Ocean-atmosphere interaction

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Ocean-Atmosphere Interaction
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
Global Climate System
Spatial Scale
Whole
globe
AMO/PDO
ENSO
AO/AAO
Half
globe
Monsoon
Glacial cycles
Global warming
Radiation feedback (T, q,
cloud, aerosol, carbon)
Ocean-atmosphere interaction
Land-atmosphere interaction
Madden-Julian Oscillation
Convectvely coupled waves
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
1 mm
1 m
10-4 m
Convection feedback
Shallow convection
Boundary layer turbulence
Cloud/precip
Radiation
Chemistry
10-15sec 1sec 1min
1day
1mon
1yr
10yr
102yr
105yr
Time Scale
Key regions for ocean-atmosphere interaction
North Pacific
Indo-Pacific
warm pool
Eastern Pacific
cold tongue
North Atlantic
Tropical mean state: Precipitation
Inter-tropical convergence
zone (ITCZ)
Strong rainfall
(heating)
Weak rainfall
GPCP Annual Mean Precipitation for 1979-2005 (mm/day)
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.
Theories of tropical mean climate:
Ocean-atmosphere feedback mechanisms
SST - SWF feedback
(e.g. Ramanathan and
Collins 1991)
SST - LHF feedback
(e.g. Wallace 1992;
Liu et al 1994; Zhang
et al. 1995)
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)
Blind men and an elephant
Movie time!
Chasing El Nino
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 NinoLa Nina cycle.
• The whole phenomena is now called
El Nino/Southern Oscillation (ENSO)
Typical ENSO period is 3-7 years, but with
significant irregularity
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)
(2) Delayer oscillator
theory (Suarez and
Schopf 1988, Battisti and
Hirst 1989)
(1) Slow coupled mode
theory (Philander et al.
1984, Gill 1985, Hirst
1986, Neelin 1991, Jin
and Neelin 1993, Wang
and Weisberg 1996)
(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)
Blind men and an elephant
The 1997-1998 El Nino event
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.
Global SST anomaly for AMO warm phase
AMO and thermohaline circulation
An theory involving atmosphere-ocean-ice
interactions (Dima and Lohmann 2007)
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? 4year period.
• Existing ENSO theories
• AMO and thermohaline circulation
Works cited
• http://www.jpl.nasa.gov/images/earth/20100325/atlantic20
100325-full.jpg
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