The atmospheric pathway between Atlantic Multidecadal Variability and European summer in a climate model

The Atlantic Multidecadal Variability (AMV) is shown to affect the central to eastern (C-E) European summer climate through an associated atmospheric baroclinic response called North-Atlantic-European East West (NEW) mode as demonstrated in the Twentieth Century Reanalysis (20CRv2). Here, using the atmospheric model ECHAM6.3, we perform sensitivity experiments  with prescribed sea surface temperature (SST) anomalies that are representative of the observed positive and the negative AMV phases and investigate the model response to the observed AMV pattern for European summer climate. The results from the experiments reveal that in the negative phase of AMV, the North-Atlantic-European (NAE) climate is mainly governed by the extra-tropical branch of the AMV through a baroclinic-like response. This response brings negative surface air temperature (SAT) anomalies over C-E Europe. The response and its influence are similar to what is found in the 20CRv2. In contrast, in the positive phase of the AMV, the NAE climate is mainly influenced by the tropical branch of the AMV. A stationary Rossby wave response excited in the tropics is associated with negative SAT anomalies over C-E Europe, which is opposite to what is found in the 20CRv2. Hence, the results demonstrate that ECHAM6.3 can simulate the observed baroclinic response, but only in the negative phase of the AMV. For the positive phase, in agreement with the previous findings, the model is very sensitive to the tropical branch of the AMV.