WIND AND PRESSURE EARTH SCIENCE UNIT: 4

PRESSURE EARTH SCIENCE UNIT: 4

AIR PRESSURE FACTS  The atmosphere is held to the earth by Earth’s gravity.  The pull of the earth’s gravity on the atmosphere creates PRESSURE  Air pressure occurs from ABOVE, BELOW, and from all directions (not just from above)  AIR PRESSURE CHANGES because of: 1. Temperature Changes 2. Altitude Changes  High Altitude = Less Pressure (less air on top)  Low Altitude = High Pressure (more air on top)  Changes in Air temperature cause changes in air pressure, which result in WIND  Air in the atmosphere has pressure because air has MASS

WARM AIR  LOW PRESSURE  EXPANDS  LESS DENSE  RISES  Warm air expands causing molecules to spread apart and becomes less dense. Less dense air rises and has low pressure.

COLD AIR  HIGH PRESSURE  CONTRACTS  MORE DENSE  WILL SINK  Cold air contracts and causes air molecules to become more dense. Dense air has high pressure and will sink.

LOW PRESSURE AIR  COLD  MORE DENSE  SINKS  NO CLOUDS  CLOCKWISE ROTATION  WINDS AWAY FROM THE CENTER  WARM  LESS DENSE  RISES  CLOUDS  COUNTER CLOCKWISE ROTATION  WINDS TOWARDS THE CENTER HIGH PRESSURE AIR

air density  Air consists of atoms and molecules, which have mass. So air has mass!!!  Because air has mass it has density, pressure, volume  Density : the amount of mass in a given volume of air. Density = mass / volume  High density: more molecules in a given volume of air. Low density: fewer molecules in a given volume of air. HIGH DENSITY LOW DENSITY

AIR PRESSURE  PRESSURE : THE FORCE PUSHING ON AN AREA OR SURFACE.  Air pressure : IS THE RESULT OF THE WEIGHT OF A COLUMN OF AIR PUSHING DOWN ON AN AREA.  DENSER AIR HAS MORE PRESSURE / LESS DENSE AIR HAAS LESS PRESSURE.  THE WEIGHT OF THE COLUMN OF AIR ABOVE YOUR DESK IS ABOUT THE SAME AS THE WEIGHT OF A LARGE SCHOOL BUS!! WHY DOESN’T AIR PRESSURE CRUSH YOUR DESK?????  BECAUSE MOLECULES IN AIR PUSH IN ALL DIRECTIONS – DOWN, UP, AND SIDEWAYS. SO THE AIR PUSHING DOWN ON THE TOP OF YOUR DESK IS BALANCED BY THE AIR PUSHING UP ON THE BOTTOM OF YOUR DESK.  BAROMETER : INSTRUMENT USED TO MEASURE CHANGES IN AIR PRESSURE

AIR PRESSURE AND CHANGES IN ALTITUDE  ALTITUDE : (ELEVATION) THE DISTANCE ABOVE SEA LEVEL. Sea level is avg level of oceans.  Air pressure decreases as altitude increases. (so does density) Which book has more pressure on it? The book second from the top or the book on the very bottom? This is the same with our atmosphere. Top of Mt. Everest has less pressure then standing on a beach near the ocean. (sea level air has pressure of the entire atmosphere pressing against it.

Notice the decreasing pressure with higher altitude. This is due to less air molecules at height and less molecules above them pressing them down. Atmospheric Pressure

Pressure Changes with Temperature In warmer air, the molecules spread apart. This means that there is lower pressure. In colder air, the molecules are compressed, causing higher pressure.

WIND EARTH SCIENCE UNIT: 4

WIND FACTS  WIND : The horizontal movement of air  WINDS ARE NAMED for the direction from which they are coming from (not the direction they are going)  WINDS ARE CAUSED by differences in air pressure  WIND BLOWS from areas of HIGH pressure to areas of LOW pressure

WIND FACTS  EARTH is unevenly heated by the sun’s rays.  The sun’s rays are the LEAST direct NEAR THE POLES  So the air becomes…..  cold air, high pressure, more dense., Sinks  The sun’s rays are MOST Direct near the EQUATOR  So the air becomes…..  Warm Air, Low Pressure, Less Dense, Rises

UNEQUAL HEATING OF THE SUN

SEA BREEZE vs LAND BREEZE SEA BREEZE : wind that blows from ocean or lake onto land  During the day.  Land warms up faster then water  Air over land becomes warmer then air over water  Warm air expands and rises, creating LOW pressure area.  Cool air blows inland from the water and moves underneath the warm air.  JIrUNk JIrUNk LAND BREEZE : wind that blows from land to ocean or lake  During the night  Land cools more quickly then water  Air over land becomes cooler than air over water  Warmer air over water rises Creating LOW Pressure area  cooler air moves from land to take its place.

Sea Breeze and Land Breeze

GLOBAL WINDS  GLOBAL WINDS : winds that blow steadily from specific directions over long distances.  Created by unequal heating of Earth’s surface

 Noon sun has direct rays near the equator. Heats that area intensely.  Near the north pole or south pole rays strike at a lower angle. Suns rays are spread out over a larger area heats much less.  Temps at Poles are much lower then equator…. PRESSURE differences.

GLOBAL WINDS  GLOBAL WINDS : the movement of air between the equator and the poles !  CORIOLIS EFFECT: The way the earths rotation makes the winds curve.  Northern Hemisphere = winds turn to their RIGHT  Southern Hemisphere = winds turn to their LEFT  If earth did not rotate….the winds would travel straight!

 CONFUSED????? ?  Winds are named for the direction in which they are COMING FROM!!!! Not where they are headed!!!  Turn to their Right or to their Left N hem. Their Right S hemi. Their Left

GLOBAL WIND BELTS  1. TRADE WINDS - 30’ N to Equator / 30’ S to Equator. Blow from SE / NE, Sailors used them to sail for trading (Trade Winds)  2. PREVAILING WESTERLIES – 30’ N and 60’ N / 30’ S and 60’ S. Blow from West to East (westerlies), important part of United States Weather.  3. POLAR EASTERLIES – Meet the prevailing westerlies at about 60’ N and 60’ S (Polar Front). Major effect on weather changes in U.S.

Important non wind belts  1. DOLDRUMS – areas near the equator with little to no wind. Sun warms surface causes wind to rise, creating an area of low pressure. Cool air moves into the area, but is warmed rapidly and rises before it moves very far. Winds are very weak.  2. HORSE LATITUDES : 30’ North and 30’ South. Air stops moving towards the poles and sinks. Sailors would get stuck, ran out of food and dumped horses overboard.