Role of Atlantic Multidecadal Oscillation (AMO) in winter intraseasonal variability over Ural

The modulation of winter intraseasonal variability (ISV) by the Atlantic Multidecadal Oscillation (AMO) is investigated through three sets of reanalysis data and numerical experiments with the NCEP's atmospheric general circulation model (AGCM). Results show that the positive phase of the AMO tends to intensify ISV activity over the northern Atlantic and shift ISV activity over the Ural Mountains toward the south, causing weakened ISV activity at 200 hPa in the north to the Urals and intensified activity in the south. The modulation of ISV activity by the AMO over the Urals is then explored through comparison of the composite evolution of anomalous ISV cases for the different AMO phases. Fewer ISV cases are found in the AMO positive phase than the negative phase, but no substantial difference in the temporal evolution of anomalous ISV events between the two opposing phases of the AMO. Thus, the AMO exerts its modulation through influencing the occurrence frequency of ISV events, rather than their development or evolution processes. A similar result is seen in the AGCM sensitivity experiments.