Research on a mechanism by which enhanced UV-radiation of the active sun affects weather and climate
Onderzoek naar de invloed van de toename van UV-straling van de zon op het weer en het klimaat
Schuurmans CJE , Tourpali K , Dorland R van
RIVM Report 410200077
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.