The Atmosphere: Part 6: The Hadley Circulation

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The AtmospherePart 6 The Hadley Circulation

• Composition / Structure
• Radiative transfer
• Vertical and latitudinal heat transport
• Atmospheric circulation
• Climate modeling

Suggested further reading James, Introduction to
Circulating Atmospheres (Cambridge,
1994) Lindzen, Dynamics in Atmospheric Physics
(Cambridge, 1990)
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Calculated rad-con equilibrium T vs. observed T
pole-to-equator temperature contrast too big in
equilibrium state (especially in winter)
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Zonally averaged net radiation
Diurnally-averaged radiation
Observed radiative budget
Implied energy transport requires fluid motions
to effect the implied heat transport
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Roles of atmosphere and ocean
net
ocean
atmosphere
Trenberth Caron (2001)
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Rotating vs. nonrotating fluids
O
O
f gt 0
Osinf
u
f
f 0
f lt 0
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Hypothetical 2D atmosphere relaxed toward RCE
2D no zonal variations
Annual mean forcing symmetric about equator
f
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A 2D atmosphere forced toward radiative-convective
equilibrium
Te(f,p)
(J diabatic heating rate per unit volume)
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Hypothetical 2D atmosphere relaxed toward RCE
Above the frictional boundary layer,
f
O
r
a
Absolute angular momentum per unit mass
f
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Angular momentum constraint
Above the frictional boundary layer,
In steady state,
f
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Angular momentum constraint
Above the frictional boundary layer,
In steady state,
f
Or 2) but m constant
along streamlines
vw0
Either 1)
(if u0 at equator)
f 0 15 30 45 60
U(ms-1) 0 32 134 327 695
T Te(f,z)
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Angular momentum constraint
Above the frictional boundary layer,
In steady state,
f
Or 2) but m constant
along streamlines
vw0
Either 1)
(if u0 at equator)
f 0 15 30 45 60
U(ms-1) 0 32 134 327 695
T Te(f,z)
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Near equator,
solution (2) no good at high latitudes
u finite (and positive) in upper levels at
equator angular momentum maximum there not
allowed
solution (1) no good at equator
Hadley Cell
T Te
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Near equator,
solution (2) no good at high latitudes
u finite (and positive) in upper levels at
equator angular momentum maximum there not
allowed
solution (1) no good at equator
Hadley Cell
T Te
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Observed Hadley cell
v,w
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Structure within the Hadley cell
In upper troposphere,
Hadley Cell
T Te
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Structure within the Hadley cell
In upper troposphere,
J
Hadley Cell
T Te
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Observed Hadley cell
v,w
u
Subtropical jets
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Structure within the Hadley cell
In upper troposphere,
Near equator,
Hadley Cell
T Te
But in lower troposphere,
(because of friction ).
Tf4
Tef2
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Structure within the Hadley cell
In upper troposphere,
Near equator,
Hadley Cell
T Te
But in lower troposphere,
Vertically averaged T very flat within cell
(because of friction ).
Tf4
Tef2
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Observed Hadley cell
v,w
T
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Structure within the Hadley cell
In upper troposphere,
Near equator,
Hadley Cell
T Te
But in lower troposphere,
TgtTe diabatic cooling ? downwelling
(because of friction ).
Tf4
Tef2
edge of cell
TltTe diabatic heating ? upwelling
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The symmetric Hadley circulation
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JJA circulation over oceans
(ITCZ Intertropical Convergence Zone)
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Monsoon circulations(in presence of land)
summer
winter
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Satellite-measured (TRMM) rainfall, Jan/Jul 2003
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Satellite-measure (TRMM) rainfall, Jan/Jul 2003
ITCZ
South Asian monsoon
deserts
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Heat (energy) transport by the Hadley cell
Poleward mass flux (kg/s) Mut
Moist static energy (per unit mass) E cpT
gz Lq Net poleward energy flux F MutEut
MltElt M(Eut Elt)

• But
• Convection guarantees
• Eut Elt at equator
• (ii) Hadley cell makes T flat across the cell
• ? weak poleward energy transport

Equatorward mass flux (kg/s) Mlt Mass balance
Mut Mlt M
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Roles of atmosphere and ocean
net
ocean
atmosphere
Trenberth Caron (2001)