Understanding Wind
Review: What is air pressure? Air pressure: the force of the weight or air on a surface exerted in all directions
How is air pressure measured? Barometer: a device used to measure air pressure when air pressure ↑, mercury in the tube ↓ when air pressure ↓, the mercury in the tube ↑ pressure is measured in millibars (mb) (Sea-level pressure = 1013.2 mb) Mercury Aneroid
High v. low air pressure High air pressure = more downward force, air sinks, clears the air of clouds! Low air pressure = less downward force, air rises, causes clouds, rain, bad weather High pressure sky Low pressure sky
What causes wind? The sun is the ultimate source for most wind Creates areas of high and low pressure
Mr. Fetch's Earth Science Class Air flows from areas of higher pressure to areas of lower pressure. This causes air to move, creating WIND! H L YouTube: Indoor Skydiving Mr. Fetch's Earth Science Class Mr. Fetch’s Earth Science Classroom
What affects wind? Three factors combine to control wind: pressure differences (pressure gradient) the Coriolis effect friction
How do pressure differences affect wind? Differences in pressure = wind The greater the difference in pressure, the greater the wind speed (= stronger wind)
What are isobars? Isobars: lines on a map that connect places of equal air pressure
What is a pressure gradient? Pressure gradient: the spacing between isobars (remember that wind moves from higher pressure to lower pressure) Closely spaced isobars = steep pressure gradient and strong winds Widely spaced isobars = weak pressure gradient and light winds
Light Winds (SLOW) Strong Winds (FAST)
What is the Coriolis effect? The Coriolis effect describes how Earth’s rotation deflects all free-moving objects or fluids, including wind and water Air does not move in a straight line because of Earth’s rotation. Coriolis Effect
How does Coriolis effect change wind? Changes only wind direction, not wind speed stronger wind = greater deflection strongest at poles, weakens toward the equator
YouTube: Coriolis
Coriolis Effect Northern Hemisphere Southern Hemisphere
How does friction affect wind? “Bumpy” surfaces such as hills and mountains increase friction, which can slow wind and change its direction If friction ↑, then wind speed ↓ If friction ↓, then wind speed ↑
What are jet streams? Jet streams: fast-moving rivers of air that travel 320-480 kilometers per hour (200-300 mph) from west to east They are above the “friction layer” and tend to blow parallel to isobars
Air pressure & Jet streams
What type of weather would you expect? What is a cyclone? Cyclone = a center of low pressure Pressure decreases from the outer isobars towards the center Moves counterclockwise in Northern Hemisphere What type of weather would you expect?
What type of weather would you expect? What is an anticyclone? Anticyclone = center of high pressure pressure increases from the outer isobars towards the center Clockwise in Northern Hemisphere What type of weather would you expect?