Enhanced stratosphere/troposphere coupling during extreme warm stratospheric events with strong polar-night jet oscillation

• Main Authors: Peters, D.H.W., Schneidereit, A., Karpechko, A.Y.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Basel : MDPI AG 2018
• Subjects: Arctic oscillation; CMIP5; EP-flux divergence; ERA-Interim; Major sudden stratospheric warmings; MPI-ESM-LR; Northern annular mode; Polar-night jet oscillation; Warm stratospheric events; Ozone layer; Troposphere; Era interims; Flux divergences; Polar-night jet; Stratospheric warmings; Climate models; CMIP; coupling; extreme event; jet; stratosphere-troposphere interaction; sudden stratospheric warming; zonal wind; ddc:550; Arctic; polar night
• Online Access: https://oa.tib.eu/renate/handle/123456789/6004; https://doi.org/10.34657/4633

Extreme warm stratospheric events during polar winters from ERA-Interim reanalysis and CMIP5-ESM-LR runs were separated by duration and strength of the polar-night jet oscillation (PJO) using a high statistical confidence level of three standard deviations (strong-PJO events). With a composite analysis, we demonstrate that strong-PJO events show a significantly stronger downward propagating signal in both, northern annular mode (NAM) and zonal mean zonal wind anomaly in the stratosphere in comparison with non-PJO events. The lower stratospheric EP-flux-divergence difference in ERA-Interim was stronger in comparison to long-term CMIP5-ESM-LR runs (by a factor of four). This suggests that stratosphere-troposphere coupling is stronger in ERA-Interim than in CMIP5-ESM-LR. During the 60 days following the central date (CD), the Arctic oscillation signal was more intense during strong-PJO events than during non-PJO events in ERA-Interim data in comparison to CMIP5-ESM-LR runs. During the 15-day phase after CD, strong PJO events had a significant increase in stratospheric ozone, upper tropospheric zonally asymmetric impact, and a regional surface impact in ERA-Interim. Finally, we conclude that the applied high statistical threshold gives a clearer separation of extreme warm stratospheric events into strong-PJO events and non-PJO events including their different downward propagating NAM signal and tropospheric impacts. © 2018 by the authors.