Transcript Air Pressure and motion

V. Air Pressure and motion
A. Air pressure is the weight of air at any
particular point. It is also called barometric
pressure.
– The units are given in the ESRT in
millibars and inches of mercury and as
atmospheres.
– A barometer is a tool used to measure
pressure,
– Air pressure depends on how tightly
packed the molecules are and how
heavy they are.
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B. Units of air pressure: page 13 ESRT
• For normal, sea level pressures,
the air pressure will be found on
this chart.
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C. What’s a ‘rising barometer’?
• When air is ‘heavy’ it pushes down (and around) on
objects. The mercury will ‘rise’ in the vacuum tube.
• So a rising barometer means clear weather.
• When air is ‘light’, it does not push down as much
and the mercury in the barometer will ‘fall’ in the
vacuum tube.
• So a falling barometer means poor weather.
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D. Remember……
• Heavy Air: (high pressure)
– cold, because the
molecules are close
together.
– Dry, because nitrogen
and oxygen are heavier
than water vapor.
• Light Air: (low pressure)
– warm; the molecules
have more_energy and
are farther apart.
– humid, because water
vapor is a very light
molecule.
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jason.org
E. The reason some air is light and some air is heavy is due to
the unequal heating of the atmosphere due to our round
rotating planet.
ffden-2.phys.uaf.edu
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VI. Why wind?
A. Air pressure and wind
• Air moves from areas of high pressure to areas of low pressure.
• Air flows from regions of heavy, sinking air to regions of light,
rising air.
• Descending air means clear skies. (clouds can’t form)
• Ascending air happens at fronts and in very warm, wet air
(afternoon thunderstorms)
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B. Isobars
• Weather maps show pressure systems using isobars. (lines that
connect points of equal air pressure)
• The closer the isobars are on the map, the greater the change
in pressure and the faster the wind is blowing, There is a rapid
change in air pressure.(like popping a balloon)
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https://courseware.eeducation.psu.edu/public/meteo/meteo101demo/Examples/Images/Section2/contour_tool_p0207.swf
allows students to practice making isobars. It will convert from station model pressure to
millibars for them and draw the lines for them to
check
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C. Comparing high pressure to low pressure
High pressure system
air is dry, and
is probably falling, creating
convection.
High pressure air blows
outward and clockwise
across the surface.
• Low pressure system air is
light and is probably rising,
creating convection.
• Air blows inward and
counterclockwise and rises.
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VI. Jet stream and Coriolis move our weather
A. Meteorologists know that
midlatitude weather tends to
move from west to east in the
continental U.S. because of the
planetary winds.
B. The Coriolis effect helps
move the air from the
southwest toward the
northeast (usually).
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C. The Jet Stream :discovered by WWII pilots flying cross
country.
• It is a high altitude wind that separates the polar air from
the warmer tropical air in the midlatitudes.
• The jet stream is caused by interactions in upper levels of
the troposphere.
• Most active during our winter season; cold, dry Canadian
air meets warm, moist air of the Gulf of Mexico.
• the jet helps determine the weather patterns for the
country.
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http://vortex.plymouth.edu/make.html
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• Self-check:
What are 2 characteristics of heavy air? Of Light air?
What air is rising: heavy or light? High pressure or
low pressure?
Why does wind blow?
Does it blow from high to low or low to high?
Can you draw wind around a high? Around a low?
Which way do storms move across the US?
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