Séminaire
Recent studies have suggested a coherent multidecadal variability between North Atlantic atmospheric blocking frequency and sea-surface temperature. In our study, a potential role of the SST Atlantic Multidecadal Oscillation (AMO) in driving multidecadal blocking variability is examined based on reanalyses and climate model simulations. Spatial and temporal variability of the winter (December-March) atmospheric blocking in the North Atlantic region are examined for 1900-2010 from the NCEP 20th Century Reanalysis (20CR).Extremely consistent interannual variability of the North Atlantic blocking is found across the all 56 individual members as well as the ensemble mean field of 20CR. A statistically significant influence from SST variability associated with the AMO is found when the positive AMO leads by 3-10 years the anomalous dipole blocking pattern with more frequent blockings near Greenland and less near Azores. This anomalous blocking pattern projects well onto the second EOF patternof the winter blocking days and associated with the negative North Atlantic Oscillation (NAO). In addition, this relationship with the AMO is substantially asymmetric and thus only robust in the positive AMO phase. The mechanism of the AMO impact on the blocking will be discussed. Furthermore, a consistent relationship between the AMO and blocking is found in the Community Earth System Model version 1 simulations, despite the strong biases in the simulated jet and blocking variability.
cf@locean-ipsl.upmc.fr