Modes of Tropical Climate Variability El Niño / Southern Oscillation Atlantic Niño Atlantic and Pacific Meridional Modes Indian Ocean Dipole  Observational description  Theory  Representation in climate models  Response to climate change Clara Deser, Climate Analysis Section, NCAR Deser et al., 2009: Annual Review of Marine Sciences, Vol. 2

1. Observations Data Coverage

Data Coverage from Ships of Opportunity % of months with at least 1 observation in a 2° latitude x 2° longitude box International Comprehensive Ocean-Atmosphere Data Set (ICOADS) Sea temp, Air temp, Pressure, Wind, Cloudiness, Humidity

Implications for Data Analysis Sea Surface Temperature Trends, “HadSST2” Data Set (quality-controlled, bucket/intake corrections applied, no infilling) % of months with at least 1 measurement -1°C 1°C0°C

1. Observations High resolution satellite data (since ~ 1982) – Anomalies (departures from the mean seasonal cycle)

Jan 1, 2008 Sea Surface Temperature ¼ degree satellite data

Jan 1, 2008 Sea Surface Temperature Jan 1 Mean ¼ degree satellite data

Jan 1, 2008 Jan 1, 2008 Anomaly Jan 1 Mean

Mean Standard deviation of monthly anomalies

Mean Standard deviation of monthly anomalies Pacific Equatorial “Cold Tongue” Galapagos Penguin

Sea Surface Temperature Mean Seasonal Cycle

Ekman Current Equatorial Upwelling Mean Seasonal Cycle Sea Surface Temperature Ekman Current

2. El Niño / Southern Oscillation (ENSO)

ENSO Ensō ( 円相 ) is a Japanese word meaning "circle" and a concept strongly associated with Zen. 円相Japanese wordcircleZen Ensō is one of the most common subjects of Japanese calligraphy even though it is a symbolJapanese calligraphy and not a character. It symbolizes enlightenment, strength, elegance, the universe, and the void. enlightenmentvoid

ENSO Ensō ( 円相 ) is a Japanese word meaning "circle" and a concept strongly associated with Zen. 円相Japanese wordcircleZen Ensō is one of the most common subjects of Japanese calligraphy even though it is a symbolJapanese calligraphy and not a character. It symbolizes enlightenment, strength, elegance, the universe, and the void. enlightenmentvoid EÑSO

Mean Standard deviation of monthly anomalies ENSO SST anomaly index “Niño 3”

“Niño 3” SST monthly anomaly index monthly standard deviation ENSO

ENSO Composite Evolution (SST, SLP)

Southern Oscillation

Annual ENSO Composite “Southern Oscillation” “El Niño” SST SLP and wind

ENSO Mechanisms Self-sustained natural oscillatory mode of the coupled tropical Pacific ocean-atmosphere system (the delayed oscillator / recharge oscillator paradigms) OR Stable mode … triggered by stochastic forcing (the noise forced paradigm) Both involve positive ocean-atmosphere (“Bjerknes”) feedback and negative oceanic feedbacks Dynamical processes and oceanic thermocline are key Wang and Fiedler, Progress in Oceanography, 2006

Oceanic Thermocline Tropical Atmosphere Ocean (TAO) Buoy Array (since ~1983 ) ~ 70 moorings Air T, wind, humidity ocean currents and temperatures (z)

Oceanic Thermocline Tropical Atmosphere Ocean (TAO) Buoy Array (since ~1983 ) 0 m 200 m 400 m Depth T (z) Oct 2007 wind thermocline

The “Recharge Oscillator”: A simple paradigm for the El Niño cycle (Instability of the tropical Pacific ocean-atmosphere system) F.-F. Jin, J. Atmos. Sci Warm event Thermocline Depth anomaly Wind stress anomaly Positive feedback

The “Recharge Oscillator”: A simple paradigm for the El Niño cycle (Instability of the tropical Pacific ocean-atmosphere system) F.-F. Jin, J. Atmos. Sci Warm event Thermocline Depth anomaly Wind stress anomaly Positive feedback “Bjerknes Feedback” positive SST anomaly negative SLP anomaly westerly wind anomaly deepened thermocline positive SST anomaly

The “Recharge Oscillator”: A simple paradigm for the El Niño cycle (Instability of the tropical Pacific ocean-atmosphere system) F.-F. Jin, J. Atmos. Sci Warm event Thermocline Depth anomaly Wind stress anomaly Positive feedbackPoleward V g anomaly L H V ~ dp/dx

The “Recharge Oscillator”: A simple paradigm for the El Niño cycle (Instability of the tropical Pacific ocean-atmosphere system) F.-F. Jin, J. Atmos. Sci Warm event Thermocline Depth anomaly Wind stress anomaly Positive feedback Neutral State Shallower Mean Thermocline Poleward V g anomaly L H V ~ dp/dx Ocean Heat Discharge

The “Recharge Oscillator”: A simple paradigm for the El Niño cycle (Instability of the tropical Pacific ocean-atmosphere system) F.-F. Jin, J. Atmos. Sci Warm event Thermocline Depth anomaly Wind stress anomaly Positive feedback Neutral State Shallower Mean Thermocline Poleward V g anomaly L H V ~ dp/dx Ocean Heat Discharge Shallow thermocline > Cold SST via upwelling Cold event Positive feedback

The “Recharge Oscillator”: A simple paradigm for the ENSO cycle (Instability of the tropical Pacific ocean-atmosphere system) F.-F. Jin, J. Atmos. Sci Warm event Thermocline Depth anomaly Wind stress anomaly Positive feedback Neutral State Shallower Mean Thermocline Poleward V g anomaly L H V ~ dp/dx Ocean Heat Discharge Shallow thermocline > Cold SST via upwelling Cold event Positive feedback Equatorward V g anomaly H L V ~ dp/dx

The “Recharge Oscillator”: A simple paradigm for the El Niño cycle (Instability of the tropical Pacific ocean-atmosphere system) F.-F. Jin, J. Atmos. Sci Warm event Thermocline Depth anomaly Wind stress anomaly Positive feedback Neutral State Shallower Mean Thermocline Poleward V g anomaly L H V ~ dp/dx Ocean Heat Discharge Shallow thermocline > Cold SST via upwelling Cold event Positive feedback Equatorward V g anomaly H L V ~ dp/dx Ocean Heat Recharge

SST East Pacific Zonally-averaged “warm water volume” (thermocline depth) Does the real ocean behave as a “Recharge Oscillator” ? TAO Web Site

Excitation of the “Recharge Oscillator” Self excitation (self sustaining) Stochastic excitation (decaying coupled oscillator sustained by noise)

ENSO in Models 1000 year simulation: GFDL Coupled General Circulation Model No external forcing other than seasonal earth-sun geometry Wittenberg, Geophysical Research Letters, 2009

ENSO in Models

ENSO response to increasing CO2 No consensus among models (period, amplitude) Mean Tropical Pacific SST response is El Nino – like Even if there were to be a change in ENSO characteristics, it may be difficult to attribute to CO2 due to high level of natural variability Guilyardi et al., Bulletin of the American Meteorol. Society, 2009

Beyond ENSO: Tropical Pacific Decadal Variability “Pacific Decadal Oscillation” or “Interdecadal Pacific Oscillation” e.g., 1976/1977 “climate shift”

Indian Ocean SST SE Pacific SST North Pacific SLP SPCZ Rainfall Eq Pacific Rainfall Eq Pacific Cloud E-W SLP Gradient (Indian – Pac) smoothed Deser et al. J. Climate 2004 Tropical Climate Indices

Tropical Atlantic and Indian Ocean Modes of Variability

Leading Modes of SST Variability in the Tropical Atlantic Ocean Niño Mode See Review in Xie and Carton 2004 Meridional Dipole Mode

Leading Modes of SST Variability in the Tropical Atlantic Ocean Niño Mode See Review in Xie and Carton 2004 Meridional Dipole Mode Typical amplitude ~ 0.5°C, period ~ 2-3 years (in some decades) Bjerknes feedback/delayed oscillator mechanism

Leading Modes of SST Variability in the Tropical Atlantic Ocean Niño Mode See Review in Xie and Carton 2004 Meridional Dipole Mode Wind-evaporation-SST feedback mechanism (Chang et al., 1997) Impacts nordeste Brazil rainfall, North Atlantic hurricanes (Vimont and Kossin, 2007) Similar mode in the Pacific (Chiang and Vimont, 2004)

Leading Modes of SST Variability in the Tropical Indian Ocean Basin Mode See Schott et al., Reviews of Geophysics, 2009 Zonal Dipole Mode Modes occur in association with, and independently of, ENSO

ENSO Composite Evolution (SST, SLP) Indian Ocean Dipole Mode Indian Ocean Basin Mode

Modes of Tropical Climate Variability Thank You Clara Deser, Climate Analysis Section, NCAR Deser et al., 2009: Annual Review of Marine Sciences, Vol. 2

HadSST2 #OBS HadSST2 MOHMAT4 Kaplan v2 ERSST v3 HadISST Night-time Marine Air T Comparison between Raw Data and Optimally Interpolated Data Sets