A Possible Transfer Mechanism for the 11-Year Solar Cycle to the Lower Stratosphere |
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Authors: | L J Gray S A Crooks M A Palmer C L Pascoe S Sparrow |
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Institution: | (1) Centre for Global Atmospheric Modelling, Department of Meteorology, Reading University, Early Gate, PO Box 243, Reading, RG6 6BB, UK;(2) Department of Atmospheric, Oceanic and Planetary Physics, Oxford University, Oxford, UK;(3) Rutherford Appleton Laboratory, Chilton, Didcot, UK |
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Abstract: | Observational evidence of the 11-year solar cycle (SC) modulation of stratosphere temperatures and winds from the ERA-40 dataset
is reviewed, with emphasis on the Northern winter hemisphere. A frequency modulation of sudden warming events is noted, with
warmings occurring earlier in solar minimum periods than in solar maximum periods. The observed interaction between the influence
of the SC and the quasi biennial oscillation (QBO) on the frequency of sudden warmings is noted as a possible clue for understanding
their mechanism of influence. A possible transfer route for the 11-year solar cycle from the equatorial stratopause region
to the lowest part of the stratosphere is proposed, via an influence on sudden warming events and the associated induced meridional
circulation. SC and QBO composites of zonal wind anomalies show anomalous wind distributions in the subtropical upper stratosphere
in early winter. Mechanistic model experiments are reviewed that demonstrate a sensitivity of sudden warmings to small wind
anomalies in this region. Various diagnostics from these experiments are shown, including EP fluxes and their divergence and
also the synoptic evolution of the polar vortex, in order to understand the mechanism of the influence. Some recent GCM experiments
to investigate the SC/QBO interaction are also described. They simulate reasonably well the observed SC/QBO interaction of
sudden warming events and appear to support the hypothesis that tropical/subtropical upper stratospheric wind anomalies are
an important influence on the timing of sudden warmings. |
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Keywords: | stratosphere quasi biennial oscillation solar cycle atmosphere stratospheric sudden warming |
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