World Geography 3200 2.4 WINDS Understand the cause of winds and how they affect climate Chapter 4 Pages 59-67

2.3.1 Air moves from areas of high pressure to areas of low pressure. Think of: Air inside a balloon Air exhaled from a person’s lungs Air powered pellet gun The movement of air from high and low pressures in the earth’s atmosphere are responsible for wind! P. 59-61

2.3.1 What is Wind? Wind: * It is the flow or movement of air. * It results from air masses of different temperatures lying next to each other * The resulting pressure variation causes “wind” to blow from high pressure area to low pressure area.

2.3.1 Define the term Prevailing Wind. p.61-63 Prevailing Winds: They are regular, predictable, normal winds in the same direction They are caused by global convection cells More on these later!

2.3.2 Describe conditions that result in Land and Sea Breezes During the day the land heats much faster than the water, consequently the air over the land heats and rises. The rising air over the land leaves a relatively low pressure. The air pressure over the water is relatively high, therefore wind blows from high pressure (water) to low pressure (land) Hence the name 'sea breeze'—the wind is blowing off the sea.

Land Breezes: 1. The sea air is warmer than land air. Because this air is warmer, it rises and leaves a relatively low pressure over the sea. 2. The land air then blows to the low pressure over the sea.

Remember—winds are named for where they come from. For example, easterly winds come out of the east; southerly winds come out of the south; sea breezes come from the sea.

2.3.2 Describe Conditions that result in Land and Sea Breezes Land Breeze Sea Breeze Sea air warmer than land air Air rises over sea, leaving a relative low pressure Land air moves to lower pressure Land air is warmer than sea air Air rises over land, leaving a relative low pressure Sea air moves to lower pressure

2.3.6 Define windward, leeward and rain shadow

Windward is on the side facing the wind. Wind carries precipitation Leeward is on the side sheltered away from the wind. Wind is usually drier Rain shadow is a dry area on the leeward side of a mountain

2.3.8 Explain the relationship between wind systems and precipitation Prevailing winds blowing off the ocean and onto the land results in high precipitation. Especially if the wind is blowing off a warm ocean, like the Indian Ocean or the south Pacific. If wind is blowing off the land, then there is very little moisture in it, resulting in low precipitation.

Knowing the direction of winds over mountains is also important in predicting precipitation. The windward side of a mountain is going to receive the greatest rainfall, while the leeward side will find itself in a rain shadow.

2.3.8 Explain the relationship between wind systems and precipitation How do the prevailing winds affect precipitation in: England Midwestern U.S. British Columbia Northern Africa Central Australia Question #26 p. 67: