Download Pressure belts

Major impacts of the Earth-Sun relationship:
Global circulation of air and water
Pressure – caused by Earth’s gravity
Earth’s gravity pulls air molecules down towards the surface of the Earth
Elevation matters – think of a cheerleader pyramid
1. Layer of molecules closest to Earth have the highest pressure
a. More molecules are pressing down on them
b. Fast fact: air pressure at sea level is approximately 15 pounds/inch
2. Layer of molecules in upper atmosphere have a much lower pressure
a. No air molecules exist above them to push down
b. Fast fact: it is harder to breath at higher elevations since there is
lower pressure, which is another way of saying there are less
molecules in the same amount of space (volume)
Not all areas of Earth’s surface have the same pressure
due to different elevations & different temperatures (uneven heating by sun)
1. High pressure air moves towards Low pressure air
a. Think of a popped tire – air rushes out from high pressure area
b. High pressure generally brings fair weather and cooler temperatures
c. Low pressure generally brings stormy weather and hotter
temperatures
Convection – caused by the Sun
Heat energy of sun causes air molecules to move
1. Sun warms some molecules and causes them to rise since their pressure and
density drops
2. Rising air bring moisture with it since water is also evaporating in the warmth
3. Air rises until it gets far from Earth’s surface
4. Air begins to cool, water vapor condenses into clouds
5. Cold air (more dense) begins to sink back to Earth, clouds drop rain
6. Process begins again
Combining Pressure and Convection: pressure bands, winds, currents, and
precipitation
1. Heat of the sun causes warm air to rise
2. Rising warm air causes a Low pressure area – since less air pushing down now
3. A local High pressure area will move in from the side to fill in the new Low pressure area
Pressure bands - latitudes where there is the same general pressure
There are 4 pressure belts in each hemisphere <DIAGRAM>
1. Equatorial Lows
a. Equator and tropics (0° N/S)
b. constantly heated and rising air
c. gets replaced by air flowing from the poles (high pressure area)
2. Polar Highs
a. 90° N and S (the poles)
b. coldest air on earth, so it is the highest pressure & wants to fill L pressure areas
near equator
Air wants to flow from poles to equator, but an interesting thing ends up happening
a. as the High pressure from the poles moves across earth it is warmed by land.
Warm air ends up rising and causing a new low pressure area
b. as the Low pressure from the Equator gets into the atmosphere it cools and
sinks back. This ends up causing a new High pressure area
3. Subpolar lows
a. 60° N and S of the Equator
b. cold air flowing from poles heats up and rises
4. Subtropical Highs
a. 30° N and S of the Equator
b. caused by air that rose at the Equator and then cooled and sank back
Winds bands – latitudes where air has a predictable motion
Air that moves horizontally from H --> L pressure
Prevailing winds: bands of wind that blow in same direction and from H to L
1. Subtropic High to Equitorial Low
2. Polar High to Subpolar Low
3. Subtropic High to Subpolar Low
Wind is also affected by the rotation of the earth
1. Coriolis Effect – motion across a spinning object is deflected by the motion of
the object <SEE IT IN ACTION> or try it with the globe
2. Pushes Northeast Trades and Polar Winds from NE to the SW
Not everywhere has wind
3. doldrums: at the equator there is a lack of wind
4. great garbage patch: an area in the east Pacific where wind and ocean
currents are slight, causing debris to build up and stay there
Fast fact: why the sea breazes?
Precipitation
Water falling from the atmosphere
Water evaporates at the equator and is carried by wind bands
It will fall for two major reasons
a. there is just too much for the cloud (or atmosphere to hold) - rainforests
b. a warm (L) air mass and a cold (H) air mass collide
Fronts: the line between the colliding air masses where the
precipitation occurs
Ocean Currents
Move in circular pattern
Move from Equator to poles (hot to cold) – Gulf Stream along eastern seaboard
Motion is helped along by the winds
Ocean has a cooling and moistening affect
Water cools/heats slower than land
keeps land warmer when cold and colder when hot
Difference in temp between land and water causes moisture to form (condensation)