Maintenance of thermal wind equilibrium;

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ATOC 4720 class 40 Thermally-driven circulation
in tropics

• Maintenance of thermal wind equilibrium
• The monsoon circulation
• 3. Circulation over the troical oceans ITCZ

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Previous class Symmetric Hadley Cells (f0)
High P
Pressure
High P
High P
Low P
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OBSERVATIONS
WINTER
EQ
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EFFECT OF ROATION!
Assume an air parcel at EQ, u0
Westerly winds!
Geostrophic winds parallel to isobars!
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Maintenance of thermal wind equilibrium
CF generate Motion along isobars
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OBSERVATIONS monsoonITCZ
SUMMER
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OBSERVED MONTHLY WIND AND
PRECIPITATION
JAN
ITCZ
APR
ITCZ
JULY
MONSOON
OCT
ITCZ
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NCEP winds and satellite TRMM SST
JAN
APR
JULY
OCT
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Heavy precipitation in the tropics are
characterized by
1 SST slightly higher than surroundings 2A
slight depression (low level low pressure, high
level high
pressure (upward bulge) of p surfaces) 3Cyclon
ic flow in the lower and anticyclonic flow in the
upper troposphere 4 Lower tropospheric
convergence and upper level divergence 5An
upward mass-flux with mamximum values in the
middle Troposphere (rising motion)
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Dynamical and thermodynamial explanations using
the equations we have learnt Demonstrate on
blackboard
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Idealized monsoon circulation no rotation
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Realistic surface feature of the monsoon
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ITCZ refer to previous figures
Low pressure beult Wind convergence part of
Hadley Cell Higher SST Heavy precipitation