Based on the NCEP–NCAR reanalysis dataset covering 1958–2012, this paper demonstrates a statistically significant relationship between the occurrence of major stratospheric sudden warming events (SSWs) in midwinter and the seasonal timing of stratospheric final warming events (SFWs) in spring. Specifically, early spring SFWs that on average occur in early March tend to be preceded by non-SSW winters, while late spring SFWs that on average take place up until early May are mostly preceded by SSW events in midwinter. Though the occurrence (absence) of SSW events in midwinter may not always be followed by late (early) SFWs in spring, there is a much higher (lower) probability of late SFWs than early SFWs in spring after SSW (non-SSW) winters, particularly when the winter SSWs occur no earlier than early January or in the period from late January to early February. Diagnosis shows that, corresponding to an SSW (non-SSW) winter and the following late (early)-SFW spring, intensity of planetary wave activity in the stratosphere tends to evolve out of phase from midwinter to the following spring, being anomalously stronger (weaker) in winter and anomalously weaker (stronger) in spring. Furthermore, the strengthening of the western Eurasian high, which appears during early to mid-January in late-SFW years but does not appear until late February to mid-March in early-SFW years, always precedes the strengthening of planetary wave activity in the stratosphere and thus acts as a tropospheric precursor to the seasonal timing of SFWs.

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Previous studies have reported that the predictive limit of stratospheric sudden warming (SSW) events in the Beijing Climate Center forecast system (BCC_CSM) is shorter than 2 weeks. This study continues to analyze the general characteristics of this model in forecasting SSWs and carries out a trial of error corrections. The ratio of the ensemble members that forecast the zonal wind reversal with a 5-day delay allowed (hit ratio) is higher for SSW events with a small decrease in the zonal mean zonal winds (moderate SSWs) than for events with a large decrease in the zonal mean zonal winds (radical SSWs) in hindcasts initialized around 1 (D-7) and 2 (D-14) weeks in advance. The underestimated cumulative eddy heat flux associated with weak wave activities accounts for the weaker-than-observed deceleration of westerlies. The preexisting extratropical wave patterns are satisfactorily forecast in D-14 for most (9/12) cases, and the wave phase bias is reasonably small for those cases. After the climatology bias is deducted from the hindcasts, an increase in the hit ratio can be identified for moderate SSW events as the evolutions of zonal winds are improved. Following the error correction by remapping the zonal wind probability distribution function in the forecast system to the reanalysis, the SSW hit ratios increase in the D-7 (43% to 57%) and/or D-14 (11% to 21%) initializations. Based on the composite result, this error correction method robustly improves the hit ratio not only for both radical SSWs and moderate SSWs but also for both polar vortex split SSWs and polar vortex displacement SSWs. The best error correction method might propel the prediction limit of SSW events to around 2 weeks.

This study reports a mass budget analysis on the year-to-year variability of the winter [December-February (DJF)]-mean Arctic (608-908N) surface pressure (Ps) using the 33-yr daily Interim ECMWF Re-Analysis (ERA-Interim; 1979-2011. The analysis reveals that the interannual variability of mass transported into the Arctic region in upper layers plays a dominant role in the interannual variability of the winter-mean Arctic Ps anomalies. When winter-mean Arctic Ps anomalies are positive, both the transport of mass into the Arctic region in the upper layer by the poleward branch of meridional mass circulation and the transport of mass out of the Arctic region in the lower layer by the equatorward branch tend to strengthen and vice versa. In the earlier winter months from November to December, mass anomalies transported in overwhelm those transported out, explaining the mass source of winter-mean Arctic Ps anomalies. The coupling between adiabatic mass transport by meridional mass circulation and diabatic processes explains why, over the Arctic region, yearly variations of winter Ps are positively correlated with mass anomalies in the upper layer (above 290 K) and near the surface (below 260 K) but negatively correlated with mass anomalies in the middle and lower troposphere (between 260 and 290 K). In winters with positive (negative) Arctic Ps anomalies, wave activity, particularly in wavenumbers 1 and 2, is stronger (weaker) in the extratropical stratosphere in the earlier winter months from November to January, coincident with the interannual variability of the meridional mass circulation intensity in winter seasons.