Poleward transport variability in the Northern Hemisphere during final stratospheric warmings simulated by CESM(WACCM)

Abstract

Observational studies of Arctic stratospheric final warmings have shown that tropical/subtropical air masses can be advected to high latitudes and remain confined within a long‐lived “frozen‐in” anticyclone (FrIAC) for several months. It was suggested that the frequency of FrIACs may have increased since 2000 and that their interannual variability may be modulated by (i) the occurrence of major stratospheric warmings (mSSWs) in the preceding winter and (ii) the phase of the quasi‐biennial oscillation (QBO). In this study, we tested these observational‐based hypotheses for the first time using a chemistry climate model. Three 145 year sensitivity experiments were performed with the National Center of Atmospheric Research's Community Earth System Model (CESM): one control experiment including only natural variability, one with an extreme greenhouse gas emission scenario, and one without the QBO in the tropical stratosphere. In comparison with reanalysis, the model simulates a realistic frequency and characteristics of FrIACs, which occur under an abrupt and early winter‐to‐summer stratospheric circulation transition, driven by enhanced planetary wave activity. Furthermore, the model results support the suggestion that the development of FrIACs is favored by an easterly QBO in the middle stratosphere and by the absence of mSSWs during the preceding winter. The lower stratospheric persistence of background dynamical state anomalies induced by deep mSSWs leads to less favorable conditions for planetary waves to enter the high‐latitude stratosphere in April, which in turn decreases the probability of FrIAC development. Our model results do not suggest that climate change conditions (RCP8.5 scenario) influence FrIAC occurrences.

The major stratospheric final warming in 2016: dispersal of vortex air and termination of Arctic chemical ozone loss

“…Vort calculated for nitric acid trihydrate PSCs and averaged over a winter) is a diagnostic commonly used to indicate the overall potential for polar processing and ozone loss (e.g., Rex et al, 2004;Tilmes et al, 2006). The polar processing potential in 2015/16 estimated using this diagnostic (Fig.…”

Quasi 10‐ and 16‐Day Wave Activities Observed Through Meteor Radar and MST Radar During Stratospheric Final Warming in 2015 Spring

“…SFWOD is influenced not only by preceding SSW events but also by PW activities, and PWs are still a substantially driving source of SFW (Black & McDaniel, 2007a). In winter, a long-lasting westward flow induced by deep major SSWs is not favorable for PW propagation, which causes a late onset of SFW (Thiéblemont et al, 2016). Earlier SFW is primarily initiated by strong PWs, and polar circulation evolution is more similar to that during major SSW (Black et al, 2006).…”

On the dynamics of the spring seasonal transition in the two hemispheric high-latitude stratosphere

“…8a), to be effectively influenced by the increasing solar radiation. In some cases the polar vortex is re-established in the upper stratosphere after mid-winter SSW (Thi eblemont et al, 2016), but the vertical propagation of planetary wave would still be prohibited by the prolonged reversed easterlies in the lower stratosphere, and the upper stratosphere is comparatively cold and dominated by stronger westerlies. In this case, the synchronous transition driven by solar radiation may easily occur.…”