Chapter 9: Weather Patterns and

Climate

Aim: How do air masses affect weather?

An air mass is a large region of the atmosphere where the air has similar properties throughout

Gets its properties from the region it is from

Are named for the region they come from

When an air mass moves it brings the conditions with them

Air Masses

4 types:1. Continental polar: cold, dry air2. Maritime polar: cool, moist air3. Continental tropical: hot, dry air4. Maritime tropical: warm, moist air

When 2 air masses meet, they form a boundary called a front

Weather changes rapidly at fronts because you are passing from one kind of air mass into another

Aim: How do fronts affect weather?

4 types:1. Cold Front Cold air moves in under a warm air

mass Brings brief, heavy storms Can cause strong winds and

thunderstorms After the storm, the weather is cooler

and drier

Types of Fronts

2. Warm Front Warm air moves in over a cold air mass

It brings light, steady rain or snow Precipitation can last for days Can bring fog After the rain, the weather is warmer and more humid

3. Occluded Front Occurs when a cold front and warm

front meet 2 ways this can happen

1. Cold front occlusion Air behind the front is cold Air ahead of the warm front is cool Cold air is moving in on cool air and

the warm is pushed up in between them

Weather is like that of a cold front2. Warm front occlusion Air behind front is cool not cold Air ahead of warm front is cold Weather is like that of a warm front

4. Stationary Front Stays over an area for days without

moving Have calm weather

Aim: How do thunderstorms form?

Most common kind of severe storm Form in cumulonimbus clouds called thunderheads

Usually have heavy rains, strong winds, thunder and lightning

Some can even produce hail There are 3 stages during a thunderstorm

Stages of Thunderstorms

1. First Stage Intense heat causes air to rise very

quickly Updrafts form and the cloud grows

bigger and bigger Water droplets and ice crystals grow

larger too2. Second Stage When the rain starts falling air moves

downward Static electricity forms from the rubbing

of upward air and downward air

Lightning occurs when static electricity builds up

Lightning is unpredictable3. Third Stage The storm dies when the downdraft

becomes stronger than the updraft Heavy rains subside and finally stop

Thunderstorms usually form in the warm air just ahead of a cold front

Aim: How do tornadoes happen?

A tornado is a violent whirling wind that moves across the ground in a narrow path

Form when dry, cold air masses mix with warm, moist air masses.

When the updraft is really strong air rushes in from all sides causing the air to curve into a spin

This spin lowers the air pressure even more, causing air to rush in even faster

Tornadoes

As the tornado gets stronger a funnel forms that touches the ground

Winds can reach up to 300 mph in the center of a tornado

The direction of a tornado can continually change

Most tornadoes occur in the Midwest of the United States

They mostly likely occur where there are big differences in the air masses

Aim: How do hurricanes form?

Are very large, swirling storms with very low pressure at their center

They form over tropical oceans Strong heating and lots of evaporation cause a large low pressure center to form

The Coriolis effect causes winds to spiral counterclockwise and clusters of thunderstorms are pulled into the spiral

The thunderstorms merge forming the storm

Hurricanes

The lower the pressure, the stronger the winds blow

In order for the storm to be considered a hurricane, the winds need to reach 75 mph or higher

Hurricanes have an eye at the center of the storm

The eye is an area of light winds and clear skies

Hurricanes can grow 400 miles in diameter

Aim: How do hurricanes affect ocean waves?

Hurricane winds cause large waves in the ocean

These waves pound the shore for days before the hurricane hits

The storm surge causes the most damage

Storm surges are caused by low air pressure

It causes the sea to rise, along with heavy rain from the hurricane

Storm surges cause flooding, which destroys homes and wears away beaches

Hurricanes begin to die when they move onto land because it has no water to replace what falls as rain

Aim: How can you be safe in a storm?

Aim: How can radar track storms?

Doppler radar is used to find storms as they form

Radar stands for radio detection and ranging

Radar sends out radio waves and records their echoes

The change in echoes gives scientists clues

It is used to track storms because radio waves reflect off storm clouds

Radar

With the radar, scientists can tell if rain is moving toward or away from an area, and spot spinning motions of clouds

Spotting motions of clouds can help warn scientists of tornadoes or hurricanes

Doppler radar helps scientists find and track thunderstorms, tornadoes and hurricanes

Aim: What is climate?

Is the average weather pattern of a region Climate can be described by the following factors: temperature, precipitation, winds, distance from coast, mountain ranges and ocean currents

We can also describe climate by the plants that live their b/c plants require their own conditions for growth, such as amount of sunlight, precipitation and temperature

Climate

Examples: 1. Alaska has a climate of long, cold

winters and short cool summers2. Florida has a climate of long, hot

summers and short, cool winters

Aim: What affects climate?

1. Latitude is the measure of how far north or

south a place is from the equator Temperatures are different at different

latitudes due to the angle of insolation 3 different zones: Tropical Zone Temperate Zone Polar Zone

Factors that Affect Climate

2. Bodies of Water Most of Earth is covered with water Land and water cool and heat at

different rates Land heats up faster in sunlight and

cools off faster Air temperatures over land are

warmer in the summer and cooler in the winter than over oceans at the same latitude

3. Winds and Ocean Currents The westerlies blow in the middle

latitudes They bring warm, moist air to the west

coast and push air masses and fronts Ocean Currents are also moved by

winds Gulf stream is a warm current that

flows up the east coast California current is a cool current that

moves down along the west coast

4. Altitude Is the measure of how high a place is

above sea level The higher a place the cooler it is

Aim: How does the Greenhouse Effect affect Earth?

Earth absorbs heat from the sun It also gives off heat into space Radiative balance is when the amount of energy gained equals the energy lost

Average temperature of Earth = 59˚F The atmosphere protects Earth from getting too hot or too cold

Only about ½ of incoming sunlight reaches Earth

Earth’s Energy

30% reflects off of particles and clouds back to space

The atmosphere absorbs 15- 20% of the heat

This keeps temperatures from rising too high

At night clouds aid in keeping the night from getting too cold

The atmosphere keeps Earth warmer than it would be

Earth’s atmosphere acts like the glass in a greenhouse by letting in sunlight, but not letting heat escape

2 main greenhouse gases are water vapor and CO2

Methane, nitrous oxide and chlorofluorocarbons (CFC’s) have a small effect

The Greenhouse Effect

These greenhouse gases are increasing due to human activity

With this increase Earth’s climate can change and make our planet warmer

The increase in these gases have a great effect on our environment

Aim: What causes climate change?

Over time Earth has undergone changes, which caused periods of cooling and heating

Shifts in the radiative balance is caused by changes in sunlight, currents and landmasses and volcanoes

1. Sunlight the amount of energy the sun sends

out changes These changes are due to sunspots

Causes of Climate Change

Sunspots are dark areas that appear on the surface of the sun

These spots are cooler than other parts of the sun

They are not permanent Sunspot maximum-large count of sunspots, which happens about every 11 years

Around the time of a sunspot maximum, earth’s temperature goes up

2. Ocean Currents They move heat from the equator to

the poles Change in speed and direction of

currents can explain sudden and long term climate changes

3. Landmasses Continents have changed positions

and continue to move climate will change with their

locations

4. Volcanoes Eruption of volcanoes send dust and

gases into the atmosphere The dust and gases could block out

the sun and cause cooling In the past volcanic eruptions were

very common and could have caused the ice ages

They are less common today, but still cause cooling, just not long term changes