Abstract
Using the historical simulation from the CESM1-WACCM coupled model and based on the JRA55 and NCEP/NCAR reanalyses, the general statistical characteristics of the major sudden stratospheric warmings (SSWs) in this stratosphere-resolving model are assessed. The statistical and diagnostic results show that CESM1-WACCM can successfully reproduce the frequency of SSW events. As in the JRA55 and NCEP/NCAR reanalyses, five or six SSW events, on average, occur in a model decade. The seasonal distribution of SSWs is also well simulated with the highest frequency in January (35%). The unprecedented low SSW frequency observed in 1990s from the two reanalyses is also identified in a model decade (1930s). In addition, the overestimated duration of SSW events in the earlier WACCM version is not identified in CESM1-WACCM when compared with the two reanalyses. The model can well reproduce the downward propagation of the stratospheric anomaly signals (i.e., zonal wind, height, temperature) following SSWs. Both the modelling and observational evidences indicate that SSWs are proceeded by the positive Pacific–North America (PNA) and negative Western Pacific (WP) pattern. The negative North Atlantic Oscillation (NAO) develops throughout the SSW life cycle, which is successfully modeled. A cold Eurasian continent–warm North American continent pattern is observed before SSWs at 850 h Pa, while the two continents are anomalously cold after SSWs in both the reanalyses and the model.
Highlights
Major sudden stratospheric warming (SSW) is a radical and rapid warming phenomenon mainly observed in the Arctic stratosphere during wintertime except the September 2002 stratospheric warmings (SSWs) overAntarctic [1,2]
Vortex-displacement SSW events are related to the anomalous amplification of wavenumber-1 planetary waves while vortex-splitting SSW events are caused by the anomalous amplification of wavenumber-two planetary waves [6,19,21]
The main findings in the study are as follow
Summary
Major sudden stratospheric warming (SSW) is a radical and rapid warming phenomenon mainly observed in the Arctic stratosphere during wintertime except the September 2002 SSW over. As various observational techniques have been used to detect the stratosphere [18], and various aspects of SSW events (e.g., dynamics, impacts, modelling, and predictions) are explored in literature [8,12,13,15], the understanding about SSW events has been improving gradually. SSW events, is helpful for improving weather forecasts and climate prediction, much effort has been put into developing stratosphere-resolving models [35].
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