atmosphere and climate changesection 1 climate average weather conditions in an area over a long...

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


• 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.


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


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


• 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


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.


• 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


• 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


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.


• 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


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


• 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


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


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.


• 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.


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


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.


• 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

Other Influences on Earth’s Climate


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


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)

atmosphere and climate changesection 1 climate average weather conditions in an area over a long...

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