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Meteorology Class
Chapter 7 Notes – The Circulation of Air
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.
Macroscale
Circulation
(Hurricane)
Mesoscale
Scale
(tornado)
Microscale
Winds
(dust devil)
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.
Breezes and Winds:
•
•
•
•
•
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
Texas Norther’
•
Not a real true local wind (mesoscale) as it deals more with a cold front and
precipitation than wind production.
Global Circulation:
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.
3 Cell Model of 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.
Specific Winds and characteristics:
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.
•
Rumor has it that this name was given due to sailors
having to throw horses off ships in order to reduce
weight and get ships to move in areas of minimal wind
production.
The Doldrums:
•
The trade winds from both hemispheres
meet near the equator in a region that
has a weak pressure gradient called the
doldrums.
•
An area of minimal winds.
Trade Winds:

Most of the United States is
located in prevailing
westerlies wind zone.
Santa Ana Winds:

Summertime wildfires in California are fanned
by the Santa Ana Winds
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,
(3) subpolar low, and
(4) polar high.
Monsoons:

A monsoon is a wind system that exhibits
pronounced seasonal reversal in direction.

The best-known monsoonal circulation is the
Asian monsoon.
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.
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.
El Niño refers to warming
of ocean waters caused by a
warm counter current flowing
along the coasts of Ecuador
and Peru that replaces the
cold Peruvian current.
El Niño events influence
weather at great distances
from Peru and Ecuador.
When surface temperatures in
the eastern Pacific are colder
than average, a La
event is triggered.
The general features of the
global distribution of
precipitation can be
explained by global winds and
pressure systems.
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.
Niña