Chapter 10

General Circulation of the Atmosphere General refers to the average air flow,

actual winds will vary considerably. Average conditions help identify driving

forces. The basic cause of the general circulation

is unequal heating of the Earth’s surfaceWarm air is transferred from the Tropics to the

PolesCool air is transferred from the Poles to the

Tropics

General Circulation of the Atmosphere Single Cell Model

Assume1. uniform water surface2. Sun always directly overhead the Equator3. Earth does not rotateResult: huge thermally direct convection cell rising at

equator and sinking at poles(Hadley) Three Cell Model

Allow earth to spin = three cells (Hadley, Ferrell, Polar)

Alternating belts of pressure starting with L at Equator (L H L H) (Eq, Sub Trop, Sub Polar, Polar)

Alternating belts of wind with NE just North of Equator

General Circulation of the Atmosphere Average Surface Wind and Pressure:

The Real WorldSemi-permanent high and lowsNorthern vs. Southern HemisphereMajor features shift seasonally with the high

sun○ North in July○ South in December

General Circulation of the Atmosphere General Circulation and Precipitation

PatternsRain where air rises (low pressure)Less rain where air sinks (high pressure)

Average Wind Flow and Pressure Patterns AloftNorth-South temperature and pressure

gradient at high altitudes creates West-East winds, particularly at mid to high latitudes.

Jet Streams

100-200 kt winds at 10-15km, thousands of km long, several 100 km wide and a few km thick (polar and subtropical)

Observations: Dishpan ExperimentIllustrates waves, with trough and ridge,

develops in a rotating pan with heat on the exterior and cold at the center.

Jet Streams Polar and Subtropical Jet

Established by steep temperature and pressure gradients between circulation cells.

Between tropical-mid-latitude cell (subtropical) and mid-latitude-polar cell (polar)

Gradients greatest at polar jet

Topic: MomentumLow-latitudes: atmosphere gains momentumHigh-latitudes: atmosphere losses momentumConservation of Momentum

Jet Streams

Other Jet StreamsTropical easterly jet streamLow-level jet (nocturnal)Polar night jet streams