| description abstract | xtratropical cyclones are responsible for much of the high-impact weather events over the U.S., including extreme cold, extreme high wind and extreme heavy precipitation. In this study, impacts from the variations of the cyclone (or storm track) activity 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 U.S., and impacts extreme precipitation around the Ohio Valley. These impacts are largely due to the changing of the tail of the distribution rather than a shifting of the mean. 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/decrease of storm track over the U.S. 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 pattern (PNA) and the El Niño Southern Oscillation (ENSO). However, composites based on either PNA or ENSO do not show as strong impacts as the map-averaged storm track. A second common SVD mode is found which 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. | |
