1. The Atmosphere Origin, Composition & Structure

2. Evolution of the Atmosphere Primary Atmosphere 4.5 by –Just formed Earth: Like Earth, the hydrogen (H 2 ) and helium (He) were very warm. These molecules of gas moved so fast they escaped Earth's gravity and eventually all drifted off into space.

3. Evolution of Secondary Atmosphere 3.8 by: Volcanoes release gases such as: H 2 O (water) as steam, carbon dioxide (CO 2 ), and ammonia (NH 3 ). Carbon dioxide dissolved in seawater. Bombardment by icy comets 3.6 by: Earth cools and water vapor condenses to form early oceans Oxygen begins to accumulate some is used to form ozone but most is taken up by rock formation. CO2 starts to decline because it is easily dissolved in oceans and becomes locked up in rock formation. 3.5 by: Chemosynthetic organisms arrive on the scene. Ammonia (NH3) molecules in the atmosphere are broken apart by sunlight, leaving nitrogen and hydrogen. Hydrogen, being the lightest element, rose to the top of the atmosphere and much of it eventually drifted off into space.

4. Volcanic Outgassing Atmosphere & Oceans are byproducts of heating and differentiation: as earth warmed and partially melted, water locked in the minerals as hydrogen and oxygen was released and carried to the surface by volcanic venting activity

5. Early Secondary Atmosphere Cont. Much of the CO 2 dissolved into the oceans. 700: my: Cyanobacteria evolve that uses even more CO 2 for photosynthesis giving off oxygen as a byproduct. 600 my: Plants begin to appear on land as well as soft bodied fauna and oxygen continues to build in the atmosphere. Oxygen builds up in the atmosphere forming a good protective layer of ozone, while the carbon dioxide levels continue to drop. 350 my: Land plant explode onto the scene polluting the atmosphere with oxygen.

6. Present ATMOSPHERE Present Composition –78% Nitrogen; 21% Oxygen; trace amounts of CO 2, Argon, ect. Earth systems cycle and release atmospheric gases through volcanoes and interactions between gases and the solid Earth & Oceans as well as biotic component Ozone (O 3 ): produced by photochemical Rx absorbs harmful UV radiation

7. N 2 retained in atmosphere, H 2 O vapor lost by condensation to ocean; CO 2 combined with Ca & Mg to form carbonate Rks; H 2 lost to space

8. Oxygen in the Atmosphere Earth only planet in solar system with oxygen thus only planet able to sustain higher forms of life Oxygen produced by –Photosynthesis- algae and plants –Photolysis-fragmentation of water molecules into Hydrogen and Oxygen Oxygen consumed by –Respiration –Decay –Weathering (chemical oxidation)

9. Today’s Atmosphere Comprised of a mixture of invisible permanent and variable gases as well as suspended microscopic particles (both liquid and solid) –Permanent Gases – Form a constant proportion of the total atmospheric mass –Variable Gases – Distribution and concentration varies in space and time –Aerosols – Suspended particles and liquid droplets (excluding cloud droplets)

10. Atmospheric Gases

11. Aerosols (or Particulates) Small (or “tiny”) solid particles or liquid droplets (excluding clouds and rain) Aerosols can be man-made (anthropogenic) or naturally occurring (like ocean salt, dust, plant emissions) Aerosols are not synonymous with pollution Some aerosols are very beneficial and, in fact, are required for precipitation processes to occur.

12. Structure of the Atmosphere The atmosphere is a reasonably well-mixed envelope of gases roughly 80 km (54 mi) thick called the HOMOSPHERE. Above 80 Km the gases are stratified such that the heavier gases decrease much more rapidly than the lighter ones; this is the HETEROSPHERE Because of the shallowness of the atmosphere, its motions over large areas are primarily horizontal. It transports and recycles water and nutrients. Typically, horizontal wind speeds are a thousands time greater than vertical wind speeds. In addition, we can identify four layers in the atmosphere that have distinct characteristics. The four layers of the atmosphere, in order from lowest to highest elevation, are: –the troposphere, –the stratosphere, –the mesosphere, –the thermosphere

13. Homosphere and Heterosphere Homosphere: Turbulent mixing causes atmospheric composition to be fairly homogenous from surface to ~80-100 km (i.e., 78% N 2, 21% O 2 ) Heterosphere: Above ~80-100km, much lower density, molecular collisions much less, heavier molecules (e.g., N 2, O 2 ) settle lower, lighter molecules (e.g., H 2, He) float to top

15. Permanent Gases 78% Nitrogen (N 2 ) 21% Oxygen (O 2 ) <1% Argon (Ar) Relative percentages of the permanent gases remain constant up to 80-100km high (~ 60 miles!) –This layer is referred to as the Homosphere (implies gases are relatively homogeneous)

16. Layers of the Atmosphere Troposphere (“overturning” sphere) -contains 80% of the mass -surface heated by solar radiation -strong vertical motion -where most weather events occur Stratosphere (“layer” sphere) -weak vertical motions -dominated by radiative processes -heated by ozone absorption of solar Ultraviolet (UV) radiation -warmest (coldest) temperatures at summer (winter) pole Mesosphere (“in-between” sphere) -heated by solar radiation at the base -heat dispersed upward by vertical motion Thermosphere (“heated” sphere) -very little mass

17. The Troposphere The density of the atmosphere decreases rapidly with increasing height. The troposphere has the following characteristics: –it is about 12 km (7 mi) thick, –the temperature decreases rapidly with altitude, –the mean temperatures at the bottom and top are 16°C & -60°C, –it is heated from below by conduction and from condensation of water vapor, –it is the region where you find precipitation, evaporation, rapid convection, the major wind systems, and clouds, and –it is the densest layer of the atmosphere.

18. The Tropopause/Stratosphere Above the troposphere is a region of relatively constant temperature, -60°C, about 10 km (6 mi) thick called the tropopause. This is where high velocity winds (jet streams) occur. The stratosphere has the following characteristics: –it is about 28 km (17 mi) thick, –the temperature increases with altitude from about -60°C to 0°C, –this is where ozone, an unstable form of oxygen, appears, –it is heated as the ozone absorbs incoming ultraviolet radiation.

19. Stratosphere/Stratopause The stratosphere offers clear, smooth conditions for flying No air exchange between it and troposphere Gases and aerosols can persist for months or years triggering short term climatic variations A constant temperature condition is described as isothermal The stratopause is at 0 o C

20. Mesosphere/Mesopause/Thermosphere Mesosphere temperatures fall with increasisng altitude until they reach the Mesopause at 80Km and -95 o C Above the mesopause is the Thermosphere where temperatures are isothermal for 10Km then rise rapidly with increasing altitude The thermosphere is very sensitive to incoming solar radiation

21. The Ionosphere From between 70 and 80Km in the Thermosphere to an indefinite altitude in the Thermosphere High concentration of ions of Oxygen and Nitrogen Solar wind strips electrons from these atoms and molecules

22. Ionosphere

23. Aurora Australis NASA Images from Space

24. Measuring the Atmosphere: Historical Perspective Rainfall measured in India using rain gauges 400 BCE Aristotle’s Meteorologica (350-340 BCE) Galileo invented the thermoscope (thermometer) 1592 Torricelli invents mercury barometer 1643

25. Galileo & Torricelli

26. Monitoring the Atmosphere

27. Upper Air Observations A three-dimensional picture of temperature, pressure, relative humidity, and wind speed and direction in the atmosphere is essential for weather forecasting and meteorological research During the latter part of the 19th century and the first quarter of the 20th century, this information was obtained mainly by meteorographs sent aloft on tethered kites, which automatically recorded, on a single sheet, the measurements of two or more meteorological parameters such as air pressure, temperature, and humidity

28. Monitoring the Atmosphere Kites & the Radiosonde

29. The Radiosonde The radiosonde is a small, expendable instrument package that is suspended below a large balloon filled with hydrogen or helium. The radiosonde consists of sensors coupled to a radio transmitter and assembled in a lightweight box. The meteorological sensors sample the ambient temperature, relative humidity, and pressure of the air through which it rises. As the radiosonde is carried aloft, sensors on the radiosonde measure profiles of pressure, temperature, and humidity. These sensors are linked to a battery powered, 300 milliwatt radio transmitter that sends the sensor measurements to a sensitive ground receiver.

30. Worldwide, there are more than 900 upper-air observation stations using 15 major types of radiosondes. Most stations are located in the Northern Hemisphere and all observations are taken at the same times each day at 00:00 and 12:00 UTC (Greenwich Mean Time), 365 days per year. Observations are made by the NWS at 93 stations - 72 in the conterminous United States, 13 in Alaska, 10 in the Pacific, and 1 in Puerto Rico

31. The Radiosonde During the flight train's ascent, the radiosonde continuously transmits temperature, relative humidity, and pressure readings to the ground-based Radiosonde Tracking System which is housed in a fiberglass dome above the inflation shelter. Wind speed and direction are determined for each minute of the flight, generally 90 minutes. They are determined from changes in the position and direction of the flight train as detected by the Radiosonde Tracking System. When winds are incorporated into the observation, it is termed a rawinsonde observation, and all National Weather Service upper air stations take rawinsonde observations

32. Monitoring the Atmosphere Those observations that reach the bursting altitude of the regular 600-gram balloon attain an average height slightly in excess of 90,000 feet. The average bursting altitude for stations using the larger 1,200-gram balloon exceeds 100,000 feet

33. Radiosonde Approximately one-third of the radiosondes released by the National Weather Service are found and returned to the Instrument Reconditioning Branch in Kansas City, Missouri, They are repaired and reissued for further use, some as many as seven times. Instructions printed on the radiosonde explain the use of the instrument, state the approximate height reached, and request the finder to mail the radiosonde, postage free

34. Other Monitoring Radar Satellites