Air, Weather, and Climate

1. Air, Weather, and Climate Chapter 17 Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

2. Outline: • Composition and Structure of the Atmosphere • Weather Engine • Solar Radiation • Weather • Jet Streams • Cyclonic Storms • Climate • El Nino • Climate Change Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

3. COMPOSITION AND STRUCTURE OF THE ATMOSPHERE • Weather - A description of physical conditions of the atmosphere. • Climate - A description of the long-term weather pattern in a particular area. • Weather and climate are primary determinants of biomes and ecosystem distribution. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

4. Past and Present Composition • Many geochemists believe the earth’s earliest atmosphere was made up of mainly hydrogen and helium. • Volcanic emissions have added carbon, nitrogen, oxygen, and sulfur. • Virtually all oxygen was produced by photosynthesis. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

5. A Layered Envelope • Troposphere • Ranges in depth from 12.5 km over the equator to 8.0 km over the poles. • All weather occurs here. • Composition is relatively uniform. • Air temperature drops rapidly with increasing altitude. • Tropopause - Transition boundary that limits mixing between the troposphere and upper zones. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

6. A Layered Envelope • Stratosphere • Extends from troposphere to about 45 km. • Air temperature is stable, or increases with altitude. • Fraction of water vapor is 1000x less and ozone is 1000x more than in the troposphere. • Relatively calm Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

7. A Layered Envelope • Mesosphere • Middle Layer. • Minimum temperature is about - 80o C. • Thermosphere • Extends to about 1,600 km. • Ionized gases and high temperatures. • Ionosphere - Lower Thermosphere • Aurora borealis (northern lights) Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

8. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

9. THE GREAT WEATHER ENGINE • Solar Radiation • Incoming solar energy at the top of the atmosphere averages about 1,330 watts/m3. • About half is reflected or absorbed by atmosphere. • Amount reaching earth’s surface is at least 10,000 times greater than all installed electric capacity in the world. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

10. Solar Radiation • Visible light passes through atmosphere undiminished. • Ultraviolet light is absorbed by ozone in the stratosphere. • Infrared radiation is absorbed by carbon dioxide and water in the troposphere. • Albedo - Reflectivity • Fresh clean snow 90% • Dark soil 3% • Net average of earth 30% Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

11. Solar Radiation Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

12. Solar Radiation • Most solar energy reaching the earth is visible light. • Energy reemitted by the earth is mainly infrared radiation (heat energy). • Longer wavelengths are absorbed in the lower atmosphere, trapping heat close to the earth’s surface. • Greenhouse Effect • Increasing atmospheric CO2 due to human activities appears to be causing global warming. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

13. Convection Currents and Latent Heat • Lighter air rises and is replaced by cooler, heavier air, resulting in vertical convection currents. • Transport energy and redistribute heat. • Much of solar energy absorbed by the earth is used to evaporate water. • Energy stored in water vapor as latent heat. • If condensation nuclei are present, or if temperatures are low enough, condensation will lead to precipitation. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

14. Convection Currents • Releasing latent heat causes air to rise, cool, and lose more water vapor. • Rising, expanding air creates an area of relatively high pressure at the top of the convection column. • Air flows out of high-pressure zone towards areas of low-pressure, where cool, dry air is subsiding. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

15. Convection Currents • Subsiding air is compressed as it approaches the earth’s surface where it piles up and creates an area of high pressure at the surface. • Air flows out of this region back towards low pressure, closing the cycle. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

16. Convection Currents Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

17. WEATHER • Energy Balance • Solar energy is unevenly distributed. • Sun strikes the equator directly all year. • Earth’s axis is tilted. • Energy imbalance is evened out by movement of air and water vapor in the atmosphere and by liquid water in rivers and ocean currents. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

18. Convection Cells and Prevailing Winds • As air warms at the equator, rises, and moves northward, it sinks and rises in several intermediate bands, forming circulation cells. • Surface flows do not move straight North and South, but are deflected due to Coriolis Effect. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

19. Convection Cells and Prevailing Winds • Major zones of subsidence occur at about 30o north and south latitude. • Where dry, subsiding air falls on continents, it creates broad, subtropical desert regions. • Winds directly under regions of subsiding air are often light and variable. • Horse latitudes Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

20. Convection Cells and Prevailing Winds Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

21. Jet Streams • Jet Streams - Large-scale upper air flows. • Generally follow meandering paths from west to east. (6-12 km above surface) • Wind speeds are often 200 km / hr. • Number, flow speed, location, and size all vary on a daily basis. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

22. Jet Streams • Usually (2) main jet streams over NA: • Subtropical - (30o) north • Northern - Circumpolar vortex • During winter, the Northern Hemisphere tilts away from the sun and the atmosphere cools, pushing cold polar air farther south. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

23. Circumpolar Vortex Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

24. Frontal Weather • Cold Front - Boundary formed when cooler air displaces warmer air. • Cold air is more dense, thus hugs ground and pushes under warm air. • Warm air cooled adiabatically. • Warm Front - Boundary formed when warm air displaces cooler air. • Warm air is less dense and slides over cool air, creating a long wedge-shaped band of clouds. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

25. Frontal Weather Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

26. Cyclonic Storms • When rising air is laden with water vapor, latent energy released by condensation intensifies convection currents and draws up more warm air and water vapor. • Storm cell will exist as long as temperature differential exists. • Hurricanes (Atlantic) • Typhoons (Western Pacific) • Cyclones (Indian Ocean) Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

27. Cyclonic Storms • Tornadoes - Swirling funnel clouds. • Rotation not generated by Coriolis forces. • Generated by “supercell” frontal systems where strong dry cold fronts collide with warm humid air. • Greater air temperature differences in Spring thus more tornadoes. • Spinning - Rolling vortex tubes • Downbursts - Disorganized supercells Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

28. Tornadoes Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

29. Seasonal Winds • Monsoon - Seasonal reversal of wind patterns caused by differential heating and cooling rates of oceans and continents. • Most prevalent in tropical countries where large land area is cut off from continental air masses by mountain ranges and surrounded by a large volume of water. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

30. CLIMATE • Driving Forces and Patterns • Periodic weather cycles detected. • Solar magnetic cycles • Milankovitch Cycles - Periodic shifts in earth’s orbit and tilt. • Change distribution and intensity of sunlight reaching the earth. • Ice cores show drastic changes may have occurred over short periods of time (decades). Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

31. El Nino Southern Oscillation • Large pool of warm surface water in Pacific Ocean moves back and forth between Indonesia and South America. • Most years, the pool is held in western Pacific by steady equatorial trade winds. • Every three-five years the Indonesian low collapses and the mass of warm surface water surges back east. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

32. El Nino Southern Oscillation • During an El Nino year, the northern jet stream pulls moist air from the Pacific over the US. • Intense storms and heavy rains. • During intervening La Nina years, hot, dry weather is often present. • Pacific Decadal Oscillation - Very large pool of warm water moving back and forth across the North Pacific every 30 years. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

33. El Nino Southern Oscillation Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

34. Human-Caused Global Climate Change • IPCC estimates average global temperature will increase over the next century by 1.4 - 5.8o C (2.5 - 10.4o F). • Difference between current temperature and the last ice age is only 5o C. • Every year of the 1990’s was among the 15 hottest of the past millennium. • Night temperatures generally increased more than daytime. • Precipitation rates also increased. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

35. Greenhouse Gases • Carbon Dioxide -Fossil-fuel burning. • Atmospheric levels increasing steadily. • Methane -Ruminants, Coal-mines • Absorbs more infrared than CO2. • Chlorofluorocarbons (CFC’s) -Refrigerants • Declined in recent years • Nitrous Oxide -Burning organic material • Sulfur Hexafluoride -Electrical insulation Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

36. Aerosol Effects • Aerosols have a tendency to reflect sunlight and cool surface air temperatures. • Short-lived, thus effects are temporary. • Mt. Pinatubo erupted in 1991 and ejected enough ash and sulfate particles to cool global climate about 1o C for nearly a year. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

37. Effects of Climate Change • Artic sea ice thinning • Alpine glaciers retreating • Wild plants and animals may be forced to alter migration patterns, or abandon current ranges. • Coral reefs bleaching. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

38. Winners and Losers • Residents of extreme northern areas would enjoy warmer temperatures and longer growing-seasons. • Plant growth patterns may be altered. • One-third of population living in areas likely flooded by rising seas. • More evaporation may cause severe storms. • Infectious disease likely to spread faster. • Circulation patterns may cause more snowfall at poles - New ice age ? Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

39. International Climate Negotiations • Kyoto Protocol (1997) • 160 nations agreed to roll back carbon dioxide, methane, and nitrous oxide emissions about 5% below 1990 levels by 2012. • Sets different limits for different countries, depending on prior output. • Developing countries exempted. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

40. Summary: • Composition and Structure of the Atmosphere • Weather Engine • Solar Radiation • Weather • Jet Streams • Cyclonic Storms • Climate • El Nino • Climate Change Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.

41. Cunningham - Cunningham - Saigo: Environmental Science 7th Ed.