The Increasing Trend of the MJO precipitation from 1979-2023 and its Global Impact on Rainfall Variability

The MJO can be a source of predictability of global high-impact weather and extreme rainfall on sub-seasonal-to-seasonal (S2S) time scales. The MJO diabatic heating results from the MJO-associated precipitation; thus, an increased MJO precipitation can change the Rossby wave source and, therefore, the well-known MJO's downstream impacts. Understanding the MJO convection and precipitation and its effects on global rainfall variability in a changing climate is a complex yet crucial for assessing future high-impact weather risks. This study provides valuable insights into this complex problem by investigating the trend of MJO precipitation using the Large-scale Precipitation Tracking (LPT) method described by Kerns and Chen (2016, 2020) with ERA5 data.

Over the period 1979-2023, analysis of 455 MJO precipitation events reveals a robust positive trend in annual MJO precipitation observed over the Indian-Pacific warm pool, primarily driven by an increase in the frequency of MJO precipitation events, with an upward trend of 2-4 events per year or 1-2 days per year². There has been an increase in MJO events initiating over the Indian Ocean compared to the western Pacific during 2001-2023 relative to 1979-2000. Additionally, over the last 2 decades, more MJO precipitation events have propagated further northward and southward, reaching the tropical northwestern Pacific and the South Pacific Convergence Zone. Despite these shifts in the MJO precipitation, no significant trends or changes were detected in the intrinsic MJO duration and propagation speed. A simple linear regression analysis indicates that MJO precipitation over the tropical western Pacific accounts for 30-50% of the interannual precipitation variability in Southeast Asia, tropical Africa, South America, and the western United States. The implications of these results for high-impact weather, particularly in the west of US, are also discussed.