Dynamic Diagnosis of Stratospheric Sudden Warming Event in the Boreal Winter of 2018 and Its Possible Impact on Weather over North America

Abstract

In the winter of 2018, a major stratospheric sudden warming (SSW) event occurred in the Northern Hemisphere. This study performs a dynamic diagnosis on this 2018 SSW event and analyzes its possible impact on the weather over North America. The result shows that the ridge over Alaska in the mid-troposphere and the trough over the northeastern North America are the prominent tropospheric precursory signals before the occurrence of this SSW event. The signals appear 10 days before the SSW, which greatly enhances the propagation of the planetary wavenumber 2 from the troposphere to the extratropical stratosphere. The collapse process of stratospheric polar vortex indicates that this SSW is a typical vortex splitting event dominated by planetary wavenumber 2. Additionally, after the SSW onset, no reflection of the stratosphere on the tropospheric planetary waves is observed. Thus, this event can also be classified as an absorbing-type SSW event. A noticeable cold wave occurs in the northwestern North America within 10 days after the 2018 SSW. This cold wave is probably associated with the SSW-related west–east dipole, namely a ridge over Alaska and a trough over the northeastern North America in the mid-troposphere that lasted up to 10 days after the onset date. The composite analysis of the other seven SSW events with an emergence of similar mid-tropospheric circulation pattern after SSW onset date yields coincident 2-meter temperature anomalies in the northwestern North America, which confirms the above conclusion to some extent.