@article{YANG2025, 
author = {Yifan YANG and Yueyue YU and Chunhua SHI and Zhiqiang DING and Yang LIU},
title = {Temporal Phasing of Stronger Warm Air Mass Transport into the Polar Stratosphere and Cold Air Outbreaks in North America},
year = {2025},
journal = {Journal of Meteorological Research},
volume = {39},
number = {5},
pages = {1211-1227},
keywords = {extreme cold, North America, stratosphere–troposphere coupling, polar vortex},
url = {https://www.sciopen.com/article/10.1007/s13351-025-5037-x},
doi = {10.1007/s13351-025-5037-x},
abstract = {Severe cold air outbreak events over North America (CAO_NA) are often accompanied with a weakening of the stratospheric polar vortex. One of the main drivers causing this weakening is the intensified warm mass transport into the polar stratosphere (ST+). However, the robustness of the linkage between CAO_NA and ST+ events has yet to be fully established. Here, the empirical orthogonal function (EOF) method is applied to daily time series of mass transport into the polar stratosphere, using lead/lag days from −10 to 10 days around the peak dates of CAO_NA as the spatial domain and the number of individual CAO_NA events as the temporal domain. The results indicate that out of 227 CAO_NA events during the 41 winters (November–March) from 1979 to 2020, only 64 are not accom-panied with ST+ events. The remaining 72% (163) coupled with ST+ events can be categorized into three types: two types are characterized by ST+ events occurring a few days before (ST+_lead) or after (ST+_lag) the peak dates of CAO_NA events, while the third type corresponds to ST+ events occurring a week before (ST+_week) CAO_NA events. Both “ST+_week” and “ST+_lead” events are associated with a strengthening of wavenumber-1 waves, followed by a strengthening of wavenumber-2 waves. The “ST+_lead” and “ST+_week” events are featured by a “warm Arctic & cold midlatitudes” pattern in the Western Hemisphere with a reversed meridional dipole pattern in the Eastern Hemisphere. The “ST+_lag” events are purely driven by wavenumber-2 waves, corresponding to the co-occurring coldness over midlatitudes of both North America and Eurasia and a warmer Arctic. Further combining with the stratospheric polar vortex and circumpolar wind conditions in each type, a set of stratospheric weather regimes for CAO_NA events is identified.}
}