WIND!

EARTH

What Wind DOESN’T do… If the Earth were smaller and did not rotate, warm air would rise in the tropics and travel to the poles where it would cool and sink. If the Earth were smaller and did not rotate, warm air would rise in the tropics and travel to the poles where it would cool and sink.

Because the Earth is not small, the air sinks long before it reaches the poles. Because the Earth is not small, the air sinks long before it reaches the poles. A Non-Rotating Earth…

But the Earth doesn’t stand still! Over long distances, wind is also affected by Earth’s rotation. Over long distances, wind is also affected by Earth’s rotation. The Coriolis effect is a change in the direction of moving air, water, or any objects on Earth’s surface due to its rotation. The Coriolis effect is a change in the direction of moving air, water, or any objects on Earth’s surface due to its rotation.

Now we’re talking!

Global Wind Systems Wind systems are wide zones of prevailing winds. Wind systems are wide zones of prevailing winds. Prevailing means the usual direction from which a wind blows. Prevailing means the usual direction from which a wind blows. Earth has three major wind systems: Earth has three major wind systems: Sailors created the term “trade winds” to name the dependable winds that helped them transport and trade goods. Sailors created the term “trade winds” to name the dependable winds that helped them transport and trade goods. The prevailing westerlies in the northern hemisphere are responsible for much of the weather in North America. The prevailing westerlies in the northern hemisphere are responsible for much of the weather in North America. The polar easterlies are cold, polar winds. The polar easterlies are cold, polar winds.

Jet Streams Jet Streams are ribbons of extremely fast moving air near the top of the troposphere. Jet Streams are ribbons of extremely fast moving air near the top of the troposphere. They are caused by contact between cold and warm air. They are caused by contact between cold and warm air. They are found at the boundaries between the polar and temperate zones and between the temperate and tropical zones. They are found at the boundaries between the polar and temperate zones and between the temperate and tropical zones. Wind speeds in a jet stream vary from 100km/h to 300km/h. Wind speeds in a jet stream vary from 100km/h to 300km/h.

Jet Streams Jet streams are not visible but sometimes they cause water to condense, forming clouds that reveal their position. Jet streams are not visible but sometimes they cause water to condense, forming clouds that reveal their position.

Jet Streams The polar jet stream, which affects Canada’s weather, forms at the junction of the prevailing westerlies and polar easterlies. The polar jet stream, which affects Canada’s weather, forms at the junction of the prevailing westerlies and polar easterlies.

Jet Streams In general, the weather north of a jet stream is cold while the weather south of the jet stream is warmer. In general, the weather north of a jet stream is cold while the weather south of the jet stream is warmer.

Jet Streams Storms often occur just to the south of the polar jet stream because the warm air is rising, creating the right conditions. Storms often occur just to the south of the polar jet stream because the warm air is rising, creating the right conditions.

Jet Streams

Fronts At any given time, several air masses over North America affect the weather in different regions. At any given time, several air masses over North America affect the weather in different regions. These air masses interact as they move. These air masses interact as they move.

Fronts Perhaps on a sunny day you have looked to the west and have seen an approaching wide band of clouds. This band of clouds would have indicated the boundary between two air masses, called a front. Perhaps on a sunny day you have looked to the west and have seen an approaching wide band of clouds. This band of clouds would have indicated the boundary between two air masses, called a front. A front may be several hundred kilometres wide as well as thousands of kilometres long. A front may be several hundred kilometres wide as well as thousands of kilometres long.

Fronts Each air mass has its own temperature and pressure. These conditions change at the front. Each air mass has its own temperature and pressure. These conditions change at the front. An approaching front means a change in the weather, and the extent of the change depends on the difference between conditions in the air masses. An approaching front means a change in the weather, and the extent of the change depends on the difference between conditions in the air masses.

Fronts Fronts usually bring precipitation. Fronts usually bring precipitation. Warm air at the front is displaced by denser cold air. The warm, moist air rises. As it cools, water vapour in the air condenses, forming clouds. Warm air at the front is displaced by denser cold air. The warm, moist air rises. As it cools, water vapour in the air condenses, forming clouds. Under the right conditions, the condensed water vapour will fall to Earth’s surface as precipitation. Under the right conditions, the condensed water vapour will fall to Earth’s surface as precipitation.

Cold Front When cold, dense air displaces warm air, it forces the warm air, which is less dense, up along a steep slope. When cold, dense air displaces warm air, it forces the warm air, which is less dense, up along a steep slope. Can bring narrow bands of thunderstorms and Can bring narrow bands of thunderstorms and severe weather severe weather

Warm Front Advancing warm air displaces cold air along a warm front, which develops a gradual boundary slope. Advancing warm air displaces cold air along a warm front, which develops a gradual boundary slope. Rainfall gradually increases as the front approaches. Forms lots of fog Rainfall gradually increases as the front approaches. Forms lots of fog

Stationary Front When two air masses meet but neither advances, the boundary between them stalls. The resulting stationary front often occurs between two modified air masses that have small temperature and pressure differences. The air masses can continue moving parallel to the front. When two air masses meet but neither advances, the boundary between them stalls. The resulting stationary front often occurs between two modified air masses that have small temperature and pressure differences. The air masses can continue moving parallel to the front. Usually form clouds and prolonged precipitation Usually form clouds and prolonged precipitation

Occluded Front Sometimes a cold air mass moves so fast that it overtakes a warm front, forcing the warm air up. As the warm air is lifted, the advancing cold air mass collides with the cold air mass in front of the warm front. Sometimes a cold air mass moves so fast that it overtakes a warm front, forcing the warm air up. As the warm air is lifted, the advancing cold air mass collides with the cold air mass in front of the warm front. Occluded means blocked or obstructed. Occluded means blocked or obstructed. A variety of weather can be expected. A variety of weather can be expected.

Homework Check your Understanding questions Check your Understanding questions Page 32: # 10, 11, 12 Page 32: # 10, 11, 12 Page 34 # 13, 14, 15, 16 Page 34 # 13, 14, 15, 16