Atmospheric Pressure and Wind

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Atmospheric Pressure and Wind
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Impact of Pressure and Wind on Landscape

• Human not sensitive to air pressure
• But sensitive to heat, air movement and humidity
• Spatial variation in pressure create air movements

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The nature of Atmospheric Pressure

• Pressure The force the gas exerts. Measured in
  force per Sq area
• Atmospheric Pressure Force exerted by gas
  molecules equal in all direction. Pressure
  decreases with latitude
• Pressure, Density and Temperature
• Variation in one affects other two
• Density is amount of matter in a unit volume
• What will rising air result in? L or H Pressure?

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The nature of Atmospheric Pressure

• Mapping Pressure
• Barometer 14.7 lbs/sq in
• Millibar (1/1, 000 of a bar or 1000 dynes/sq cm)
• Isobar
• Pressure gradient Pressure slope, horizontal
  rate of pressure change

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The Nature of Wind

• Always in motion but more horizontal that
  vertical
• Updrafts and downdrafts Small scale vertical
  motion
• Ascents and subsidences Large scale vertical
  motion
• Direction of movement
• Depends on Pressure gradient
• Earths rotation (Coriolis effect)
• Friction

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Pressure Gradient
Figure 5-5
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Coriolis Effect
Figure 5-A
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Friction
Figure 5-7
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The Nature of Wind (cont.d)

• Cyclones (low pressure cell)-4 and Anticyclones
  (high Pressure cell) -4.
• Wind speed Pressure gradient, Persistent winds
  in coastal and high mountain areas

Hurricane
severe tropical storm in the North Atlantic
Ocean
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Circulation Patterns
Figure 5-8(b)
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Vertical Variation in Pressure and Wind

• Atmospheric pressure decreases with height
• Wind speed increases with height

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The General Circulation of the Atmosphere

• Rotation of Earth and surface variability play a
  role
• Hadley Cell only tropical regions have a
  complete vertical cell ( 50, 000 ft or 15 KM),
  cools and moves poleward and descends at about 30
  Degrees of Latitude.
• Midlat (Ferrel Cell) and High latitude cell
  (polar cell) are weakly or sporadically
  developed.
• No or weak vertical cells at mid-latitudes and
  high altitudes

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Hadley Cells
Figure 5-13
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Seven surface components

• 1. Polar high (Arctic less persistent that
  Antarctic)
• 2. Polar easterlies,
• 3. Subpolar low,(50-60degrees)
• 4. Westerlies (30-60 degrees WE, Rosby waves NS
  in upper atmosphere)
• 5. Subtropical high,(from descending Hadley cell
  200 miles wide)
• 6. Trade winds (Wind system in tropics NE and SE)
  
• 7. Intertropical convergence zone ( calm, NE and
  SE trades converse)

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(No Transcript)
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Inter Tropical Convergence Zone( ITCZ)
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Horse, latitude, Doldrums
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Seven surface components

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Modification of General Circulation

• http//www.usatoday.com/weather/tg/wglobale/wgloba
  le.htm
• Seasonal Variations
• Seven components shift latitudinally with the
  changing seasons
• Monsoons seasonal reversal of winds onshore
  during summer or offshore winter

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MonsoonsMonsoon Areas of the World
Figure 5-38
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South Asian Monsoon
Figure 5-39(a)
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Localized Wind Systems

• Sea and Land Breezes from sea to land and land
  to sea
• Valley and Mountain Breezes Upslope during day,
  downslope during night
• Katabatic winds originates from cold uplands and
  travels downslope under the influence of gravity
  (Mistral in Rhone, France)
• Chinook winds Warm dry air moves downslope on
  leeward side.Foen in Europe

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Focus Studies

• The Coriolis Effect
• North right, South left
• More deflection at poles and less at Equator
• Proportional to speed so fast moving appears to
  be more deflected
• Coriolis effect influences direction not speed
• Effects winds and ocean currents

• Wind Chill
• Combination of temperature and low temp and high
  wind
• No windchill lt 4.5 mph
• Wind scorch at high temperature

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El Nino, La Nina ENSO, Pacific Decadal Oscillation

• There is a normal pattern in pressure wind and
  ocean currents. Because of easterlies in eastern
  pacific, there is westward movement of warm
  equatorial current. This causes upwelling of cold
  water.
• In El Nino water on the surface is warm occurs
  around Christmas time every few years.
• La Nina Cold temperature in eastern Equatorial
  Pacific
• Every few years the pattern changes. High
  pressure develops over Australia and low pressure
  to the east. This is known as Southern
  Oscillation. When El Nino and Southern
  Oscillation coincide then you have ENSO

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El Nino An anomalous weather phenomena, depends
on pressure wind and precipiation When SE
tradewinds reverse direction Triggers warm flow
replacing cold nutrient rich upwelling. Impacts
fisheries Triggering mechanisms are
unclear Flooding and drought
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El Niño Conditions
Figure 7-D
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Wind Energy

• Started in 1980s
• 10 times more now than 15 years ago
• Germany and Europe are ahead
• CA has given good tax credits
• New US administration is focusing on reducing
  dependence on imported petrolium by adopting a
  green energy policy