Subtropical High-pressure Cells Westerlies Bermuda high Azores high Figure 6.14.
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Transcript of Subtropical High-pressure Cells Westerlies Bermuda high Azores high Figure 6.14.
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Subtropical High-pressure Cells
• Westerlies
• Bermuda high
• Azores high
Figure 6.14
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Rossby WavesRossby Waves
Great waving undulations within the westerlies flow of
geostrophic winds.
IInstrumental 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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Strong boundaries often
occur between warm and cold
air. In the mid-latitudes, the
polar front marks this thermal
discontinuity at the surface.
The Polar Front and Jet Streams
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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)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)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
Figure 6.22
Peru Current
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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: 1982–1983, 1986–1987, 1991–1993, 1997–1998, 2002–2003
• 1997–1998 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