Atmosphere and Weather

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Atmosphere and Weather

• AP Environmental Science
• Mark Ewoldsen, Ph.D.
• Dr. E

www.ai.mit.edu/people/jimmylin/pictures/2001-12-se
attle.htm
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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

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Seasonal Changes

• Occur because the earths axis is tilted
• Creates opposite seasons in the northern and
  southern hemisphere
• Factor that determines global air circulation
  patterns

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Earths Seasons

When the north pole tilts toward thesun, it gets
more radiation more warmth during the summer
SUMMER (Northern Hemisphere)
North Pole


Equator
Earth
When the north pole tilts toward thesun, the
south pole tilts away So when its summer in the
north, its winter in the south
South Pole
WINTER (Southern Hemisphere)
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Earths Seasons Continued.
Tilt of the Earths 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 its colder during the
winter

Earth

When the north pole tilts away from thesun, the
south pole tilts toward it When its winter in
the north, its summer in the south
SUMMER (Southern Hemisphere)
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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.

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High Latitudes

• During the year, the high latitudes near the
  poles have great differences in temperature and
  daylight hours.

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http//www.usatoday.com/weather/tg/wglobale/wgloba
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Hadley Cells
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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 gt clouds gt precipitation

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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 155211 EST

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http//worldbook.bigchalk.com/wbgifs/lr001421.htm
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Precipitation

• Air containing water vapor cools in atmosphere
  and therefore condenses to form droplets of
  liquid water
• Rain liquid, falls, d gt0.5 mm (sphere)
• Freezing Rain occurs when drop touches frozen
  surface
• Sleet ice pellets, d lt 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

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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

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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

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transcripts/1999/07/07.htm
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Fronts

• Warm Front
• separates warm air from the cooler air it moves
  into (6 mph, NE)
• rises over cool air masses
• develops clouds and light precipitation

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Fronts

• Cold Front
• cold air advancing into warm (9 to 30 mph, SE)
• pushes under warm air rising air just ahead of
  front
• vertical movement strong and thus thunderstorms

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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 gt 3/4 inch

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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!

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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 gt80oF) provides energy
  for huge evaporation, cloud formation, and
  atmospheric lifting

Thorpe, Gary S., M.S., (2002). Barrons How to
prepare for the AP Environmental Science Advanced
Placement Exam
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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

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Closeness to Large Bodies of Water
Water moderates the temperature creating cooler
summers and warmer winters
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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

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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.

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The El-Niño Southern Oscillation (ENSO)

• Occurs every few years
• ENSOs 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

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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
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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.

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Climate

• 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

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Climate Continued

• Factors that effect temperature
• Latitude
• Elevation
• Closeness to large bodies of water

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Elevation
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Short Term Changes in Climate

• Some short-term changes may be the result of
  changes in ocean currents and global winds.
• Ocean currents help transfer heat to the
  atmosphere. This process generates global winds.
  The global winds help move ocean currents.
• Any major change in an ocean current can cause a
  change in climate. El Nino is an example.

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Elevation
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The Rain Shadow Effect
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