Transcript Chapter 24

Chapter 24
Weather and Climate
24.1 The Atmosphere
• It’s the protective layer that surrounds
Earth
• It protects Earth from UV rays
• It moderates the temperature
• It contains gases that are essential for life.
Composition of Atmosphere
• 78% is nitrogen
• 21% is oxygen
• The remaining 1%
is a mixture of
water vapor and
other gases
Air Pressure
• The force of gravity pulling the
atmosphere toward Earth causes air
pressure.
• It is equal to 101,325 Newton per square
meter at sea level
• Pressure decreases as altitude increases
• Density decreases as altitude increases
Barometer
• Air pressure is measured
with a barometer
• A mercury barometer
measures pressure at sea
level at 760 mm Hg
• It uses a column of Hg to
measure pressure
Aneroid Barometer
• More portable than a mercury barometer
• It uses a metal chamber to measure
pressure
Atmospheric layers
• Temperature drops as
altitude increase
• Changes in
temperatures define
the layers in the
atmosphere
Layers in
Atmosphere
Defined by
Temperature
Troposphere
Stratosphere
Mesosphere
Thermosphere
Troposphere
• Lowest layer
• Contains almost all of the water vapor and
suspended particles
• Weather happens here
• 9 km at poles 12 km at the equator
• Temperature decreases by 6.5° per km
Stratosphere
• Next Layer
• 12 km to 50 km above the earth
• Temperature remains the same near the
boundary of the troposphere then increase
after about 20km
• The ozone layer warms the upper
stratosphere by absorbing UV radiation
Mesosphere
• The layer above the stratosphere
• 50km to 80km
• Gets cooler the higher it gets
• Most meteoroids burn up in this layer
Thermosphere
• Outer most layer
• Gets warmer as it gets further from earth
• Starts at -90°C and goes to 1000°C
• It has no upper boundary but instead
gradually enters outer space
Ionosphere
• Not a layer but instead a region of
charged particles that covers the
thermosphere
• AM radio waves bounce back to earth from
the ionosphere
• Aurora is a colorful display at night occurs
when charged particles from the sun are
attracted to Earth’s Magnetic poles
24.2 The Sun
and
the Season
Motions
Rotation
Revolution
Rotation
• Spinning of Earth on
its axis
• Takes 24 hours
Revolution
• The movement of one
•
body in space
around another
Earth’s movement
around the sun
• Takes 365 days
Latitude Zones
Regions
Tropic
23.5° South
to
23.5° North
Temperate
23.5° S to 66.5° N
23.5° N to 66.5° S
Polar Zones
66.5° N to North Pole
66.5° S to South Pole
The Season
• Earth is on a tilt of 23.5° N
• It is the cause of the season
• Seasons are NOT caused by the distance
from the sun. In fact, the Earth is closest
to the sun during winter in the Northern
hemisphere
Solstices
• Occurs when the Sun is directly overhead
at 23.5 ° N and 23.5 ° S
• Northern hemisphere it occurs on June
21st
• Daylight hours are longest in the northern
hemisphere and shortest in the southern
hemisphere
• December 21st is the winter solstice and
the reverse occurs
Equinoxes
• Days are about equal darkness and light
• Occurs approximately half way between
solstices
• Neither hemisphere is tilted toward the
sun
• Vernal equinox occurs on March 21
• Autumnal equinox occurs September 22
24.3 Solar Energy and Winds
• Most of the
energy that
heats the
troposphere is
radiated from
Earth
• The greenhouse
effect reflects
that energy back
toward the Earth
Energy Transfer
Radiation
Convection
Conduction
Wind
• Caused by
differences in air
pressure
• Differences in air
pressure caused by
unequal heating of
Earth’s surface
• Warm air expands
and rises
• Cooler air is
and moves
to take its place
denser
Local Winds
• Wind that occurs
in a small area
• Caused by
unequal heating
in a small area
• Sea breezes are
an example
Global Winds
• Winds that blow in specific
direction
• Move in bands called
convection bands
• Examples are trade winds,
westerlies and polar
easterlies
• The rotation of
the Earth
causes the
winds to turn –
Coriolis effect
Monsoons
• Characterized
by reversal in
weather over
a large
region for a
large amount
of time.
Jet
Stream
• Fast moving
stream of
air that
occur
because of
great
differences
in air
pressure
that
develop at
high
altitudes
24.4 Water in the Atmosphere
• Humidity – amount of water vapor in the
air
• Relative humidity is the ratio of the
amount of water vapor in the air
– Expressed in percentage
– Cooler air holds less water vapor than warm
air
• Dew point is the temperature at which
water condenses
Cloud Formation
• Form as warm, moist air rises and water
vapor condenses in the atmosphere
• Must have solid suspended particles to
form
• When water vapor is cooled below its dew
point, water vapor condenses onto these
particles
Precipitation
• Rain, sleet, snow, hail, and freezing rain
• Rain forms in nimbostratus clouds or
cumulonimbus clouds
• Hail is ice of more than 5 mm in diameter
• Sleet is ice smaller than 5mm
• Freezing rain is rain that freezes after it
hits the surface
24.5 Weather Patterns
• Consists of
– Warm Fronts
– Stationary Fronts
– Occluded Fronts
– cold Fronts
Air Masses
• Large body of air that covers a large area
and has uniform properties
• They are classified by how they are
formed over land or water and the latitude
where they form
Fronts
• After air masses form, they move
• When they move they meet other air
masses and form a front
– Cold front
– Warm front
– Stationary front
– Occluded front
Cold Fronts
• Fronts when a cold air mass overtakes a
warm air mass
• Produces cumulus and cumulonimbus
clouds
• Produces severe thunderstorms,
precipitation, and strong winds
Warm Fronts
• Occurs when a warm air mass overtakes a
cold air mass
• Stratus clouds forms
• May have a steady rain, may have some
thunderstorms
• Temperature rises after the front passes
Stationary Fronts
• Occur when two unlike fronts meet but do
not overtake one or the other
• May results in clouds and steady rain or
snow for several days
Occluded Fronts
• Forms when a warm air mass is caught
between two cooler air masses.
• The cooler masses cut the warm air mass
off from the ground. The warm air rises
and cools
• Results in cloudy skies and precipitation
Cyclones
• Low air pressure in the center
• Rotates counterclockwise in the Northern
Hemisphere
• Doesn’t stay in one place
• Associated with strong winds and
precipitation
Anticyclones
• Center is a high air pressure
• Rotate clockwise in the Northern
hemisphere
• Has clear skies, very little precipitation,
and generally calm conditions
Storms
• Thunderstorms
• Tornadoes
• Tropical Storms and Hurricanes
Thunderstorms
• Small weather system that includes
thunder and lightning
• Accompanied by strong winds and heavy
rain or hail
• Occur when columns of air rise within a
cumulonimbus cloud
Lightning
• Sudden electrical discharge in the
atmosphere
• Positive charges accumulate at the top of
the cloud, negative charges at the bottom
• When there is enough difference in
charge, lightning flashes
Thunder
• Occurs from the expansion of gases that
results from the extreme heat the released
when lightning discharges
• You hear thunder after you see lightning
because light travels faster than sound
Tornadoes
• A small but intense windstorm that is a
rotating column of air that touches the
ground
• Usually occur at the leading edge of an
advancing cold front
• Occurs in a thunderstorm
• Wind can reach 500 km/hr usually
150km/hr
Hurricanes
• Cyclone that develop in the tropics
• Hurricane is a large tropical cyclone with
winds of at least 110 km/hr
24.6 Predicting the Weather
• Meteorologists study Earth’s weather
• They use:
– Doppler radar
– Automated weather stations
– Weather satellites
– High- speed computer
Doppler Radar
• Bounces radar waves off the clouds
• Measure the frequency of the waves that
return
• Speed of the storm can be calculated
Weather Stations and Satellites
• Have sensors that measure
– Temperature
– Precipitation
– Winds speed
– Direction
High Speed Computers
• Used to predict weather
• Accurate from 12 hrs to 3 days
• Large weather systems 3-7 days
• Difficult to predict beyond 7 days
Weather Maps
• Temperatures
• Sun, cloud symbols
• Cloud cover
• Drawings of rain or snow
Isotherm
• Line on a map that connects points of
equal air temperature
Isobar
• A line on a map that connect points of
equal air pressure
24.7 Climate
• Long term- weather conditions
• Natural
– Ice Ages
– El Nino
• Caused by Humans
– Global Warming
Classifying Climates
Temperature
precipitation
Temperature
• Latitude
• Distance from large bodies of water
• Ocean currents
• altitude
Precipitation
• Latitude
• Distribution of air pressure systems
• Global winds
• Existence of a mountain barrier
desert
• Receive less than 25 cm of rain per year
• Can be hot or cold
• Direction of prevailing winds
Natural Climate Change
• Possible causes are
– Variations in Earth’s orbit around the sun
– Changes in the angle of Earth’s axis
– Global levels of volcanic activity
El Nino
• Occurs about every 3-8 years
• The cold water upwelling fails to occur off
the coast of Peru causing a warming tend
Global Warming
• Possibly caused by human activities
• Burning of fossil fuels raises CO2 levels
• 1990’s hottest decade on record
• Hotter temperatures cause the oceans to
swell which floods low lying areas causing
many people’s homes to be flooded