Winds Measuring wind Winds are described by their

Winds

Measuring wind § Winds are described by their direction and speed. § Speed of wind is measured by an anemometer. ( Has three cups mounted at the end of spokes that spin on an axle. The spinning of the cups is measured by a speedometer § The direction measured by a weather vane. The name of the wind tells you the direction it is coming from. Ex. South winds blow from the south to the North

What causes the winds? § Air is a fluid, so it can move easily from place to place. § Fluids move areas of from high pressure to low pressure § All winds are caused by difference in air pressure!!!! § Turn to your partner and discuss the density of low pressure, compared to the density of a high pressure

Local winds § This wind occurs when there is a large body of water near by. § During the day: There might not be wind inland, but there may be a wind blowing from the water towards the beach or large body of water. § They are caused by unequal heating of the Earth’s surface in a small area. § Local winds blow when there is no other winds blowing from far away. § It takes more energy to heat water § § § than the land. So land heats quicker than water. The water is cooler, so it’s density is greater than the heat molecules on land. The higher pressure above the water moves underneath the hot lower pressure and pushes the air up causing a breeze. This is called a sea or lake breeze At night the opposite happens, this is called a land breeze Turn to your partner and draw what causes sea breezes during the day on the white boards.

Monsoons § Similar to sea breezes, but occurs § § § over wider areas. In South and Southeast Asia The land gets hotter than the ocean, and this heating occurs all summer. In the winter the land cools faster than the ocean, so the higher pressure above the land, moves under the higher pressure above the ocean. This causes humid heat to rise into the air inside the water vapor. As it cools condensation takes place and then heavy precipitation occurs, which is needed for crops

Global Winds § Caused by unequal heating of § § the Earth’s surface. The direct rays near the equator are more intense the light hitting the poles The pressure at the poles is greater than at the equator. This uneven heating causes giant convection currents. The High pressure moves down towards the lower pressure at the equator, this moves under the low pressure at the equator pushing the air at the equator up to the poles.

Coriolis Effect § If the Earth didn’t spin the § § § global wind would blow in a straight line from poles to equator The Earth spins from east to west, making these winds curve counterclockwise In Northern Hemisphere the global winds turn right In Southern Hemisphere the winds turn to the left

Other types of Winds § Doldrums: Near the equator. § The sun heats strongly, warm air rises and creates low pressure, when cool air comes in (Higher pressure) It gets warmed to quickly to push the low pressure anywhere (heated air) Is sailing a sail boat in this region wise? Explain to your partner.

Horse Latitudes § 30 degrees north and south of the equator the air stops moving towards the poles and sinks, so another area of very little wind forms. § Hundreds of years ago sailors, ran out of food and water for their horses that they brought with them, and they had to throw the horses overboard.

Trade Winds § When cold air over the horse latitudes sinks, it produces § § a region of high pressure This high pressure causes surfaces winds to blow towards and away from the equator The winds toward the equator are turned west by the coriolis effect These winds are constant. In the Northern Hemisphere the blow from 30 degrees latitude towards the equator from the northeast. In the Southern Hemisphere the blow from 30 degrees latitude towards the equator from the southeast.

Westerlies § In the middle latitudes, winds that blow towards the poles are turned toward the East because of the Coriolis effect § Called westerlies because they blow from west to east § Blow from the southwest between 30 and 60 degrees latitude at both hemispheres § They play an important part in the weather in the United States

Jet Streams § 10 km above the Earth’s surface are high speed winds called the jet stream. § They are hundreds of km. wide, but only a few km deep § They blow from west to east § At speeds of 200 -400 km/h § Pilots fly east in the jet stream § Why might they do this?

Polar Easterlies § Cold air near the poles sink and flows back toward the lower latitudes § The coriolis effect shifts these polar winds to the west producing winds § The Easterlies meet the westerlies at about 60 degrees in both hemispheres along the Polar Front § This mixing of high and low pressures has a major effect on weather changes in the United States.