Community Research and Development Information Service - CORDIS

Final Activity Report Summary - SOLVO (The Influence of Solar Variability on Climate)

The sun is the fundamental energy source of the climate system. Hence changes in solar irradiance are one potential source of natural climate variability. Observational and previous modelling studies have shown that direct radiative changes in the upper stratosphere can lead to indirect dynamical changes throughout the atmosphere. However, previous General circulation models (GCMs) had an insufficient representation of atmospheric chemistry and were restricted to the lower parts of the atmosphere. Observational data sets are short and make it difficult to extract reliable decadal signals. Therefore modelling studies are useful to enhance the understanding of the underlying physical mechanism(s).

The aim of this project was to investigate the solar influence on climate with a model that was specifically designed to look at interactions between radiation, chemistry and dynamics from the Earth's surface to the thermosphere (~140 km). A unique set of (idealised) experiments with the Whole atmosphere community climate model (WACCM) developed at the National Center for Atmospheric Research (NCAR) in Boulder, United States (US), was performed during the project to investigate the response of the atmosphere to 11-year solar cycle changes and especially interactions with the equatorial stratospheric wind oscillation (QBO) for which observational evidence is strong.

Through the analysis of a systematic set of model simulations with WACCM (under different constant or time-varying solar cycle and QBO forcings) it was possible to confirm the observed evidence for a dependence of the solar signal on the phase of the QBO at polar winter latitudes as well as an influence on large-scale atmospheric circulation patterns. This enhances the understanding of the role of the QBO for the chemical-dynamical response to the solar cycle and contributes to a better understanding of the mechanism for Sun-climate interactions and natural climate variability in general.

A better understanding of natural climate variability is essential to reliably estimate the anthropogenic contribution to the recent global warming and to improve the accuracy of climate predictions in forthcoming Intergovernmental Panel on Climate Change (IPCC) reports and World Meteorological Organisation (WMO) ozone assessments.

Reported by

Carl-Heinrich-Becker-Weg 6-10
12165 BERLIN
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