| Description |
Changes in the stratospheric circulation have the potential to affect weather and climate in the troposphere, especially over the high latitudes. In order to better understand such influences, we analyze the relationships among stratospheric, tropospheric, and oceanic variability. We reach our goal with the aid of coupled chemistry-climate models and coupled atmosphere-ocean models. Over the past decades, ozone depletion in the Antarctic stratosphere has been accelerating the poleward side of the stratospheric polar vortex. We suspect that the change in the winds in turn affects the concentrations of ozone. This idea is investigated with coupled chemistry-climate models. We find a strong indication for the existence of a positive feedback between ozone depletion and change in the circulation: the chemical ozone loss feeds back into the stratospheric circulation, and changes in the circulation produce more ozone deficit. Climate models tend to systematically overestimate the persistence time scale of extratropical variability, in particular over the Southern Hemisphere. The systematic overestimation in climate models raises the concern that the models are overly sensitive to external forcings and that future projections based on those models are unreliable. We investigate issues concerning the persistence time scale of the annular mode using reanalysis and model data. We find that the 50-year record of historical observations is probably too short to derive a stable estimate of the annular mode time scale that may be used to evaluate climate models. We also find a robust relationship between the magnitude and the seasonal timing of the time scale in both stratosphere and troposphere, confirming and extending earlier results of a dynamical coupling between the stratosphere and the troposphere and of influences of stratospheric variability on the troposphere. Extreme events in the stratosphere are known to alter tropospheric weather and climate. However, it is still unclear whether the stratosphere also has the capacity to affect the ocean and its circulation. This possibility is suggested from observations which show low-frequency covariability between the stratosphere and the Atlantic thermohaline circulation. We use simulations from coupled atmosphere-ocean models to explore more systematically a possible stratospheric influence on the oceanic circulation over the North Atlantic Ocean on multidecadal time scales. Our analysis identifies the stratosphere as a previously unknown source for decadal climate variability in the troposphere and suggests that the stratosphere forms an important component of climate that should be well represented in models. |
