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Download Chapter 1: Introduction to the Atmosphere Weather: the state of the
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Chapter 1: Introduction to the Atmosphere Weather: the state of the atmosphere at a given time and place Climate: a description of aggregate weather conditions based on observations that have been accumulated over many decades Climate is often defined as the average weather but Climate includes average high and low conditions Climate includes record high and low conditions Weather and climate are expressed by six elements 1. temperature of the air 2. humidity of the air 3. type and amount of cloudiness 4. type and amount of precipitation 5. pressure exerted by the air 6. speed and direction of the wind The four spheres of the Earth 1. Lithosphere: the rigid outer layer of the earth (includes the crust and the uppermost part of the mantle, sometimes referring to the entire solid planet) 2. Atmosphere: the thin, gaseous envelope of air that surrounds the Earth 3. Hydrosphere: the water found in the oceans, lakes, streams, glaciers, and clouds 4. Biosphere: all the life on Earth The systems of the Earth System: any size group of interacting parts that form a complex whole Open system: matter and energy do flow into or out of the system Closed system: matter does not flow into or out of the system (while energy can) Most open systems are far more complex than most closed systems Most of Earth’s systems are open systems Feedback mechanisms: tend to enhance or resist change in natural systems Negative feedback mechanisms: tend to resist changes in natural systems As Earth’s climate warms the oceans, more clouds form which tend to cool the planet Positive feedback mechanisms: tend to enhance changes in natural systems As Earth’s climate warms, more CO2 degases from the oceans which tends to warm the planet due to the greenhouse effect Composition of the atmosphere Variable components Dust and water vapor amounts vary widely Major components (of clean dry air) 78.084 % Nitrogen (N2) 20.946 % Oxygen (O2) Argon (Ar) 0.934 % Carbon dioxide (CO2) 0.037 % Ozone depletion Ozone (O3) forms when energetic UV rays from the sun strike the oxygen (O2) in the stratosphere Ozone depletion can cause an ozone hole over Antarctica due to the decomposition of CFCs by UV which forms Cl2 which then reacts with ozone The danger is that without ozone, deadly UV rays strike the Earth Atmospheric probes Radiosondes – instrument packages sent up via balloons Rockets Airplanes Weather radar Satellites Extent of the Atmosphere Atmosphere is measured in pressure Atmospheric pressure changes constantly Standard atmospheric pressure (at sea level) is taken to be 101.325 kPa or 1013.25 millibars 50% of the atmosphere lies below 5.6 km (3.5 miles or 18 500 ft) – Mt Everest is 29 029 ft A graph of altitude vs air pressure would be inverse 5.6 km 50% 16 km 10% 100 km 0.00003% (300 ppb or .3 ppm) – better than the best vacuum on Earth Thermal structure of the atmosphere Initial studies of the lower atmosphere showed temperature decrease with increasing altitude Used kites It was assumed that T declined to -273 ºC at the edge of the atmosphere Leon Philippe Teisserenc de Bort Used balloons in 1902 Showed T leveled off between 8 and 12 km Today, we divide the atmosphere into four layers based on temperature Troposphere – 0 to 12 km Thickness is about 9 km at the poles and 16 km at the equator Environmental lapse rate: T decreases 6.5 ºC / km (on average) 20 ºC to -57 ºC Most weather events occur in the troposphere (sometimes called the weather sphere) Stratosphere – 12 to 50 km Below the tropopause, atmospheric properties are transferred by mixing Not so in the stratosphere T is constant from 12 to 20 km (-57 ºC) T rises quickly from 20 to 50 km due to ozone is concentrated here (UV heating) -57 ºC to 0 ºC Mesosphere – 50 to 80 km One of the least explored regions of our atmosphere Too low for satellites, too high for balloons T drops from 0 ºC to -90 ºC (coldest region) Thermosphere – 80 km to no defined upper limit T increases due to absorption of high energy (short λ) solar radiation by O2 and N2 T max = 1000 ºC Vertical variations in the atmosphere – in terms of composition, the atmosphere can be divided into two zones Homosphere: uniform composition (78% N2, 21% O2, 0.9% Ar, 0.037% CO2) Heterosphere: layered by composition due to different mass of each gas (N2, O – atomic, He H – atomic) Ionosphere: (80 to 400 km or 50 to 250 miles) nitrogen molecules of nitrogen and atoms of oxygen are readily ionized by high energy UV light The ions exist in three layers (from bottom to top) D, E, and F layers Ions in the D and E layers recombine at night The F layer is too rarified to recombine and lasts through the night When ions from solar flares hit the Earth’s magnetic field, they are funneled to the north and south poles where they crash into the ionosphere and form spectacular light displays called the aurora Aurora borealis (northern lights) Aurora australis (southern lights)
