MJO Phase Speeds: Using MIROC5 and ERA-Interim to Analyze Impacts on Global Circulation

The Madden-Julian Oscillation (MJO) is often described as having an eastward phase speed of 5 ms^-1, but observations show the phase speed can vary. This study uses data from the Model for Interdisciplinary Research on Climate (MIROC5) and reanalysis data to analyze the impacts that MJO signals characterized by differing phase speeds have on the global circulation. For each data source we calculated a zonal momentum budget during the boreal winter. We then applied a space-time wavelet transform and used that as a base point for regression against each term in the momentum budget. These methods allow us to diagnose structures associated with each phase speed of the MJO signal. Comparing the results between differing phase speeds, as well as the relationships between the MIROC5 model and reanalysis data, allow us to analyze the circulation and convective structures of varying MJOs. While the primary goal of this study is to improve understanding of factors that govern MJO phase speeds, it could also identify divergence between the model data and reanalysis data, leading to more robust and accurate MJO modeling.