vapour (H O): 2 ▯ highest concentration in tropical regions, generally decreases with altitude and toward poles ▯ water exists in atmosphere as gas (water vapour), liquid (cloud droplets), solid (ice crystals). ▯ change from gas to liquid: condensation; change from liquid to gas: evaporation ▯ very important atmospheric gas (primary subject of lecture #4): condensation releases large amounts of heat (latent heat) which is large source of atmospheric energy; water vapour potent greenhouse gas. • Carbon dioxide (CO ): 2 ▯ atmospheric sources: respiration (decay of vegetation), oceanic emissions, volcanic outgassing, combustion of fossil fuels, deforestation, biomass burning ▯ sinks: photosynthesis, dissolution in ocean water; the ocean holds ~50 times as much CO as 2he atmosphere! ▯ important greenhouse gas ▯ Varies on seasonal timescales as vegetation grows in spring/summer and decays in autumn/winter; concentration lower in Northern Hemisphere summer because of greater local biomass. ▯ Concentration now 24% higher than in 1958 (increase from 315 to 390 ppm). Increase due to burning of fossil fuels and deforestation. • Methane (CH ): 4 ▯ Sources: Anaerobic biological activity (cattle, rice fields, wetlands, landfills), fossil fuel burning ▯ Sink: reaction with hydroxil (OH) radicals ▯ Concentrations have doubled since the beginning of the industrial era; increase has slowed over past few years ▯ Potent greenhouse gas • Nitrous oxide (N O2: ▯ Sources: Bacterial and microbial processes in soil, biomass burning ▯ Sink: destruction by ultraviolet light (photolysis) ▯ Greenhouse gas • Chlorofluorocarbons (CFCs): ▯ Anthropogenic molecules ▯ Used in spray-can propellant, refrigerator coolant, solvent ▯ Only weakly reactive, therefore long-lived ▯ Greenhouse gases, participate in stratospheric ozone destruction • Surface Ozone (O ): 3 ▯ Sources: photochemical reactions (reactions that take place in the presence of sunlight) ▯ Tropospheric ozone is pollutant; irritates eyes and throat, damages vegetation ▯ Primary ingredient of photochemical smog (also known as Los Angeles-type smog) • Stratospheric Ozone (O ): 3 ▯ 97% of atmospheric ozone resides in upper atmosphere (stratosphere). ▯ Produced naturally by photochemical reactions ▯ Shields earth surface from ultraviolet radiation ▯ Concentration has been decreasing, particularly over Antarctica (ozone hole) due to effect of chlorofluorocarbons (CFCs) ▯ 2 Lecture Notes GEOG 214 Lecture 1 • Aerosols: ▯ Suspended solid or liquid particles (e.g. saltwater drops, soot, ash, dust, pollen)
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