Class 22 -- The Oceans ATMOSPHERE CIRCULATION AND WINDS Coriolis effect Prevailing winds and vertical circulation Factors modifying these winds -- Differential.

Class 22 -- The OceansClass 22 -- The Oceans

ATMOSPHERE CIRCULATION AND WINDSATMOSPHERE CIRCULATION AND WINDS

Coriolis effectCoriolis effect

Prevailing winds and vertical circulationPrevailing winds and vertical circulation

Factors modifying these winds Factors modifying these winds

-- Differential heating of land and sea-- Differential heating of land and sea

What drives the global wind patterns?What drives the global wind patterns?

Warm, moist air rising at low latitudesWarm, moist air rising at low latitudes

Cold, dry air sinking at higher latitudesCold, dry air sinking at higher latitudes

Fig. 6-7

If the earth were NOT rotating, convection cells in the atmosphere would look like this.

http://ww2010.atmos.uiuc.edu/

Coriolis effectCoriolis effect

Winds traveling long distances are deflectedWinds traveling long distances are deflected

……turn to the turn to the rightright in Northern Hemis. in Northern Hemis.

……turn to the turn to the leftleft in Southern Hemis. in Southern Hemis.

Why? --Speed due to earth’s rotation…Why? --Speed due to earth’s rotation…

90˚90˚ 0 km/hr 0 km/hr

60˚60˚ 800 km/hr 800 km/hr

30˚30˚ 1400 km/hr1400 km/hr

0˚0˚ 1600 km/hr1600 km/hr

But a person in Chicago is

moving toward the east at

~1000 km/hr.

Missile fired exactly southward from the north pole.

Viewed from space, the missile follows a straight path....

What does that person see?

Student animations CD-ROM

Coriolis effect animations

Coriolis Effect: Practical result:Coriolis Effect: Practical result:

•Things moving long distances on earth Things moving long distances on earth tends to be tends to be deflecteddeflected by Coriolis “force” by Coriolis “force”

•Deflection in N hemis.: “TO THE RIGHT”Deflection in N hemis.: “TO THE RIGHT”…(i.e., right hand turn relative to initial …(i.e., right hand turn relative to initial direction)direction)

•……in S hemis.: TO THE LEFTin S hemis.: TO THE LEFT

Amount of deflection depends on ... Amount of deflection depends on ...

... time of travel (how long it moves)... time of travel (how long it moves)

... distance of travel (how far it moves)... distance of travel (how far it moves)

Winds are deflected a large amount- they move Winds are deflected a large amount- they move for long time periods over long distances.for long time periods over long distances.

Fig. 6-7

If the earth were NOT rotating, convection cells in the atmosphere would look like this.

GLOBAL WIND SYSTEM

Major zonesTrade Winds

Westerlies

Polar Easterlies

1. Convection Cells1. Convection Cells

Occur at the Global scale, the continental Occur at the Global scale, the continental scale, and the local scalescale, and the local scale

Land/Ocean surface

Convergent & divergent zones between cells :Convergent & divergent zones between cells :•Convergent -- air masses come together + riseConvergent -- air masses come together + rise•Divergent -- sinking air comes down and Divergent -- sinking air comes down and spreads outspreads out

DescendingDescending air: air:–high atm. Pressure, dry airhigh atm. Pressure, dry air

•AscendingAscending air: air:–low atm. Pressure, rising moist air, high rainfall low atm. Pressure, rising moist air, high rainfall

1. Convection Cells1. Convection Cells

Occur at the Global scale, the continental Occur at the Global scale, the continental scale, and the local scalescale, and the local scale

Earth surface

Seasonal heating/cooling cyclesSeasonal heating/cooling cycles

Daily “ / “ “Daily “ / “ “

•Oceans and lakes -- little T changeOceans and lakes -- little T change•Land areas -- greater T changeLand areas -- greater T change

Wind patterns, cont’dWind patterns, cont’d-- Air vs. land Temperature Contrasts:-- Air vs. land Temperature Contrasts:

Daily cycle of winds in many places:Daily cycle of winds in many places:

(think Miami Beach)(think Miami Beach)

Day: onshore winds Day: onshore winds

Night: offshore windsNight: offshore winds

Example 1. Convection in coastal areasExample 1. Convection in coastal areas

Day

Night

San Francisco in the summer: San Francisco in the summer:

Leave your shorts at home!Leave your shorts at home!

•Land heats up-Land heats up- air rises air rises

•Onshore winds Onshore winds bring warm, moist air bring warm, moist air over cool water over cool water (upwelling)(upwelling)

•This creates Fog- This creates Fog- moves inlandmoves inland

Same idea, larger scale:Same idea, larger scale:

Summer: Hot continent - rising air above itSummer: Hot continent - rising air above it

Creates onshore winds (and rain)Creates onshore winds (and rain)

Winter: Cold continent, offshore windsWinter: Cold continent, offshore winds

2. Seasonal monsoon winds 2. Seasonal monsoon winds

(India, Southeast Asia)(India, Southeast Asia)

Summer (Wet) Winter (Dry)

Summer

Winter

3. Seasonal changes in H and L pressure zones over continents and oceans

Land

Ocean

Ocean

Summer- Where’s the Low Pressure Area?

Land

Ocean

Ocean

Where’s the High Pressure Area?

Winter

Winter:

Low Pressure areas over oceans

High ….. continents

Winter:

Low Pressure areas over oceans

High ….. continents

JanuaryFig. 6-11

Summer:

High Pressure areas over oceans

Low …. continents

January

4. Winds circle around low/high pressure zones: 4. Winds circle around low/high pressure zones: Coriolis effect:Coriolis effect:

Northern Hemisphere:Northern Hemisphere:

•Clockwise around Clockwise around H’sH’s•Counterclockwise Counterclockwise

around around L’sL’s

•These motions are These motions are superimposed on the superimposed on the Trades, Westerlies, etcTrades, Westerlies, etc..

4 Jan., 2008

• Hot, humid air rising-- Intense LOW PRESSURE• High Storm tides- sea surface “dome” in low-P center• Plus wind-driven surface currents• Flooding of coastal areas

Hurricanes

Summer

Winter