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2 Global atmospheric circulation

3 Objectives 1.List/describe factors that shape global atmospheric circulation 1.Tilt 2.Rotation 3.Land/water differences 4.Coriolis Force 2.Describe/draw components of the three-cell model 3.Explain how components shape regional patterns of climate 4.Explain the function of the global atmospheric circulation system

4 Circulation without rotation (no Coriolis Force) on a uniform surface (no land/water differences) and no tilt (no differential heating between hemispheres)

5 Circulation with rotation on a uniform surface with no tilt

6 Circulation with rotation, on non-uniform surface, and tilt (the 3-cell model)


8 Global atmospheric circulation redistributes heat from the tropics to the poles

9 Intertropical convergence zone (ITCZ) Belt of low air pressure around equator Forms from surface heating Associated with clouds and rain Current position

10 Subtropical high pressure Semi-permanent high pressures along 20 - 35 degrees N and S latitude



13 Atlantic and Pacific STHP


15 The Atlantic Bermuda STHP can bring drought conditions to the southeastern US when it moves closer to the North American continent. The Atlantic Bermuda STHP can bring rainfall is its location is sufficiently offshore from North America to allow its winds to pick up moisture and become unstable.

16 Tradewinds and westerlies Air descending from the STHP forms –Northeast tradewinds –Westerlies

17 Polar high Deep, cold high pressure Descending air forms the polar easterlies

18 Polar front Zone of collision between westerlies and the easterlies

19 Polar front Very changeable weather Location of polar jet stream

20 Polar jet stream

21 Arctic Amplification: cause of polar vortex cold air outbreaks Loss of sea ice and warming in the Arctic alters pressure gradient between pole and tropics Polar jet stream becomes more azonal Colder weather moves further south and stays in place longer

22 Midlatitude cyclones, storm system of the polar front

23 Midlatitude cyclones

24 Subtropical jet stream

25 Pineapple Express Branch of subtropical jet stream that brings moisture up from tropics to enhance precipitation within mid-latitude cyclones


27 Animation 3.Explain how components shape regional patterns of climate

28 Components of global circulation shift throughout the year


30 California coast (32 – 42 N) San Francisco (37 N) Winter wet –Pacific STHP diminishes and high pressure shifts south and offshore –Midlatitude cyclones bring precipitation Summer dry –Pacific STHP dominant –Dry conditions –Track of cyclones along polar jet stream is further north

31 1. Pacific Northwest coast (40 – 50 N)

32 Pacific Northwest coast (40 – 50 N) Greater year-round influence of polar front More rainfall, more evenly distributed all seasons Winter wet from midlatitude cyclones Summer becomes wetter to the north Weaker influence of STHP moving north

33 Dry all year but seasonal variability in rainfall along peninsula 2. Baja Peninsula (22 – 35 N)

34 N C S

35 Baja Peninsula (22 – 35 N) North: winter wet from midlatitude cyclones and summer dry from STHP Central: dry all year from STHP Southern: winter dry from STHP, summer wet from ITCZ

36 Kentucky weather and climate and their global controls Winter – MLCs create alternating periods of cold and dry then warmer and humid conditions. Some tstorms along cold fronts can be severe. Summer – weather and climate under more local controls, fewer MLCs. Rainfall from convective thunderstorms with occasional upper level support from polar jet stream. Droughts can set up because of Omega blocks.


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