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Chapter 9

Chapter 9. Atmosphere’s Planetary Circulation. Three main concepts in this chapter: Scales of a tmospheric motion Global Circulation El Nino/La Nina. Scales of atmospheric motion –. Macroscale (largest) includes: Planetary synoptic lasts weeks to years

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Chapter 9

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  1. Chapter 9 Atmosphere’s Planetary Circulation

  2. Three main concepts in this chapter: • Scales of atmospheric motion • Global Circulation • El Nino/La Nina

  3. Scales of atmospheric motion – • Macroscale (largest) includes: • Planetary synoptic lasts weeks to years • and range from 10,000 – 40,000 km. • Examples are westerlies and trade winds. • Synoptic lasts days to weeks and range • from 100 – 5000 km. Examples are • cyclones, anticyclones, and hurricanes.

  4. Mesoscale • Lasts minutes to days and ranges from • 1 – 1000 km. Examples include • land-sea breeze, T-storms, and tornadoes Microscale • Lasts seconds to minutes and are less • than 1 km in scope. Examples include • turbulence, dust devils, and gusts

  5. Wind roses help to get a feel for the dominant winds in a location. For example: N N W E W E S S Eastern US Westerlies N. Australia SE Trades

  6. Local Winds (mesoscale) – • Land – sea breezes • Mtn – valley breezes • Chinook winds • Katabatic winds All winds follow the PG (hi to lo) and are named for the direction from which they come.

  7. Land – sea breeze: • Diurnal temperature contrast (land vs. water) • that creates a PG. • In the daytime, the sun shines, land is • heated (low – rising air) more than the water • (high – sinking air). Highs flow to lows = sea • breeze. • At night, the land cools (high), water is • warmer (low). Highs flow to lows = land breeze

  8. Mtn – valley breezes – • Diurnal heating contrast (sun angle) • that creates the PG. • Day - slopes heat more intensely, • higher solar angle (SA) (low), valley is • cooler (high). Highs flow to lows = valley • breeze. • Night – slopes cool more quickly (high) • and valley is warmer (low). Highs flow to • lows = mtn. breeze

  9. Chinook Winds (Foehn, Santa Ana) • Air pulled over the mountains by PG; warms and dries adiabatically in descent. • Called “snoweater” in NA. • Santa Ana – special case of fire danger in • southern California seasonally

  10. Katabatic winds – • Cold air over a highland area (ice • sheets of Greenland & Antarctica) and • set in motion by gravity. • Cascades down over highland rim like • a waterfall – dense, cold, velocity may • be destructive.

  11. Global Circulation – • Conceptual model (assumes a • homogeneous earth surface). • Key is hot air rises and cool air sinks. • Ties together mixing of hot and cold air • to achieve a balance, PG, and Coriolis. • Wind belts, pressure zones, and types • of lift • Defines geographic regions

  12. and winds!

  13. ITCZ – Inter-tropical Convergence Zone

  14. Shift of ITCZ

  15. Shift of ITCZ

  16. Zonal Disruptions: Zones are truly continuous only in high lats of S-hemi where there are few landmasses. 2) Unequal heating of land – water causes great disruptions in N-hemi. 3) Semi-permanent features associated with land/water seasonally:

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