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Today – Friday, 1/20/12
 Attendance
 Calendar
 Review
Lab
Weather
# 26
Isoline
Review
Weather
Hey, is this cool or what?
Weather – the short term
condition of the atmosphere
Meteorologist – scientist who
studies the weather
A. Temperature – the amount of
heat energy
The angle of the sun influences
the temperature.
It is colder at night where there
are no clouds.
Rotation – spinning on an axis
Seasons occur because 1) the
Earth is tilted 2) the Earth
revolves around the sun.
Temperature
is measured
with a
thermometer.
B. Air has weight that presses
down on the
earth.
Aneroid Barometers – measure
air pressure by measuring how
much air is pushing in on the
can.
Mercury Barometers – measure
the force of air pressing on liquid
mercury.
Fair Weather – blue skies, less
humid
Stormy Weather
High air pressure gradients
make high winds.
C. Water Vapor – water in the
form of a gas.
 mini
movie on phases of water - brain pop
Humidity – the amount of water
vapor in the air.
 humidity
brainpop
Sling Psychrometer - used to
measure relative humidity
Relative Humidity Chart
Dew – drops of water that form
on substances when the air gets
too cold to hold water vapor.
Dew Point Chart
D. Air Movements
 Why
does air circulate (move) around in
the atmosphere?
D. Air Movements

Less dense (warmer) air rises

More dense (cooler) air sinks
D. Air Movements

Some Definitions:

Air currents: are vertical movements of air

Wind: horizontal movement of air
• Described in both direction and speed
• Named for the direction from which it blows
D. Air Movements


Wind Vane – is a
pointer that shows
direction
Anemometer – an
instrument that
measures wind speed.
E. Atmospheric Transparency
 All
the gases in our atmosphere are
transparent (see through).
 There
are many substances that become
suspended in the atmosphere that are not
transparent (dust, ash, smoke, salt,
droplets of liquid called aerosols)
E. Atmospheric Transparency

Visibility is the horizontal distance through
which the eye can distinguish objects in
miles.
III. Weather Stations

Know how to read
weather stations.
 Cloud cover is the
fraction of the sky that
is blocked by the
clouds.
IV. Relationships
 A.

Air Temperature and Pressure
As temperature increases, the pressure
decreases
• When the temperature increases, the molecules
move faster, spread out and become less dense.

As temperature decreases, the air pressure
increases.
• Colder, slower, closer, more dense, more pressure
IV. Relationships
 A.

Air temperature and pressure
As P increases, T increases
• Move closer, more friction, more heat

As P decreases, T decreases
• Move away, less friction, less heat
IV. Relationships
 B.

Air pressure and humidity
Water Vapor is much lighter than the other
gases in the atmosphere.
• So if the amount of water vapor increases, the
other heavier molecules are pushed out.


The higher the humidity, the ___ the air
pressure.
The lower the humidity, the ___ the air
pressure.
IV. Relationships
 C.

Air Temperature and humidity
If the temperature increases, the relative
humidity will decrease.
• Warmer air has the capacity to hold more, %
decreases

If the temperature decreases, the relative
humidity increases.
• Cooler air has holds less water vapor, %
increases.
IV. Relationships
 D.

Air pressure and wind
Winds blow from regions of HIGH air pressure
to regions of LOW air pressure.
H
L
IV. Relationships
 Winds
curve to the right in the Northern
Hemisphere because of the Coriolis Effect.

(Curve to the left in the Southern Hemisphere)
Get it? SEA BREEZE
IV. Relationships

E. Global Winds/Planetary Winds
E. Cloud Formation

Clouds and precipitation are formed
when air is cooled below its dew point
and water vapor condenses into tiny
water droplets or ice crystals.


Condensation means changing phases from
a gas to a liquid.
Precipitation removes dust/dirt and many
pollutants from the atmosphere.
E. Cloud Formation
 Sublimation
is the change of phase from a
gas directly to a solid
 Fog is a cloud whose base is at ground
level. It forms when moist air at the
ground level is cooled below its dew point.
More on Clouds
 brainpop
clouds