Air Weather and Climate 1 Earths Atmosphere Compared

Air, Weather, and Climate 1

Earth’s Atmosphere §Compared to the size of the Earth (12000 km), the atmosphere is a thin shell (120 km) §Composed of: – – – ~78% N 2 gas 21% O 2 gas 1% argon gas and other permanent gases 22

If the Earth is compared to this Orange… the Earth’s atmosphere would be thinner than the layer of pesticide on this Orange’s surface 33

Layers of the Atmosphere § § § Troposphere Stratosphere Mesosphere Thermosphere Ionosphere Exosphere 4

Troposphere § Closest to the earth’s surface § Where we live – Weather § very thin (averaging 11 km or 7 miles high) § Densest layer – Most of nitrogen, oxygen and water vapor here § Temp decreases as altitude increases 5

Stratosphere § § § Above the troposphere extends to 50 kilometers (31 miles) high dry and less dense UV rays reach higher altitudes and warm them Ozone layer – Absorbs? 6

Mesosphere § extends to 85 kilometers (53 miles) high § temperature decrease with altitude reaching 90°C at the top - 7

Thermosphere § extends to 600 kilometers (372 miles) high § temperatures go up as altitude increases due to absorption of solar radiation by oxygen § molecules so few and far between that they collide rarely § Farthest away from earth’s surface 8

Ionosphere § Within thermosphere § Contains ions when hit by solar energy begin to glow and produce light – Aurora Borealis § reflects many types of radio waves allowing them to bounce around the world 9

Exosphere § Top of thermosphere and continues until it merges with interplanetary gases, or space (372 to 6200 miles) 10

Seasonal Changes § Occurs due to earth’s axis being tilted § Creates opposite seasons § Determines global air circulation patterns 11

Seasons § Seasons are short periods of climatic change. § Certain areas receive changing amounts of radiation throughout the year 12

Earth’s Seasons SUMMER (Northern Hemisphere) ole P rth No r ato u q E h t r Ea t Sou e ol h. P WINTER (Southern Hemisphere) 13

Earth’s Seasons Continued…. Tilt of the Earth’s axis towards or away from the sun creates the seasons WINTER (Northern Hemisphere) le o P th Nor th r a E r o at Equ Sou le o P th SUMMER (Southern Hemisphere) 14

Weather § Weather – daily temperature and moisture conditions in a place – driven by atmosphere – atmospheric conditions over short time periods (hours or days) in small geographic areas – produced by interacting air masses – Types of weather § Warm Front-warm air displaces cool air § Cold Front-cooler air displaces warmer air § Severe-hurricanes, thunderstorms, tornadoes 15

Weather § Contribute to Weather – – – Air temperature Air pressure Humidity Cloud cover Precipitation Winds 16

Air Temperature § As solar energy reaches the equator, regions heat up more than the poles. § Warm air and water at the equator travel toward the poles while cold air and water at the poles travel toward the equator in an attempt to equalize the temperature – Constant struggle = changing weather 17

18 http: //www. usatoday. com/weather/tg/wglobale. htm

Air Pressure § Caused by the weight of air pressing down on the Earth § High pressure-cool, dense air that descends towards surface of earth – Fair weather § Low pressure-less dense warm air goes toward the center of a low pressure air mass – Produces cloudy and stormy weather § Air pressure changes with weather 19

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Humidity and Cloud Cover § Relative humidity-amount of water vapor in the air § Cloud Cover – clouds cool the planet by reflecting sunlight § Albedo – reduces the amount of heat that radiates into space 21

Winds § Speed is determined by differences in pressure § Coriolis effect – Deflection of objects moving in a straight path relative to the earth’s surface – Proportional to the speed of the earth’s rotation at different latitudes § as latitude increases and the speed of the earth’s rotation decreases, Coriolis effect increases 22

Winds cont. § Hadley cells – Solar energy warms humid air in tropics – Warm air rises, cools, condenses and precipitates – Dry air sinks and is warmed § Hot dry air causes deserts 23

Climate § Climate – long term weather patterns – driven by atmosphere – determines distribution of biomes across Earth 24

What Factors Control Climate? § § § § Latitude Elevation/topography Nearby water Uneven heating of earth’s surface Ocean currents Vegetation Prevailing winds Seasons 25

Ocean Currents § Warm/cold currents influence land climate § Currents redistribute heat from sun which influences climate – Gulf Stream current § Upwelling-occurs along the west coasts of most continents – Cold, nutrient filled water 26

ENSO (El Nino Southern Oscillation) Cycle § Warm phase of ENSO § El Nino – trade winds near SA weaken; allows warm equatorial water from the western Pacific to move eastward toward the west coast of SA – Suppresses upwelling; decreases productivity – Alters weather § Cooler, wetter conditions in the se US § Cold phase of ENSO § La Nina – Trade winds strengthen – Upwelling of nutrient rich waters – Alters weather § Drier conditions in the se US 27

“Natural” Greenhouse Effect § Solar radiation passes through the atmosphere. – ~51% of the sun's radiation reaches the surface § This energy is then used in number of processes including: – – heating of the ground surface melting of ice and snow evaporation of water plant photosynthesis – ~30% is reflected back to space by clouds and the surface – ~19% of the energy available is absorbed by clouds and gases § absorb and reradiate this outgoing radiation, storing some of the heat in the atmosphere, thus producing a net warming of the surface 28

“Natural” Greenhouse Effect cont. § Kept the Earth's temperature about 60° F warmer than it would otherwise be. § 29