Local and Global Winds

Wind Wind is created by the unequal warming of the Earth (convection currents) Differences in atmospheric pressure cause the movement of air. A low pressure system is formed when hot air rises. A high pressure system is formed when cold air falls.

Wind There are two types of wind: – Global – Local

Local Winds Contrary to global winds, local winds can change speed and direction frequently. These are the winds that we feel on the Earth. They are created by local weather and temperature conditions.

Local Winds Sea Breeze – During the day, the Earth warms faster then the water. Therefore the breeze blows from the ocean to the Earth. This is called a Sea Breeze.

Local Winds Land Breeze – During the night, the Earth cools down faster then the water, which creates a land breeze. The wind blows from the land to the Ocean. – Video Video

Fill in sheet – land and sea breeze

Global Winds They generally blow at the same speed and direction. They are due to the combination of convection currents and the Coriolis effect (rotation of the Earth). Some are very high in the atmosphere so we cannot feel them on Earth.

Each hemisphere contains 3 major wind systems that divide the global winds. The Trade winds, the Prevailing westerlies and the Polar easterlies

Global Wind Patterns Main wind currents: Polar Easterlies (north and south) Prevailing Westerlies (north and south) Northeast Tradewinds (north only) Southeast Tradewinds (south only) See Figure 1.19, page 31 Note: ‘prevailing’ means to the usual direction from which the wind blows!

Global Wind Systems Wind System LocationPath Trade winds Between equator and 30 o N latitude Between equator and 30 o N latitude Between equator and 30 o S latitude Between equator and 30 o S latitude Air at equator warms, rises and travels to 30 o N or S lat. Air at equator warms, rises and travels to 30 o N or S lat. At 30 o N or S, air cools, sinks & moves W toward Equator & deflected W At 30 o N or S, air cools, sinks & moves W toward Equator & deflected W Prevailing westerlies Between 30 o and 60 o N latitude Between 30 o and 60 o N latitude Between 30 o and 60 o S latitude Between 30 o and 60 o S latitude Air circulation pattern is opposite to that of the trade winds Air circulation pattern is opposite to that of the trade winds Surface winds blow from W to E and towards Poles Surface winds blow from W to E and towards Poles Polar Easterlies Between 60 o N latitude and NP Between 60 o N latitude and NP Between 60 o S latitude and SP Between 60 o S latitude and SP Air circulation pattern is similar to that of the trade winds Air circulation pattern is similar to that of the trade winds Surface winds blow from E to W and away from Poles Surface winds blow from E to W and away from Poles See Table 1.3, page 31

Global Warming and Cooling of Air Air is warmest at the equator and coolest at poles So air should rise at the equator and sink at the poles However, due to the size of the Earth, air from the equator cools before it reaches the poles and air from the poles will warm before it reaches the equator See Figures , page 30

Actual Wind Currents More realistically, we see pockets of convection currents above the Earth’s surface.

Coriolis Effect Due to the rotation of the Earth, any object that moves across the surface of the Earth will be pushed to the left or right Video

In the Northern Hemisphere, the coriolis effect blows the winds from West to East (prevailing Westerlies). That’s the reason why most of our weather systems come from the West of Canada.

Video – Atmospheric Circulation Video Notes/practice sheet

Jet Streams A narrow band of fast- moving wind Between the troposphere and the stratosphere Aided by the Coriolis Effect Up to 300 kph Altitude 10 – 12 km

Polar Jet Streams Major jet streams are polar jet streams Separate the polar easterlies from prevailing westerlies in NH and SH Move west to east See Figure 1.20, page 32

Subtropical Jet Streams Minor jet streams are subtropical jet streams Occur where trade winds meet westerlies Move west to east Storms form along jet streams & cause large- scale weather systems Weather systems usually follow the path of jet streams See Figure 1.20, page 32

Jet Streams The polar jet stream, which mostly affects the Canadian climate, forms when the Prevailing westerlies and polar Easterlies meet. In general, the weather is colder North of the jet stream and warmer South of the Jet stream.

Jet Streams What happens to the jet stream when the seasons change? – During the winter, the jet stream moves South. – During the summer, the jet stream moves up to the North.

Jet Streams – VideoVideo Notes Practice sheet: Worldwide Wind Currents Quiz

Video – Wind Power Video Bill Nye - WindWind