David Marsico, Physical Sciences Laboratory, National Oceanic and Atmospheric Administration (NOAA)

Modal Interference drives Madden-Julian Oscillation Evolution and Predictability

A data-driven dynamical filter is developed to characterize Madden-Julian Oscillation (MJO) variability by representing tropical variability with non-orthogonal dynamical modes that allow for constructive and destructive interference. We find that two intraseasonal atmospheric modes, an MJO-fast mode with a period of approximately 45 days and an MJO-slow mode with a period of approximately 70 days, alongside El Niño-Southern Oscillation (ENSO) modes that are not entirely removed by temporal filtering, explain nearly all observed Real-time Multivariate MJO (RMM) index-based variability. The fastest growing and most predictable MJO events are initiated primarily by the MJO-fast mode over the Indian Ocean, with subsequent progression across the Maritime Continent resulting from destructive and then constructive interference of the MJO-fast, MJO-slow, and ENSO modes. These events, which we demonstrate can be identified at forecast initialization time by calculating optimal initial conditions that maximize growth over a finite interval, are shown to be forecasts of opportunity in an operational weather forecast model. In such cases, MJO skill is extended by roughly a week compared to all other forecasts.

Passcode for this talk is math-geo