global average barometric pressure: january figure 4.11
TRANSCRIPT
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Global Average Barometric Pressure: January
Figure 4.11
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Global Average Barometric Pressure: July
Figure 4.11
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Primary High Pressure & Low Pressure Areas
• Equatorial low pressure zone: (aka Intertropical Convergence Zone) band of cloudiness & abundant precipitation. Thermally induced
• Polar high pressure cells: subsiding air, stronger in winter. When strong, are associated with minimal precipitation. Thermally induced
• Subtropical high pressure cells: areas of subsiding air, dry climates when on west side of continents. Dynamically induced
• Subpolar low pressure cells: mean locations are Iceland & Aleutian Islands. Cause winter precip. (mid-latitude cyclones) Dynamically induced
• All of above pressure cells move north and south in response to seasonal changes in the subsolar point. Same w/ wind systems.
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OPTIONAL Comparing July & January Isobar Maps, Northern Hemisphere
• Remember that maps are of average pressures, so they just show general tendencies
• Aleutian Low not evident in July (but it is a weak feature)
• High pressure cells are more developed (have more isobars) over oceans in July
• High pressure cells are located farther north in July (both location and strength driven by land-sea temperature difference, with land warming in summer)
• Note presence of continental high pressure over N Asia and North America in January (thermal highs)
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Other pressure cell terms
• Doldrums
• Horse Latitudes
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Primary Wind Systems• Trade Winds: most constant of all wind systems.
Zone also source region for tropical storms and hurricanes.
• Westerlies: intensity positively related to Equator-Polar temperature differences. What season are they strongest? Which hemisphere the most persistent?
• Polar Easterlies: velocity related to strength of polar high; stronger in winter
• Polar Front: (not a wind) boundary where polar easterlies and the westerlies converge, bad weather zone
• Actual global wind circulation is modified by the effects of continents and their different levels of heating and cooling as compared with the oceans
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General Atmospheric Circulation: This is similar to your model to know!
Figure 4.13
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Upper Atmospheric Circulation
• Jet Stream: the core of upper-level westerly geostrophic winds, generally of high velocity.
• Rossby Waves are found in the upper-air westerly circulation of middle and high latitudes. See “Jet Streams” slide below.
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Cross Section of General Atmospheric Circulation
Figure 4.13
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Jet Streams
Figure 4.17
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Local Winds
• defined
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Monsoonal Wind Systems
• Seasonal wind changes that happen at a regional/continental scale due to seasonal reversals of onshore-offshore temperature differences.
• Summer: onshore circulations, rain!• Winter: offshore circulations, dry
• Where? S & SE Asia, Eq. Africa, a bit of S. America