Intraseasonal Variability in the Tropics-Extratropics System: Internal Dynamics versus External Influences

Idealized numerical experiments are designed to assess the role of tropics-extratropics (TE) interactions on the intraseasonal variability in the tropics (i.e., MJO) and extratropics. Previous studies have concentrated on assessing the influence of MJO on the extratropical variability or vice versa, instead of having a unified approach to address the origin of intraseasonal variability in the TE system.

First, we document the MJO structure and its propagation under suppressed TE interactions. Seasonal variability and the relative roles of the northern and the southern extratropics are also documented. Second, using the same set of numerical experiments, we document the structure of intraseasonal variability in the extratropics under suppressed TE interactions. The relative changes in the intraseasonal variability in the tropics and extratropics under suppressed TE interactions from that of control simulation provide insight about the origin of intraseasonal variability. The results indicate that TE interactions might be more important in the southern hemisphere than that in the northern hemisphere for the intraseasonal variability in the TE system. Implications of the results will be discussed in the meeting.