scostep 2010 (stp12) - Leibniz-Institut für Atmosphärenphysik an der ...

STP12 Abstracts
Berlin, 12 - 16 July 2010
SCOSTEP Symposium 2010
The atmospheric response to solar cycle variability simulated by MAECHAM5 with and
without ocean coupling
Misios Stergios , Schmidt Hauke
Max Planck Institute for Meteorology
The 11-year solar cycle variation has a well demonstrated impact on the Northern Hemisphere
winter stratosphere. During early winter of maximum solar activity years the stratospheric
vortex tends to be stronger and colder in contrast to minimum activity. While there is a
relative consensus on the stratospheric response, the pathways through which the solar signal
is propagated into the troposphere are still under debate. The surface response in particular
regions, as in the Equatorial Pacific, further perplexes our understanding. In this work, we
explore the inseparable troposphere-stratosphere response of the 11-yr solar cycle with the aid
of fully coupled atmosphere-ocean general circulation model (GCM).
Simulations with the MAECHAM5 GCM with a realistic time varying solar forcing (as
observed from 1955 to 2006) and prescribed ozone anomalies are carried out. No other
external forcing is considered. The quasi-biennial oscillation (QBO) is spontaneously
generated in the model. We conduct 9 ensemble runs over 52 years each with MAECHAM5
coupled to the MPI ocean model (MPIOM) and compare the results to another 9 member
ensemble with prescribed sea surface temperature (SST).
In this study, the domain of interest is the equatorial and subtropical stratosphere and
troposphere with a special focus on the Pacific region. Our analysis reveals that the
tropospheric response in the coupled runs differs substantially from the uncoupled. The
prescribed SSTs damp the temperature solar signal and statistically significant results are
obtained only in the experiments with time varying SSTs. Both coupled and uncoupled
simulations show a pronounced secondary maximum in the lower equatorial stratosphere
which is somewhat stronger in the coupled ensemble. In the equatorial Pacific a tongue of
weak negative temperature anomalies can also be found. In our presentation, we further
elaborate on the mechanisms that may explain the simulated solar response.