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

Radiation

Cloud/precip

Shallow convection Boundary layer turbulence

Mesoscale convective system Tornado/Thunderstorm

Extratropical cycloneHeat waveTropical cyclone

Diurnal variation

Madden-Julian Oscillation Convectvely coupled waves

Monsoon

AMO/PDOENSOAO/AAO

Glacial cyclesGlobal warming

105yr102yr10yr1yr1mon1day1min1sec10-15sec

Global Climate SystemWhole globe

Half globe

103 km

102 km

1 km

1 mm

1 m

Global model grid

Regional model grid

Spatial Scale

Time Scale

Land-atmosphere interaction

Ocean-atmosphere interaction

Radiation feedback (T, q, cloud, aerosol, carbon)

Convection feedback

10-4 m Chemistry

Key regions for ocean-atmosphere interaction

Indo-Pacific warm pool

Eastern Pacific cold tongue

North AtlanticNorth Pacific

Tropical mean state: Precipitation

GPCP Annual Mean Precipitation for 1979-2005 (mm/day)

Inter-tropical convergence zone (ITCZ)

Strong rainfall (heating)

Weak rainfall

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 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)

SST - SWF feedback (e.g. Ramanathan and Collins 1991)

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 Nino-La 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

(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)

(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)

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? 4-year period.

• Existing ENSO theories

• AMO and thermohaline circulation

Works cited• http://www.jpl.nasa.gov/images/earth/20100325/atlantic20

100325-full.jpg