Solar Influences on Dynamical Coupling Between the Stratosphere and Troposphere |
| |
Authors: | J D Haigh M Blackburn |
| |
Institution: | (1) Blackett Laboratory, Imperial College of Science, Technology and Medicine, London, SW7 2BW, UK;(2) Centre for Global Atmospheric Modelling, University of Reading, Reading, UK |
| |
Abstract: | We use a simplified atmospheric general circulation model (AGCM) to investigate the response of the lower atmosphere to thermal
perturbations in the lower stratosphere. The results show that generic heating of the lower stratosphere tends to weaken the
sub-tropical jets and 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 heating displacing them poleward, and uniform
heating displacing them equatorward. The patterns of response to the low latitude heating are similar to those found to be
associated with solar variability in previous observational data analysis, and to the effects of varying solar UV radiation
in sophisticated AGCMs. In order to investigate the chain of causality involved in converting the stratospheric thermal forcing
to a tropospheric climate signal we conduct an experiment which uses an ensemble of model spin-ups to analyse the time development
of the response to an applied stratospheric perturbation. We find that the initial effect of the change in static stability
at the tropopause is to reduce the eddy momentum flux convergence in this region. This is followed by a vertical transfer
of the momentum forcing anomaly by an anomalous mean circulation to the surface, where it is partly balanced by surface stress
anomalies. The unbalanced part drives the evolution of the vertically integrated zonal flow. We conclude that solar heating
of the stratosphere may produce changes in the circulation of the troposphere even without any direct forcing below the tropopause.
We suggest that the impact of the stratospheric changes on wave propagation is key to the mechanisms involved. |
| |
Keywords: | solar variability climate variability stratosphere-troposphere coupling storm tracks |
本文献已被 SpringerLink 等数据库收录! |
|