Transcript Atmosphere and Climate Change Section 1 Seasonal Changes in

Atmosphere and Climate Change
Section 1
Climate
• average weather conditions in an area over a long period
of time.
• determined by factors that include: latitude, atmospheric
circulation patterns, oceanic circulation patterns, the
local geography of an area, solar activity, and volcanic
activity.
• most important factor: distance from the equator
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• Latitude: distance north or south from the equator, is
expressed in degrees
• Equator at 0° latitude, most northerly latitude is the
North Pole, at 90° north; most southerly latitude is the
South Pole, at 90° south
• affects climate because the amount of solar energy an
area of the Earth receives depends on its latitude.
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Low Latitudes (near equator)
• more solar energy falls on these areas
• night and day both about 12 hours year-round
• temperatures high year-round, no summers or winters
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High Latitudes (closer to poles)
• sun is lower in the sky, reducing the amount of energy
arriving at the surface
• sunlight hits the Earth at an oblique angle and spreads
over a larger surface area than it does at the equator
• temperatures lower than they are at the equator
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• hours of daylight vary
• 45° N and S, as much as 16 hours of daylight during the
summer ; 8 hours of sunlight in the winter
• Near poles, sun sets for only a few hours during the
summer, rises for only a few hours during the winter
– yearly temperature range very large
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Atmospheric Circulation
• Air circulation affects climate
• Cold air (denser than warm ) sinks, compresses and
warms
• Warm air rises, expands and cools
• Warm air can hold more water vapor than cold air
can. When warm air cools, the water vapor it
contains may condense to form rain, snow, or fog.
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• Solar energy heats the ground, warms the air above
• Warm air rises, cooler air moves in to replace it. This
movement is called wind.
• Earth’s rotatation, energy differences N & S create
pattern of global atmospheric circulation
– circulation pattern determines precipitation pattern
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• Ex: intense solar energy at the equator causes the
surface and air above to become very warm
– warm air can hold large amounts of water vapor
– as it rises and cools, its ability to hold water is
reduced, producing large amounts of rain
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Global Circulation Patterns
• Cool air over the equator cannot descend because hot
air is rising up below it.
• Forced away, accumulates at about 30º N & S
– Some sinks becomes warmer. This warm, dry air then
moves across the land, causes water to evaporate
from the land, creating dry conditions.
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• At about 60º N & S air from equator air collides with cold
air from the poles
– the warm air rises, most forced toward the poles
– cold, dry air descends
– poles essentially very cold deserts
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Prevailing Winds, (Belts)
• Winds that blow predominantly in one direction
throughout the year
• Because of the Earth’s rotation not directly northward or
southward
– deflected right, from northeast, Northern Hemisphere
– deflected left, from southeast, Southern Hemisphere
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• Belts produced between 30º N & S latitude and the
equator, trade winds
• Belts produced between 30º and 60º N & S, westerlies
• Belts produced between poles to 60º N & S, easterlies
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Oceanic Circulation
• Ocean currents have a great effect on climate because
water holds large amounts of heat.
– surface currents caused mostly by winds, Earth’s
rotation
– redistribute warm and cool masses of water around
the world
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El Niño–Southern Oscillation (ENSO)
• El Niño: warm phase
• periodic occurrence in eastern Pacific Ocean when
surface-water temperature becomes unusually warm
• winds in the western Pacific Ocean, strengthen, push
warm water eastward
• rainfall increased southern half of U.S., drought in
Australia.
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• La Niña: cool phase
• periodic occurrence in the eastern Pacific Ocean when
surface water temperature becomes unusually cool
• El Niño and La Niña are opposite phases of cycle.
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Pacific Decadal Oscillation (PDO)
• Long-term, (20 to 30 year) change in location of warm
and cold water masses in the Pacific Ocean
– influences climate in the northern Pacific Ocean, N.A.
– affects ocean surface temperatures, air temperatures,
and precipitation patterns
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Topography
• Height above sea level (elevation) has an important
effect on climate.
• Temperatures fall by about 6°C (about 11°F) for every
1,000 m increase in elevation.
• Mountain ranges also influence the distribution of
precipitation.
– rain on the western side, eastern side dry
– effect known as a rain shadow.
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Other Influences on Earth’s Climate
• At a solar maximum, increased amount of ultraviolet
(UV) radiation
– produces more ozone, which warms the stratosphere
– can also warm the lower atmosphere, surface a little
• Large-scale volcanic eruptions produce sulfur dioxide
gas that can reach the upper atmosphere.
– can remain in the atmosphere for up to 3 years
– reacts with water vapor and dust to form a bright layer
of haze that reflects enough sunlight to cause a
global temperature decrease
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Seasonal Changes in Climate
• The seasons result from the tilt of the Earth’s axis, about
23.5° relative to the plane of its orbit
– the sun’s rays strike the Earth at different angles as
the Earth orbits the sun
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Seasonal Changes in Climate
• Summer, Northern Hemisphere, earth tilts toward the
sun and receives direct sunlight.
– hours of daylight greatest
– Southern Hemisphere tilts away from the sun,
receives less direct sunlight (their winter)