8 th grade weather notes

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Transcript 8 th grade weather notes

Weather Factors
Chapter 16
15.1The Air Around You
► Earth's
Atmosphere is:
A mixture of gases with some suspended
solids and liquids.
► Three common solids in atmosphere:
► Ice
► Dust
► Salt
► Gas
- from ocean spray
Composition of Earth's atmosphere:
 Nitrogen -78% of atmosphere
 Oxygen - 21% of atmosphere
 Trace gases -1% - Carbon Dioxide , Argon,
Neon, Helium, Hydrogen, Methane
15.2 Air Pressure
► Air
consists of atoms & molecules therefore
air has mass
 Because it has mass it also has Density
 Density = Mass/Volume
 Pressure – weight of air pressing down on you
is the same as a school bus BUT air is pushing
in all directions so it balances out
► Measure
by a barometer:
 Mercury Barometer – liquid mercury
 Aneroid Barometer – without liquid
Altitude or Elevation
above sea
►Air Pressure
decreases as Altitude
Increases thus so
does density
►Molecules are spaced
more thus it is more
difficult to breath
15.3 Layers of the Atmosphere
► 1. Troposphere – area closest to the
ground, 75%of the gases, dust, ice and
liquid water-Weather, Clouds, and smog
occur here
► 2. Stratosphere – Ozone layer
► 3. Mesosphere –
► 4. Thermosphere – contains the
ionosphere where electrical charged
particles are (get AM radio at night when
sun goes down, particles quit jumping)
► 5. Exosphere – upper most portion
Earth’s Atmosphere and its Energy
► Energy
comes from the sun in the form of
Electromagnetic Waves
Energy Transfer occurs by:
► Radiation
– electromagnetic waves, no
contact but still feel it, moves from object
with a higher temperature to one with a lower
► Conduction – direct contact, fast moving
molecules to slow moving molecules
► Convection – density differences, air is
warmed, the air molecules move apart which
increases the volume of air which reduces its
density thus the air raises and causes a
circular movement of air called a convection
► Earth’s
Movement of Air
surface is curved rather than flat, air
equator is heated more than any other place on
► Coriolis Effect – caused by Earth’s rotation,
air masses moving south in the Northern
Hemisphere are turned
westward (because
Earth is moving to the
► Doldrums
Wind Systems
– windless zone at the equator
► Trade Winds – 15o North or South of the
equator blow to the southwest (NH)/northwest
► Prevailing Westerlies – 30o and 60o North and
South winds blow in the opposite direction as
the trade winds SW to NE in NH and in SH NW
to SE
► Polar Easterlies – NE to SW near the North
Pole and from the SE to the NW in the SH
► Jet Streams – winds near top of troposphere
► Sea and Land Breezes – convection current
where land meets the sea (sea/day – land/night)
Factors of Weather
► Humidity
– amount of water vapor in the air
► (cooler air, slower, condenses – rains
► Hot air, faster, air holds more moisture
► Relative humidity – amount of water vapor in air as a
percentage of amount it can hold
 Saturated air – 100% relative humidity
 Dew Point – temperature at which it condenses
► Clouds
formed when the humid air is cooled to its dew
point and condenses
► Fog- is a stratus cloud close to the ground
► Precipitation – occurs when water droplets reach .2
► Air
Weather Patterns
mass – large body of air that has the same
properties as the surface over which it develops
► Fronts – boundary between 2 air masses as they
► Warm Front – warm air mass slides under cold air
mass (less dense) High cirrus clouds,
► Cold Front – cold air invades cold, cumulus clouds
and rain
► Stationary Front – pressure differences and it
doesn’t move lights winds and rains
► Occluded Front – 2 cool air masses forces warm air
up, heavy precipitation and wind
► Precipitation from warm air being cooled