A Three-Type classification of Sudden Stratospheric Warming

• Main Author: 최혜선
• Other Authors: 최우갑, 자연과학대학 지구환경과학부, 대기과학
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: 서울대학교 대학원 2020
• Subjects: 550; North Atlantic; North Atlantic oscillation
• Online Access: https://hdl.handle.net/10371/167856; http://dcollection.snu.ac.kr/common/orgView/000000159659

학위논문(박사)--서울대학교 대학원 :자연과학대학 지구환경과학부,2020. 2. 최우갑. In existing literature, sudden stratospheric warming (SSW) events have been typically defined as displacement or split types. Detailed reexamination of SSW evolution has revealed that an SSW event often alters its type before and after the central day of the warming event. On the basis of this observation, we objectively define three types of SSW using wave amplitude: displacement–displacement (DD) type, displacement–split (DS) type, and split–split (SS) type. The geopotential height (GPH) amplitude of zonal wavenumbers 1 and 2 averaged over 55o–65oN at 10 hPa was used as a criterion for the classification. If the amplitude of zonal wavenumber 1 is larger (smaller) than that of wavenumber 2 before and after the central day of SSW, the event is regarded as a DD (SS) type. If the amplitude of zonal wavenumber 1 is larger than that of wavenumber 2 before the central day but is smaller after that day, the event is regarded as a DS type. The above classification algorithm has been applied to both reanalysis data and model results. We observe that conventional split-type SSW events identified by previous studies can be categorized as either DS- or SS type events, each type of which exhibits different evolution characteristics. In particular, they are distinctively different during the prewarming period. In the SS type, the characteristics of the conventional split type are more obvious, and the features that differ from those of the DD type are the most robust. The model results generally resemble the reanalysis data, particularly in the DD cases. Here, we also show that existence of a type-transition during the course of the SSW life cycle can be attributable to the condition of North Atlantic Oscillation (NAO) preceding before onset: Positive NAO favors SSW of DD type with no transition while negative NAO favors the DS type. We show that, in positive NAO precondition, vertical flux of wave activity immediately before onset is mostly contributed only by wavenumber 1 ...