outline further reading: chapter 07 of the text book - surface winds on an ideal earth - subtropical...

Outline

Further Reading: Chapter 07 of the text book

- Surface Winds on an Ideal Earth

- Subtropical High-Pressure Belts

- Wind and Pressure Features at Higher Latitudes

Natural Environments: The AtmosphereGE 101 – Spring 2007

Boston University

MyneniLecture 17: Atmospheric Circulation

Feb-28-07(1 of 11)

- The ITCZ and Monsoon Circulation


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Surface Winds on an Ideal Earth-1

• Ideal Earth– No pattern of land and water

– No seasonal changes

– Equatorial regions receive the most insolation

• Surface has the warmest temperature

• Air rises

– Poles recieve the least insolation• Surface has the coolest

temperature

• Air descends

– Pressure gradients exist between the equator and poles


Feb-28-07(2 of 11)


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Surface Winds on an Ideal Earth-2


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H

L

L

H

Equatorial Trough

Inner-tropical Convergence Zone

Hadley Cell

Polar front ~ 60N

Mid-latitude Westerlies

Subtropical High ~ 30N

Trade winds

Polar High

Polar Easterlies


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• Equatorial Region

– Air rises at the equator

– Produces the “equatorial trough” at the surface

– Surface winds blow into this low pressure, forming the “inter-tropical convergence zone (ITCZ)”

– Winds veer to the right/left in the northern/southern hemisphere under the influence of the Coriolis force

– Produce the “Northest/Southeast Trades” at the surface

– Aloft air moves towards the poles, then cools and sinks around 30o N/S

– This closed circulation is called the “Hadley cell”

• Sub-tropical Region– Sinking air creates “subtropical high”

– Surface winds blow both towards the equator and towards the pole


– Produces the “Westerlies” at the surface

Surface Winds on an Ideal Earth


Feb-28-07(4 of 11)


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• The Poles

– Cold air descends over the poles

– Produces the “polar high” at the surface

– Surface winds blow out of this high pressure


– Produces the “polar easterlies”

• Midlatitudes– “Polar easterlies” converge with the “Westerlies”

– Convergence produces a low, air rises and subsides over the poles and the mid-latitudes

– The circulation in this region is very noisy and is only seen in the average patterns

• How do seasons affect this ideal circulation?– change the latitude of most intense solar heating

– change the temperature contrast between land and ocean, and hence the surface pressure patterns

Surface Winds on an Ideal Earth


Feb-28-07(5 of 11)


Boston University

Subtropical High-Pressure Belts


Feb-28-07(6 of 11)

July


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• Southern Hemisphere

– Confirms well to the pattern of the ideal circulation

– Three large high pressure-cells persist year long

– A fourth forms in July due to the cooling of Australia (southern hemisphere winter)

• Northern Hemisphere– Hawaiian High in the Pacific

– Azores High in the Atlantic

– Intensify in summer and move northward

– Have effects on east and west coasts• Rainless summer in west coast due to Hawaiian High

• Hot and humid summer in central and eastern US due to Azores High

Subtropical High-Pressure Belts


Feb-28-07(7 of 11)


Boston University

The ITCZ and the Monsoon Circulation


Feb-28-07(8 of 11)


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• The ITCZ

– As the seasons change, the region with the most insolation changes, hence the position of the ITCZ changes

– Over the ocean the shift is moderate ~10 degrees

– Over land, because of large seasonal changes in temperature, large shift occurs particularly over Asia

• Monsoon in Asia– In the summer, high insolation warms the continent and produces low-pressure

• Winds blow from the ocean to the land and then rise

• These warm and moist air brings heavy precipitation

– In the winter, the continent cools quickly, producing high-pressure• Winds blow from the continent to the ocean

• Dry conditions prevail

The ITCZ and the Monsoon Circulation


Feb-28-07(9 of 11)


Boston University

Wind and Pressure Features of Higher Latitudes


Feb-28-07(10 of 11)


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• Difference in land-water patterns

– Northern Hemisphere: large continental masses

– Southern Hemisphere: large ocean area with glacial ice sheet in the center

• Northern Hemisphere– In the winter

• Siberian High and Canadian High over continents

• Icelandic Low and Aleutian Low over the oceans

• Brings cold air to the south

– In the summer• Low pressure over continents (Asiatic Low)

• High pressure over the oceans (Hawaiian High and Azores High)

• Warm and dry conditions in west coasts

• Warm and moist conditions in east coasts

• Southern Hemisphere– South Polar High persists all year long due to the glacial ice sheet

– Surrounding low pressure

– Strong prevailing westerlies over higher latitudes

Wind and Pressure Features of Higher Latitudes


Feb-28-07(11 of 11)

outline further reading: chapter 07 of the text book - surface winds on an ideal earth - subtropical...

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