How are clouds formed. Weather Clouds form when air is cooled to its dew point as it rises.

Air Pressure and Wind

What is Air Pressure? Video Air pressure is the pressure exerted by the weight of air above Exerted in all directions (up, down, and sideways) The air pressure pushing down on an object exactly balances the air pressure pushing up on the object Average Air Pressure at sea level is 1 kg/cm2, 1013.2 mb, or 29.92 in. of mercury

Measuring Air Pressure Barometer: device used for measuring air pressure Unit: millibars (mb) inches of mercury Torricelli: invented the mercury barometer in 1643

Wind – What causes it? Wind is a result of horizontal differences in air pressure Air flows from areas of high pressure to areas of lower pressure. Video

How do we get pressure differences on Earth? The unequal heating of earth’s surface generates pressure differences Solar radiation is the ultimate energy source for most wind

Factors Affecting Wind Pressure Differences Coriolis Effect

Pressure Differences Isobars lines on a map that connect places of equal air pressure A pressure gradient The spacing of isobars indicates the amount of pressure change over a given time

Isobars Closely spaced isobars: indicate a steep pressure gradient and high winds. Widely spaced isobars: indicate a weak pressure gradient and light winds.

Coriolis Effect The Coriolis effect describes how Earth’s rotation affects moving objects. Northern Hemisphere Deflected to right, Moves counterclockwise Southern Hemisphere Deflected to the left, Moves clockwise

Jet Streams Animation Jet streams are fast-moving rivers of air Speed: 120 and 240 kilometers per hour Direction: West-to-east direction. Drive weather systems Animation

High and Low Pressure System Low Pressure Centers High Pressure Centers Centers of Low Pressure High Pressure AKA Cyclones Anti-cyclones Pressure Behavior Pressure drops Pressure increase Wind Behavior Winds blow counterclockwise Winds blow outward and clockwise Weather Associated Severe and stormy Fair and Sunny Symbol “L” that is RED “H” that is BLUE

Measuring Wind Direction Labeled by the direction from which they blow Ex: winds blowing from the Southeast. Tool: Wind Vane

Wind Speed Anemometer Measures how fast wind is blowing

Global Winds The atmosphere balances itself by acting as a giant heat-transferring system Moves warm air to the poles and cool air towards the equator

Global Winds Trade winds Westerlies Polar easterlies Polar front Two belts of winds that blow almost constantly from east to west Westerlies Dominate west to east motion of the atmosphere (Jet Stream occurs here) Polar easterlies Winds that blow east to west Polar front Interaction of warm and cool air masses produces a stormy belt