Wednesday, 10 January 2018
Exhibit Hall 3 (ACC) (Austin, Texas)
The strength and position of the Northern Hemisphere (NH) stratospheric polar vortex are two indicators of NH wintertime weather. As such, projected trends of these measures may provide insight into the nature of future winters. Previous work has explored possible connections between vortex trends and climate change impacts, though the results thus far remain inconclusive. This study explores several metrics of the strength and position of the NH stratospheric polar vortex throughout the 20th and 21st centuries in both reanalyses and coupled climate models. Analysis of polar cap heights during the 20th century reveals high variance in the strength of the stratospheric polar vortex over time, with decadal periods of strong and weak regimes detected. Furthermore, we also find the recent shift of the polar vortex toward Eurasia but also find some variability in this spatial shift over the 20th century. This internal variability must be taken into account when assessing the role of climate change on recent and future trends. Next, we assess the output from several coupled-climate models from the Coupled Model Intercomparison Project Phase 5 (CMIP5) Historical ensemble to compare against the observed vortex trends, thereby putting any future projections into context. The CMIP5 Historical suite of models does not adequately reproduce the observed 20th century polar vortex trends; i.e., there is high spread among the ensemble members in the strength and overall location of the stratospheric polar vortex. These trends are related to the way that the models handle stratosphere-troposphere coupling dynamics, including vertical wave propagation and downward propagation of anomalies. Finally, the CMIP5 RCP8.5 runs (i.e., future climate change projections) systematically project a shift in the stratospheric polar vortex toward Northeast Asia during the 21st century, but are inconclusive regarding the strength of the polar vortex. Relations between these findings and the nature and characteristics of NH winters in the middle and high latitudes will also be discussed.
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