Long-term changes and variability in a transient simulation with a chemistry-climate model employing realistic forcing M. Dameris1, V. Grewe1, M. Ponater1, R. Deckert1, V. Eyring1, F. Mager1,*, S. Matthes1, C. Schnadt1,**, A. Stenke1, B. Steil2, C. Brühl2, and M. A. Giorgetta3 1Institut für Physik der Atmosphäre, DLR-Oberpfaffenhofen, Wessling, Germany 2Max-Planck-Institut für Chemie, Mainz, Germany 3Max-Planck-Institut für Meteorologie, Hamburg, Germany *now at: University of Cambridge, Centre for Atmospheric Science, Department of Geography, Cambridge, UK **now at: ETH Zürich, Institut für Atmosphäre und Klima, Zürich, Switzerland
Abstract. A transient simulation with the interactively coupled chemistry-climate model
(CCM) E39/C has been carried out which covers the 40-year period between
1960 and 1999. Forcing of natural and anthropogenic origin is prescribed where
the characteristics are sufficiently well known and the typical timescales are
slow compared to synoptic timescale so that the simulated atmospheric chemistry
and climate evolve under a "slowly" varying external forcing. Based on
observations, sea surface temperature (SST) and ice cover
are prescribed. The increase of greenhouse gas
and chlorofluorocarbon concentrations, as well as nitrogen oxide emissions
are taken into account. The 11-year solar cycle is considered in the calculation of
heating rates and photolysis of chemical species. The three major volcanic
eruptions during that time (Agung, 1963; El Chichon, 1982;
Pinatubo, 1991) are considered. The quasi-biennial oscillation (QBO) is forced
by linear relaxation, also known as nudging, of the equatorial zonal wind in
the lower stratosphere towards observed zonal wind profiles. Beyond a
reasonable reproduction of mean parameters and long-term variability
characteristics there are many apparent features of episodic similarities
between simulation and observation: In the years 1986 and 1988 the Antarctic
ozone holes are smaller than in the other years of that decade. In
mid-latitudes of the Southern Hemisphere ozone anomalies resemble the
corresponding observations, especially in 1985, 1989, 1991/1992, and 1996.
In the Northern Hemisphere, the episode between
the late 1980s and the first half of the 1990s is dynamically quiet, in
particular, no stratospheric warming is found between 1988 and 1993.
As observed, volcanic eruptions strongly influence
dynamics and chemistry, though only for few years. Obviously, planetary
wave activity is strongly driven by the prescribed SST and modulated by the
QBO. Preliminary evidence of realistic cause and effect
relationships strongly suggests that detailed process-oriented studies will be
a worthwhile endeavour.
Citation: Dameris, M., Grewe, V., Ponater, M., Deckert, R., Eyring, V., Mager, F., Matthes, S., Schnadt, C., Stenke, A., Steil, B., Brühl, C., and Giorgetta, M. A.: Long-term changes and variability in a transient simulation with a chemistry-climate model employing realistic forcing, Atmos. Chem. Phys., 5, 2121-2145, doi:10.5194/acp-5-2121-2005, 2005.