Subtropical High-pressure Cells

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Subtropical High-pressure Cells

• Westerlies
• Bermuda high
• Azores high

Figure 6.14
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Rossby Waves

• Great waving undulations within the westerlies
  flow of geostrophic winds.
• Instrumental to the latitudinal transportation
  of energy.
• Play an important role in determining divergence
  and convergence areas of the upper atmosphere.

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Upper Atmospheric Circulation

• Rossby waves
• Jet stream

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Rossby Waves
Figure 6.17
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Rossby Waves
Figure 6.17
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Constant Isobaric Surface
Figure 6.16
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Jet Stream
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Jet Streams
Figure 6.18
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The Polar Front and Jet Streams

• Strong boundaries often occur between warm and
  cold air. In the mid-latitudes, the polar front
  marks this thermal discontinuity at the surface.

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Multiyear Oscillations

• North Atlantic Oscillation
• Believed to regulate hurricane activity
• Pacific Decadal Oscillation
• Operates on 20-30 year cycles
• Now known to heavily influence climate and
  wildfire activity

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North Atlantic Oscillation (NAO)

• A large scale seesaw in atmospheric mass between
  the subtropical high and the polar low.
• Positive NAO versus negative NAO

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Arctic Oscillation (AO)

• Opposing atmospheric pressure patterns in
  northern middle and high latitudes. Warm phase
  versus cold phase.

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Pacific Decadal Oscillation
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Local Winds

• Land-sea breezes
• Mountain-valley breezes
• Katabatic winds
• Monsoon patterns

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Land-Sea Breezes
Figure 6.19
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Mountain-Valley breezes
Figure 6.20
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Katabatic winds
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Chinook Santa Ana Winds

• Winds that flow down the lee side of mountain
  ranges

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Monsoonal Winds
Figure 6.21
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Oceanic Currents

• Surface Currents
• Cold high latitude
• Warm low latitude
• Gyres circulate in which directions?

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Major Ocean Currents
Peru Current
Figure 6.22
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Oceanic Currents

• Deep Currents
• Thermohaline circulation
• Distributes energy
• Effects of global warming?

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Deep Currents
Figure 6.23
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ENSO events

• ENSO events are a disruption of the
  ocean-atmosphere system in the tropical Pacific
• El Nino Southern Oscillation
• El Nino ocean
• Southern Oscillation atmosphere
• How are they reconstructed?

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El Niño

• Changes in pressure patterns
• Changes in wind patterns
• Mainly concentrated in the Pacific Ocean
• Measured using Southern Oscillation Index
• Differences in pressure observed in Tahiti and
  Darwin, Australia
• Combined to form ENSO
• Affects weather globally

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Buoys
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El Niño
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Impacts of ENSO Events

• Marine environments
• Atlantic hurricanes
• Global precipitation patterns
• Wildfires

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• Australia-Drought and bush fires
• Indonesia, Philippines-Crops fail, starvation
  follows
• India, Sri Lanka-Drought,fresh water shortages
• Tahiti-6 tropical cyclones
• South America-Fish industry devastated
• Across the Pacific-Coral reefs die
• Colorado River basin-Flooding, mud slides
• Gulf states-Downpours cause death, property
  damage
• Peru, Ecuador-Floods, landslides
• Southern Africa-Drought, disease, malnutrition

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El Niño
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ENSO

• When high and low pressure systems exist in some
  locations, they not only impact local weather
  conditions, but also influence the overall size,
  shape, and position of the entire Rossby wave
  pattern
• Teleconnections relationship between weather or
  climate patterns at two widely separated locations

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ENSO
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ENSO

• Occurs once every 3 to 5 years (but varies)
• Is regulated by (what else) PDO
• Switch to PDO warm phase in 1999 appears to have
  dampened ENSO
• Major ENSO events in last 25 years 19821983,
  19861987, 19911993, 19971998, 20022003
• 19971998 was so intense, it disrupted global
  weather

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Normal
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Normal Year
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ENSO
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ENSO
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ENSO Year
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La Nina

• El Niño warm phase, La Niña cool phase
• La Niña brings extreme normal conditions
• Not all El Niño events are followed by La Niña
  events
• La Niña events increase wildfires in the SE and
  Atlantic hurricanes

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La Nina