The Role of MJO Propagation, Lifetime, and Intensity on Modulating the Temporal Evolution of the MJO Extratropical Response

The Madden-Julian Oscillation (MJO) is the dominant mode of tropical intraseasonal variability. Many studies have found that the MJO has significant impacts on extratropical weather. Since the MJO can act as a tropical heat source that excites Rossby waves, midlatitude weather is modulated by the MJO due to the Rossby waves that propagate into the midlatitude and modulate the midlatitude circulation. Heat sources of individual MJO events are different since each event has different eastward propagation speed, lifetime, intensity, and structure. The background flow is also different for each event. These result in different Rossby waves and different extratropical response for each MJO event. In this study, the role of MJO propagation speed, lifetime, and intensity on modulating the structure and temporal evolution of the MJO extratropical response is systematically explored by using an idealized general circulation model. By adding the MJO-associated heating into the general circulation model as an external forcing, the extratropical response in the Reanalysis is captured reasonably by the model. However, large ensemble model simulations show that the response in the Reanalysis is not robust. Experiments with MJO events of different propagation speed, lifetime, and intensity show that to excite a strong extratropical response, the MJO has to propagate through specific phases (Phases 1–3 and 5–7). The intensity, timing, and duration of the extratropical response strongly depend on when the MJO is initiated and when the MJO decays. The extratropical impacts of slow- and fast-propagating MJO also have significant differences, especially on intensity and duration.