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Transcript
The Atmosphere: Climate and Weather John Todd 6 lecture mini-series Teaching Goals • Stimulate your interest in this subject • Basic understanding of main processes: energy flow, air movement, water cycle, air pressure • Present some of the terminology • Demonstrate where climate/meteorology is useful across many disciplines Your Lecturer • PhD in atmospheric physics • Interest in atmospheric transmission as an astronomer • Air pollution control (Dept of Env) • Lecturing Environmental Studies – Interdisciplinary • First time with this class Jobs • Competitive advantage • Core Business – – – – – – – Meteorologist Architect Engineer Pollution control Farmer Fisher Renewable energy – – – – Sailor Commodity trading Insurance Outdoor sports • Assists understanding – – – – – Sociologists Psychiatrists Medical science Fashion design Novelist Mini-Series on Weather and Climate 1. 2. 3. 4. 5. 6. Atmosphere: composition, temperature Radiant energy flows, seasons Global circulation Water cycle Weather Human changes to atmosphere The Atmosphere: composition, structure and temperature • Chapter 3 of Christopherson • Need to know – Magnitude – Changes with height – Main gases The Atmosphere • How thick? – 10km, 480km, 32,000+km • How much? – 5x1015tonnes – 1 million t each! • What is it? – Nitrogen and oxygen – H2O, CO2 12,700km Pressure • Air behaves like any gas – it is compressible, hence it becomes denser near the Earth’s surface. – – – – – – At sea level pressure of about 1kg/cm2 Measured as hectopascal (1013 hPa) [1hPa=1mb] Drops about 1hPa per 10m near sea level By 16km down to 100hPa, by 32km down to 10hPa This means most air (75%) is below 16km Mt Everest (8850m) ~ 300hPa (i.e. 1/3 the oxygen) Temperature • In troposphere (up to about 16km) temperature decreases with height by about 1oC every 150m. • Gas laws: reduce pressure lower temp. – Important from pollution perspective • Higher up more heating by sun A tm o s p h e ric te m p e ra tu re p ro file 120 TH E R M O S P H E R E 100 M e s o p a us e M E S OS P HE RE 60 O zo ne la ye r S tra to p a us e 40 S TR A TO S P H E R E 20 Tro p o p a us e TR O P O S P H E R E -1 0 0 -8 0 0 -6 0 -4 0 -2 0 d e g re e s C 0 20 40 Altitude km 80 Upper layers • Exosphere (above 480km) – Outer reaches, Earth’s influence detectable, essentially ‘outer space’, satellites • Thermosphere (about 80 to 480km) – Extremely thin atmosphere, aurora, meteors, temperature not as we would sense it • Mesosphere (about 50 to 80km) – Cooling because not much air to heat Noctilucent clouds Below 50km • Stratosphere (about 18 to 50km) – Temperature rise due to absorption of solar UV – Ozone layer – Little mixing from below • Troposphere (below about 16km equator and 8km at poles) – Well mixed – Most clouds, water vapour , dust, pollutants – Weather A tm o s p h e ric te m p e ra tu re p ro file 120 TH E R M O S P H E R E 100 M e s o p a us e M E S OS P HE RE 60 O zo ne la ye r S tra to p a us e 40 S TR A TO S P H E R E 20 Tro p o p a us e TR O P O S P H E R E -1 0 0 -8 0 0 -6 0 -4 0 -2 0 d e g re e s C 0 20 40 Altitude km 80 Composition in Troposphere Gas Per cent Nitrogen 78 Oxygen 21 Water vapour Argon up to 3.5 Variable Rad. Active Yes (UV) very yes yes yes yes yes 0.9 Carbon dioxide 0.035 Neon 0.002 Helium 0.0005 Ozone 0.00006 Hydrogen 0.00005 Nitrogen dioxide Trace Krypton Trace yes Pollutants • Waste from human activities • Combustion – CO, NOx, SO2, ‘air toxics’, ….. • Evaporation – Volatile organic compounds, petrol, ….. • Direct discharge – CFCs, odour, CH4, …… Inversions Prevent Dispersion • Inversion Prevents the air mixing upwards TEMPERATURE Summary • Atmospheric composition – Mainly N2 and O2, some variable, some radiatively active, pollutants • Pressure – Air follows gas laws • Temperature – Decrease ~6.5oC per km in troposphere • Terminology – Troposphere, etc., lapse rate, see handout Next Week • • • • • RADIATION BALANCE Incoming solar radiation Outgoing long-wave radiation How this interacts with the atmosphere The seasons • CHAPTERS 2 & 4 of CHRISTOPHERSON