06.06.2016: FB1-Seminar

11:00 h, Hörsaal, Düsternbrooker Weg 20

Abstract:

The El Niño/Southern Oscillation (ENSO) is characterized by a seasonal phase locking, with strongest sea surface temperature (SST) anomalies in the eastern and central equatorial Pacific during boreal winter and weakest SST anomalies during boreal spring. Here we identify key feedbacks that control ENSO phase locking in the Kiel Climate Model (KCM) by employing the Bjerknes (BJ) index in a seasonal stability analysis. A large ensemble of simulations performed with the KCM is analyzed, where the individual runs differ in either the number of vertical atmospheric levels or coefficients used in selected atmospheric parameterizations. When considering the ensemble-mean the KCM features realistic ENSO phase locking. The ENSO phase locking is very sensitive to changes in the mean state. An excessive equatorial cold tongue leads to weaker phase locking by reducing ocean upwelling and thermocline slope sensitivity to zonal wind stress forcing in late boreal fall and early boreal winter. Another important factor for ENSO phase locking is the shortwave feedback in early boreal spring, which strongly depends on eastern equatorial SST. The results obtained from the KCM are discussed in the context of the models participating in the Coupled Model Intercomparison Project phase 5 (CMIP5).

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