MJO Diversity Across Timescales: Observations and Model Simulations

Madden-Julian oscillation (MJO) is the dominant mode of intraseasonal (30–60-day) variability in the tropics and an important predictability source on subseasonal-to-seasonal (S2S) timescales. A canonical MJO consists of large-scale convective systems that propagate eastward across the Indo-Pacific warm pool at speeds of about 5 m s⁻¹. However, individual MJO events exhibit distinct variations in propagation characteristics, including zonal extent and propagation speed. Understanding these diverse MJO propagation patterns and achieving accurate model simulation are crucial for enhancing S2S predictability. To understand the underlying mechanisms of this variation, recent studies have classified MJO events into four distinct types: standing, jumping, slow-propagating, and fast-propagating MJOs. This classification is termed the "MJO diversity" concept that comprehensively considers both zonal extent and propagation speed variations. This study investigates the underlying mechanisms of MJO diversity across various timescales using observational and model datasets. In particular, we examine MJO diversity on both interannual and inter-seasonal timescales. On interannual timescales, ENSO-like moisture distributions control MJO propagation characteristics. On inter-seasonal timescales, the Australian monsoon-induced background moisture variations control MJO diversity. In this talk, we will explore how these moisture distributions control MJO propagation diversity on different timescales.