1 / 46

Modes of Tropical Climate Variability

Modes of Tropical Climate Variability. Clara Deser, Climate Analysis Section, NCAR. 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.

jenny
Download Presentation

Modes of Tropical Climate Variability

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Modes of Tropical Climate Variability Clara Deser, Climate Analysis Section, NCAR • 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 Deser et al., 2009: Annual Review of Marine Sciences, Vol. 2 www.cgd.ucar.edu/cas/cdeser/

  2. 1. Observations • Data Coverage

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

  4. Implications for Data Analysis Sea Surface Temperature Trends, 1900-2008 “HadSST2” Data Set (quality-controlled, bucket/intake corrections applied, no infilling) % of months with at least 1 measurement 0°C 1°C -1°C

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

  6. Jan 1, 2008 Sea Surface Temperature ¼ degree satellite data

  7. Jan 1 Mean 1982-2008 Jan 1, 2008 Sea Surface Temperature ¼ degree satellite data

  8. Jan 1 Mean 1982-2008 Jan 1, 2008 Jan 1, 2008 Anomaly

  9. Mean 1982-2008 Standard deviation of monthly anomalies

  10. Mean 1982-2008 Galapagos Penguin Pacific Equatorial “Cold Tongue” Standard deviation of monthly anomalies

  11. Mean Seasonal Cycle Sea Surface Temperature

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

  13. 2. El Niño / Southern Oscillation (ENSO)

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

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

  16. Mean 1982-2008 Standard deviation of monthly anomalies ENSO SST anomaly index “Niño 3”

  17. ENSO “Niño 3” SSTmonthly anomaly index monthly standard deviation

  18. ENSO Composite Evolution (SST, SLP)

  19. ENSO Composite Evolution (SST, SLP) Southern Oscillation

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

  21. 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

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

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

  24. The “Recharge Oscillator”:A simple paradigm for the El Niño cycle(Instability of the tropical Pacific ocean-atmosphere system) Warm event Wind stress anomaly Thermocline Depth anomaly Positive feedback F.-F. Jin, J. Atmos. Sci. 1997

  25. The “Recharge Oscillator”:A simple paradigm for the El Niño cycle(Instability of the tropical Pacific ocean-atmosphere system) Warm event “Bjerknes Feedback” positive SST anomaly negative SLP anomaly westerly wind anomaly deepened thermocline positive SST anomaly Wind stress anomaly Thermocline Depth anomaly Positive feedback F.-F. Jin, J. Atmos. Sci. 1997

  26. The “Recharge Oscillator”:A simple paradigm for the El Niño cycle(Instability of the tropical Pacific ocean-atmosphere system) Warm event Wind stress anomaly Thermocline Depth anomaly Poleward Vg anomaly L H V ~ dp/dx Positive feedback F.-F. Jin, J. Atmos. Sci. 1997

  27. The “Recharge Oscillator”:A simple paradigm for the El Niño cycle(Instability of the tropical Pacific ocean-atmosphere system) Neutral State Warm event Wind stress anomaly Shallower Mean Thermocline Thermocline Depth anomaly Poleward Vg anomaly L H V ~ dp/dx Positive feedback Ocean Heat Discharge F.-F. Jin, J. Atmos. Sci. 1997

  28. The “Recharge Oscillator”:A simple paradigm for the El Niño cycle(Instability of the tropical Pacific ocean-atmosphere system) Neutral State Warm event Wind stress anomaly Shallower Mean Thermocline Thermocline Depth anomaly Poleward Vg anomaly L H V ~ dp/dx Positive feedback Shallow thermocline > Cold SST via upwelling Ocean Heat Discharge Positive feedback F.-F. Jin, J. Atmos. Sci. 1997 Cold event

  29. The “Recharge Oscillator”:A simple paradigm for the ENSO cycle(Instability of the tropical Pacific ocean-atmosphere system) Neutral State Warm event Wind stress anomaly Shallower Mean Thermocline Thermocline Depth anomaly Poleward Vg anomaly L H V ~ dp/dx Positive feedback Shallow thermocline > Cold SST via upwelling Ocean Heat Discharge Equatorward Vg anomaly H L V ~ dp/dx Positive feedback F.-F. Jin, J. Atmos. Sci. 1997 Cold event

  30. The “Recharge Oscillator”:A simple paradigm for the El Niño cycle(Instability of the tropical Pacific ocean-atmosphere system) Neutral State Warm event Wind stress anomaly Shallower Mean Thermocline Thermocline Depth anomaly Poleward Vg anomaly L H V ~ dp/dx Positive feedback Shallow thermocline > Cold SST via upwelling Ocean Heat Discharge Equatorward Vg anomaly H L V ~ dp/dx Positive feedback F.-F. Jin, J. Atmos. Sci. 1997 Cold event Ocean Heat Recharge

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

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

  33. 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

  34. ENSO in Models

  35. 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

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

  37. Deser et al. J. Climate 2004 1-2-1 smoothed North Pacific SLP Indian Ocean SST Tropical Climate Indices SE Pacific SST SPCZ Rainfall Eq Pacific Rainfall Eq Pacific Cloud E-W SLP Gradient (Indian – Pac)

  38. Tropical Atlantic and Indian Ocean Modes of Variability

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

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

  41. Leading Modes of SST Variability in the Tropical Atlantic Ocean Niño Mode 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) See Review in Xie and Carton 2004

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

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

  44. Modes of Tropical Climate Variability Thank You Clara Deser, Climate Analysis Section, NCAR Deser et al., 2009: Annual Review of Marine Sciences, Vol. 2 www.cgd.ucar.edu/cas/cdeser/

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

More Related