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Atmospheric Circulation and Pressure

Atmospheric Circulation and Pressure. -years. Scale of Winds. -weeks. -1000’s km. Scale Time Distance Example Planetary weeks global Westerlies Synoptic days 100’s Cyclones Mesocale minutes 1-100km sea breeze Microscale seconds <1km wind gust. -days. thunderstorm. -minutes.

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Atmospheric Circulation and Pressure

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  1. Atmospheric Circulation and Pressure

  2. -years Scale of Winds -weeks -1000’s km Scale TimeDistance Example Planetary weeks global Westerlies Synoptic days 100’s Cyclones Mesocale minutes 1-100km sea breeze Microscale seconds <1km wind gust -days thunderstorm -minutes

  3. General circulation - term that refers to planetary scale winds • Westerly winds - winds blowing west to east. • Easterly winds - winds blowing east to west.

  4. Single Cell Model George Hadley (1738)

  5. Single Cell Model • George Hadley (1685-1768) • 1738 - proposed a simple model to explain global circulation • Wanted to explain why sailors often easterly winds in the lower latitudes • Single Cell Model - • Air is heated at the equator • expands upward and diverges toward the poles • Sinks back down at the poles • Returns toward the equator

  6. Three Cell Model William Ferrel (1865) Polar Cell Ferrel Cell Hadley Cell

  7. Image after Lutgens & Tarbuck 10th Ed. Prentice Hall

  8. Three Cell Model • William Ferrel (1817-1891) • 1865 - developed the three cell model • Hadley Cell - circulates air between the tropics and subtropics (0o-30o) • Ferrel Cell - circulates air between the subtropics and subpolar regions (mid-latitudes 30o to 60o) • Polar Cell - circulates air between the subpolar and polar regions. (60o-90o)

  9. Hadley Cell • Equatorial low - zone of low pressure along the equator • Also called intertropical convergence zone (ITCZ) • Rainiest zone in the world. • Also called doldrums • Subtropical high - zone of high pressure at ~30o latitude. • Horse latitudes • Northeast tradewinds - develop from the PGF between the equatorial low and the subtropical high.

  10. Ferrel Cell- circulates air between the subtropics and subpolar regions (mid-latitudes 30o to 60o) • Subpolar low - zone of low pressure at ~60o latitude. • Westerlies - develop from the PGF between the subtropical high and the subpolar low and the effects of the coriolis force. • mid-latitudes

  11. Polar Cell - circulates air between the subpolar and polar regions. (60o-90o) • Polar high - zone of high pressure at the poles. • Polar easterlies - result from the PGF that develops between the subpolar low and polar high. • Polar front - transition zone between the cold polar air and the warmer mid-latitudes. • Jet stream - streams of air within the westerlies that travel at speeds of 200km/hr. in the winter and 100km/hr. in the summer.

  12. Polar Cell • Polar Jet stream - Jet stream that develops above the polar front, resulting from the strong pressure gradient. Subtropical Jet Stream - a jet stream that develops just north of the equator.

  13. Polar Cell Polar Front Theory for mid-latitude cyclones

  14. Cyclones and Anticyclones • Sea level pressure across the globe are divided into high and low pressure centers.

  15. Upper Troposphere Winds Jet Streams - streams of fast moving air in the upper tropospere. Ridges and Troughs Ridges - upward bulges in the pressure surface. Troughs - depressions in the pressure surface. Wave-like flow Speed divergence Speed convergence

  16. Ocean Currents - horizontal movement of the surface waters found along the rims of the major ocean basins • winds are the primary driving force of the currents - Coriolis force also affects the currents Equatorial Current - “backbone” of the ocean current system - derive energy from the tradewinds.

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