English Abstract The aim of this study was to investigate the degree of
climate response to changes in the UV radiation of the active sun during the
11- year solar cycle, and to examine the physical mechanisms involved, with
the use of an interactively coupled chemistry- General Circulation Model
(GCM). The solar forcing is represented by changes in incident irradiance,
with solar fluxes adjusted in the model's spectral intervals, according to
the difference between observed solar maximum and solar minimum conditions.
Results so far, based upon a model run of 10 years, show that enhanced UV
results in increases of stratospheric ozone, associated with temperature
increases and seasonally varying changes in the zonal wind structure. The
simulated changes are in reasonable agreement with observed changes in the
stratosphere between solar minimum and solar maximum conditions. Changes in
the troposphere include an increase of the tropical easterlies in all months
and a banded structure of zonal wind changes at higher latitudes. The
latter have also been found in similar model experiments elswhere.
Simulated temperature changes in the upper troposphere are mainly positive,
but near the surface also large areas of cooling are found. This brings us
to the general conclusion that regionally climate response to enhanced UV
might be significant, but on a global scale, e.g. on global mean
temperature, it is most probably small. It is very likely that dynamical
processes are responsible for the response of the troposphere, but the
precise nature of these remains as yet unclear.