Download Global Winds Reading and Questions

Name _______________________ Period
Global Wind Patterns
The earth’s surface is constantly being heated by energy from the sun. Because tropical regions are warmed
more efficiently than are polar regions, differences in atmospheric pressure develop between these latitude
extremes. Such pressure differences result in planet wide winds.
Air heated at the surface in the lower latitude is lifted and replaced by cooler, denser air flowing from higher
latitudes. If the earth did not rotate, if it was not inclined on its axis, and if the surface was uniform
throughout, planetary circulation would be simple. However, global wind systems are extremely complex and
are not completely understood. Basic circulation patterns do exist and are used to explain worldwide climate
and weather.
At the equator, radiation from the sun is direct and intense, and the air above the topical oceans warms
rapidly each day. When the air is heated, it expands and becomes less dense, with the result that moist, hot air
rises far above the equator. But expanding air cools and cannot retain moisture. Instead, water vapor
condenses to liquid water, cloud form and rains fall in the tropics. The dry air then moves north or south as
strong winds, convecting heat towards the poles. As these high winds move towards the poles they press
laterally against each other as they converge in higher latitudes. Eventually this air become so dense that it
starts to sink, at approximately 30 degrees north and 30 degrees south latitude. This brings down dry air onto
the major desert regions of the Earth. These drier air masses flow back across the surface toward the Equator,
completing one full cycle of atmospheric circulation cell called Hadley cells (named after a scientist). The calm
equatorial area where the northern and southern Hadley cells meet is called the doldrums.
North of the 30 degree north and 30 degree south latitudes are two more circulation cells called Ferrel Cells,
that circulate low altitude air masses towards the poles, to approximately 60 degrees north and south
latitudes. When these relatively warm, temperate zones winds reach 60 degrees, they rise into the upper
atmosphere above colder air masses blowing down from the poles. At high altitudes the Ferrell Cell winds flow
back toward lower latitudes (toward the equator) until they converge with the winds of the Hadley Cell and
wink into the lower atmosphere to repeat the temperate zone cycle.
Farther north and south are two polar circulation cells that are responsible for the flow of air in the Arctic and
Antarctic regions. Although, then, there are three atmospheric circulation cells in the northern hemisphere
and three atmospheric circulation cells in the southern hemisphere. Collectively, the winds in these circulation
cells transport heat towards the poles, but excess heat from the topics is redistributed indirectly in these
cycles through the atmosphere.
Because the Earth is rotating, the winds that carry heat energy into the upper atmosphere do not blow in
straight lines towards north or south. The eastward rotation of the Earth results deflects air moving north to
the northeast and air moving south to the southwest in the Northern Hemisphere. In the Southern
Hemisphere air moving north is deflected to the northwest and air moving south is deflected to the southeast.
The deflection of air or ocean currents due to the rotation of the Earth is called the Coriolis Effect. The winds
that blow across the surface of the oceans from the northeast to the southwest between equator and 30
degrees latitude, both north and south, are called trade winds. The trade winds are the dominant winds over
the Pacific and Atlantic Oceans.
Global wind patterns (displayed in Figure One) are complex but you need to remember three basic principles:
a) Air tends to flow out of regions characterized by relative high pressure and into regions characterized
by relative low pressure.
b) Because of the earth’s rotation, winds tend to be deflected or directed toward the right in the north
hemisphere and toward the left in the southern hemisphere.
c) Winds are named according to the direction from which they flow. For example, a northerly wind is
one which flows from the north.
Figure One:
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Using the above reading, prior background knowledge, and your notes answer the following questions:
1. What causes planet wide winds?
2. Where are the suns’ rays the most direct and intense?
3. Air at the equator is (moist or dry)?
4. The calm __________________ area where the northern and southern Hadley cells meet is called the
_____________________________.
5. What is the range of latitude where you can find Hadley Cells?
6. What is the range of latitude where you can find Ferrel Cells?
7. What is the range of latitude where you can find Polar Cells?
8. True or False. Winds blow directly North and South.
9. The earth rotates (eastward or westward)?
10. Things in the Northern Hemisphere deflect to the (right or left). ____________Things in the Southern
Hemisphere deflect to the (right or left). _____________.
11. The ________________ of air or ocean currents due to the ____________ of the Earth is called the
Coriolis Effect.
12. True or False. The Coriolis Effect can change the speed of winds.
13. Air tends to flow from areas of (high or low) pressure to areas of (high or low) pressure.
14. How are winds named?
15. Looking at figure one, write the letter (s) next to the correct wind features listed below:
______ Polar Cell
______ Northeast Tradewinds
______ Hadley Cell
______ Southeast Tradewinds
_ _____ Ferrel Cell
______ Doldrums
___ and ____ Polar Easterlies
___ and ____ Westerlies
___ and ____ Horse Latitudes
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