http://www-news.uchicago.edu/releases/05/050601.fultzlab.shtml

Global atmospheric circulation

http://www.ssec.wisc.edu/data/composites.html

Objectives1. 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

Circulation without rotation (no Coriolis Force) on a uniform surface (no land/water differences) and no tilt

(no differential heating between hemispheres)

Circulation with rotation on a uniform surface with no tilt

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

Global atmospheric circulation redistributes heat from the tropics to

the poles

Intertropical convergence zone (ITCZ)

• Belt of low air pressure around equator

• Forms from surface heating

• Associated with clouds and rain

• Current position

Subtropical high pressure

• Semi-permanent high pressures along 20 - 35 degrees N and S latitude

Atlantic and Pacific STHP

The Atlantic Bermuda STHP can bring drought conditions to the southeastern USwhen it moves closer to the North American continent.

The Atlantic Bermuda STHP can bring rainfall is its location is sufficiently offshorefrom North America to allow its winds to pick up moisture and become unstable.

Tradewinds and westerlies

• Air descending from the STHP forms– Northeast tradewinds – Westerlies

Polar high

• Deep, cold high pressure• Descending air forms the

polar easterlies

Polar front

• Zone of collision between westerlies and the easterlies

Polar front

• Very changeable weather• Location of polar jet stream

Polar jet stream

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

Midlatitude cyclones, storm system of the polar front

Midlatitude cyclones

Subtropical jet stream

Pineapple Express

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

Animation

3. Explain how components shape regional patterns of climate

Components of global circulation shift throughout the year

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

1. Pacific Northwest coast (40 – 50 N)

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

• Dry all year but seasonal variability in rainfall along peninsula

2. Baja Peninsula(22 – 35 N)

N

C

S

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

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.