Wind Atmospheric Circulation (22:39min)

Wind The horizontal movement of air from an area of high pressure to an area of lower pressure. Caused by the uneven heating of Earth’s surface by the sun. – Cooler, more dense air has higher air pressure and sinks. – Warm, less dense air has lower air pressure and rises.

Isobar Maps Isobar Maps show air pressure changes over an area. – The closer the isobars = higher the wind speeds. – The farther the isobars = slower the wind speeds. L H H Fast Winds Slow Winds

Wind Winds are classified by their direction and speed – Direction is described by the direction the wind is coming from. Arrows point in the direction that the wind is blowing to. – Ex. South wind blows from the south toward the north. – Speed is measured in miles per hour (mph) or a knot (kn). 1 knot = mph – ½ feathers = 5 knots – Full feathers = 10 knots

Determining Wind Speed & Direction Direction: Speed: From the Southeast 25 knots

Wind Types Winds are classified by how large of an area they affect. 1.Local Winds - blow over short distances. 2.Global Winds - blow steadily from specific directions over long distances.

Local Winds Blow from any direction and usually cover short distances Causes: – The sun heats the land faster than the water. – Land loses heat faster than water. 2 Types: – Land Breeze – Sea Breeze

Land Breeze Land Breeze – The flow of air from the land to the sea. – Occurs during the night when the land cools off faster than the sea. (Nighttime ONLY) Convection currents drive the cooler air out over the sea.

Sea Breeze Sea Breeze – the flow of air from the sea to the land. – Occurs during the day when air over the land is warmer than the air over the sea. (Daytime ONLY) Convection currents drive the cooler air in over the land.

Global Winds Winds that blow steadily from specific directions over long distances. – Warm air rises at the equator and cold air sinks at the poles thus producing global winds. Due to Earth’s rotation, global winds do not follow as straight path but curve – Coriolis effect.Coriolis effect – Northern Hemisphere = curve to the right – Southern Hemisphere = curve to the left – Equator = doldrums, calm to no wind – 30°N & S Latitude = Horse Latitudes, calm to no winds

Doldrums & Horse Latitudes Equator Doldrums Horse Latitudes Northern Hemisphere Southern Hemisphere

Global Wind Belts Trade Winds – Winds that blow between the equator and 30° N and S latitude, east to west. – Belt of warm, steady wind. Prevailing Westerlies – Winds that blow between 30° and 60° N and S latitude, west to east. – Very strong winds! Polar Easterlies – Winds that blow between 60° N and S latitude and the poles, east to west. – Extremely cold but weak.

Global Wind Belts Equator Polar Easterlies Prevailing Westerlies Trade Winds Prevailing Westerlies Trade Winds

Jet Streams Approximately 10km above Earth’s surface are bands of high-speed winds that blow from west to east. – Form at boundaries of adjacent air masses with significant differences in temperature. 2 Types: – Polar Jet Stream – 30-60° N and S latitude Polar Jet Stream Arctic cold meets warm air mass – Strongest jet stream – Subtropical Jet Stream – 30° N and S latitude Tropical hot meets warm air mass – Weaker jet stream

Jet Streams

Subtropical front