Atmosphere and
Weather
AP Environmental Science
www.ai.mit.edu/people/jimmylin/pictures/2001-12-seattle.htm
Origin of Modern Atmosphere
• original atmosphere surrounded the homogenous planet
Earth and probably was composed of H and He
• second atmosphere evolved from gases from molten
Earth
– H2O, CO2, SO2, CO, S2, Cl2, N2, H2, NH3, and CH4
– allowed formation of oceans and earliest life
• modern Atmosphere
– evolved after Cyanobacteria started photosynthesizing
– oxygen produced did not reach modern levels until about 400
million years ago
www.degginger.com/digitalpage.html
Earth’s Atmosphere
• Compared to the size of the
Earth (104 km), the atmosphere
is a thin shell (120 km).
• If the Earth was an orange, the
atmosphere would be the
pesticides on its peel
http://www.gsfc.nasa.gov/gsfc/earth/pinatuboimages.htm
Atmosphere
Layers
•
•
•
•
•
•
Exosphere
Thermosphere
(Ionosphere)
Mesosphere
Stratosphere
Troposphere
Stratosphere
• extends to 50 kilometers (31 miles) high
• dry and less dense
• temperature in this region increases
gradually to -3 degrees Celsius, due to the
absorption of ultraviolet radiation
• ozone layer absorbs and scatters the solar
ultraviolet radiation
• ninety-nine percent of "air" is located in
first two layers
• every 1000-m 11% less air pressure
Troposphere
• 8 to 14.5 kilometers high (5 to 9 miles)
• most dense
• the temperature drops from about 17 to -52
degrees Celsius
• almost all weather is in this region
Composition
•
•
•
•
Nitrogen (N2, 78%)
Oxygen (O2, 21%)
Argon (Ar, 1%)
myriad of other very
influential components are also
present which include the Water (H2O, 0 - 7%),
"greenhouse" gases or Ozone (O3, 0 - 0.01%),
Carbon Dioxide (CO2, 0.01-0.1%),
Weather
Humidity
• relative humidity is the amount of water vapor in
the air compared with the potential amount at the air's
current temperature
– expressed as a percentage
– depends on air temperature, air pressure, and water
availability
• the Earth has about 326 million cubic miles of water
• only about 3,100 cubic miles of this water is in the air
as water vapor > clouds > precipitation
www.rowcamp.com/photos.htm
Cloud cover
• moisture in the atmosphere forms clouds which cover
an average of 40% of the Earth at any given time
• a cloudless Earth would absorb nearly 20 percent more
heat from the sun
• clouds cool the planet by reflecting sunlight back into
space. This is known as Albedo
However
• clouds reduce the amount of heat that radiates into
space by absorbing the heat radiating from the surface
and reradiating some of it back down
• the process traps heat like a blanket
•
“Cloud www.nasm.si.edu/earthtoday/ cloudlg.htm
•
-Dec-2002 15:52:11 EST
http://worldbook.bigchalk.com/wbgifs/lr001421.htm
Precipitation
• Air containing water vapor cools in atmosphere
and therefore condenses to form droplets of
liquid water
– Rain: liquid, falls, d >0.5 mm (sphere)
– Freezing Rain: occurs when drop touches frozen
surface
– Sleet: ice pellets, d < 0,5 mm, begins as rain but
enters air below freezing
– Snow: water deposits in hexagonal nuclei below
freezing
– Snow Pellets: grains of ice, d = 2-5 mm
– Hail: 5-190 mm in diameter, concentric rings of ice
Other Factors that effect precipitation:
- Prevailing winds
- Mountain ranges
Winds
• horizontal wind moves from areas of high
to low pressure
• vertical wind moves from low to high
pressure
• speed is determined by differences in
pressure
• Coriolis effect causes winds to spiral from
high pressure zones and into low pressure
zones
www.iiasa.ac.at/Admin/INF/OPT/ Spring98/feature_story.htm
Winds
• wind speed is detected by an anemometer
• direction is detected by a weather vane
• wind direction is based on where the wind
is coming from: wind from the east is an
easterly
• Beaufort Wind Speed Scale is has a range
from 0 for calm to 12 for a hurricane with
waves greater than 37 feet
www.mountwashington.org/notebook/ transcripts/1999/07/07.htm
Severe Weather - Thunderstorms
• occur from equator to Alaska
• may have hail, strong winds, lightning, thunder, rain &
tornadoes
• moist air rises due to frontal zone lifting causing loss of
heat leading to cumulus clouds with updrafts
• at 42,000 feet downdrafts and precipitation start
• may last an hour
• severe thunderstorms occur when cold front approaches
warm front (which supplies moisture and energy)
– winds over 60 mph
– hail > 3/4 inch
Severe Weather - Tornadoes
• swirling masses of air with speeds of 300 mph+
• waterspouts occur over water
• center of tornado is extreme low pressure which
causes buildings to implode
• destruction is usually less than 0.5 miles wide
and 15 miles long
• tornado alley is from Texas to Indiana (usually
trailer homes)
• Wizard of Oz!
Severe Weather - Hurricanes
•
•
•
•
cause most property damage and loss of life
winds speeds greater that 74 mph at the center
begin over warm oceans of the tropics
solar insolation (water >80oF) provides energy
for huge evaporation, cloud formation, and
atmospheric lifting
Thorpe, Gary S., M.S., (2002). Barron’s How to prepare for the AP Environmental Science Advanced Placement Exam
Severe Weather - Hurricanes
• stages
– separate thunderstorms over tropical ocean
– cyclonic circulation which causes them to pick up
more more moisture and heat energy from ocean
– winds speeds of 23 to 40 mph lead to Tropical
Depression
– Tropical Storms have lower pressure and higher
wind speeds (40-75)
• center is called the eye
• rainfall may exceed 24 inches in 24 hours
The El-Niño Southern
Oscillation (ENSO)
• Occurs every few years
• ENSO’s occur when
the prevailing westerly
winds weaken or cease
and surface waters
along the South and
North American
Coasts become warmer
• Upwellings of cold
nutrient rich waters
are suppressed
• Leads to declines in
fish populations
ENSO events result from
weakening of tropical Pacific
atmospheric and oceanic
circulation
Climatic connections carry
these climate effects
throughout
the globe
(e.g., El Niño creates
warm winters in AK and
lots of rain in
California)
2.19
La Nina
• The opposite of el Nino is La
Nina.
• During La Nina, the winds
blowing across the Pacific
are stronger than normal and
warm water accumulates in
the western Pacific. The
water near Peru is colder.
• This causes droughts in the
southern United states and
excess rainfall in the
northwestern Untied States.
• Definitions: Average
long term weather of an
area
– Seasonal variations and
weather extremes
averaged over a long
period (at least 30 years)
• 2 Main factors
– Temperature
– Precipitation
• amount
• distribution
Climate
Climate Continued…
Factors that effect temperature:
– Latitude
Unequal
Heating of
Earth
•This unequal heating is because:
• The variation in angle at which the Sun's
rays strike
• The amount of surface area over which
the Sun's rays are distributed
• Some areas of Earth reflect more solar
energy than others. (Albedo)
Latitude
• Latitude is the measure of the distance
north and south of the equator.
– Measured in degrees.
• Areas close to the equator, or 0 degrees
latitude, receive the direct rays of the
sun. These direct rays provide the most
radiant energy.
– Areas near the equator are warm.
– Polar regions are cold.
High Latitudes
During the year,
the high latitudes
near the poles have
great differences in
temperature and
daylight hours.
Seasonal Changes
• Occur because the
earth’s axis is tilted
• Creates opposite
seasons in the
northern and
southern
hemisphere
• Factor that
determines global
air circulation
patterns
Seasons
• Seasons are short periods
of climatic change.
• Because the Earth is
tilted, certain areas of
Earth receive changing
amounts of radiation
throughout the year.
Earth’s Seasons
When the north pole tilts toward the SUMMER (Northern Hemisphere)
sun, it gets more radiation – more warmth
during the summer
When the north pole tilts toward the
sun, the south pole tilts away
So when it’s summer in the north,
it’s winter in the south
WINTER (Southern Hemisphere)
Earth’s Seasons Continued….
Tilt of the Earth’s axis towards or away from the sun creates the seasons
WINTER (Northern Hemisphere)
When the north pole tilts away
from the sun, it gets less radiation –
So it’s colder during the winter
When the north pole tilts away from the
sun, the south pole tilts toward it…
SUMMER (Southern Hemisphere) When it’s winter in the north,
it’s summer in the south
Atmospheric Convection Currents
•Air has four properties that determines its
movement:
– Density- less dense air rises, denser air sinks.
– Water vapor capacity- warm air has a higher
capacity for water vapor than cold air.
– Adiabatic heating or cooling- as air rises in the
atmosphere its pressure decreases and the air
expands. Conversely, as air sinks, the pressure
increases and the air decreases in volume.
– Latent heat release- when water vapor in the
atmosphere condenses into liquid water and
energy is released.
Formation of Convection Currents
• Atmospheric convection currents are global patterns
of air movement that are initiated by the unequal
heating of Earth.
• Hadley cells- the convection currents that cycle
between the equator and 30˚ north and south.
• Intertropical convergence- the area of Earth that
receives the most intense sunlight and where the
ascending branches of the two Hadley cells converge.
• Polar cells- the convection currents that are formed by
air that rises at 60˚ north and south and sinks at the
poles (90˚ north and south)
Coriolis Effect
• As Earth rotates, its surface moves
much faster at the equator than in
mid-latitude and polar regions.
• The faster rotation speeds closer to
the equator cause a deflection of
objects that are moving directly
north or south.
You Tube on Coriolis Effect
Climate Continued…
Factors that effect temperature:
– Latitude
– Elevation
Elevation
Climate Continued…
Factors that effect temperature:
– Latitude
– Elevation
– Closeness to large bodies of water
Closeness to Large Bodies of Water
Water
moderates the
temperature
creating cooler
summers and
warmer
winters
Ocean Currents
• Sea-surface temperature influences
air temperature as the ocean
exchanges heat with the overlying
atmosphere.
• Evaporation rates are generally
higher where sea-surface
temperature is higher
• Some of the water that flows from the Gulf of
Mexico to the North Atlantic freezes or
evaporates, and the salt that remains behind
increases the salt concentration of the water.
• This cold, salty water is relatively dense, so it
sinks to the bottom of the ocean, mixing with
deeper ocean waters.
• These two processes create the movement
necessary to drive a deep, cold current that
slowly moves past Antarctica and northward to
the northern Pacific Ocean.
Ocean Currents
• There are two type of Ocean Currents:
• 1. Surface Currents--Surface
Circulation
– These waters make up about 10% of all
the water in the ocean.
– These waters are the upper 400 meters of
the ocean.
Ocean Currents
• 2. Deep Water Currents
• These waters make up the other 90% of the
ocean
• These waters move around the ocean basins
by density driven forces and gravity.
• These deep waters sink into the deep ocean
basins at high latitudes where the
temperatures are cold enough to cause the
density to increase.
Ocean Currents
Ocean Currents are influenced by two
types of forces
1. Primary Forces--start the water moving
1. Solar Heating
2. Winds
3. Gravity
4. Coriolis
2. Secondary Forces--influence where the
currents flow
The Rain Shadow Effect