The Sensitivity of the Subtropical Cells in the Pacific to Global Warming

M. Latif
Institute for Marine Research, Kiel, Germany

K. Lohmann
Max-Planck-Institute for Meteorology, Hamburg, Germany

E-mail: mlatif@ifm.uni-kiel.de

Recent observational and modelling studies report a weakening of the shallow tropical cells (STCs) in the Pacific Ocean, and this may have been the cause of the warming in the equatorial Pacific observed over the last decades (McPhaden and Zhang 2002). The STCs control the upwelling at the equator and thus a changing STC strength has a direct impact on the SST, which may be reinforced by coupled feedbacks. As such, the STCs may play an important role in regional and global climate change. Furthermore, a change in the STCs may also affect ENSO variability.

We would like to explore the sensitivity of these cells to global warming. The background is that two different models developed at the Max-Planck-Institute simulate rather different responses. The situation may be similar to the problem of the stability of the thermohaline circulation (THC): The ensemble of CMIP models shows a large spread in the behavior of the THC when forced by increased levels of greenhouse gases. Our subproject is aiming at quantifying the spread in the Pacific STC behavior within the CMIP2 model ensemble.

Variables needed from the CMIP database:

1. 20 year means of the overturning in the Pacific from the control integrations,
2. 20 year means of the overturning in the Pacific from the 1% integrations.

References

McPhaden, M.J. and D. Zhang (2002): Slowdown of the meridional overturning circulation in the upper Pacific Ocean. Nature, 415, 603-608.