atm.ppt

Look For The Following Key

Ideas In Chapter 8

✓ The interaction of ocean and atmosphere moderates surface temperatures, shapes Earth's weather and climate, and creates most of the sea's waves and currents.

✓ Different amounts of solar energy are absorbed at different latitudes. The tropics are warmer than the polar regions because of this difference.

✓ Uneven solar heating causes convection currents to form in the atmosphere. The direction of air flow in these currents is influenced by the rotation of Earth.

✓ To observers on the surface, Earth's rotation causes moving air (or any moving mass) in the Northern Hemisphere to curve to the right of its initial path, and in the Southern Hemisphere to the left. The apparent curvature of path is known as the Coriolis effect.

Key Ideas Continued…

✓ The atmosphere responds to uneven solar heating by flowing in three great circulating cells over each hemisphere. The flow of air within these cells is influenced by Earth’s rotation (Coriolis effect).

✓ Large storms are spinning areas of unstable air that develop between or within air masses. Extratropical cyclones originate at the boundary between air

masses.

Earth’s Atmosphere

• Consists of the nearly homogenous mix of gases that surround the Earth and extend to approximately 90 km above the Earth

• Components:

Nitrogen 78.084% Oxygen 20.946%

Carbon Dioxide 0.033%

Layers of the Atmosphere

Atmospheric Circulation

Is powered by sunlight

Earth intercepts 1/2,200,000,000 of Sun’s radiant energy

Earth is in NEAR thermal equilibrium: Incoming heat = outgoing heat (we have disturbed balance - and shifted it to

absorbing more than is being re-radiated...temp. is shifting to a new equilibrium)

Heating at different latitudes is uneven rotation and striking angle

Reasons for Uneven Heating

The heat absorbed at latitudes is also influenced by the season…since the Earth is tilted 23.5 degrees on axis, facing of

hemispheres

Fig. 8-6, p. 207

Winter (Northern Hemisphere tilts away from sun) Spring (sun aims

directly at equator)

Earth’s Uneven Solar Heating Results in

Large-Scale Atmospheric Circulation

A convection current forms in a room when air flows from a hot radiator to a cold window and back.

Crude Circulation Model From Heating

• Density of air is controlled by:

– Temperature (decreases with increased temp)

– Pressure (increases with pressure)

– Moisture content (decreases with moisture)

• Warm air is less dense than cold air and moist air is

less dense than dry air.

• Air pressure is the

weight

of the air from Earth’s

surface to the top of the atmosphere.

– It equals 1.04kg/cm2 (standard air pressure, one

• Low pressure zone is where

air density is

lower

than in surrounding areas because the

air:

– is warmer

or

– has a higher moisture content

– associated with

rising air

• High pressure zone is where

air pressure is

higher

than in surrounding area because the

air:

– is cooler

or

– has lower moisture content

•

Fluids (air and water) flow from areas

of high pressure to areas of low

pressure.

• Change in pressure across a horizontal

distance is a pressure gradient.

• Greater the difference in pressure and the

shorter the distance between them → the

Rotation of the Earth strongly

influences winds.

Coriolis deflection

is the apparent deviation of

objects moving across Earth’s surface.

– Objects are deflected to the

right

of direction of

travel in the

northern hemisphere

,

Three major convection cells are present

in each hemisphere

• The

Hadley cell

extends from the Equator to about 30

latitude.

• The

Ferrel Cell

extends from 30

to about 50

latitude.

• The

Polar Cell

extends from 90

to about 50

latitude.

Global Wind Circulation

Wind Circulation

Monsoons Are Wind

Patterns That Change with

the Seasons

Monsoons are patterns of wind circulation that change with the

season. Areas with monsoons generally have dry winters and wet summers.

Sea breeze is cool air from over the water moving toward land.

Sea breezes occur after sunrise.

Land breezes occur after sunset when air warmed by the land

Monsoons Are Wind Patterns That

Change with the Seasons

A monsoon is a pattern of wind circulation that changes with the

season. (The word monsoon is derived from mausim, the Arabic word for

season). Locations where monsoons occur typically have wet summers and dry winters.

(left) Monsoon patterns.

During the monsoon circulations of January (a) and July (b), surface

Storms Are Variations in

Large-Scale Atmospheric

Circulation

Storms are regional atmospheric disturbances. Storms have high

winds and most have precipitation.

Tropical cyclones occur in tropical regions. These storms can

cause millions of dollars worth of damage and endanger life.

Extratropical cyclones occur in Ferrel cells, and are winter

weather disturbances. These storms can also cause extensive damage.

Storms

Are regional atmospheric disturbances characterized by strong winds and often accompanied by

precipitation

Cyclones - rotating masses of low-pressure air in which winds converge and ascend.

Extratropical Cyclone - form at the boundary between Polar Cell and Ferrel Cells (called the Polar Front)

Extratropical Cyclone Development

Formation process…

Winds in the Polar (from east) and Ferrel Cells (from west) moving in different directions. Flow is

disrupted by zones of alternating high/low pressure - this bends the flow into waves - since different flows have

different densities, the cold Polar Cell air slides under the warm air.

As the warm air is lifted - it cools, and precipitation develops…

Cold Front: Cold air doing the lifting

Warm Front: Warm air blowing on top of

Extratropical Storm

Hurricane Allen

(1980)

Tropical Cyclones Form in One Air

Mass

Air starts moving toward a zone of low pressure and veers off course to right

Core of tropical

cyclone rotating to the left, or counterclockwise

Air starts moving

toward a zone of low pressure and veers

off course to right

N

Equator

Fig. 8-25, p. 221

Hurricane Formation

Origin not well understood…but, source of power is!

Storm development occurs as

moisture is pulled up by air. When a tropical depression (low) occurs over water at about 26 degrees, higher circular winds begin to blow, some warm humid air is forced upward. This moisture condenses - releasing energy - which increases the

• Movement of air across a pressure gradient

parallel to Earth’s surface is called a

wind

.

• Winds are designated according to the

direction from which they come.

• In contrast, ocean currents are designated

according to the direction towards which they

travel.

• Global winds blow in response to variation in

pressure related to uneven solar heating

(insolation) of Earth’s surface.

Wind-driven currents are produced by the

interaction between the wind and the water

• As wind moves across the water, air

molecules collide with water molecules.

• When they collide, energy is transferred from

the air to the water.

• This energy transfer is inefficient:

•

Zonal wind flow

is wind moving nearly

parallel to latitude.

– This is a result of Coriolis deflection.

• A

gyre

is a circular current caused by:

– Westerly-driven ocean currents in the trade

winds

– easterly-driven ocean currents in the

Westerlies