MJO Schematic showing the eastward moving disturbance of clouds, rainfall, winds, and pressure that circles the planet in the tropics and returns to its points of origin in 30 to 60 days, on average. Read the full description on climate.gov.
Zhang, C. (PMEL), A. Adames, B. Khouidar, B. Wang, and D. Yang (2020): Four theories of the Madden-Julian Oscillation. Rev. Geophys., 58(3), e2019RG000685. https://doi.org/10.1029/2019RG000685
The Madden-Julian Oscillation (MJO) is the leading intraseasonal (20–100 days) variability in the tropics. It affects many weather-climate phenomena globally. Tremendous progress has been made in observing, describing, simulating, understanding, and forecasting the MJO since its first documentation in the early 1970s. In particular, theoretical understanding of the MJO has flourished during the past decade or two, with very diverse ideas on the fundamental components of MJO dynamics.
This article, which appeared in an issue of Reviews of Geophysics in late 2020, compares four MJO theories. They are based on very different thinking by focusing on different processes as the central dynamics of the MJO. These processes are: moisture supply by the atmospheric boundary layer, dependence of precipitation on water vapor, energy transport to the MJO from smaller perturbations, and gravity waves. All these theories share common emphases on interactions between atmospheric convection, moisture, and circulation.