12Thickness, Composition & Thermal Structure of the Atmosphere Thickness = pressure and density of air decrease with elevationChemical composition = elements (gasses) that make up air and remain nearly constant (so ignoring water, aerosols [very fine dust], pollution)Thermal Structure = How temperature changes with elevation in the atmosphere
13Atmosphere Thickness and Pressure Pressure is caused by weight of air above, so pressure decreases with altitudePressure compresses air, so air becomes less dense or ‘thinner’ with altitudeAtmosphere has no distinct top; it just becomes less and less dense until for practical purposes there is no air, above ~ 100 kmNote: 1 km = 0.62 miles
14Atmosphere Thickness and Pressure Sealevel Pressure =14.7 lb/in2 or 1013 mb or 29.9 inches (of mercury)Orem Pressure =12.5 lb/in2 or 855 mbWhere is the air?50% below 6km altitude90% below about 18km% above 100km
15Composition of the Atmosphere Below ~ 80 km altitude; Ionosphere exists higher Oxygen gas = O2Nitrogen gas = N2
16Gasses in Dry Air N2 (‘Nitrogen’) – 78% O2 (‘Oxygen’) – 21% Ar (Argon)– 1%CO2 (Carbon dioxide) – 0.37%Ne (Neon), He (Helium), CH4 (Methane), Kr (Krypton), H2 (Hydrogen) – < 0.002%
17Other, Variable Components of Air Water Vapor (H20) – 0 to 4%Aerosols (dust)Ozone (03)All are important!
20Aerosols Examples include dust and air pollution Aerosols are variable in concentration and location
21Ionosphere Exists above ~ 80 km Radiation from Sun knocks electrons off gas molecules & atoms, ionizing themIonosphere protects lower atmosphere from radiation by absorbing the energy (meaning we need it!)
22Thermal Structure of the Atmosphere Temperature changes with altitude create 4 distinct layers to the atmosphere:Thermosphere – Above stratos.; T increase w/ heightMesosphere – Above stratosphere to ~ 90 km; T decreases w/ heightStratosphere – Above troposphere to ~ 50 km; T increases w/ heightTroposphere – Ground to 10 – 15 km altitude; T decreases w/ height. Weather happens in this layer!
23Temperature in Troposphere and lower Stratosphere