The Atmosphere in Motion

The Atmosphere in The Atmosphere in MotionMotion

What is air pressure?What is air pressure?

It is the weight of the atmosphere It is the weight of the atmosphere above as it pushes down on earth’s above as it pushes down on earth’s

surface.surface.

Air pressure surrounds us from all Air pressure surrounds us from all sides.sides.

Air pressure decreases Air pressure decreases as you go as you go up in the atmosphere. The balloon up in the atmosphere. The balloon

above will expand as a result.above will expand as a result.

We use a barometer to measure air We use a barometer to measure air pressure.pressure.

What are the 3 things that cause What are the 3 things that cause changes in air pressure?changes in air pressure?

ElevationElevation. Higher elevations exert . Higher elevations exert less pressure.less pressure.

HumidityHumidity. More humid air exerts . More humid air exerts less pressure.less pressure.

TemperatureTemperature. Warmer air exerts . Warmer air exerts less pressure.less pressure.

How do we plot pressure How do we plot pressure differences?differences?

By using By using isobarsisobars on a weather map on a weather map

How does wind blow?How does wind blow?Wind blows from High to Low Wind blows from High to Low

PressurePressure

But the But the Coriolis Force Coriolis Force causes wind causes wind to deflect to the right in the to deflect to the right in the

Northern Hemisphere and to Northern Hemisphere and to the left in the Southern the left in the Southern

HemisphereHemisphere

Will the Will the Coriolis Force Coriolis Force have an have an effect on your bathtub, toilet, or effect on your bathtub, toilet, or

kitchen sink?kitchen sink?

Absolutely Absolutely NOTNOT! Coriolis only takes ! Coriolis only takes effect when there are large effect when there are large

distances, high velocities, and distances, high velocities, and large time scales!large time scales!

The Coriolis Effect is greatest near the The Coriolis Effect is greatest near the poles and the least near the Equator.poles and the least near the Equator.

The effect is greater on fast moving The effect is greater on fast moving objects.objects.

The effect does not depend on an The effect does not depend on an object’s direction of movement.object’s direction of movement.

It is only noticeable for objects It is only noticeable for objects traveling great speeds over great traveling great speeds over great

distances.distances.

This causes This causes wind directions wind directions around around high and low pressure systems high and low pressure systems

to change.to change.

Northern HemisphereNorthern HemisphereClockwise Counter-Clockwise

This causes This causes wind directions wind directions around around high and low pressure systems high and low pressure systems

to change.to change.

Southern HemisphereSouthern HemisphereClockwise Counter-Clockwise

FrictionFriction of wind with the ground will of wind with the ground will cause Coriolis Effect to be cause Coriolis Effect to be

weakened. Winds will flow more weakened. Winds will flow more perpendicular to isobars.perpendicular to isobars.

Northern HemisphereNorthern HemisphereClockwise Counter-Clockwise

The The Jet Stream Jet Stream is a high altitude stream of is a high altitude stream of air at the boundary between warm air air at the boundary between warm air

and cold air.and cold air.

Global Wind PatternsGlobal Wind Patterns

Global Wind Patterns are the result of Global Wind Patterns are the result of earth’s rotation and temperature earth’s rotation and temperature

(pressure) differences around the (pressure) differences around the globeglobe

If the Earth did not rotate, this is what the If the Earth did not rotate, this is what the global wind patterns would look like. global wind patterns would look like.

Winds would only respond to Winds would only respond to temperature (pressure) differences.temperature (pressure) differences.

Because the Earth rotates, this is what the Because the Earth rotates, this is what the global wind patterns look like. Winds global wind patterns look like. Winds respond to temperature (pressure) respond to temperature (pressure)

differences differences andand Earth’s rotation. Earth’s rotation.

The rising motion of air at low pressure The rising motion of air at low pressure areas and descending motion of air at areas and descending motion of air at high pressure areas creates Hadley high pressure areas creates Hadley

cells.cells.

If the Earth did not rotate, one large If the Earth did not rotate, one large circulation cell would occur in each circulation cell would occur in each

hemisphere.hemisphere.

Because Earth rotates, the circulation Because Earth rotates, the circulation pattern looks like this. We call this the pattern looks like this. We call this the

Three-celled Circulation ModelThree-celled Circulation Model

Weaknesses of the Three-celled ModelWeaknesses of the Three-celled ModelIt assumes that surface winds are It assumes that surface winds are

uniform. Surface winds can be uniform. Surface winds can be determined by local High and determined by local High and

Low pressure weather systemsLow pressure weather systems

It assumes that all of the It assumes that all of the Earth’s surface is the same. In Earth’s surface is the same. In

actuality, Earth has oceans actuality, Earth has oceans and landmasses.and landmasses.

It assumes that upper-level It assumes that upper-level winds travel north or south. winds travel north or south.

Actually, upper level winds are Actually, upper level winds are primarily westerly, except near primarily westerly, except near the equator where the Coriolis the equator where the Coriolis

effect is weak.effect is weak.

Prevailing winds are the result of the global Prevailing winds are the result of the global circulation model.circulation model.

Doldrums

Horse Latitudes

Horse Latitudes

The The Horse LatitudesHorse Latitudes, which have little or no , which have little or no wind, got their name because horses wind, got their name because horses were dumped overboard to lighten the were dumped overboard to lighten the ship’s load and conserve fresh water.ship’s load and conserve fresh water.

Doldrums

Horse Latitudes

Horse Latitudes

The The DoldrumsDoldrums, which have little or no wind, , which have little or no wind, got their name because sailors would got their name because sailors would get trapped there in between the trade get trapped there in between the trade winds for days or weeks. Hence, the winds for days or weeks. Hence, the

saying “stuck in the doldrums.”saying “stuck in the doldrums.”

Doldrums

Horse Latitudes

Horse Latitudes

El NiEl Niñño occurs when the tropical easterlies o occurs when the tropical easterlies (trade winds) die off about every 3-5 (trade winds) die off about every 3-5

years. Go here for the latest years. Go here for the latest information.information.

Southeast Trade Winds

Northeast Trade Winds

Tracking El NiTracking El Niñño was the NOVA video that o was the NOVA video that we saw in class. Click here for the we saw in class. Click here for the latest Topex-Poseidon El Nilatest Topex-Poseidon El Niñño Sea o Sea

Surface Temperature Image.Surface Temperature Image.

The warm flux of ocean water from the 1997-1998 El Niño

Local Wind PatternsLocal Wind Patterns

The Indian MonsoonThe Indian Monsoon

Sea BreezesSea Breezes during the day during the day

Rising warm air over the land is replaced by cooler air from the ocean. The wind goes from the ocean to the land, High to Low.

Valley Breeze during the dayValley Breeze during the day

Rising warm air over the valley flows uphill as a valley breeze.

Land Breezes Land Breezes during the nightduring the night

Rising warm air over the ocean is replaced by cooler air from the land. The wind goes from the land to the ocean, High to Low.

Mountain Breezes during the nightMountain Breezes during the night

Cool air at the top of the mountain sinks and causes a mountain breeze.

The Indian MonsoonThe Indian Monsoon

Increased rainfall occurs over India in the Summer Increased rainfall occurs over India in the Summer months. This is because the warmer continent months. This is because the warmer continent

creates rising air and a sea breeze pattern.creates rising air and a sea breeze pattern.Cooler, moist air from the Indian Ocean brings Cooler, moist air from the Indian Ocean brings

monsoon rains to the Indian landmass.monsoon rains to the Indian landmass.

The Indian MonsoonThe Indian Monsoon

Decreased rainfall occurs over India in the Winter Decreased rainfall occurs over India in the Winter months. This is because the colder continent months. This is because the colder continent creates sinking air and a land breeze pattern.creates sinking air and a land breeze pattern.Rain stays offshore over the warmer Indian Rain stays offshore over the warmer Indian

Ocean.Ocean.