General circulation in the tropics - part I -v2010v3

General circulation in the tropics - part I -v2010v3 -...

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Unformatted text preview: General circulation in the General circulation in the tropics tropics Outline: • Global circulation and tropical regions • Winds in low and high levels • Hadley Cell and horizontal (trade winds) and vertical movements • Concept of convergence of mass Tropical Circulation in a Global Context Mean surface pressure and winds during DJF Westerlies Westerlies Westerlies W e s te r lie s S E S E t r a d e s t r a d e s N E N E t r a d e s t r a d e s S E S E t r a d e s t r a d e s N E N E t r a d e s t r a d e s N E N E t r a d e s t r a d e s E a s t e r l i e E a s t e r l i e s E a s t e r l i e E a s t e r l i e s N E N E t r a d e s t r a d e s Mean surface pressure and winds during JJA Westerlies W e s t e r l i e s W e s te r lie s S E S E t r a d e s t r a d e s N E N E t r a d e s t r a d e s S E S E t r a d e s t r a d e s N E N E t r a d e s t r a d e s N E N E t r a d e s t r a d e s Westerlies S E S E t r a d e s t r a d e s TRADE WINDS ARE EASTERLY WINDS Sketch of the global circulation Hadley Cell Hadley Cell Ferrel cell Ferrel cell Ferrel cell Ferrel cell Polar cell Polar cell Polar cell Polar cell How is the circulation in high levels in January ? H H How is the circulation in high levels in July ? Equator West East North Pole High level Subtropical Jet Radiative cooling High level Subtropical Jet F c Fc Radiative cooling Low level SE Trades Low level SE Trades NE Trades NE Trades Fc=Coriolis Force – perpendicular to the wind – left of the wind SH, Right NH Fc=Coriolis Force – perpendicular to the wind – left of the wind SH, Right NH THE HADLEY CELL THE HADLEY CELL Now including Ferrel cell and polar cell Subtropical Westerly Jet Subtropical Westerly Jet Polar W Jet Polar W Jet Changes in the Hadley cell Changes in the Hadley cell • The Hadley cells show seasonal variations in their intensity, geographical extent and latitudinal position. • They are not restricted to their respective hemispheres but display regular cross- equatorial incursions into the opposite hemisphere • Let’s examine the cross section of the atmosphere (vertical components exaggeration) • Vertical velocity maximum represent the mean position of the intertropical convergence zone (ITCZ) Vertical motion z dz dt dz w = p- 4dp p- 3dp p- 2dp p- 1dp p An ascending volume (parcel) experiences changes in pressure and density The hydrostatic equation states that: dz g dp ρ- = Where : ρ is the air density and g is gravity Vertical velocity w is defined as gw dt dz g dt dp ρ ρ- =- ≡ Vertical motion...
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This note was uploaded on 12/28/2011 for the course GEOG 133 taught by Professor Leila during the Fall '09 term at UCSB.

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General circulation in the tropics - part I -v2010v3 -...

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