Impacts of MJO Phase Speeds on Global Circulations in MIROC5 Model Data

The Madden-Julian Oscillation (MJO) is known to propagate eastward with a phase speed around 5 ms^-1, however observations show that the phase speed can vary. This study utilizes the Model for Interdisciplinary Research on Climate (MIROC5) to investigate properties of MJOs with differing phase speeds. The MIROC5 model was chosen for its ability to simulate MJO characteristics, and it provided the data for a zonal momentum budget analysis during the boreal winter. We applied a space-time wavelet transform centered at a given grid point to the model data, which returned a time series characterized by a specified wavenumber and frequency. The time series was then used as a base point for regression against each term in the momentum budget, in order to diagnose the structures associated with MJO signals in the data. Evaluating the results at different phase speeds then provides comparisons between the circulation and convective structures of varying MJOs. While the primary goal of this study is to improve understanding of MJO phase speeds, it could also identify divergence between the model data and reanalysis data, leading to enhanced MJO modeling.