Atmosphere and Climate Chapter 13-1

1. Atmosphere and ClimateChapter 13-1

2. Review from Chapter 12:The atmosphere • Atmosphere = the thin layer of gases that surrounds Earth • Absorbs radiation and moderates climate • Transports and recycles water and nutrients • 78% nitrogen gas, 21% oxygen gas, 1% other gases • Its four layers differ in temperature, density and composition • Minute concentrations of permanent (remain at stable concentrations) and variable gases (varying concentrations) • Human activity is changing the amounts of some gases

3. The atmosphere drives weather and climate • Weather = specifies atmospheric conditions over short time periods and within a small geographic areas • Climate = describes patterns of atmospheric conditions across large geographic regions over long periods of time Mark Twain said “Climate is what we expect; weather is what we get”

4. Factors that affect climate • Latitude – distance from the equator • At the equator, sun’s rays are more direct – result is higher and consistent temperatures, more precipitation (tropical rainforests) • At higher latitudes – sun’s rays are at an angle, less intense, also seasons occur, so climate is cooler and less consistent year-round Oblique rays Vertical rays

5. Factors that affect climate 2. Atmospheric circulation • Air near Earth’s surface is warmer and moister than air at higher latitudes • Convective circulation = less dense, warmer air rises and creates vertical currents • Warm air is less dense, it expands, rises and cools • As it cools, water condenses out as precipitation • Cool air sinks replacing warm air • Influences both weather and climate

6. Factors that affect climate Wind – movement of air within the atmosphere Prevailing winds – blow predominantly in one direction throughout the year Trade winds – belts of prevailing winds that are found in both hemispheres between 30° north and south latitudes Westerlies – prevailing winds blowing from the west between 30° and 60° north and south latitudes Polar easterlies – prevailing winds blowing from the east in the polar regions

7. Factors that affect climate • Oceanic circulation patterns • Two types of ocean currents: 1. surface 2. deep – very slow moving • These currents result in a redistribution of heat on the planet – from the equator to the poles • Also affects location of nutrients and oxygen Notice that how the warm (red) currents move away from the equator and the cool (blue) currents move toward the equator and around the south pole

8. Ocean currents have an effect on coastal climates Why is there a difference between San Diego vs Savannah when they are almost at the same latitude? San Diego Savannah Avg high: 71°F Avg low: 58°F Annual Precip: 11” Avg high: 77°F Avg low: 55°F Annual Precip: 50”

9. San Diego Savannah

10. Although ocean currents help establish general climate patterns, sometimes the ocean currents change and so does the climate for a location. El Niño-Southern Oscillation (ENSO) Changes in climate pattern in the Pacific Ocean which involve a back-and-forth change (oscillation) in the direction of tropical winds The two extremes are called El Niño and La Niña El Niño means “the boy” and was chosen because the phenomenon usually occurs around Christmas and can last a few weeks, but sometimes up to 18 months or more

11. El Niño video clip http://esminfo.prenhall.com/science/geoanimations/animations/26_NinoNina.html

13. El Niño Drought Unusually high rainfall Unusually warm periods

14. ENSO results in changes in upwellings that affect productivity For the southwestern coastline of S. America:

15. Factors that affect climate • Topography – as you go up every 1000 feet, temp drops about 6°F (on a sunny day)

16. Effect of Rain Shadow on Climate Winds carrying moisture from the ocean rise up the windward side of the mountain As air cools, moisture condenses and precipitation falls on the windward side of the mountain Dry air flows down leeward side of the mountain, often there are deserts on that side of the mountain – called the rain shadow

17. Examples of deserts formed by rain shadows Gobi Desert – rainshadow of Himalayas Mohave Desert, U.S. – rainshadow of Sierra Nevada Mountains

18. Other factors that affect climate • Others • Solar variation – 11 year cycle of the sun from minimum to maximum activity affects our climate

19. Other factors that affect climate • Volcanoes – emit gases and particles that block sunlight 1816 – called the “Year without a Summer” – due to combination of low solar activity and powerful volcanic eruptions (Tamboro) Pinatubo 1991

20. Other factors that affect climate c. Seasons occur because the Earth is tilted • Each hemisphere tilts toward the sun for half the year • Results in a change of seasons • Equatorial regions are unaffected by this tilt, so days average 12 hours through the year