Air Pressure and motion 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 device used to measure pressure,
Air pressure depends on how tightly packed the molecules are and
how heavy they are.
Slide 2
http://erkki.kennesaw.edu/GCII1/gc00002.htm
Slide 3
Units of air pressure: page 13 ESRT For normal, sea level
pressures, the air pressure will be found on this chart.
Slide 4
Whats a falling 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 ________ 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 ____________
weather.
Slide 5
Remember Heavy Air: (high pressure) cold, because the molecules
are closer 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.
Slide 6
The reason some air is light and some air is heavy is due to
the unequal heating of the atmosphere due to our round tilted
planet. ffden-2.phys.uaf.edu
Slide 7
Why wind? AIR PRESSURE AND WIND Air flows from areas of high
pressure to areas of low pressure. Air flows from regions of
descending, heavy air to regions of ascending, light air.
Descending air is clear weather. Ascending air happens at fronts
and in very warm, wet air (afternoon thunderstorms) jason.org
Slide 8
Practice wind direction and gradient
Slide 9
Weather maps show pressure systems, using isobars. The closer
the isobars are on the map, the greater the difference in pressure
and the faster the wind is blowing, There is a rapid change in air
pressure.(popping a balloon)
Slide 10
https://courseware.e-
education.psu.edu/public/meteo/meteo101demo/Examples/Images/Section2/contour_tool_p0207.swf
https://courseware.e-
education.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
Slide 11
From high to low High pressure systems air is heavy, is
probably falling creating convection. High pressure air blows
outward and clockwise across the surface. Low pressure systems
indicate the air is light and therefore it is probably rising,
creating convecction. Air blows inward and counterclockwise and
up.
Slide 12
Slide 13
Forecasters know that bad weather tends to move from west to
east in the continental U.S. because of the prevailing winds. The
jet stream :discovered by WWII pilots flying cross country. The jet
stream is caused by interactions in upper levels of the
troposphere. Most dramatic during our winter season; cold, dry
Canadian air meets warmer, moist air of the Gulf of Mexico. the jet
helps determine the weather patterns for the country.
Slide 14
http://vortex.plymouth.edu/make.html
Slide 15
Slide 16
free-online-private-pilot-ground-school.com Local winds caused
by daily heating and cooling
Slide 17
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? Review book pages 172- 174 and
179-182 https://castlelearning.com/review/login/l ogin.aspx
https://castlelearning.com/review/login/l ogin.aspx