Solar Heating of the Lower Stratosphere and Its Influence on Tropospheric Climate
Joanna D. Haigh [j.haigh@imperial.ac.uk], Imperial College, London, UK; Michael Blackburn, University of Reading, UK

Analyses of NCEP zonal wind data have shown a particular pattern of response to solar activity in which the sub-tropical jets weaken and move poleward when the sun is more active. GCM studies of the solar influence have managed to reproduce this pattern and have also shown an impact on tropospheric mean meridional circulation with a weakening and expansion of the tropical Hadley cells and a poleward shift of the Ferrel cells. In order to understand the mechanisms whereby these changes take place we have carried out experiments with a simplified global circulation model. The results show that any heating of the lower stratosphere results in a weakening of the sub-tropical jets and of the tropospheric mean meridional circulations. The positions of the jets, and the extent of the Hadley cells, respond to the distribution of the stratospheric heating with low latitude perturbations forcing them to move poleward and high latitude, or latitudinally uniform, perturbations forcing them equatorward. We present an analysis of the time development of perturbations in the runs to identify a chain of causality for these effects. We also show results from a series of baroclinic lifecycle experiments performed under each of the perturbed regimes which show how baroclinic waves enforce the initial.