Transcript I. What is air? - Champlain Valley Union High School

The Atmosphere
I. What is air?
--A mixture of gasses
78.04% Nitrogen
20.94% Oxygen
Enlarged 10x
0.93% Argon
0.06% Others
0.03% Carbon dioxide
Nitrogen (78%)
•needed for growth of plants and animals
•absorbed in the form of nitrates, made by
bacteria
Oxygen (21%)
• needed by animals, produced by plants
• energy released when it combines with
other compounds
• breaks down some elements in rocks by
oxidation
Carbon dioxide (.03%)
• needed by plants for photosynthesis
• important in greenhouse effect
Ozone (a “trace gas”)
• a form of oxygen-- O3
• in stratosphere absorbs
ultraviolet radiation
• at ground level is
dangerous pollutant
(smog)
Argon (0.9%)
• inert, does not form
compounds
Water vapor (0 to 4%)
• only gas that varies much
• absorbs heat
G. Trace gases
• neon, helium, methane, krypton, xenon,
hydrogen, ozone
II. What is the structure of our
atmosphere?
A. troposphere-- to 11 km, zone where
weather occurs
B. stratosphere-- 11-50 km, contains ozone
layer, where jets fly
C. mesosphere-- 50-80 km, coldest layer
D. thermosphere-- 80-85 km up,
temperatures rise, contains ionosphere and
exosphere
III. What role does air
pressure play in weather?
• Close to the earth atoms & molecules are
pushed together because of pressure from
mass above therefore greatest at sea level
and decreases upward
• Differences in air’s density can cause air
pressure variations
• Barometer measures air pressure, average in
millibars is 1013 mb
Highs
• Cool air more dense, causes high
pressure
• Highs are associated with cool dry
air—clear skies
Lows
• Warmed air less dense, causes low
pressure areas
• Lows are associated with warm and
moist conditions—rain and storms
Air moves from areas of high pressure to
areas of low pressure
IV. How does temperature affect the
circulation of air in the atmosphere?
• Energy supplied by
sun
• Greenhouse effect
keeps heat in
troposphere, makes
life possible
• Heat is reflected by ice, water, snow, sand
• Heat is absorbed by vegetation and dark
surfaces
Heat is transferred by radiation,
conduction, and convection
• Convection currents are caused
by differences in density
between warm and cool fluids
• Convection causes air to rise
over Equator, sink at Poles
Coriolis effect causes moving objects to be
deflected to right in Northern hemisphere,
left in Southern)
• Unequal heating can also cause movement, as
in sea and land breezes
V. How does temperature affect the
ability of air to hold moisture?
• Warm air “holds more moisture” than cool
air
• In warm air gas molecules are farther apartmore space for water vapor
• Relative humidity is the amount of water in
air compared to how much it could hold at
that temperature
• Air at 100 percent relative humidity is
saturated, water may condense from it
May be measured with hygrometer or
wet bulb / dry bulb psychrometer
• Temperature at which condensation
will occur is called dew point
VI. How do clouds form
and produce precipitation?
• Condensation occurs when
– 1. air is cooled below dew point and
– 2. condensation nuclei (dust or salt particles)
are present
• Clouds are collections of tiny water droplets
suspended in air
• At a certain size they fall as precipitation
• Snow is formed by water vapor turning
directly to solid
VII. What are the names and
characteristics of common cloud types?
Cloud families
• 1. cirrus-- high, white, feathery, ice clouds,
also called “mare’s tails”
• 2. cumulus-- thick, puffy, “fair weather
clouds”
• 3. stratus-- clouds in layers
• 4. nimbus-- produce precipitation
• Clouds also
classified by
height
• Stratus clouds
close to ground
are called “fog”
VIII. What is the significance of air
masses to weather?
An “air mass” is body of air that has
characteristic properties
Properties depend on where mass originated
From air mass, air flows down and spirals out
clockwise, causing anticyclone (fair)
Air pushes into low pressure areas, spiraling
in counterclockwise cyclone (stormy
weather)
IX. How do fronts influence the
weather?
• Boundary between air masses is called a
front
Warm front
• 1. Warm air mass meets cold air
mass
• 2. Warm air slides up over cold
air in long wedge
• 3. Nimbostratus clouds form and
may cause precipitation over
long period
Cold front
• 1. Cold air mass meets warm
air mass
• 2. Cold air forces warm air
up along steep front
• 3. Showers and
thunderstorms result
Stationary front causes
weather to remain the
same over long time
Occluded front when two
cool air masses trap
warm air between
them, causing high
winds and precipitation
X. How is weather portrayed
on weather maps?
Local collecting
stations contribute
data in form of
station models
Weather maps show
• 1. isobars, lines connecting points of equal
pressure
• 2. isotherms- line connecting points of equal
temperature
• 3. high and low pressure areas
4. position of fronts
El Nino and La Nina
El Niño is an oscillation of the ocean-atmosphere system in
the tropical Pacific having important consequences for
weather
• Information on the names El Niño and La NiñaEl Niño
was originally recognized by fisherman off the coast of
South America as the appearance of unusually warm water
in the Pacific ocean, occurring near the beginning of the
year. El Niño means The Little Boy or Christ child in
Spanish. La Niña means The Little Girl. La Niña is
sometimes called El Viejo, anti-El Niño, or simply "a cold
event" or "a cold episode". El Niño is often called "a warm
event". To provide necessary data, NOAA operates a
network of buoys which measure temperature,
currents and winds in the equatorial band. These buoys
daily transmit data which are available to researchers and
forecasters around the world in real time.
El Nino
• Warm air over warn Pacific water in red
Some years are normal and other
years show strong El Nino
conditions.
The warming of the Earth’s oceans is
believed to increase El Nino.
Some of the effects include droughts,
floods and heat waves
That’s all, folks!
(It’s safe to wake up now)