The role of North Atlantic-European weather regimes in the surface impact of sudden stratospheric warming events

• Main Authors: Domeisen, Daniela I. V., Grams, Christian M., Papritz, Lukas
• Format: Text
• Language: English
• Published: 2020
• Subjects: Greenland; North Atlantic
• Online Access: https://doi.org/10.5194/wcd-2019-16; https://wcd.copernicus.org/preprints/wcd-2019-16/

Sudden stratospheric warming (SSW) events can significantly impact tropospheric weather for a period of several weeks, in particular over the North Atlantic and Europe. However, not all SSW events exhibit the same tropospheric response, if any, and it remains an open question what determines the existence, location, timing, and strength of the downward impact. We here explore the role of the state of the tropospheric flow in the North Atlantic region at the onset of SSW events for determining the subsequent surface impact. A refined definition of seven North Atlantic tropospheric weather regimes indicates the Greenland blocking (GL) and Atlantic Trough (AT) regimes as the most frequent large-scale patterns following the weeks after an SSW. While GL is dominated by high pressure over Greenland, AT is dominated by a southeastward shifted storm track in the North Atlantic. We find that a blocking situation over western Europe and the North Sea (European Blocking) at the time of the SSW onset favours the GL response and the associated cold conditions over Europe. In contrast, an AT response and mild conditions are more likely if GL occurs already at SSW onset. For the remaining tropospheric flow regimes during SSW onset, we find no clear response. The results indicate that the tropospheric impact of SSW events critically depends on the tropospheric state during the onset of the SSW, which could provide crucial guidance for subseasonal prediction.