What is Wind? Winds are caused by differences in air pressure. This is horizontal movement of air of high pressure to low pressure. Unequal heating of the atmosphere.
Measuring Wind Wind direction is determined by a wind vane. The name of a wind tells where the wind is coming from. Ex: A north wind comes from the north blowing south.
Measuring Wind Wind speed is measured with a anemometer. The device has usually 3 to 4 cups mounted at the end of spokes that spin on an axis. The force of the wind against the cups causes the axis to move. A meter on the axle shows the wind speed.
Wind-Chill Factor Wind blowing over your skin removes body heat. The stronger the wind the colder you feel. The increased cooling of a wind is what we call the wind-chill factor.
Local Wind Local winds are winds that blow over a short distance. Local winds are caused by the unequal heating of Earth s surface within a small area.
Local winds Sea Breeze Land Breeze
Local Winds
Sea Breezes It takes more energy to warm up a large body of water than the same area of land. Heat rises from land, expands creating a low pressure, then cooler air from the body of water moves beneath the warm air. This causes the sea breezes during the daylight hours.
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Land Breezes Process is reversed at night. Land cools more quickly than water. Water warmed during the day expands and rises, cooler air over land moves beneath it. This creates land breezes moving back toward the body of water.
Global Winds Key point Like local winds and global winds are effected by the unequal heating of Earth s surface. The difference is that global winds occur over a large area.
Global Winds
Global Winds How it all begins. Warm air rises at the equator and cold air sinks at the poles. Air pressure is lower at the equator and higher near the poles.
Global Winds The difference in pressure causes wind from the poles to blow towards equator. However, higher in the atmosphere, air flows from the equator towards the poles. These currents creates global winds.
The Coriolis Effect If the Earth did not spin, global winds would blow in a straight line from the poles to the equator. Earth rotates from East to West This curves the winds.
The Coriolis Effect The curving of the winds through the rotation of the Earth is called the Coriolis Effect. Global winds in the Northern Hemisphere turn right. Global winds in the Southern Hemisphere turn left.
Global Wind Belts There are areas of the globe that are areas of calm. These are called the Doldrums and Horse Latitudes.
Global Wind Belts Doldrums are found near the equator where air rises rapidly but does not move far horizontally. Winds near the equator are very weak or none at all.
Global Wind Belts Horse Latitudes were named for an area where at 30⁰ N and 30⁰S latitude sailors reached an area where air stops moving towards the poles and sinks. This created an area with virtually no winds and sailors ran out of food and water for their horses and had to throw the horses overboard.
Global Wind Belts Trade Winds Prevailing Winds Prevailing Easterlies
Global Wind Belts Trade winds occur between 30⁰ latitude to the equator. High pressure builds near Horse latitudes blowing surface winds back towards the equator. In Northern Hemisphere the Coriolis Effect turns the winds west. Therefore, the winds are blowing from the Northeast to the Southwest.
Global Wind Belts Prevailing Westerlies occur between 30⁰ and 60⁰ latitude north and south. The Coriolis Effect turns the winds toward the east. In the Northern Hemisphere the winds blow from the Southwest and in the Southern Hemisphere from the Northwest.
Global Wind Belts Cold air near the poles sinks and flows back towards lower latitudes. The Coriolis Effect shifts the polar winds west, producing the Polar Easterlies. These winds have a great effect on our weather in North America.
Jet Streams Above 10 kilometers above Earth s surface are bands of high-speed winds called jet streams. Jet streams generally blow from west to east at speeds of 200 to 400 kilometers per hour. These are the polar and subtropical jet streams. These jet streams move in waves up and down depending on the time of the year.