Chapter%207%20Circulation%20of%20the%20Atmosphere

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Chapter 7 Circulation of the Atmosphere
A Synoptic-scale Event
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Planetary-scale wind patterns

• macroscale winds are called synoptic scale, or
  weather-map scale. Mesoscale winds are
  thunderstorms, tornadoes, and breezes.
• The smallest scale of air motion is the
  microscale. Examples of these winds include gusts
  and dust devils.

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Hurricane
Tornado
Microscale Winds
Macroscale Circulation
Mesoscale System
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Winds

• Caused by differences in pressure and
  temperatures. In addition to land and sea breezes
  caused by the daily temperature contrast between
  land and water, other mesoscale winds include
• mountain and valley breezes,
• chinook (foehn) winds,
• katabatic (fall) winds, and
• country breezes.

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Valley and Mountain Breeze
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Winds Breezes

• Mountain and valley breezes develop as air along
  mountain slopes is heated more intensely than air
  at the same elevation over the valley floor.
• Chinooks are warm, dry winds that move down the
  east slopes of the Rockies.
• In the Alps, winds similar to chinooks are called
  foehns.
• Katabatic (fall) winds or drainage winds
  originate when cold air is set in motion under
  the influence of gravity.
• Country breezes are associated with large urban
  areas

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Texas Norther

• Not a real true local wind (mesoscale) as it
  deals more with a cold front and precipitation
  than wind production.

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Global Circulation
Three-cell Model
Single-cell Model
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Single-Cell Model

• According to the single-cell circulation model
  proposed by George Hadley, the most important
  factor causing the global atmospheric circulation
  was temperature contrasts between the equator and
  pole.

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Global Circulation

• According to the three-cell circulation model,
  atmospheric circulation cells are located between
  the equator and 30 latitude, 30 and 60
  latitude, and 60 latitude and the pole.

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Horse Latitudes

• The areas in the zone between 20 and 35 are
  called the horse latitudes.
• In each hemisphere, the equator ward flow from
  the horse latitudes forms the reliable trade
  winds.

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Doldrums

• The trade winds from both hemispheres meet near
  the equator in a region that has a weak pressure
  gradient called the doldrums.

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Summertime wildfires in California are fanned by
the Santa Ana Winds
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Trade winds

• Most of the United States is located in
  prevailing westerlies wind zone.

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ITCZ

• Beginning at the equator, the four belts would
  be the (1) equatorial low, also referred to as
  the intertropical convergence zone (ITCZ), (2)
  subtropical high, at about 20 to 35 on either
  side of the equator, (3) subpolar low, situated
  at about 50 to 60 latitude, and (4) polar high,
  near Earth's poles.

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Monsoon Circulation
A monsoon is a wind system that exhibits
pronounced seasonal reversal in direction.
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The best-known and most pronounced monsoonal
circulation is the Asian monsoon.
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Jet Streams
The temperature contrast between the poles and
equator drives the westerly winds located in the
middle latitudes. Embedded within the westerly
flow are narrow ribbons of high-speed winds,
called jet streams, that meander for thousands of
kilometers.
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Ocean Currents

• ocean currents play a major role in maintaining
  Earth's heat balance.
• In addition to producing surface currents, winds
  may also cause vertical water movements, or
  upwelling of cold water from deeper layers to
  replace warmer surface-water.

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Ocean Currents
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El Niño
El Niño refers to episodes of ocean warming
caused by a warm countercurrent flowing southward
along the coasts of Ecuador and Peru that
replaces the cold Peruvian current.
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El Niño events influence weather at great
distances from Peru and Ecuador.
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When surface temperatures in the eastern Pacific
are colder than average, a La Niña event is
triggered. A typical La Niña winter blows colder
than normal air over the Pacific Northwest and
the northern Great Plains, while warming much of
the rest of the United States.
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Global Distribution of Precipitation
The general features of the global distribution
of precipitation can be explained by global winds
and pressure systems.
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Pressure Belts and Precipitation
regions influenced by high pressure experience
dry conditions. regions under the influence of
low pressure and converging winds receive ample
precipitation.
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Chapter 7

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