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Ma, C. G., & Chang, E. K. (2017). Impacts of storm track variations on winter time extreme weather events over the continental US. Journal of Climate, (2017).

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Ma, C. G., & Chang, E. K. (2017). Impacts of storm track variations on winter time extreme weather events over the continental US. Journal of Climate, (2017).

ECA Impacts on wintertime extreme weather events over the Continental US  (Ma and Chang, 2017)

Link to paper

Extratropical cyclones are responsible for many of the high-impact weather events over the United States, including extreme cold, extreme high wind, and extreme heavy precipitation. In this study, impacts from the variations of the extratropical cyclone activity (ECA) on these extreme events are examined through composites based on map-averaged cyclone activity. Increased cyclone activity enhances the frequency of extreme cold and high wind events over much of the United States, and impacts extreme precipitation around the Ohio River valley. These impacts are largely due to a changing of the tail of the distribution rather than a shifting of the mean.

Composite difference between 10 high-ECA winters and 10 low-ECA winters for (a) mean ECA difference; (b) 99th percentile extreme cold events frequency; (c) 99th percentile extreme high wind frequency; and (d) 99th percentile extreme precipitation frequency. The dotted and hatched regions show the regions that are significant at the 5% level.

Composite difference between 10 high-ECA winters and 10 low-ECA winters for (a) mean ECA difference; (b) 99th percentile extreme cold events frequency; (c) 99th percentile extreme high wind frequency; and (d) 99th percentile extreme precipitation frequency. The dotted and hatched regions show the regions that are significant at the 5% level.

To systematically study these impacts, three singular value decomposition (SVD) analyses have been conducted, each one between the cyclone activity and one kind of extreme event frequency. All three SVD leading modes represent a pattern of overall increase or decrease of storm tracks over the United States. The average of the time series of these leading modes is highly correlated with the observed map-averaged storm track and strongly associated with the Pacific–North America (PNA) pattern and El Niño–Southern Oscillation (ENSO). However, composites based on either the PNA pattern or ENSO do not show as strong impacts as the map-averaged storm track. A second common SVD mode is found that correlates weakly with the North Pacific mode and is likely to be largely due to internal variability. Finally, the potential impacts of projected storm-track change on the frequency of extreme events are examined, indicating that the projected storm-track decrease over North America may give rise to some reduction in the frequency of extreme events. Reduction in extreme cold events will reinforce the direct impact of global warming, while a reduction in extreme precipitation events may partially offset the direct global warming impacts related to increase in moisture content. These results are published in the article “Impacts of storm-track variations on wintertime extreme weather events over the Continental United States” in the Journal of Climate, 30, 4601-4624 (Ma and Chang 2017)

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March 15, 2017