Probabilistic Predictability of the MJO Journal of the Atmospheric Sciences

Studies of natural or intrinsic MJO predictability have typically estimated its limit at a fixed, single lead time. The interpretation of such a predictability limit has remained ambiguous. This study introduces a concept of probabilistic predictability, which defines MJO predictability in terms of the expected probability of predictable MJO events across different lead times. In this concept, the source of MJO predictability is the observed repeatable patterns of the MJO. The predictability is limited because of unknown external environmental influences. Probabilistic predictability is measured by the observed natural spread or dispersion of MJO events that would occur even if their initial states were identical. The applicability of this concept is illustrated in two examples: the longitudinal position and amplitude of the MJO. The results clarify the meaning of the MJO predictability limit at a single lead time. They demonstrate how MJO predictability varies with lead time and how it depends on the tolerance for forecast errors.