Ocean-Atmosphere Interaction

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Ocean-Atmosphere Interaction
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Review of last lecture

• Large spread in projected temperature change
  comes from uncertainties in climate feedbacks
• Main climate feedbacks for global warming
  albedo, lapse rate, water vapor, cloud, aerosol,
  carbon cycle
• Feedback strength in climate models cloud
  feedback causes the largest uncertainty

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Global Climate System
Spatial Scale
Glacial cycles Global warming
Whole globe
Radiation feedback (T, q, cloud, aerosol, carbon)
AMO/PDO ENSO AO/AAO
Ocean-atmosphere interaction
Half globe
Monsoon
Land-atmosphere interaction
Madden-Julian Oscillation Convectvely coupled
waves
Convection feedback
Diurnal variation
103 km
Extratropical cyclone Heat wave Tropical cyclone
Global model grid
102 km
Mesoscale convective system Tornado/Thunderstorm
Regional model grid
1 km
Shallow convection Boundary layer turbulence
1 mm
Cloud/precip
Radiation
1 ?m
10-4 ?m
Chemistry
105yr
102yr
10yr
1yr
1mon
1day
1min
1sec
10-15sec
Time Scale
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Key regions for ocean-atmosphere interaction
North Atlantic
North Pacific
Indo-Pacific warm pool
Eastern Pacific cold tongue
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Tropical mean state Precipitation
Inter-tropical convergence zone (ITCZ)
Strong rainfall (heating)
Weak rainfall
GPCP Annual Mean Precipitation for 1979-2005
(mm/day)
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Tropical mean State Walker Circulation

• The SST contrast between warm pool and cold
  tongue leads to an atmospheric circulation cell
  oriented along the equator with rising motion in
  the west and sinking motion in the east, which is
  induced by
• Interacts with underlying Pacific Ocean with
  stronger upwelling (cooling) in the east, leading
  to a positive feedback.

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Theories of tropical mean climate
Ocean-atmosphere feedback mechanisms
SST - SWF feedback (e.g. Ramanathan and Collins
1991)
SST gradient - trade wind (Bjerknes) feedback
(e.g. Bjerknes 1969, Neelin and Dijkstra 1995
Pierrehumbert 1995 Sun and Liu 1996 Jin 1996
Clement et al. 1996 Liu 1997 Cai 2003)
SST - LHF feedback (e.g. Wallace 1992 Liu et al
1994 Zhang et al. 1995)
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Blind men and an elephant
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Movie time!

• Chasing El Nino

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El Nino/Southern Oscillation (ENSO) The 4-year
oscillation

• El Nino Very warm sea surface temperature over
  central and eastern tropical Pacific, which
  occurs every 3-7 years. The Walker Circulation
  becomes disrupted during El Niño events, which
  weakens upwelling in eastern Pacific.
• La Nina the opposite condition to El Nino
• Southern Oscillation The atmospheric oscillation
  associated with the El Nino-La Nina cycle.
• The whole phenomena is now called El
  Nino/Southern Oscillation (ENSO)

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Typical ENSO period is 3-7 years, but with
significant irregularity
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Existing ENSO theories
(6) Stochastic forcing theory (McWilliams and
Gent 1978, Lau 1985, Penland and Sardeshmukh
1995, Blanke et al. 1997, Kleeman and Moore 1997,
Eckert and Latif 1997)
(1) Slow coupled mode theory (Philander et al.
1984, Gill 1985, Hirst 1986, Neelin 1991, Jin and
Neelin 1993, Wang and Weisberg 1996)
(2) Delayer oscillator theory (Suarez and Schopf
1988, Battisti and Hirst 1989)
(3) Advective-reflective oscillator theory
(Picaut et al 1997)
(4) Western Pacific oscillator theory (Weisberg
and Wang 1997)
(5) Recharge oscillator theory (Jin 1997a,b)
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Blind men and an elephant
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The 1997-1998 El Nino event
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Atlantic Multi-decadal Oscillation (AMO)

• The Atlantic Multidecadal Oscillation (AMO) is a
  60yr oscillation in water temperatures and is a
  major factor in the increase in Atlantic
  hurricane activity.

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Global SST anomaly for AMO warm phase
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AMO and thermohaline circulation
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An theory involving atmosphere-ocean-ice
interactions (Dima and Lohmann 2007)
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Summary

• Mean state The two basic regions of SST? Which
  region has stronger rainfall? What is the Walker
  circulation? Two types of ocean upwelling
• Mean state ocean-atmosphere feedback
• ENSO Which region has warm SST anomaly during El
  Nino? 4-year period.
• Existing ENSO theories
• AMO and thermohaline circulation

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Works cited

• http//www.jpl.nasa.gov/images/earth/20100325/atla
  ntic20100325-full.jpg