The Atmosphere Composition & Structure

What do you know about it? Atmosphere? (T.B. p.206) What is its importance to us? What is its importance to the climatic system? Where is the boundary that separates the Earth from the Space? Is the thickness of the atmosphere the same on all latitude? Why or why not?

The Composition I. "permanent" gases II. “variable" gases How do they differ from each other?

The Composition I. "permanent" gases - are those with concentrations virtually constant near the earth's surface What are the two main component gases of dry air (under a theoretical atmosphere that contains no water vapour)? Are they important in affecting weather and climate?

The Composition II. “variable" gases - are those with concentrations found variable in the earth's atmosphere - except for water vapor (0-4%), each of these variable substances exists in concentrations far > than 1% by volume Quote examples of variable gases. How do they affect weather and climate?

The Composition III. Are there any solid materials in the atmosphere? What are they? Are they important in affecting weather?

The Composition is gradually changing over time due to the natural processes that occur on earth as well as the many anthropogenic processes that have been introduced by humans. Natural biological processes such as the respiration of animals, including humans, removes oxygen from the atmosphere and in turn produces carbon dioxide The photosynthesis of plants uses the carbon dioxide to produce oxygen which is released back into the atmosphere.

The Composition Other natural processes include geologic events such as volcanic eruptions. Not only do these violent eruptions eject massive amounts of particle debris into the atmosphere, but they also spew out large amounts of carbon dioxide and water vapor. While much of the atmosphere's composition is maintained by natural processes occurring on and within the earth, how human activities interact with the atmosphere has profound implications upon the quality and continuance of life on earth.

The Composition Although the percent volume of man-made substances is only a minute fraction of the total volume of the atmosphere, this amount is significant because it is this portion of the atmosphere that comprises most of what we term as pollutants. How do they change our weather?

The Structure I. Troposphere - extends from the earth’s surface to a height of about 8 km in the polar areas & km over the equatorial regions - the zone where weather phenomena & atmospheric turbulence are most marked

The Structure I. Troposphere (cont’) - this unstable layer contains most (75%) of the atmospheric water, vapour, cloud, dust and pollutants - why? - how does temperature change with height? i.e. __________ lapse rate - why?

The Structure I. Troposphere (cont’) - environmental / normal lapse rate - why? - the surface is warmed by incoming solar radiation which in turn heats the air next to it by conduction - pressures in this layer falls as the effect of gravity decreases - but wind speeds usually increases with height (why?)

The Structure I. Troposphere (cont’) - the tropopause - the upper limit to the earth’s climate and weather - as marked by an isothermal layer - where temperatures remain constant despite any increase in height

The Structure II. Stratosphere - extends upwards from the tropopause to about 50 km - which is characterised by a steady increase in temperature - why? the process involved?

The Structure II. Stratosphere (cont’) - winds are light in the lower parts - pressure continues to fall - the air is dry - it acts as a protective shield against meteorites which usually burn them- selves out as they enter the earth’s gravitational field

The Structure II. Stratosphere (cont’) - the stratopause: - another isothermal layer - where temperatures do not change with an increase in height

The Structure III. Mesosphere - temperatures fall rapidly - why?

The Structure III. Mesosphere - temperatures fall rapidly - why? - as there is no water vapour, cloud, dust or ozone to absorb incoming radiation - this layer has the lowest temperatures (how low?) - and the strongest wind speed of nearly 3000 km/h in the atmosphere

The Structure III. Mesosphere (cont’) Examples of different speeds (Adopted from Wikipedia) Main article: Orders of magnitude (speed)Orders of magnitude (speed) Speed of a common snail = m/s; km/h; mph (1 millimeter per second).snail A brisk walk = 1.7 m/s; 6 km/h; 4 mph (5.5 feet per second).walk OlympicOlympic sprinters (average speed over 100 metres) = 10 m/s; 36 km/h; 22 mph.sprinters Speed limit on a French autoroute = 36 m/s; 130 km/h; 80 mph.Frenchautoroute Taipei 101Taipei 101 observatory elevator = 1010 m/min ; 16.7 m/s ; 60.6 km/h; 37.6 mph Cruising speed of a Boeing = 290 m/s; 1050 km/h; 650 mph; (Mach 0.85)Boeing 747-8Mach The speed of sound in dry air at sea-level pressure and 20 °C (293 kelvin) = 343 ms-1 ≈ 1235 km/h ≈ 768 mph ( = Mach 1 by definition).speed of soundkelvin Official flight airspeed record = 980 m/s; 3,530 km/h; 2,194 mph.flight airspeed record Escape velocityEscape velocity on Earth: 11.2 km/s Space shuttleSpace shuttle on re-entry = 7,800 m/s; 28,000 km/h; 17,500 mph. Average orbital speed of planet Earth = 29,783 m/s; 107,218 km/h; 66,623 mph.Earth Speed of lightSpeed of light in vacuum (symbol c) 299,792,458 m/s (exactly, by definition).vacuum

The Structure IV. Thermosphere - extending from the mesopause and having no well-defined upper limit - temperatures rise rapidly with height, perhaps reaching 1500 o C - why?

The Structure IV. Thermosphere - extending from the mesopause and having no well-defined upper limit - temperatures rise rapidly with height, perhaps reaching 1500 o C - why? Due to an increasing proportion of atomic oxygen in the atmosphere which, like ozone, absorbs incoming ultra-violet radiation.

The Structure IV. Thermosphere (cont’) Aurora in Alaska

The Structure IV. Thermosphere (cont’) Communication

Conclusion What have we learned about our atmosphere concerning its - composition ? - structure? - relative important to our study of weather and climate?