Observed Evidences of an Impact of Preceding Antarctic Sea Ice and Southern Ocean SST Anomalies on the Antarctic Oscillation

A lagged maximum covariance analysis (MCA) is applied to investigate the linear covariability between monthly sea ice concentration (SIC) and 500-mb geopotential height (Z500) in the Southern Hemisphere (SH). The dominant signal is the atmospheric forcing of SIC anomalies throughout the year, but statistically significant covariances are also found between austral springtime Z500 and prior SIC anomalies up to four months earlier. The MCA pattern is characterized by an Antarctic dipole (ADP)-like pattern in SIC and a positively polarized Antarctic Oscillation (AAO) in Z500. Such long lead-time covariance suggests the forcing of the AAO by persistent ADP-like SIC anomalies. The leading time of SIC anomalies provides an implication for skillful predictability of springtime atmospheric variability.

A lagged maximum covariance analysis (MCA) is also applied to capture the cross-seasonal coupled patterns between the Southern Ocean sea surface temperature (SOSST) and extratropical Z500 anomalies in the SH. Statistically significant results show that the dominant feature of ocean–atmosphere interaction is likely the effect of atmosphere on SOSST anomalies, with a peak occurring when the atmosphere leads the SOSST by 1 month. However, the most eye-capturing phenomenon is that the austral autumn atmospheric signal, characterized by a negatively polarized AAO, is significantly related to the gradual evolution of preceding SOSST anomalies, suggesting that the SOSST anomalies tend to exert an effect on the SH atmospheric circulation. It is also demonstrated that the gradual evolution of changes in SOSST is mainly driven by internal atmospheric variability via surface turbulent heat flux associated with cold or warm advection and that the atmospheric circulationexperiences a change from a typical positive AAO to a negative phase in this process. These findings indicate that such a long lead cross-seasonal covariance could contribute to a successful prediction of AAO-related atmospheric circulation in austral autumn from the perspective of SOSST anomalies, with lead times up to 6–7 months.

References

Wu, Q.*, and X. Zhang, 2011: Observed evidence of an impact of the Antarctic sea ice dipole on the Antarctic Oscillation. Journal of Climate. 24. 4508-4518.

Hu, C., Q. Wu*, et al. 2016: A linkage observed between austral autumn Antarctic Oscillation and preceding SST anomalies. Journal of Climate, 29, 2109-2122.