Interactions between volcanic eruptions and El Niño: Studies with a

coupled atmosphere-ocean modelC. Timmreck, M. Thomas, M. Giorgetta, M. Esch, H.-F. Graf1, H. Haak,

J. Jungclaus, W. Müller, E. Roeckner, H. Schmidt and G. Stenchikov2

Max Planck Institute for Meteorology, Hamburg

1Centre Atmospheric Sciences University, Cambridge 2Rutgers-The State University of NJ, New Brunswick

AGU Spring meeting 2007

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The last three biggest eruptions (Agung (1963), El Chichón (1982) and Pinatubo (1991)) occurred at the time as an El Niño event.

Dynamic response due to the combined effects of El Niño and volcanic eruptions are still uncertain.

Paleo reconstructions (Adams et al, 2003) show that large volcanic eruptions enhance the probability of an El Niño event.

AOGCMs are an important tool to improve our understanding of the atmospheric and oceanic response to the combined effects of El Niño and large volcanic eruptions.

Coupled El Niño Volcanic runs

Coupled El Niño Volcanic runs

We have carried out a series of volcanic simulations with the AOGCM, ECHAM5/MPIOM.

The volcanic radiative forcing is calculated online in the model. A realistic spatial-temporal distribution of aerosol optical parameters for the Pinatubo episode is used.

Optical depth in the visible

Niño 3.4 SST anomalies in ECHAM5/MPIOM

The frequency analysis of the El Niño events show good agreement with observations. However, the amplitude of 1.7 K is higher than in the IPCC runs (1.5 K) and in the AMIP cases (1.K)

Three different cases are selected from a 100 year control run.

5 ensembles for Jan and June, perturbed / unperturbed.

Each ensemble run has been performed for two years.

Coupled El Niño Volcanic runsNiño 3.4 Case I Niño 3.4 Case IIINiño 3.4 Case II

Stratospheric temperature response [K]

ERA 40 Reanalysis Case I June

30 hPa

100 hPa

50 hPa

Temperature response at 50 hPa

Case I June

Case II June

Case III June

Case II January

Case I January

Case III January

GPH Anomaly 50 hPa DJF „91/92“

Era 40 Reanalysis

Case I JuneCase I January

Case II January

Case II June

2m temperature anomaly [k] DJF „91/92“

Era 40 Reanalysis

Case I January Case I June

Case II JuneCase II January

Case II June 2m temp. anomalies [K] DJF 91/92

Atmospheric response

The stratospheric tropical temperature response is similar for all cases and in agreement with observations.

The dynamical response in the NH high latitudes is highly variable. Only in a few cases the observed pattern is mirrored. However, some ensemble members reflect the observed pattern.

Further analysis (EP fluxes, refractive indices) is necessary

Note: model top at 10 hPa !

January

June

Niño 3.4 Case III CTRL

Niño 3.4 SST anomalies [k] Case III

Niño 3.4 SST anomalies [k] Case II

January

June

Niño 3.4 Case II CTRL

Niño 3.4 SST anomalies [k] Case I

Niño 3.4 Case I CTRL

January

June

U10 [m/s]+ 4

- 4

+ 2

- 2

0

Ocean T 6 m [K]

Hovmoeller diagram of anomalies 5N-5SCase I June

Ocean T 100 m [K]

Oceanic response

Large interannual variability can be detected in the tropical dynamical ocean heat response.

Significant ocean response only in two cases: Case I June

where the model is triggered into a La Niña state. Ekman pumping in the mid equatorial Pacific leads to significant cooling in the perturbed model run.

Case II January

where radiative effects damp the El Niño signal

Conclusion I

Based on our model results we cannot support the hypothesis from Adams et al.(2003) that volcanic eruptions enhance the possibilty of an El Niño event.

The dynamical response in the atmosphere and in the ocean is highly variable and differs between the selected cases, but also quite strongly between the single ensemble members.

Further analysis is necessary to learn more about

the physical mechanisms behind and why the ensemble members behave differently

Ongoing work

Conclusion II

Thank you very muchfor your attention!

We had some questions before we started.

Now we have even more.

Coupled El Niño Volcanic runs

Oceanic response

Temperature differences (K) and respective significances in the equatorial pacific. The grey scale indicates significances of 90, 95, and 99%.

Oce

an d

epth

(m

)

199201, 7 months after eruption

Oce

an d

epth

(m

)Temperature response in the equatorial Pacific

Case I June

Nino 82/83

Nino 91792

Coupled El Niño Volcanic runs

Atmospheric response

Case I June 2m temp. anomalies

Case I June GPH anomalies at 50 hPa

Case II June 2m temp. anomalies

Case II June GPH anomalies at 50 hPa