17.03.2014: FB1-Seminar

 11:00 h, Hörsaal, Düsternbrooker Weg 20

Abstract:

Despite rising greenhouse gas concentrations the global mean temperature has not increased much since 1998. Some recent studies attributed this to a strengthening of the trade winds over the equatorial Pacific, driving enhanced equatorial upwelling and thereby cooling equatorial Pacific SST, which in turn cooled the global mean temperature by roughly 0.1°-0.2° over the last decade.

Here we analyse the trends of El Niño Southern Oscillation (ENSO) and the Walker Circulation in observations and 21st century climate model projections from the Coupled Model Intercomparison Project Phase 5 (CMIP5). We focus on the following questions:

1. What changes in ENSO and the Walker Circulation do the CMIP5 models project under global warming?
2. El Niño events are often categorized in central Pacific (CP) and east Pacific (EP) El Niños. Here we use the centre of heat index (CHI) to locate the centre of action of El Niño and La Niña events  to further investigate  CP and EP El Niños. Is the split into CP and EP El Niños justified?
3. ENSO and the Walker Circulation exhibit an asymmetry in the location of maximum SST anomalies during El Niño and La Niña events, with El Nino SST anomalies peaking more in the east than the La Niña anomalies. How well do state-of-the-art climate models simulate this asymmetry and does the asymmetry change in the considered climate projections?
4. Most CMIP5 climate models project a weakening and eastward shift of the Walker Circulation under global warming, i.e. a more El Niño-like trend. Observations over the last three decades, however, show a strengthening and westward shift of the Walker Circulation, as mentioned above. How consistent is this trend with internal variability in climate models? 

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