Joanna D. Haigh

Imperial College
I will review some of the evidence for an influence of solar variability on climate and discuss mechanisms which might produce the apparent signals. When the Sun is more active the response in temperature is not a warming of the tropics, as might be anticipated in response to a higher input of solar energy, but bands of warming throughout the mid-latitude troposphere. Associated with this the jet streams weaken and move polewards, along with the mid-latitude storm-tracks. With GCM runs we have identified that an important factor driving this response is the absorption of solar UV radiation in the stratosphere and, by running idealised experiments, we have identified a mechanism for dynamical coupling between the stratosphere and the atmosphere below. These results have more general application in understanding the climate effects of other stratospheric perturbations such as ozone or volcanic aerosol. The solar mechanism depends fundamentally on changes in UV. I will discuss the implications of different estimates of changes in the solar spectrum (from satellite measurements and empirical models) for both the stratosphere and for radiative forcing of climate. I will finish by describing recent work on a statistical approach to assessing consistency between solar and atmospheric measurements.