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.
Highlights
The stratospheric sudden warming (SSW) event occurs mostly in winter, and it dominates the inter-annual and intra-seasonal variations of the winter stratospheric circulation in the polar region.During the occurrence of the SSW events (SSWs), the stratospheric temperature in high latitudes increases sharply, accompanying with the adjustment of the atmospheric circulation
According to the definition of SSW given by the WMO, this SSW event is a typical major warming event with the central date or so-called onset date on 11 February
Reanalysis is usedwith to analyze theNortheastern evolution of significantly negative temperature daily anomalies appear data and expand time in the andthe extratropical stratospheric circulationofand dynamicmid-tropospheric characteristics during occurrence of the Central Canada with the emergence the the pronounced dipolethe after the SSW onset in theThe winter
Summary
The stratospheric sudden warming (SSW) event occurs mostly in winter, and it dominates the inter-annual and intra-seasonal variations of the winter stratospheric circulation in the polar region. It is generally believed that the major SSWs defined by WMO produce a greater impact on the tropospheric circulation, yet many major SSW signals cannot be observed in the troposphere, such as the major SSW event in the December of. Kodera et al [9] put forward that compared with the horizontal structure of the stratospheric polar vortex during the occurrence of SSW, the tropospheric circulation is more related with the vertical structure of the planetary wave after the SSW onset. With the increase of sample numbers and the utilization of reanalysis data, the evolutions of circulation and wave activity during the onset, development, mature and decay phase of either the minor or major SSW event are revealed in detail [3,17].
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