Statistical Characteristics of Major Sudden Stratospheric Warming Events in CESM1-WACCM: A Comparison with the JRA55 and NCEP/NCAR Reanalyses

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.

Multidecadal Changes in the Influence of the Arctic Oscillation on the East Asian Surface Air Temperature in Boreal Winter

“…Gong et al [29] further indicated that the varied North Pacific center of AO may be related to the oscillating coupling of dominant atmospheric circulation variability between the North Pacific and North Atlantic. Moreover, some other studies reported that the intensity of Pacific center of the AO pattern can also be modulated by the stratospheric polar vortex [34][35][36][37][38]. It is strong and clear when the stratospheric polar vortex is strong, and it is weak when the stratospheric polar vortex is weak [34].…”

The effect of interactive ozone chemistry on weak and strong stratospheric polar vortex events

“…We identify SSWs in the model output following the definition in Charlton and Polvani (2007a) (see the corrigendum Charlton-Perez and Polvani, 2011). We define an SSW as a reversal of zonal mean zonal wind at 60 • N and 10 hPa from westerly to easterly from November through March, with the central date being the first day of easterly zonal mean zonal winds.…”

“…Different methods have been used in the literature (Limpasuvan et al, 2004;Tripathi et al, 2015;Scaife et al, 2016;Beerli and Grams, 2019). We here follow the definition used in Scaife et al (2016) and Smith et al (2018), which is designed to be analogous to the SSW definition of Charlton and Polvani (2007a) and to result in a similar number of events in reanalysis. We define an SPV as zonal mean zonal wind at 60 • N and 10 hPa reaching 48 m s −1 or higher (westerly) from November through March, with the central date being the first day of zonal mean zonal winds above 48 m s −1 .…”

Features and Possible Causes of the Extreme Precipitation Anomaly in China During Winter 2019/2020

“…This is mainly because the anomalous activity of the polar vortex propagates downward and cooperates with the blocking high, the East Asian trough, the East Asian winter monsoon and other circulation systems in the lower atmosphere, thus having an important influence on the weather and climate changes in the troposphere (Baldwin and Dunkerton, 1999;Kodera et al, 2000;Baldwin and Dunkerton, 2001;Zhou et al, 2002;. The downward propagation of polar vortex anomaly leads to the anomalies of the Arctic Oscillation (AO) and the East Asian winter monsoon (Wang and Chen, 2010;Cao et al, 2019;Liu et al, 2019). When the AO is strong, the East Asian trough and the Siberian high are always weak, which results in the weak East Asian Winter Monsoon and the anticyclone anomaly in Northeast China, which is conducive to the water vapor transport from the Northwest Pacific to China, and then causes more precipitation in the central and eastern regions of China (Shuai et al, 2010).…”