1. Weather and Climate

2. Weather
Weather: the atmospheric conditions of a certain place at a certain time; including temperature, pressure, humidity, precipitation and wind.
Temperature: the measure of the average kinetic energy of the particles in a material
Pressure: pressure caused by the weight of a column of air pushing down on an area

3. Weather Humidity: the amount of water vapor in the air
Precipitation: water, in liquid, or solid form, that falls from the atmosphere
Wind: The horizontal movement of air from an area of high pressure to an area of low pressure
Climate: the long-term average weather conditions that occur in a particular region

4. Air Air is all around us, and although we cannot see it, it has mass.
Recall that mass is the amount of matter in an object, and that matter is anything that has mass and takes up space.
Because air has mass, it also has pressure

5. What is the atmosphere?
The atmosphere is the outermost Earth System of gases and particles of matter

6. Why is the atmosphere important?
The atmosphere is essential to life on Earth:
contains oxygen and carbon dioxide, and water necessary for life
acts like insulation on a house to keep the Earth warm
protects living organisms from some of the Sun’s harmful rays
protects Earth’s surface from being hit by meteoroids

7. Layers of the Atmosphere
The atmosphere has several different layers
Each layer has unique properties, including composition of gases and how temperature changes with altitude
Altitude is height above sea level

8. Layers of the Atmosphere

9. The Troposphere
Troposphere: The atmospheric layer closest to Earth’s surface
Extends from the face of Earth’s surface to altitudes between 8 – 15km
Temperature decreases as you move away from the surface
This is the layer where most of Earth’s weather occurs

10. The Stratosphere
Stratosphere: The atmospheric layer directly above the troposphere
Extends from about 15 km to about 50 km
Contains the ozone layer
The area of the stratosphere with a high concentration of ozone
Due to the ozone layer, temperature increases as altitude increases within the stratosphere

11. The Mesosphere and Thermosphere
The mesosphere extends from the stratosphere (50 km) to about 85km
The thermosphere can extend from the mesosphere to more than 500 km above Earth’s surface
Combined these layers are much broader than the troposphere and stratosphere, yet only 1% of the atmosphere’s gas molecules are found here

12. The Mesosphere and Troposphere
The ionosphere is region within the mesosphere and thermosphere that contains ions
Between 60 km and 500 km
The ions in this layer reflect AM radio waves transmitted at ground level
Auroras- stunning display of lights in the ionosphere
Ions from the Sun strike air molecules, causing them to emit vivid colors of light (can be viewed at higher latitudes)

13. The Exosphere
Exosphere: The atmospheric layer furthest from Earth’s surface
Extends from 500 km out to space
It has no definite end, the molecules here can escape Earth’s gravity and travel into space
Pressure and density is so low here that individual gas molecules rarely strike each other
Molecules here move at incredibly fast speeds after absorbing the Sun’s radiation

14. Energy in the Atmosphere
Energy in the form of heat is transferred throughout the atmosphere
Recall that there are three types of heat transfer
Radiation – transfer of heat through space
Conduction – transfer of heat through direct contact
Convection – transfer of heat within a fluid/air
The troposphere is heated mostly through convection

15. Wind Winds are caused by differences in air pressure
Winds are described by their direction and speed
The name of a wind tells you where it is coming from, a south wind blows from the south towards the north
Wind direction is determined with a wind vane
Wind speed is measured with an anemometer

16. Local Winds Local Winds: winds that blow over short distances
Local winds are caused by the unequal heating of Earth’s surface within a small area

17. Global Winds
Global winds: winds that blow steadily from specific directions over long distances
Like local winds they are created by unequal heating of earth’s surface, but unlike local winds they occur over a large area
Recall that areas near the equator receive the most direct sunlight, and are therefore warmer than the poles. This difference in temperature creates giant convection currents
Warm air rises at the equator and cold air sinks at the poles, therefore air pressure tends to be lower near the equator and greater near the poles

18. Coriolis Effect
Coriolis Effect: change that Earth’s rotation causes in the motion of objects and that explain how winds curve
Global winds in the Northern
Hemisphere gradually turn towards
the right and in the Southern
Hemisphere winds curve to the
left

19. Global Wind Belts
Doldrums: areas near the equator with little or no winds; calm areas where warm air rises
Horse Latitudes: areas at 30 degrees north and south of the equator; calm areas of falling air.
Trade Winds: blow from the horse latitudes toward the equator; generally blow from the northeast in the Northern Hemisphere and from the southeast in the Southern Hemisphere.

20. Global Wind Belts
Prevailing Westerlies: blow west to east and away from the horse latitudes; play an important role in the weather of the United States.
Polar Easterlies: cold air near the poles sinks and flows back toward the lower latitudes; blow east to west; major effect on the weather in the U.S.
Jet Streams: bands of high-speed winds about 10 kilometers above Earth's surface.

21. Wind Belts

22. Air Masses
Scientists classify air masses according to two characteristics: temperature and humidity
Temperature affects air pressure
Cold, dense air has a higher pressure, while warm, less dense air has a lower pressure

23. Types of Air Masses Tropical: warm, form in tropics, low air pressure
Polar: cold, form at the poles, high air pressure
Maritime: humid, form over oceans
Continental: dry, form over land

24. Air Masses Maritime Tropical: warm, humid air mass
Air masses are referred to as either maritime or continental, and as either tropical or polar
Maritime Tropical: warm, humid air mass
Maritime Polar: cold, humid air mass
Continental Tropical:
dry, warm air mass
Continental Polar:
dry, cold air mass

25. Fronts Front: the boundary where two different air masses meet
cold – colder air mass move towards a warmer air mass
showers and thunderstorms form along cold fronts
warm – warm air moves toward cold air
creates a wide blanket of clouds, steady rain or snow for several hours/days
stationary – when an approaching front stalls for several days
cloudy skies and light rain
occluded – faster moving cold front catches up with a slow-moving warm front
usually brings precipitation

26. Fronts