Current Research

MJO’s Forecast Performance with Different Initial Phases in the UFS

Date: 2024

As depicted in Figure a, the MJO composites initialized from phases 1&8 and phases 6&7 exhibit relatively longer durations, with RMM amplitudes exceeding 0.5 for 35 days or longer, compared to the composited MJO initialized from phases 2&3 and phases 4&5. Moreover, the former two types of MJO propagate over longer distances than the latter two, indicating potentially important implications for prediction over expanded regions of the tropics. Despite the UFS’ general ability to reforecast the evolution of the MJO in the phase-space diagram (Figure b), a common deficiency in the ensemble mean of all four groups of initial phases is that the MJO events move slower with slower phase transitions, and decay more quickly than observed. For instance, in MJO composite predictions initialized from phase 1&8, the convective center is positioned between phases 2 and 3 at day 15, while the observed MJO has transitioned to the center of phase 3 by that time. Similarly, the forecasts of MJO events from initial phases 6&7 are situated in phase 8 on day 15, while the observed MJO has progressed to phase 1, accompanied by a higher RMM amplitude. It is worth noting that the simulated MJO events in the UFS generally present weaker propagation signals after 15-day than observed, especially for MJO events starting from phases 2&3 and phases 6&7. We note however that Prototype 8, the most recent version, displays much clearer propagation signals after 15-days and characteristics that are closer to observations, indicating a significant improvement in the MJO’s propagation.