Section 3: Winds

1.What is Wind? a.Wind: the horizontal movement of air from an area of high pressure to an area of lower pressure i.Caused by differences in air pressure 1.Which are mostly caused by unequal heating of the atmosphere ii.As air becomes less dense, its air pressure decreases iii.Cool, dense air with a higher pressure flows underneath the warm, less dense air—forcing warm air to rise

b. Measuring wind i.Described by their direction and speed 1.Direction is determined with a wind vane a.The name of a wind tells you where the wind is coming from i.Ex: a south wind blows from the south toward the north

2. Anemometer: an instrument used to measure wind speed a.Has three or four cups mounted at the ends of spokes that spin on an axle b.A meter on the axle shows the wind speed

c. Wind-chill factor: the increased cooling a wind can cause i.The wind blowing over your skin removes body heat 1.The stronger the wind, the colder you feel

2. Local winds: winds that blow over short distances a.Caused by the unequal heating of Earth’s surface within a small area i.Form only when large-scale winds are weak

b. Sea breeze: a local wind that blows from an ocean or lake i.Unequal heating often occurs along the shore of a large body of water ii.It takes more energy to warm up a body of water than it does to warm up land iii.The air over land becomes warmer than the air over the water 1.The warm air expands creating a low-pressure area 2.Cool air blows from over the water and moves underneath the warm air causing a sea breeze

c. Land breeze: the flow of air from land to a body of water i.The process of a sea breeze is reversed at night 1.Land cools more slowly than water, so the air over the land becomes cooler than the air over the water. 2.As the warmer air over the water expands and rises, cooler air from the land moves beneath it

3. Global winds: wind that blow steadily from specific directions over long distances a.Created by the unequal heating of Earth’s surface, and occur over a large area b.Global Convection Currents i.Temperature differences between the equator and the poles produce giant convection currents in the atmosphere

ii. Warm air rises at the equator, and cool air sinks at the poles 1.Air pressure tends to be lower near the equator 2.Difference in pressure causes winds at Earth’s surface to blow from the equator 3.Higher in the atmosphere, air flows away from the equator toward the poles producing global winds

c. Coriolis effect: the way Earth’s rotation makes winds curve i.If Earth didn’t rotate, global winds would blow in straight lines from poles to the equator ii.Global winds in the Northern Hemisphere gradually turn toward the right 1.In the Southern Hemisphere, winds gradually curve toward the left

4. Global Wind Belts a.The Coriolis effect and other factors combine to produce a pattern of calm areas and wind belts i.The major global winds are the trade winds, the polar easterlies, and the prevailing westerlies.

b. Doldrums i.A calm area above the equator where warm air rises

c. Horse Latitudes i.Warm air that rises at the equator divides and flows both north and south 1.At about 30° north and south latitudes, the air sinks ii.Latitude: distance from the equator, measured in degrees iii.Hundreds of years ago, sailors becalmed in these waters and ran out of food and water for their horses, hence the name horse latitudes

d. Trade Winds i.The area of high pressure created when the cold air over the horse latitudes sinks 1.Causes winds to blow toward the equator and away from it a.Toward the equator are turned west by the Coriolis effect i.Winds in the Northern Hemisphere generally blow from the northeast ii.Southern Hemisphere—blow from the southeast 2.Sailors have relied on these winds to move ships of cargo from Europe to the West Indies and South America

e. Prevailing Westerlies i.Between 30° and 60° north and south ii.Blow toward the poles and are turned toward the east by the Coriolis effect iii.Blow generally from the southwest in north latitudes and from the northwest in south latitudes iv.Play an important role in the weather of the US

f. Polar Easterlies i.Cold air near the poles sinks and flows toward the equator ii.The Coriolis effect shifts these polar winds to the west, producing polar easterlies iii.Meet polar westerlies at about 60° north and south latitudes along the prevailing westerlies 1.Mixing of cold or warm air has a major effect on weather in the US

g. Jet streams: bands of high-speed winds i.Hundreds of kilometers wide but only a few kilometers deep ii.Generally blow from west to east at speeds of 200 to 400 kilometers per hour

* What is wind?

* Compare the conditions that cause a sea breeze with those that cause a land breeze.

* Briefly describe the three major global wind belts and where they are located.