AMS Weather Studies Introduction to Atmospheric Science, 5 th Edition

1. AMS Weather StudiesIntroduction to Atmospheric Science, 5th Edition Chapter 2 Atmosphere: Origin, Composition, & Structure

2. Driving Question • What is the composition and structure of the atmosphere? • This chapter covers: • Evolution of the atmosphere • Investigation of the atmosphere • How meteorologists monitor the atmosphere • Surface and upper-air observations and remote sensing • The temperature profile of the atmosphere • Electromagnetic characteristics of the upper atmosphere

3. Atmosphere viewed from space

4. Case-in-PointAfrican Origins of Wind-Borne Dust in the Americas • Weather and climatic issues in one part of the world can affect those in another part. • North African dust storms can affect the weather and air quality of the southeastern U.S. • Dust can harbor microscopic disease-causing organisms. • This dust may be harming coral reefs in the Caribbean. • This dust may increase the frequency of red tides.

5. Evolution of the Atmosphere • Earth System • Made up of atmosphere, hydrosphere, geopshere, biosphere • Atmosphere • Composed of gases and suspended particles • Half of mass found within 5500 m (18,000 ft) of Earth’s surface. • 99% of the mass is below 32 km (20 mi)

6. Evolution of the Atmosphere • Primeval Phase • Earth evolved from a nebula • Gases surrounding Earth were primarily helium and hydrogen • Also hydrogen compounds, including methane and ammonia • Eventually, these escaped to space • 4.4 billion years ago, enough gravity to retain an atmosphere • Outgassing – principal source of Earth’s atmosphere • Rocks outgassed as they solidified and cooled • Primarily carbon dioxide, nitrogen and water vapor • Trace amounts of methane, ammonia, sulfur dioxide, hydrogen sulfide and hydrochloric acid • Water vapor broken into hydrogen and oxygen by UV radiation The Eagle Nebula Outgassing

7. Evolution of the Atmosphere • Primeval Phase • 4.5-2.5 billion years ago, sun 30% fainter • CO2 combined with rainwater to form carbonic acid • Reacted with rock, locking carbon into solid, so less in atmosphere • Living organisms took CO2 out of the atmosphere via photosynthesis, locking carbon into carbohydrates • Oxygen the 2nd most abundant gas in atmosphere • Nitrogen is the 1st • Inert, out-gassing product • Nitrogen removed from atmosphere by biological and atmospheric fixation • CO2 minor component of atmosphere for the last 3.5 billion years • Fluctuations play important roles in climate change

8. Evolution of the Atmosphere • Modern Phase • Lower atmosphere (80 km or 50 mi) circulates, maintains uniform ratios of gasses (homosphere) • Above this, gases separate based on weight • Results in stratified layers • Heterosphere • Nitrogen ~78.08%, Oxygen ~20.95% of the homosphere • Argon < 1% • CO2 < 0.04% • Oxygen • O2 in the homosphere • O in the heterosphere • 150 km (95 miles) above Earth’s surface • UV radiation splits O2

9. Evolution of the Atmosphere Note: Water vapor varies greatly by location and so is not included.

10. Evolution of the Atmosphere • Modern Phase • Earth’s atmosphere also has aerosols • Liquid and solid particles • Sources: wind erosion of soil, ocean spray, forest fires, volcanic eruptions, agricultural & industrial activities • Water vapor • By volume: < 4% of the lowest 1 km of the atmosphere • Necessary for clouds and precipitation • CO2 required for essential function to all life (photosynthesis) • Both CO2 and water vapor absorb and emit infrared radiation • Keeps the lower atmosphere warm • Allows for life to exist

11. Evolution of the Atmosphere • Air pollution • Gas or aerosol that occurs at a concentration threatening the well-being of living organisms • Most are human-made, some are natural • Dust storms, volcanoes, pollen, decay of plants/animals • Primary air pollutants • Harmful immediately as emitted • Secondary air pollutants • Harmful after combination with one or more substances • Photochemical smog Coal-fired electric power plant in Green Bay, WI. Smog near Los Angeles, CA.

12. Evolution of the Atmosphere • The Environmental Protection Agency (EPA) • Standards for 6 air pollutants: • carbon monoxide ■ lead ■ ozone • nitrogen oxides ■ particulates ■ sulfur dioxide • Primary air quality standards • Maximum exposure levels humans can tolerate without ill effects • Secondary air quality standards • Maximum exposure levels allowable to minimize the impact on crops, visibility, personal comfort, and climate • Compliance with standards • Attainment areas – geographic regions where standards are met or below • Non-attainment areas – geographic regions where the primary standard is not met

13. Investigating the Atmosphere • Scientific method • Identify questions related to the problem • Propose an answer • This is an educated guess • State the educated guess in a manner that can be tested • This is the hypothesis • Predict the outcome as if the hypothesis were correct • Test the hypothesis to see if the prediction is correct • Reject or revise the hypothesis if the prediction is wrong • Scientific theory – hypothesis accepted by the scientific community

14. Investigating the Atmosphere • Scientific models • Approximations or simulations of real system • Scientific models of the Earth-atmosphere system • Conceptual model • Statement of a fundamental law or relationship • Example: the geostrophic wind model • Graphical model • Compiles and displays data in a format that readily conveys meaning • Example: a weather map • Physical model • Miniaturized version of a system • Example: a tornado vortex chamber

15. Investigating the Atmosphere Purdue University's Tornado Vortex Chamber (A), which simulates tornadoes (B). This is a physical model.

16. Investigating the Atmosphere • Scientific models of the Earth-atmosphere system • Numerical Models • Used by meteorologists • Mathematical equations represent relationships among system variables • Example: a global climate model and rising CO2 • All other climate variables are held constant • CO2 is increased • Results are noted • All models have inherent errors • Missing/erroneous observational data • Accuracy of component equations may be a problem

17. Monitoring the AtmosphereHistorical Perspective • Surface Observations • Systematic observations as 1644-45 (in North America) • Old Swedes Fort (Wilmington, DE) had 1st systematic observations • Long-term instrument-based temperature records • 1732: Philadelphia, 1738; Charleston, SC; 1753: Cambridge, MA; 1781: New Haven, CT (uninterrupted to today) • 1814: Army monitored weather to understand troop health • Mid-1800s: national network of volunteer observers • 1849: telegraph companies transmitted weather conditions free of charge • 1860s: loss of ships in Great Lakes • Government took a greater role in forecasting. • 1870: President Grant established 24 stations under the U.S. Army Signal Corps

18. Monitoring the Atmosphere • Surface Observations • 1891: nation’s weather network transferred from military to civilian • New weather bureau under U.S. Department of Agriculture • 1940: Transferred to Commerce Department • 1965: Weather Bureau reorganized into National Weather Service (NWS) • Under Environmental Science Services Administration (ESSA), which became National Oceanic and Atmospheric Administration (NOAA) • 1990s: NWS modernized and expanded • Today, 123 NWS Forecast Offices. • Added Automated Surface Observing Systems (ASOS)

19. Monitoring the Atmosphere • Automated Surface Observing System (ASOS) • Consists of electronic sensors, computers, fully automated communications ports • Feeds data to NWS Forecast Offices 24 hours a day

20. Monitoring the Atmosphere • NWS Cooperative Observer Network • Member stations record daily precipitation, maximum and minimum temperatures • Used for hydrologic, agricultural, climatic purposes 20

21. Monitoring the WeatherHistorical Perspective • Upper air observation • Kites • 1749: Glasgow, Scotland, Alexander Wilson • Balloons • Manned balloon, 1804, Gay-Lussac & Biot • Air samples taken, measured temperature, humidity • Up to 7,000 m (23,000 ft) • Manned balloon, 1862, Glaisher & Coxwell • Weather measurements to 7600 m (25,000 ft) • Nearly perished from cold and oxygen deprivation • Kites • 1894: carried the first thermograph aloft • 1907-1933: box kites with meteorographs • Up to 3000 m (10,000 ft)

22. Monitoring the WeatherHistorical Perspective • Upper air observations • First radiosonde in the late 1920s. • Small instrument package equipped with a radio transmitter • Carried aloft by a helium or hydrogen filled balloon • Allowed for monitoring at higher altitudes • Transmits altitude readings of temperature, air pressure, and dewpoint • First official U.S. Weather Bureau radiosonde launched at East Boston, MA in 1937. • A radiosonde tracked from the ground to measure variations in wind direction/speed with altitude is a rawinsonde

23. Monitoring the Atmosphere Temperature Sensor GPS Pressure Sensor Launching a radiosonde Radiosonde

24. Monitoring the Atmosphere Data from radiosonde shown in a Stüve diagram

25. Monitoring the Atmosphere • Remote Sensing • Measurement of environmental conditions by processing signals either emitted by an object or reflected back to a signal source • Radar • Satellites

26. Temperature Profile of the Atmosphere

27. Temperature Profile of the Atmosphere • Troposphere • Lowest layer • Weather occurs within • Temperature decreases with altitude • Exceptions: inversion, isothermal layer • Average temperature drop is 6.5 °C/1000 m (3.5 °F/1000 ft) • ~6 km (3.7 mi) thick at the poles • ~20 km (12 mi) thick at the equator • Tropopause • Transition zone to next layer It is generally colder on mountain peaks than in lowlands.

28. Temperature Profile of the Atmosphere • Stratosphere • From troposphere to ~50 km (30 mi) • In isothermal condition in lower stratosphere • Constant temperature constant • Above 20 km (12 mi), temperature increases with altitude • Stable conditions ideal for jet aircraft travel • Trap pollutants (e.g. from volcanic eruptions) in lower stratosphere • Stratopause – transition zone to next layer • Mesosphere • From stratopause up to about 80 km (50 mi) • Temperature decreases with increasing altitude • Mesosphere – transition zone to next layer • Thermosphere • Temperatures isothermal initially then rise rapidly • Sensitive to incoming solar radiation • More variable than in other regions

29. The Ionosphere and the Aurora • Ionosphere • Located mostly in thermosphere. • High concentration of ions and electrons • Electrically-charged, atomic-scale particles • Caused by solar energy stripping electrons from oxygen and nitrogen molecules • Leaves a positive charge • Auroras are found in ionosphere. • Caused by solar wind • Sub-atomic, super-hot, electrically charged particles • Earth’s magnetic field deflects the solar wind • Makes a teardrop-shaped cavity known as the magnetosphere • Auroras are only visible at higher latitudes

30. The Ionosphere and the Aurora Average variation of particle density with altitude in the ionosphere

31. The Ionosphere and the Aurora • Magnetosphere • Caused by the deflection of the solar wind by Earth’s magnetic field Aurora borealis

32. The Ionosphere and the Aurora The Northern Hemisphere auroral oval, an area of continuous auroral activity.