Key Idea #20
Weather and climate are influenced by the
atmosphere and oceans.
http://www.google.com/imgres?imgurl=http://www.kidsgeo.com/images/weather-and-climate.jpg&imgrefurl=http://www.kidsgeo.com/geography-for-kids/0052-weather-andclimate.php&h=298&w=300&sz=13&tbnid=8udQUroMPUYk_M:&tbnh=115&tbnw=116&prev=/search%3Fq%3Dweather%2Band%2Bclimate%26tbm%3Disch%26tbo%3Du&zoom=1&q=weather+and+climate&hl=en&usg=__Alm3OQA8Ye70EKngAXpWocTtGA=&sa=X&ei=dorZTa7_KMrh0QG8yqn8Aw&sqi=2&ved=0CEMQ9QEwAg
Weather is the mix of events that happen each day
in the atmosphere and include temperature, rainfall,
and humidity.
Causes of Different Weather
Most weather occurs at the lower portion of the atmosphere,
in the troposphere, and is due to changes in the temperature
of air masses (convection currents).
Rising warm air eventually cools and sinks.
Cool air is warmed by the Earth’s surface and rises.
An air mass is a huge body of air that has similar
temperature, humidity and air pressure throughout it.
http://www.google.com/imgres?imgurl=http://www.fas.org/irp/imint/docs/rst/Sect14/airmasses_schem.jpg&imgrefurl=http://www.fas.org/irp/imint/docs/rst/Sect14/Sect14_1b.html&h=325&w=410&sz=120&
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The sun’s heat causes air masses to form and circulate in
the atmosphere in the form of convection currents.
This movement creates
differences in air
pressure.
warm, moist (humid) air
rises
cooler, denser air sinks
Differences in air
pressure creates winds.
Temperature changes in air masses and upper air
currents cause air masses to move in the atmosphere.
Air masses form
mostly in tropical
or polar regions.
When air masses
move from their
regions of origin,
they bring heat
waves and cold
spells.
tulane.edu
FYI: Types of Air Masses
Tropical air masses (pink)
are warm, low pressure
air masses that form in
the tropics.
Polar air masses (blue)
are cold, high air pressure
air masses that form north
of 50° north latitude and
south of 50° south
latitude
uwsp.edu
Warm air masses are forced to rise and expand
over and above cold air masses because
warm and cold air
masses don’t mix
easily.
cool, dense air sinks.
warm,less dense air
rises.
http://www.atmoz.org/img/warm-front.png
FYI: Jet streams form at the boundaries of adjacent
air masses that have huge differences in
temperature.
ww2010.atmos.uiuc.edu
Jet streams are
concentrated, high altitude
streams of fast moving wind
that blow from west to east
across the Northern and
Southern Hemispheres.
FYI
located about 10-11 km above
Earth’s surface (just below the
tropopause).
hundreds of kilometers wide
and blow from west to east
between 200 and 400 km/h
(124-248 mph).
www.merrittcartographic.co.uk/jet_streams.html
The jet stream
is constantly shifting.
is responsible for the
movement of major
weather features from
west to east across
North America and the
Earth.
http://heatusa.com/blog/wp-content/uploads/2009/06/jet-stream-paths.jpg
Air Masses Video
A front is an area where two air masses with
different temperatures and densities collide.
Fronts occur when huge
masses of air bump into each
other as they move across the
land and oceans.
A frontal boundary refers to
the boundary that forms
between warm and cold air
masses.
Rain or snow typically forms along fronts.
As a warm, moist air mass
rises above a cooler air mass
it cools and the water vapor
in it condenses to form
clouds.
Rain or snow may form if the
warm air mass continues to
rise, expand, and cool in the
atmosphere.
The type of front
that develops
depends on the
characteristics
of the air masses
and how they are
moving.
Cold Front
A cold front is a situation where a cold air mass is moving
in and replacing warmer air.
Cold fronts generally move from northwest to southeast.
www.physicalgeography.net/.../coldfront.GIF
Weather Associated with Cold Fronts
Cold fronts usually move quickly causing abrupt weather
changes.
Thunderstorms (sometimes violent) in the summer and
snowfalls in the winter are associated with cold fronts.
Weather Conditions Associated with a Cold Front
Weather
Phenomenon
Prior to the Passing of the Front
Contact with the Front
After the Passing of
the Front
Temperature
Warm
Cooling suddenly
Cold and getting
colder
Atmospheric
Pressure
Decreasing steadily
Leveling off then
increasing
Increasing steadily
Winds
South to southeast
Variable and gusty
West to northwest
Precipitation
Showers
Heavy rain or snow, hail
sometimes
Showers then
clearing
Clouds
Cirrus and cirrostratus changing later to cumulus
and cumulonimbus
Cumulus and
cumulonimbus
Cumulus
www.physicalgeography.net
Warm Front
A warm front occurs when a warm air mass advances on
a cold air mass.
Since cold air is more dense than warm air, the warm air
moves over the cold air and condenses forming clouds.
www.physicalgeography.net
Weather Associated with Warm Fronts
Steady, long lasting rains in the summer and steady snowfalls
in the winter are associated with warm fronts.
Weather Conditions Associated with a Warm Front
Weather Phenomenon
Prior to the Passing of the
Front
Contact with
the Front
After the Passing of the Front
Temperature
Cool
Warming
suddenly
Warmer then leveling off
Atmospheric Pressure
Decreasing steadily
Leveling off
Slight rise followed by a
decrease
Winds
South to southeast
Variable
South to southwest
Precipitation
Showers, snow, sleet or
drizzle
Light drizzle
None
Clouds
Cirrus, cirrostratus,
altostratus, nimbostratus, and
then stratus
Stratus,
sometimes
cumulonimbus
Clearing with scattered stratus,
sometimes scattered
cumulonimbus
www.physicalgeography.net
Cold Front and Warm Front Animation
http://www.mesoscale.iastate.edu/agro
n206/animations/05_cnWfronts.html
http://www.educypedia.be/education/cli
mateanimations.htm
Stationary Front
A stationary front is a situation where a cold air mass
and a warm air mass meet and neither one is moving.
When a warm or cold front stops moving, it becomes a
stationary front. Once this boundary resumes its
forward motion, it once again becomes a warm front
or cold front.
Credits and Acknowledgments for WW2010.Department of Atmospheric Sciences (DAS) at the University of Illinois at Urbana-Champaign
http://www.windows.ucar.edu/tour/link=/earth/Atmosphere/tstorm/stat_front.html
Weather Associated with a Stationary Front
A stationary front can last for days, producing nothing but
altocumulus clouds and/or precipitation.
Temperatures remain stagnant and winds are gentle to
non-existent.
Occluded Fronts
Occluded fronts are produced when a fast moving cold
front catches and overtakes a slower moving warm front.
http://206.251.19.76/weather/wofront.htm
Occluded Fronts
An occluded front occurs when warm, cool, and cold air
masses come together and the warm air is pushed above the
cooler air masses. Occluded fronts are not common.
http://206.251.19.76/weather/wofront.htm
Air Masses and Fronts Video
Predicting the Weather (FYI)
Meteorologists
are scientists who study the causes of weather and try
to predict it.
analyze data using maps, charts, and computers.
prepare weather forecasts.
They get their data from
local weather observers.
instruments carried by balloons.
ocean buoys.
satellites.
weather stations around the world.
Reading Weather Maps (FYI)
Areas in the same temperature range are shown
in the same color.
FYI: Fronts move in the direction the symbol is
pointing.
The cold fronts are
moving from the
northwest to the
northeast.
The warm front is
moving from the south
towards the north.
According to this map, what type of weather
can Michigan expect in a few days?
According to this map, Michigan can expect warmer
temperatures and rain in a few days as a warm front
moves in.
According to this map, what type of weather can
Michigan expect in a few days?
According to this map, Michigan can expect cooler
temperatures and rain as a cold front moves in.
Climate is the average weather pattern in a
place over many years.
Weather vs Climate
Weather
is the mix of events
that happen each
day in the
atmosphere
includes
temperature,
rainfall, and
humidity.
Climate
is the average
weather pattern in a
place over many
years.
is useful for weather
forecasting.
The two main factors that determine the
climate of a region are temperature and
precipitation.
Oceans
make up 70% of Earth’s
surface.
absorb more energy from
the sun than land does.
warm up and cool down
much slower than land
does.
retain their heat better
than land does.
members.virtualtourist.com/m/b47ab/c57/
The temperature of the oceans affects the different climates
on Earth because water in the oceans hold a large amount
of heat.
Oceans take a long time to
warm up in the spring and
summer.
Oceans take a long time to
cool down in the fall and
winter.
In the spring and summer,
winds from the cooler
ocean waters keep the
coastal regions cooler in
than inland areas.
In the fall and winter,
winds from the warmer
ocean waters keep coastal
regions warmer than
inland areas.
Uneven Heating of the Earth
FYI: The sun is the major cause of the heating
and cooling of our atmosphere.
The Earth gets the
same amount of light
each day, but since the
Earth is tilted on its
axis, the light is
unevenly divided into
two hemispheres.
More hours of sunlight
= more solar heating.
http://www.coryvannote.com/images/more/biology/Earth_sunlight.jpg
The hemisphere that is
tilted toward the sun
receives more direct
sunlight and
experiences spring and
summer.
The hemisphere that is
tilted away from the
sun is receiving less
direct light and
experiences fall and
winter.
http://web.srv.cmes.utah.edu:8080/west/k12/EarthsTiltPic/view