Atmosphere Shallow Meridional Circulations: A New Mechanism for ITCZCold Tongue Interaction

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Atmosphere Shallow Meridional Circulations A
New Mechanism for ITCZ-Cold Tongue Interaction

• Chidong Zhang
• RSMAS, University of Miami
• Miami, FL

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10-12 km
1 km
Equator
ITCZ
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Outline of the talk

• Observations (Zhang et al. 2004, J. Climate)
• Mechanism
• Global reanalyses
• Implications

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• Observations
• Madden and Zipser (1970) Line Island Experiment
  soundings
  
• Tomas and Webster (1997), Trenberth et al
  (2000) divergent
  
• wind component from global reanalyses

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Januray
July
Trenberth et al (2000)
Africa (10-40E)
Australia (60-180E)
Pacific (170-90W)
N. Americas (110-80W)
S. Americas (60-40W)
Atlantic (30W-10E)
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FGGE dropsondes (May - June 1979)
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EPIC2001 dropsondes (September 2001)
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TAO soundings (1996 - 2001)
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Wind profilers at Galapagos (2N, 157.4W) and
Christmas Island (2N, 157.4W) (1995 - 2001)

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Wind profilers at Galapagos (2N, 157.4W) and
Christmas Island (2N, 157.4W) (1995 - 2001)

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Mechanisms

• Wave propagation (Madden and Zipser 1970)
• Vorticity advection (Tomas and Webster 1997)
• Sea-breeze dynamics (Nolan and Zhang 2004)

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p(z) p0(T0- Gz)/T0g/RT
cool
warm
G0.006Km-1
GGd0.01Km-1
zb1000m
GGd0.01Km-1
GGd0.01Km-1
cool
warm
T1295K p11010 hPa
T2298K p21008 hPa
convergence
descent
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(No Transcript)
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Effects of convection in the ITCZ
10-12 km
1 km
Equator
ITCZ
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August
(w x 20)
ERA40
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August
v at the equator
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NCEP
W. Africa (5E-15W) April
ERA40
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Galapagos
ERA40
Christmas Island
ERA40
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Implications

• Bimodal distribution in clouds in the ITCZ

10-12 km
1 km
Equator
ITCZ
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courtesy of James Mather
courtesy of Walter Peterson
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Implications

• Bimodal distribution in clouds in the ITCZ
• Momentum balance of the boundary layer

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Momentum balance in the mixed layer (EPIC2001
dropsondes)
?p/?y/?vUCd/h(v-vT)we/h?v/?tu?v/?xv?v/?yu
0
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Implications

• Bimodal distribution in clouds in the ITCZ
• Momentum balance of the boundary layer
• Effect of ITCZ deep convection on surface wind

?p/?y/?vUCd/h0
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Entrainment Braking Mechanism
?p/?y/?vUCd/h(v-vT)we/h0
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Implications

• Bimodal distribution in clouds in the ITCZ
• Momentum balance of the boundary layer
• Effect of ITCZ deep convection on surface wind
• Meridional water vapor transport

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TAO ship soundings
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Implications to the Tropical Atlantic Variability

• A new mechanism for the interaction among the
  ITCZ convection, surface trade wind, and the
  equatorial cold tongue
  
• A new mechanism for the West African Monsoon to
  affect the springtime development of the
  equatorial cold tongue

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(Mitchell and Wallace 1992)
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Parker et al (2003)
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END