1 Air, Weather, and Climate

2 2 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

3 3 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

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

5 Troposphere  Closest to the earth’s surface  Where we live –Weather occurs here  very thin (averaging 11 km or 7 miles high)  Contains 75% of mass most from water vapor  Temp decreases as altitude increases

6 Stratosphere  Above the troposphere  extends to 50 kilometers (31 miles) high  dry and less dense  Warmer temps higher up and cooler layers farther down, due to the absorption of uv rays  Ozone layer

7 Mesosphere  extends to 85 kilometers (53 miles) high  extremely low air pressure  temperature decrease with altitude reaching -90°C at the top

8 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

9 Ionosphere  when solar energy is absorbed directly by air molecules, the atoms gain or lose electrons and become charged particles called ions  reflects many types of radio waves allowing them to bounce around the world

10 Exosphere  Top of the thermosphere and continues until it merges with interplanetary gases, or space (372 to 6200 miles)  H and He are the primary components

11 Weather  Contribute to Weather –Air temperature –Air pressure –Humidity –Cloud cover –Precipitation –Winds  Types of Weather –Fronts –Severe Weather

12 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

13

14 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

15

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

17 Winds  Horizontal wind moves from areas of high to low pressure  Vertical wind moves from low to high pressure  Speed is determined by differences in pressure  Coriolis effect –As air moves from high to low pressure in the N. hemisphere, it is deflected to the right –Opposite for S. hemisphere

18 Winds cont.  Hadley cells –Carries heat and moisture from the tropics to the northern and southern mid-latitudes  Rising air motion near the equator  Descending air motion in the subtropics –Lost most of water vapor –Where deserts are located

19

20 Convection Currents

21

22 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

23 Climate  Climate – long term weather patterns –driven by atmosphere –Uneven heating of earth’s surface  Equator  Seasonal changes in temp and precip  Opposite seasons in N&S hemispheres –determines distribution of biomes across Earth

24 What Factors Control Climate?  Latitude  Elevation/topography  Nearby water  Ocean currents  Vegetation  Prevailing winds

25 Ocean Currents  Warm/cold currents influence land climate  Currents redistribute heat from sun which influences climate –El Nino – change in the direction of tropical winds warms SA and NA coastal surface waters, suppresses upwellings, and alters weather  Warm water spreads from the west Pacific to the east Pacific  Effects –Distorts jet stream –Reduces primary productivity  Some fish species decline –La Nina -cooling counterpart  Upwelling of nutrient rich water

26 “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  Gases absorb and reradiate this outgoing radiation, effectively storing some of the heat in the atmosphere, thus producing a net warming of the surface

27 “Natural” Greenhouse Effect cont.  This process has kept the Earth's temperature about 60 degrees Fahrenheit warmer than it would otherwise be.  Life on Earth could not be sustained without the natural greenhouse effect.