Download Atmospheric Circulation

Atmospheric Circulation
Earth’s Atmosphere & Oceans
• Earth’s atmosphere and oceans are intimately
related. Gases from the water influence the
climate and gases from the air affect acidity of
the water and where life will survive in the
ocean.
Weather vs. Climate
• The difference between weather and climate is
that weather is what the atmosphere is doing at
a given place and time for instance what is
happening in Blue Hill at noon today, while
climate is the average of the weather over a
long period.
Water Vapor in the Atmosphere
• Water vapor is the form in which water is
found in the atmosphere. It has varied paths
of getting into the atmosphere, coming from
evaporation from plants, the ground and the
oceans and lakes. When it falls out of the air,
it returns to Earth in some form of
precipitation such as snow, rain or dew.
The Water Cycle
• The Water Cycle involves water vapor
evaporating from the oceans and lakes into the
atmosphere where as it rises, it cools and
condenses forming clouds. When enough
droplets join together, the condensation
becomes heavy and falls out of the atmosphere
as precipitation. The precipitation runs off
through streams to rivers to the ocean, where it
then evaporates into the atmosphere. There is
one more way that water vapor gets into the
atmosphere and that is through evaporation
from plants called transpiration.
The Water Cycle
Air’s Mass
Air has mass and it is more dense the nearer to
Earth it gets because of the mass of the column
of air above it. Warm air will occupy more
space than the same mass of cold air, making it
less dense, so it rises. Also, humid air is less
dense than dry air at a given temperature
because the water vapor molecules weigh less
than the oxygen and nitrogen molecules that
they are displacing.
Latitudes and Uneven Heating
The Equator is 0o latitude. As you move away
from the Equator either north or south, the
latitude increases until it reaches 90o latitude at
the Poles. The North Pole is 90o North and the
South Pole is 90o South. At higher latitudes
(like the poles), sunlight has to pass through
more atmosphere and spreads out over a larger
area than the same amount of sunlight at the
Equator.
Latitudes
The Poles vs. the Equator
Sun’s Rays Striking Earth
Sun’s Rays & Atmosphere
Seasons and Uneven Heating
• Seasons: Due to the 23.5 degree tilt of the
rotational axis of the Earth relative to the plane
of orbit around the sun, the northern and
southern hemispheres are closer or farther
away from the sun at different times of the
year, causing the seasons.
23.5o Rotational Axis
Seasons
Vernal & Autumnal Equinox
Seasons
Convection Currents
Heat Transport on Earth
• Through convection currents, the warm air
rises at the Equator and moves northward
toward the poles where it radiates its heat into
the atmosphere, cools and sinks towards
Earth’s surface and flows back toward the
Equator.
Overall Convection Currents
Coriolis Effect
• Due to the rotation of the Earth, winds are
diverted to the right. Depending on your
perspective, if you are looking north it appears
that the item moves east and if facing south, it
looks as if they are moving west. This also
causes low pressure areas to move
counterclockwise and high pressure areas to
move in a clockwise motion.
Atmospheric Circulation Cells
• In actuality, the warm air does rise at the
Equator but it becomes dense enough to sink
back to Earth long before reaching the poles.
At about 30o north and south, the air has
cooled enough to fall back to the Earth’s
surface. These are known as the Hadley cells.
Hadley Cell in Red
Ferrel and Polar Cells
• Some of the air that descends at 30o north and
south moves toward the poles. The air is
heated at the surface as it moves northward
and is driven by colder air moving from the
poles toward the Equator. These mid-latitude
cells are called the Ferrel cells. There are
small cells that circulate at the poles known as
the Polar cells. These are all driven by uneven
heating of the air.
Ferrel Cell in Black and
Polar Cell in Blue
Wind Patterns
• Areas where the circulation cells meet, have
little or no wind at times. The doldrums is
area at the surface where the two Hadley cells
come together. This is also known as the
Intertropical Convergence Zone or (ITCZ).
The horse latitudes are also areas where there
is little surface wind. They are found at the
intersections of the Hadley and Ferrel cells.
Wind Patterns
Areas of Dependable Surface Winds
• In between the areas of convergence, are the
areas of reliable winds, such as the trade winds
and the westerlies. These are the areas ship
captains headed for to make forward progress.
Wind Patterns
Monsoons
• Monsoons are affected by the heating of land
and ocean and the seasonal movement of the
ITCZ. In the spring the land heats faster than
the ocean. Warm air over the land rises while
cooler air from the ocean moves in over the
land to take its place. The ocean air brings
with it humidity and as the humid air is
warmed by the land and rises, the water vapor
condenses and rain is produced.
Monsoons
• In the fall, the reverse happens, the land cools
more quickly than the ocean. Air above the
land sinks as it cools and causes dry surface
winds to move toward the ocean. The location
and intensity of monsoon season depend on the
location of the ITCZ. Monsoon rains are a
necessity for the people of Africa and Asia as
they depend on them for drinking water and
farming.
Seasonal ITCZ Location
Monsoon Circulation
Sea and Land Breezes
• The sea breeze we feel in the summer and land
breeze in the winter are actually minimonsoons. As the land heats up in the summer
more quickly than the ocean, the air above the
land rises and air from the ocean fills in
creating a nice, cool sea breeze. The opposite
forms the land breeze.
Sea Breeze
Sea Breeze
Land Breeze
Land Breeze
El Nino & La Nina
• The trade winds are responsible for dragging
warm surface water across the Pacific Ocean to
the Far East. Every 3 to 8 years, the atmospheric
circulation changes and the trade winds weaken or
reverse. The warm water that has piled up on the
western side of the Pacific, spreads eastward
along the Equator. El Nino is a warm water
current that flows back toward the Central and
South America. It changes the weather patterns as
well as altering ocean conditions. La Nina is
colder than normal events occurring both on land
and in the ocean.
El Nino
La Nina
Water Temperature for
El Nino & La Nina
Air Masses
• An air mass is large body of air with uniform
humidity and temperature. Air moving over
land or water takes on the characteristics of the
surface below. It will be chilly and dry if it is
formed over cold, dry land. The air will be
dense and cause higher pressure pushing
down, thus it is called “High Pressure.” Air
over warm, moist water takes on its
temperature and humidity. Warm air is less
dense than cooler air and rises forming a “Low
Pressure” area.
High and Low Pressure Areas
Fronts
• Air masses usually have different densities
depending on whether they are a high or low
pressure area. A front is the boundary between
two different air masses (areas of density) in
the atmosphere. When there is a large
difference in density, humidity and
temperature, extreme storms can be spawned.
• A storm is a regional atmospheric disturbance.
Storms over Joplin, MO
Weather Map of Joplin, MO
Tornados forming near Joplin, MO
Joplin, MO
Fronts
Warm and Cold Fronts
Storms
• A storm is a regional atmospheric disturbance
caused by low pressure areas. Rain and wind
are usually associated with these systems. It is
the Earth’s method of trying to reaching
dynamic equilibrium for the amount of water
and heat on the surface of the Earth.
Hurricanes bring large amounts of water from
the tropics and drop it on the higher latitudes.
Extratropical Cyclones
• These storms form between the Polar and
Ferrel cells in the winter when the density and
temperature of the cells have the most
difference. This is called a Polar front.
Nor’easters (northeasters) are the most violent
storms that move up the eastern seaboard of
the United States. They get their name from
the direction from which the strongest winds
blow.
Tropical Cyclones
• Tropical cyclones usually start near the
Equator and are formed in one warm, humid
air mass. They start from tropical depressions
that increase in intensity to a tropical storm
and finally if conditions are right to a
hurricane. A hurricane gains energy from the
warm water over which it is moving. The
parts of the storm causing damages are the
wind, rain and storm surge. The storm surge
being the most dangerous part.
Tropical Cyclones
• The names of tropical cyclones are as follows:
• Eastern Pacific and Atlantic Oceans –
Hurricanes
• Western Pacific Ocean – Typhoons
• Indian Ocean – Tropical cyclones
• Australia - Williwillis
Tropical Cyclones
• The eye of a tropical cyclone is usually 8 to 10
miles across and is an area of calm, sunny
skies. The tropical cyclone itself can be up to
1000 miles in diameter and 50,000 feet high.
• When a tropical cyclone moves over land or
cold water, it loses its energy due to friction
over land and lack of heat to drive the storm.
Redistributing Energy
• These tropical cyclone are Mother Nature’s
way of moving solar energy from the Equator
toward the Poles to equalize the amount of
energy on Earth.
A Hurricane
Hurricane Sandy
Storm Surge
Sandy’s Storm Surge
Sandy’s Storm Surge
Sandy’s in NYC
Storm Surge in NYC
The End