12th Conference on Middle Atmosphere

Wednesday, 6 November 2002: 1:30 PM
The role of the stratosphere in tropospheric weather & climate
Mark P. Baldwin, Northwest Research Associates, Bellevue, WA
There is increasing evidence that stratospheric processes play an important role in tropospheric climate variability across a wide range of timescales. On intraseasonal timescales, observations show that large amplitude anomalies in the strength of the Northern Hemisphere wintertime stratospheric polar vortex frequently precede long-lived (up to ~two months) changes to the tropospheric circulation that resemble the Arctic Oscillation (AO) or North Atlantic Oscillation (NAO).

On year-to-year timescales, stratospheric volcanic aerosols have been found to influence tropospheric climate both radiatively and dynamically, and the stratospheric quasi-biennial oscillation has been found to exhibit a signature in surface climate. On decadal to centennial timescales, both ozone depletion and anthropogenic greenhouse gas increases appear to have had a large impact on stratospheric temperatures and circulation, and there is evidence that these changes may have had both a radiative and dynamical impact on surface climate. Stratospheric mechanisms have also been proposed to explain the larger than expected impact of solar variability at the surface.

Despite this evidence, the dynamical mechanisms by which circulation anomalies in the lower stratosphere induce changes to surface weather patterns are not understood. Stratospheric conditions are usually not assimilated into numerical weather prediction models, the stratosphere is not used in seasonal forecast models, and numerical simulations of climate change frequently do not include well-resolved stratospheres.

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