9 CONVECTION CURRENTS move the air in our atmosphere! We have global winds that blow because of these large convection currents
10 CONVECTIONWind over the shore changes direction because of EARTH’S UNEVEN WARMING & COOLING! We can these local winds
11 Click the Video button to watch a movie about convection currents.
12 CONVECTION DEMOS! Tea bag http://www.youtube.com/watch?v=G9QJ1vv2WyM Colored Water
13 Why does hot air rise and cold air sink? Cool air is more dense than warm air, so the cool air ‘falls through’ the warm air.Why are the heating elements placed beneath hot water tanks in people’s homes?Hot water rises.So when the element heats the water, and the hot water rises, the water tank is filled with hot water.
15 Wind is the movement of air from an area of high pressure to an area of low pressure. This is caused by the unequal heating of the Earth’s surface.As air is heated, it becomes less dense and rises. The air pressure is also lower .Cooler, more dense air, has a higher pressure, and moves under the warmer air.This causes a convection current,creating windThe greater the pressuredifference, the faster the airmoves, and the stronger thewind blows.
16 How is Wind Measured?Wind direction is measured with a wind vane, which points in the direction the wind is coming from.This is how the wind is named.A western wind is blowing from the west.This means a northern wind actually blows toward the south.Wind speed is measured with an instrument called an anemometer.
17 Why We have Global Winds Since the air near the equator is less dense, it rises forming areas of low pressure.The cold air near the poles sinks because it is more dense, forming areas of high pressure.The air moves in large circular patterns called convection currents.The change in density is due to the unequal heating of Earth’ssurface
18 L H 90 30 60 Cold Moist Air Rises Cool Dry Air Sinks 6090Warm Moist Air RisesVery Cold Air SinksCold Moist Air RisesCool Dry Air SinksCool Dry Air SinksCold Moist Air RisesVery Cold Air Sinks
19 Wind Moves from HIGH to LOW 306090Wind Moves from HIGH to LOW
20 Objects are deflected to the RIGHT in the Northern Hemisphere 306090Objects are deflected to theRIGHT in the Northern HemisphereBut why?
21 The Coriolis EffectAs Earth rotates, the Coriolis effect turns winds in the Northern Hemisphere toward the right.
22 Northern Global Wind Patterns Polar Easterlies90 – 60 latitude from the eastPrevailing Westerlies60 – 30 latitude from the westTrade winds30 – 0 latitude from the East
23 Global WindsPolar Easterlies are the wind belts that extend from the poles to 60° latitude in both hemispheres. They form as cold, sinking air moves away from the poles. They can carry cold arctic air over the U.S. which can produce snow and freezing weather.Westerlies are the wind belts found between 30° and 60° latitude in both hemispheres. They blow toward the poles from west to east. These winds can carry moist air of the U.S. producing rain and snow.Trade Winds are the winds that blow from 30° latitude almost to the equator in both hemispheres. They curve to the West as they blow toward the equator.
24 Global Winds, continued The Doldrums The trade winds of the Northern and Southern Hemispheres meet in an area around the equator called the doldrums. there is very little wind because the warm, rising air creates an area of low pressure. The name doldrums means “dull” or “sluggish.”
26 Jet StreamsNarrow belts of high-speed winds that blow in the upper troposphere and lower stratosphere. Knowing the path of a jet stream is important not only to pilots but also to meteorologists. Because jet streams affect the movement of storms, meteorologists can track a storm if they know the location of a jet stream.
27 Jet StreamsJet Streams form at latitudes where wind systems come togetherHigh speed westerly winds form high above the surface
28 Local Winds Sea Breeze Land Breeze Local winds move over a short distanceCaused by the heating of a small area of Earth’s surfaceSea BreezeThe sun warms the land faster than the water, so the air abovethe land becomes warmer.The cooler air over the water moves inlandLand BreezeAt night, the land cools faster than the water, so the air abovethe land becomes cooler.The cooler air over the land moves out to the water.
29 Local WindsLocal winds generally move short distances and can blow from any direction.Mountain and valley breezes are examples of local winds caused by an area’s geography.Sea and land breezes are affected by temperature.