The subpolar low polar front is

General Atmospheric Circulation

Unit 6b

General Circulation of the Atmosphere

• Single-cell model (Hadley, 1735) • Assumes:

– non-rotating earth – uniform surface

• Low Pressure at Equator (warm air rising) • High Pressure at Poles (cold air sinking) • Creates a thermal convection cell

Three Cell Model • Due to earth’s rotation and other

dynamic factors there are typically 3 primary cells – Hadley Cell (tropics) – Midlatitude Cell (Ferrel) – Polar Cell (polar zones)

Three Cell Model

Hadley Cell

Primary High & Low Pressure Areas Equatorial Low Pressure (ITCZ) Subtropical High Pressure Subpolar Low Pressure Polar High Pressure

Equatorial Low Pressure Intertropical Convergence Zone (ITCZ) ±10° N & S

Thermally-induced low pressure

Clouds and rain

Limited wind (doldrums)

Seasonal shift N-S

Subtropical High Pressure • Dynamic high pressure

– subsiding air of Hadley Cell – between 20° - 35° N & S

• Creates hot, dry air – Clear skies, limited wind (horse latitudes) – e.g., Bermuda High, Hawaiian High

• Strengthen/weaken seasonally

• Shift N & S with sun’s declination

Subpolar Low Pressure • Dynamic low pressure – air forced to rise – along polar front

• Cool, moist, cloudy

• Frequent cyclonic storms – e.g., Aleutian Low, Icelandic Low

• strengthen/weaken seasonally

General Circulation (Side-View)

General Circulation – Surface Winds

Trade Winds (tropical)

Westerlies (midlatitudes)

Polar Easterlies

Trade Winds

Trade Winds (tropical) – from subtropical highs to equatorial lows – northeast trades & southeast trades

Westerlies

Westerlies (midlatitudes) – from the subtropical highs to the subpolar lows (west à

east) – tend to be wavy (meridional flow)

Polar Easterlies

Polar Easterlies – from polar highs to subpolar lows – variable, cold, dry winds

www.atmo.arizona.edu

General Circulation – Upper Air Flow (geostrophic winds)

• Westerlies – subtropics à poles – occur as Rossby Waves Jet Streams – areas of high wind velocity within the westerlies

• Subtropical Jet – 20° - 50° N & S – 10,000 – 15,000 m

• Polar Jet – 30° - 70° N & S – 8,000 – 12,000 m

Jet Stream

Rossby Waves

http://svs.gsfc.nasa.gov/vis/a010000/a0 10900/a010902/

http://www.geography.hunter.cuny.edu/tbw/wc .notes/7.circ.atm/rossby_waves.htm