Early‐to-late winter 20th century North Atlantic multidecadal atmospheric variability in observations, CMIP5 and CMIP6

• Published in: Geophysical Research Letters
• Main Author: Bracegirdle, T.J.
• Format: Article in Journal/Newspaper
• Language: English
• Published: American Geophysical Union 2022
• Subjects: North Atlantic
• Online Access: http://nora.nerc.ac.uk/id/eprint/532678/; https://nora.nerc.ac.uk/id/eprint/532678/1/Geophysical%20Research%20Letters%20-%202022%20-%20Bracegirdle%20-%20Early%E2%80%90to%E2%80%90Late%20Winter%2020th%20Century%20North%20Atlantic%20Multidecadal.pdf; https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL098212

The strong multi-decadal variability in North Atlantic (NA) winter atmospheric circulation is poorly understood and appears too weak in climate models. Recent research has shown peak atmospheric multi-decadal variability over the NA in late winter, particularly March, linked to Atlantic multi-decadal variability (AMV) of the ocean. Here a range of NA atmospheric circulation indices are assessed to provide a comprehensive picture of early-to-late winter low-frequency variability and its representation in the latest generation of climate models (Coupled Model Intercomparison Project Phase 6 (CMIP6)). As found for CMIP5, CMIP6 models exhibit too-weak multi-decadal NA atmospheric variability compared to reanalysis data over the period 1862-2005. Consistent with previous research, the eastern part of the NA westerly jet (U700NA) exhibits peak low-frequency variability in March. However, for NA-wide jet speed and the NAO, low-frequency variability and model-reanalysis discrepancies are strongest in January and February, associated with too-weak NA ocean-atmosphere linkages.