Global Wind PatternsGlobal Wind Patterns

Science 1206Science 1206

Lesson ObjectivesLesson Objectives

► using scientific theory, describe and explain using scientific theory, describe and explain heat transfer and its consequences in both heat transfer and its consequences in both the atmosphere and hydrosphere, relating the atmosphere and hydrosphere, relating this science to natural phenomena this science to natural phenomena

► identify the different prevailing winds identify the different prevailing winds around the Earth around the Earth

► recognize that high heat transfer between recognize that high heat transfer between oceans and the air above creates convection oceans and the air above creates convection currents within the atmosphere currents within the atmosphere

► explain the importance of convection and explain the importance of convection and the Earth's rotation in causing prevailing the Earth's rotation in causing prevailing winds winds

Prevailing WindsPrevailing Winds

►This lesson will concentrate on the This lesson will concentrate on the major winds of the Earth called the major winds of the Earth called the prevailing windsprevailing winds. . 

►The prevailing winds are also know as The prevailing winds are also know as the the trade windstrade winds due to their due to their importance to trade by sailing ship importance to trade by sailing ship back in the time of the great explorers. back in the time of the great explorers.

Prevailing Wind Patterns:Prevailing Wind Patterns:

► The winds are one of the most important The winds are one of the most important features when discussing weather. features when discussing weather.

►WindWind - the movement of air in the - the movement of air in the atmosphere. atmosphere.

► Some winds are local while others are Some winds are local while others are prevailing. prevailing.

► Local windsLocal winds – occur in a fairly small region. – occur in a fairly small region. ► Prevailing windsPrevailing winds – affect large areas of the – affect large areas of the

earth. earth.

The Coriolis Effect:The Coriolis Effect:

►Coriolis Effect -Coriolis Effect - In any rotating In any rotating system anything that moves long system anything that moves long distances appear to change direction. distances appear to change direction.

► In the In the northern hemispherenorthern hemisphere, The , The Coriolis effect causes winds to twist to Coriolis effect causes winds to twist to the the rightright of the direction of flow. of the direction of flow.

► In the In the southern hemispheresouthern hemisphere, The , The Coriolis effect causes winds to twist to Coriolis effect causes winds to twist to the the left left of the direction of flow.of the direction of flow.

Coriolis EffectCoriolis Effect

►The prevailing winds are mainly the The prevailing winds are mainly the result from the transfer of heat energy result from the transfer of heat energy from the land and oceans to the from the land and oceans to the atmosphere. atmosphere.

►The resulting convection currents and The resulting convection currents and interaction with the interaction with the CoriolisCoriolis effect effect creates major wind currents over the creates major wind currents over the globe. globe.

Prevailing WindsPrevailing Winds

Equator

30o north

60o north

30o south

60o south

Northeast Trade Winds

Mid-latitude Westerlies.

Mid-latitude Westerlies.

Causes of Prevailing Causes of Prevailing Winds:Winds:

There are combinations of things that There are combinations of things that causecause

prevailing winds. They are: prevailing winds. They are: ►Convection currents set up in the Convection currents set up in the

atmosphereatmosphere►Earth’s west to east rotation Earth’s west to east rotation

Northeast Trade Winds:Northeast Trade Winds:

Warm air from the equator area Warm air from the equator area forms forms equilateral convection currentequilateral convection current..

This warm air rises and expands This warm air rises and expands leaving behind an area of low leaving behind an area of low pressure.pressure.

As it moves northward, it gets so cold As it moves northward, it gets so cold and dense that it sinks down towards and dense that it sinks down towards the earth’s surface, causing an area the earth’s surface, causing an area of high pressure.of high pressure.

Northeast Trade Winds:Northeast Trade Winds:

The surface air then moves away The surface air then moves away from this area of high pressure from this area of high pressure toward the low pressure area at the toward the low pressure area at the equator.equator.

This surface air twists to the right as This surface air twists to the right as it moves toward the equator causing it moves toward the equator causing the Northeast Trade Winds.the Northeast Trade Winds.

Mid-latitude WesterliesMid-latitude Westerlies

At 30° latitude some of the equatorial At 30° latitude some of the equatorial convection current is deflected northward convection current is deflected northward toward another low pressure area around toward another low pressure area around 60° latitude.60° latitude.

The mid-latitude convection current The mid-latitude convection current results when its warm air meets the cold results when its warm air meets the cold air.air.

The air twists to the right as it flows The air twists to the right as it flows northward, causing the mid-latitude northward, causing the mid-latitude westerlies.westerlies.

Polar EasterliesPolar Easterlies

Near the north pole the air is cold and Near the north pole the air is cold and dense, so it sinks. This causes a high dense, so it sinks. This causes a high pressure area at the surface. The surface pressure area at the surface. The surface air moves southward, away form this air moves southward, away form this high-pressure area, at the same time high-pressure area, at the same time twisting to the right, causing the polar twisting to the right, causing the polar easterlies.easterlies.

Effects of Prevailing Winds:Effects of Prevailing Winds:

Distributes large amounts of solar Distributes large amounts of solar energy to colder parts of the world.energy to colder parts of the world.

Returns a flow of colder air Returns a flow of colder air southward.southward.

Carry moisture, causing snow and Carry moisture, causing snow and rain.rain.

Jet Streams

►High altitude, fast moving, winds High altitude, fast moving, winds in the troposphere that generally in the troposphere that generally flows from west to east over the flows from west to east over the mid-latitudes. mid-latitudes.

►The jet streams separate cold The jet streams separate cold polar air to its north from warmer polar air to its north from warmer air to its south.air to its south.

http://www.stuffintheair.com/images/SeparationJet.jpg

Summary: Summary:

►Air pressure gradients, or the Air pressure gradients, or the difference between regions of difference between regions of high and low air pressure, impel high and low air pressure, impel air in the direction of lowest air in the direction of lowest pressure, creating wind. The pressure, creating wind. The larger the air pressure gradient, larger the air pressure gradient, the greater the wind speed. The the greater the wind speed. The Coriolis effect also affects wind Coriolis effect also affects wind speed and direction. speed and direction.