Barometric Pressure – The pressure due to the weight of the atmosphere.

Barometric Pressure is also called atmospheric pressure or air pressure.

Air Pressure is measured using a barometer.

Differences in air pressure causes wind.

WARM AIR Holds more water than

cold air. Is less dense (it will

rise)

COLD AIR Holds less water than

warm air. Is more dense (it will

sink)

Earth’s rotation affects the direction of wind.

Coriolis effect – The change in the direction of an object’s path due to Earth’s rotation.

Winds in the Northern hemisphere curve clockwise

Winds in the Southern Hemisphere curve counterclockwise.

Global wind patterns form circulation cells.

Warm and cold fronts create different types of precipitation.

Warm frontForms layered,

stratus-type clouds or fog

Produces only drizzle or steady rain.

Cold frontForms cumulus

cloudsProduces

showers and thunderstorms

There are 3 stages to a thunderstorm

1)Cumulus2)Mature3)Dissipating

Cumulus Stage First stage Wind

movement is all upward

Rain has not yet started.

Mature Stage Lightning, wind,

and rain Hail and

tornadoes may occur

Wind movement is both up and down.

Dissipating Rain and wind

gusts start to slow down/stop

All wind movement is downward

Severe thunderstorms can develop supercells, which have intense, rotating updrafts.

About 10% of thunderstorms are severe.

Lightning – friction between the clouds creates regions of air with opposite charges.

To balance, a stepped leader (channel of (-) air) nears the ground and a return stroke (channel of (+) air) rushes upward to meet it.

Lightning heats the air to about 300,000 C.

Thunder – sound made by the rapid expansion of air around the lightning bolt.

Hazards of thunderstorms:

• lightning• violent winds• hail• floods• tornadoes

Hail – precipitation in the form of balls or lumps of ice. Most commonly occurs in the spring.

Floods – produced when the rain falls faster than the ground can absorb it or faster than streams and rivers can transport it out of the area. Floods are the main cause of thunderstorm-related deaths each year.

Cold air downdrafts can produce severe weather.

Cold air descends and hits the ground

On hitting, it bursts outward like spokes on a wheel.

Wind speed can be up to 260 km/h.

Tornadoes: Intense Short-lived Localized in the

mid-latitudes Formed when dry

air meets warm, moist air.

Tornadoes – violent, whirling column of air in contact with the ground. Before it reaches the ground, it is called a funnel cloud.

The Fujita tornado intensity scale –classifies tornadoes.

They usually form in the spring in the late afternoon. Tornado alley – northern Texas through Oklahoma, Kansas, and Missouri.

Hurricanes: Cover a vast area May last for days The center is

called the eye. Get their energy

from the warm, moist air over the ocean.

Tropical cyclones – large, rotating, low-pressure storms.

• common in the summer and fall

• thrives on energy from warm, tropical oceans

• air pressure in the center is low

• moves because wind currents steer them

eye – the calm center of the storm

eyewall – band immediately surrounding the eye that has the strongest winds

The Saffir-Simpson hurricane scale classifies hurricanes according to their wind speed, air pressure in the center, and potential for property damage.

A hurricane will end when it moves over land and no longer has access to the warm ocean surface to draw its energy, or when it moves over colder water.

A storm surge occurs when hurricane-force winds drive a mound of ocean water toward coastal areas, where it washes over the land. They can reach 6m above normal sea level. Lots of rain and flooding also causes enormous damage.

Climate is the weather pattern over a long period of time.

Ocean and Land influence the climate in a specific area.

Climate and Weather

• Latitude is the primary factor that determines climate at a given location.

• The amount of radiation received from the Sun and the prevailing circulation features depend on latitude.

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Ocean and Land Influence33

Continental climate – Area with little direct ocean influence.

Maritime climate – Area with strong ocean influence.

Ocean and Land Influence• Wind and pressure patterns determine

precipitation.

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Maritime climates are milder:

Summers are cooler Winters are warmer Daily temperature

varies less than a continental climate

Mountain influence on climate

Act as barriers, blocking weather systems.

When wind blows on one side, a lee rain shadow forms on the other side.

Causes of climate change

Mountain building Continental

movement Ocean currents Changes in the tilt of

Earth’s axis of rotation.

Sunspot activity Volcanoes Human activity

El Nino and La Nina Involves the

atmosphere and ocean.

Opposite of El Nino is La Nina.