Toward Understanding MJO Diversity

The Madden-Julian Oscillation (MJO) is one of the dominant climate variability in the tropics. The MJO strongly modulates tropical cyclone activity on its way eastward and affects high-latitude weather through tele-connection, thus serving as a key agent for subseasonal-to-seasonal (S2S) forecasting. However, with more than 40-years’ efforts, present-day weather and climate models still have tremendous problems to simulate the MJO and its impacts, thus severely hindering the progress of S2S forecasting. The slow progress in modeling and predicting the MJO and its impacts reflects our lack of comprehensive understanding of the nature of the MJO, partly due to our treatment of the MJO simply as a canonical mode depicted in Madden-Julian’s two seminary papers (1971, 1972).

In fact, the MJO represents a quasi-oscillating mode with a broad wavenumber-frequency band, manifesting as a phenomenon with diverse nature (referred as MJO diversity here): for example, primary versus successive, propagating versus non-propagating, and coupled versus uncoupled etc. The author likes to argue that in order to accelerate the progress in modeling and predicting the MJO and its impacts, it is time to pay more attention to the diverse nature of the MJO and to go beyond the canonical picture depicted in Madden and Julian (1971, 1972). Specially, this presentation will try to answer following two questions: (i), what are the possible causes of the MJO diversity in nature and models and, (ii), to what degree those different flavors of the MJO are interrelated?