Understanding Weather and Climate: The Atmosphere, Seasons, and Weather Patterns

1. Chapter 24 Weather and Climate

2. 24.1 The Atmosphere • Atmosphere- layer of gases surrounding the Earth • It forms a protective boundary between Earth and space and provides conditions that are suitable for life • It protects us from meteoroids, chunks of rock and metal. • It holds in heat and helps moderate temperature. • 78% N, 21%O, 1% other gases

3. Air Pressure • The force exerted by the weight of a column of air on a surface • As altitude increases, air pressure and density decrease • Barometer- how to measure air pressure

4. Layers of the Atmosphere • Troposphere • Lowest layer • Contains almost all water vapor in atmosphere • Weather- condition of the atmosphere @ a place and time • Stratosphere • Above troposphere • Has the ozone layer, which absorbs UV • Mesosphere • Above stratosphere • Meteoroids burn here • Thermosphere • Outermost layer • No boundary marks • High temperature • Ionosphere- charged particles • Aurora- colorful display of light in sky due to magnetic attraction

5. 24.2 The Sun and Its Seasons • Earth rotates and revolves • Rotate- spinning on its axis • Revolve- movement of one body in space around another (Earth around sun) • 365.25 days to revolve

6. Latitude Zones • Tropic • 23.5 degrees south and 23.5 degrees north • warm • Temperate • 23.5-66.5 degrees north and south • Cooler than tropics • Polar • 66.5 degrees to poles • cold

7. Seasons • Axis is tilted 23.5 degrees, which causes seasons • Solstice- two days each year when sun is directly overhead @ 23.5 degrees north or south. Summer solstice is June 21 (days longest), winter is December 21 (shortest day). • Equinox- neither hemisphere is tilted toward the sun, and daylight is equal to darkness • March 21 • September 22

8. 24.3 Solar Energy and Winds • Some solar energy that reaches Earth’s atmosphere is reflected back, some is absorbed by the atmosphere, and some is absorbed by Earth’s surface • 30% reflected, 20% absorbed by clouds • Greenhouse effect- gases radiate some of absorbed energy back to Earth, warming the lower atmosphere • Energy is transferred to the troposphere by radiation, convection, and conduction

9. Wind • Mainly horizontal movement of air • Caused by difference in air pressure • Local wind- wind that blows over a short distance, like breezes over body of water to land • Land heated more quickly than water, warm air rises, and cooler air from water rushes towards land- sea breeze • Land cools more quickly than water, cooler air is more dense- land breeze

10. Global Winds • Winds that blow over long distances • Convection cells- global winds in huge bands, like loops • Trade winds, westerlies, polar easterlies • Coriolis effect- effect that Earth’s rotation has on all free-moving objects • Monsoon- wind system that is characterized by seasonal reversal of direction, longer time than land, sea breeze • Jet stream- belt of high-speed wind in upper troposphere, caused by difference of air pressure at high altitudes

11. 24.4 Water in the Atmosphere • Humidity- amount of water vapor in the air • Warm carries more than cold • Relative humidity- ratio of amount of water vapor in the air to the maximum amount of water vapor that can exist at that temperature • Dew point- temperature at which air becomes saturated • Water vapor typically condenses as dew, frost, clouds, or fog

12. Cloud Formation • Cloud- dense, visible mass of tiny water droplets or ice crystals that are suspended in the atmosphere • Form as warm, moist air rises and water vapor condenses in the atmosphere; below dew point • Dust or salt must be present to condense upon

13. Types of Clouds • Stratus • Flat • Nimbo or nimbus means precipitation • Cumulus • Puffy white clouds • Fair-weather • Nimbus has thunder, lightning • Cirrus • Feathery • On a clear, sunny day • No rain, but sometimes come before those that do • Fog-cloud near the ground

14. Forms of Precipitation • Rain • Liquid from nimbostratus or cumulonimbus • Snow • Solid from nimbostratus or cumulonimbus • Sleet • Ice particles less than 5 mm, rain that freezes as it falls • Freezing Rain • Rain that freezes at the ground level, slippery • Hail • Solid more than 5 mm in diameter from cumulonimbus, hits other hail particles, refreezes

15. 24.5 Weather Patterns • Air mass- large body of air that has fairly uniform physical properties • Forms when a large body of air becomes fairly stationary over a region of Earth’s surface or as air moves over a large, uniform region like an ocean • Warm or cold due to where it forms (continental vs. maritime tells where)(polar vs. tropical tells temperature) • Front- sharply defined boundary that forms when two unlike air masses meet

16. Types of Fronts • Cold • Cold air mass overtakes warm • Goes close to ground • Cumulus and cumulonimbus • Strong winds, severe thunderstorms, large amount of precipitation, quick • Warm • Warm overtakes cold • Stratus • Steady rain • Stationary • Neither cold nor warm moves • Steady rain or snow for days • Occluded • Warm between two colds • Cloudy skies and precipitation

17. Low and High Pressure Systems • Cyclones • Low air pressure • Clouds, precipitation, stormy weather • Direction of global wind • Anticyclones • High air • Clear skies, little precipitation, calm

18. Storms • Thunderstorm- small weather system that includes thunder and lightning, wind and hail • Form when column of air rise within cumulonimbus • Lightning- sudden electrical discharge in the atmosphere • Thunder- sound produced by rapidly expanding air in path of lightning • Tornado- small but intense windstorm, rotating column of air formed from thunderstorm’s rotating vertical column • Hurricane- large tropical cyclone with winds at least 119 km/hr (74 mph)

19. 24.6 Predicting the Weather • Folk tales • Meteorologists study weather using Doppler radar, automated weather stations, weather satellites, and high-speed computers • Doppler radar- change in frequency of waves as source of waves moves • Weather stations and satellites- temperature, precipitation, wind speed, direction • Can’t predict accurately beyond a week • Weather maps- show predicted temperatures and include sun or cloud symbols to indicate cloud cover, and have drawings of rain or snow to show precipitation • Isotherm- line on a map that connects points of equal air temperature; used to see patterns • Isobar- line that connects points of equal air pressure

20. 24.7 Climate • Long-term weather condition • Temperature and precipitation • Affected by latitude, distance from large bodies of water, ocean currents, and altitude • Precipitation affected by latitude, distribution of air pressure systems and global winds, and existence of mountain barrier • Desert- dry region that gets less than 25 cm rain/year

21. Natural Climate Change • Ice age • Climate colder than usual • 4 major • Glaciers over continents • El Nino • Periodic warming of water in central and eastern Pacific • Global warming • Caused by CO2 • Atmosphere temperature rising • Oceans could expand • Conserve energy to stop it