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Troposphere’s Pattern of Air
Movement & Its Influence on
Regional Climates & Local Weather
AICE EM: Atmosphere
Key Content 2
Troposphere’s Pattern of Air Movement & Its
Influence on Regional Climates & Local Weather
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Difference between climate & weather
Factors that influence weather
Global insolation
High & low pressure
Global & local wind systems
Effect of land, relief & ocean currents
Formation & characteristics of anticyclones,
temperate frontal depressions, and tropical
cyclones
• Weather forecasting
Difference Between Climate &
Weather
WEATHER is…
• short-term conditions of
the atmosphere
• For example, the observed
weather in Seattle,
Washington, on Saturday,
October 16, 2010 was sunny
with a high of 57°F
CLIMATE is…
• average daily weather for
an extended period of time
at a certain location
• the average high
temperature for Seattle,
Washington, on October 16
for 1971-2000 is 60°F.
Factors That Influence Weather
• Atmosphere: greenhouse effect, latent heat due to water
phase changes, water cycle, winds, air mass collisions
• Latitude: Direct rays vs. oblique rays, snow creates albedo
area
• Topography:
– Uneven surface ultimately causes winds
– rain falls on mountain sides closer to oceans
• Water’s heat carrying capacity: range of temperature
different for coastal vs. inland at same latitude,
• Human Influence: ∆ in topography → less trees → less
oxygen, water & more CO2; Burning fuels → adds green
house gases to atmosphere, puts particulates in
atmosphere
Global Insolation- total amount of solar
radiation energy received on a given surface area
during a given time.
Latitude
a measure of the distance you
are located from the
equator. The tilt of the earth
affects the seasons we
experience throughout the year.
Interrelation Between Water Cycle &
the Atmosphere
• Cloud condensation nuclei
– Natural: Dust storms, volcanic eruptions, pollen, sea salt,
respiration, combustion particles (fire)
– Anthropogenic (pollution due to humans): combustion
particles
• Clouds (water vapor) absorb infrared radiation
• Thick clouds reflect solar radiation (albedo-is the fraction of
solar energy (shortwave radiation) reflected from the Earth back into space)
• Evaporation cools surfaces (latent heat of vaporization)
heat is absorbed by water molecules
• Latent heat of condensation – heat is ______
HIGH PRESSURE
 Energy transfer by LOW PRESSURE
Heat released radiates
convection in the
to space
Condensation and
atmosphere.
Cool, dry
precipitation
air
Convection-when hot
and wet warm air
Falls, is compressed, Rises, expands,
rises, cools, and
cools
warms
releases heat and
moisture as
precipitation (right
Hot,
Warm,
side).
wet air
dry air
Then the denser
Flows toward low pressure, picks
cool, dry air sinks,
up moisture and heat
gets warmer, and
picks up moisture as HIGH PRESSURE Moist surface warmed LOW PRESSURE
it flows across the
by sun
earth’s surface to
begin the cycle again.
Fig. 7-4, p. 143
Cloud & Precipitation Formation
Adiabatic temperature changes –
expands – cools; compresses - warms
Global Air Circulation
Westerlies
Northeast trades
Southeast trades
Westerlies
The largest input of solar energy occurs at the equator.
• As this air is heated it rises and moves toward the poles. However, the earth’s
rotation deflects the movement of the air over different parts of the earth.
• This creates global patterns of prevailing winds that help distribute heat and
moisture in the atmosphere.
Fig. 7-3, p. 142
Four lifting processes
Windward side
Leeward side
Global & Local Wind Systems
• Wind – caused by differences in horizontal air
pressure (High to low)
• Uneven heating of earth’s surface creates
pressure differences
– Solar energy basis of wind energy
• Wind controlled by
– Pressure-gradient force
– Coriolis force
– Friction
High &
Low
Pressure
• Air pressure – force (Newtons) against a surface due to
constant collision of gas molecules (1 millibar = 1000 N)
• Horizontal air pressure compensated to be sea level due to
altitudinal differences
HIGH
MORE dense→ ____
• Cold air is ______
pressure
LESS
LOW pressure
• Warm air is ______
dense→ ____
• Water vapor actually reduces density.
Pressure-gradient force
• Isobars
• Closely spaced –
strong pressure
gradient with high
wind speeds
• High speeds
generally around
Lows
Coriolis Effect on Horizontal Direction
Coriolis effect: deflection in
northern hemisphere is to
RIGHT
_____________;
southern
LEFT
hemisphere is to _________
Degree of deflection due to
Coriolis forces are stronger at
higher latitudes and stronger
winds.
The Different Forces That Effect Winds
• Aloft air = Less friction
• Wind speeds increase until
Coriolis force = pressuregradient force (geostrophic
balance)
• Ultimately, winds
travel parallel to
isobars (geostrophic
wind)
• Steep pressure
gradient = strong
winds
• IDEALIZED situation
P-G force causes
winds to move
perpendicular to
isobars
Isobars & wind speeds
Can you figure out / remember
the relationship between
isobars & wind speed?
The closer the isobars are to each other, the stronger the
pressure gradient will be. The stronger the pressure gradient,
the stronger the horizontal winds will blow from higher
pressure towards lower pressure at the surface.
• Circular isobars means winds
follow circular path to be parallel
to isobars
• Notice direction of L and H
pressure system in Northern
Hemisphere
Recall Device time:
Cyclone – Low Pressure
center, winds travel to left
(same as Earth’s rotation
CCW), isobar trough
Friction’s Effect
• P-G force
causes wind
to move . . .
• Coriolis force
balances
wind to
move . . .
• Frictional
force causes
wind to
move . . .
• air with similar properties of temperature and moisture which covers a large area.
• air in neighboring air masses doesn't mix because of differences in density and
temperature.
• When air masses meet, fronts are formed.
The weather of the British Isles and surrounding countries is influenced by several
different air masses. Broadly speaking there are four main ones:
 Tropical Continental (Tc): mainly from the south-east and south, i.e. the tropics.
 The air travels over a warm land mass (hence the term 'continental' ).
 The air is usually warm and dry.
 Tropical Maritime (Tm): originates from the south-west and travel over a warm
sea (hence 'maritime').
 air is usually warm and moist because the air picks up moisture from the sea.
 Polar Continental (Pc): comes from polar regions, travelling over a cold land mass.
 In the UK this means air from the north-east that has travelled over Russia and
Scandinavia.
 Such air masses tend to be cold and relatively dry.
 Polar or Arctic Maritime (Pm or Am): originate from the Canadian Arctic or from
around Greenland and arrive in the British Isles from the north or north-west.
 The air has travelled over a cold sea.
• Day-to-day changes in the weather are caused by the influence of different air masses as
they pass over the land.
• The front is the boundary where these different air masses meet.
• Fronts can either be Warm, Cold, or Occluded.
 Clouds are formed when the warm air
rises, cools and moisture condenses
(changes from a vapor to a liquid).
 Fronts may be seen on a satellite weather
photograph as thick bands of clouds.
Diagram showing a WARM FRONT.
• The warm air mass is moving to
replace the cooler air mass and at the
boundary a warm front forms.
Diagram showing a COLD FRONT.
• The cold air mass is moving to replace
the warmer air mass and at the
boundary a cold front forms.
Diagram showing an OCCLUDED
FRONT.
• When a depression forms, there
is usually a warm front and a
faster moving cold front.
• To the north of the warm front is
the cool air that was in the area
before the depression
developed.
Symbols on the Map:
Thin black lines: These are isobars-They link
areas with equal air pressure. the values are
pressures in millibars, with inches in brackets
Arrows: Direction of the wind (wind speed is
shown in miles per hour)
Numbers in black circles: Air temperature in
degree Celsius (degree Fahrenheit is shown
in brackets)
Icons: Show main weather features such as
light cloud, rain, sunshine, etc.
Thick lines: Fronts, either
cold (marked with triangles),
warm (semi-circles), or
occluded (both marks)
Notice the direction of wind of the two
pressure systems.
• larger than depressions
• produce periods of settled and calm weather lasting many days or weeks.
• block the path of depressions;
• slowing down the bad weather or forcing it around the outside of the high pressure
system.
• They are then called 'Blocking Highs'.
• As air descends, air pressure increases.
• When air hits the ground the earth's rotation makes the air change direction.
• In the Northern Hemisphere the air is pushed clockwise.
northern
• In the Southern Hemisphere the air is pushed anticlockwise.
hemisphere
• Where is the diagram located, northern or southern hemisphere?
anticyclone
• When areas of warm and cold air
meet, the warm air rises up and
over the colder air.
• fast moving area of cold air moves
into a region of warmer air it forces
its way under the warm air, which
is pushed upwards.
• As it rises, air pressure falls.
• This rising air can lead to a low
pressure system or depression.
• Viewed from above, the air within a
depression circulates in an anti-clockwise
direction in the Northern hemisphere (they
circulate clockwise in the Southern
hemisphere).
• This is the opposite of anticyclones.
Isobars with Fronts
1. Which direction
is the wind
blowing?
2. Why is the cold
front “chasing”
the warm
front?
3. Is this
hurricane
status? How
do you know?
4. What kind of
weather is the
DC area
experiencing?
5. What kind of
weather is TN
experiencing?
Climatology: averaging weather statistics
accumulated over many years to make the
forecast. For example, if you were using the
climatology method to predict the weather for
New York City on July 4th, you would go
through all the weather data that has been
recorded for every July 4th and take an
average.
Weather Charts: a synoptic chart showing
weather conditions, compiled from
simultaneous observations taken at various
weather stations