Climate & Weather

Chapters 12, 13, 14

What are climate & weather?

• Climate is the long term variation in weather for a particular area.

• Weather is the current state of the atmosphere, including short-term variations.

How is energy related to climate & weather?

• The amount of the sun’s energy reaching Earth is equal to the amount of energy radiated back to space in a year.

• Air and water carry (distribute) energy from one place to another.

• Climate and weather are a result of the redistribution of Earth’s heat energy.

What are air masses?

• An air mass is a large body of air that takes on the characteristics of the area in which it forms.• Cold areas produce cold air

masses; warm areas produce warm air masses

• Air masses over water have higher moisture; air masses over land have lower moisture

• Air masses change as they move to new areas.

How do air masses move?

• Air masses move as a result of varying densities• More dense air masses sink• Less dense air masses float• Air generally moves from high

to low pressure• The Coriolis effect deflects

this movement• Air is deflected to the right in the

northern hemisphere (clockwise)

• Air is deflected to the left in the southern hemisphere (counterclockwise)

• This results in three basic wind systems• Trade winds—occur at 30N and

30 S; move west• Prevailing westerlies—occur

between 30 and 60N and S; move east

• Polar easterlies—occur between 60N and S and the poles; move west

Weird fact:Winds are named according to the direction they come from. (That’s why the names seem backwards.

What are fronts?

• A front is the narrow region separating two air masses with different densities.

• Fronts can cause dramatic weather changes.

• Types of fronts• Cold front

• Cold dense air steeply pushes up warm air

• Produces clouds, rain, & thunderstorms

• Warm front• Warm air gradually pushes cold air

away• Produces lots of clouds &

precipitation

• Stationary front• Two air masses meet and don’t

move• Temperature & pressure

differences are small• Little weather is produced

• Occluded front• Warm air is squeezed up by two

colliding cold air masses• Produces precipitation on both

sides

What are pressure systems?

• Moving air creates pressure variations in the atmosphere

• Sinking air produces high pressure

• Sinking air pushes air below it out of the way.

• The Coriolis effect moves this air clockwise

• Clouds can’t form (at least not very easily)

• Rising air produces low pressure

• Rising air is replaced by air nearby• The Coriolis effect moves this air

counterclockwise• Clouds form easily

What are the features of the weather?

• Temperature—the amount of movement of the molecules in the air• High temperature & low

temperature are measured• Measured using a thermometer

• Precipitation—all forms of water that fall from clouds• Forms of precipitation

• Rain• Snow• Hail• Sleet

• Precipitation is measured in inches or centimeters

• Air pressure—the amount of pressure the air puts on our bodies• Air pressure decreases as

altitude increases• Air pressure increases as

temperature increases• Measured using a barometer, in

mm Hg or in Hg

• Wind• Both speed and direction are

measured• Measured using an

anemometer

• Relative humidity—ratio of water vapor in the air compared to the amount of water vapor the air is capable of holding• Measured using a

psychrometer, in percent

• Dew point—the temperature at which dew forms• Dew forms because air has

cooled to the point of saturation, so condensation occurs

What are Earth’s climates?

• Climates are classified by two factors:• Temperature• Precipitation

• There are six main climates• Tropical• Dry• Mild• Continental• Polar• High elevation

• Climate is correlated with latitude

• Recall that climate is defined as long term weather patterns