Transcript Worldwide Wind Currents

Worldwide Wind
Currents
Weather Dynamics
Science 10
The Flow of Air
• Due to the uneven heating of the Earth’s
surface, the temperatures of the air above it
are also uneven.
• When air warms it expands and becomes
less dense.
• Cooler air is denser than warm air and exerts
more pressure on its surroundings.
• Cool air flows toward and under warm air,
pushing the warm air up and away.
• Hence, warm air rises and cold air falls.
At the Equator
• The air that is close to Earth’s surface warms
to nearly the same temperature as the land
or water.
• As air warms it becomes less dense and
begins to rise.
• Cooler air moves in below and then it warms.
• The denser, colder air at the poles moves
along the Earth’s surface and moves the
warm air toward the poles.
• This is the concept of convection.
Wind Patterns on Earth
• Technically, if the Earth was rotating and the
atmosphere was not, we would all feel wind of 300m /
s (1080 km / hr).
• Since this is not the case, the atmosphere must be
moving with the Earth.
• In fact, for the most part the atmosphere spins with
the Earth at the same speed as the surface below it.
• Different places of the Earth are moving at quite
different speeds.
• Think about someone living in Nova Scotia versus
someone who is living on the Equator. Both people
need to move around the Earth completely in 24
hours.
Coriolis Effect
• Due to the rotating of the Earth, any object moving on
the Earth’s surface does not move in a perfectly
straight line. It too rotates!
• This influence on moving object due to the rotating of
the Earth is known as the Coriolis Effect.
• Scientists, Meteorologists, as well as military
personnel all need to take the Coriolis Effect in to
consideration.
• If the military are trying to fire a missile a large
distance, they need to consider that the Earth is
moving and therefore the object will move counterclockwise with the Earth.
Prevailing Westerlies
• The Coriolis effect causes wind to blow from
west to east.
• These winds are called prevailing westerlies
and are generally why weather systems
move from the west toward the east in
Canada.
Jet Stream
• Ribbons of extremely fast moving air near the top of
the atmosphere are known as jet streams.
• They are found at the boundaries of temperate and
polar zones and temperate and tropical zones.
• The jet streams vary from 100 km/h to 300km/h, are
thousands of kilometres long and a few hundred
kilometres wide.
• In general the weather north of the jet stream is cold
and the weather south of the jet stream is warmer.
• The jet streams change quite often and are not perfect
circles which is why they are usually a part of weather
forecasts.
Do You Understand?
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Why does air over the equator tend to rise?
How do we know that the atmosphere rotates with Earth and does
not remain stationary while Earth rotates under it?
What property of Earth causes the Coriolis Effect?
Describe the overal result of the Coriolis Effect in the Northern
and Southern Hemispheres.
Where would you expect to find a jet stream?
A round-trip airplane ticket between Calgary and Toronto states
that the actual flying time in the air is 3h 38min from Calgary to
Toronto and 4h 6min from Toronto to Calgary. From your
knowledge about winds explain why it is half an hour longer to fly
west than east.