The Analysis of DYNAMO Precipitation in TRMM and in Coupled COAMPS Using the EOF Based “Mesoscale MJO Index”

We develop the method for isolating and assessing features that are essential to MJO, but can be observed on the regional scale. The majority of methods that diagnose the behavior of MJO in large scale dynamical models are based on global characteristics of the system and are not appropriate for a short term forecast with a limited area model. On the other hand, the MJO is a multi-scale phenomenon and the development of convection on smaller scales is important for organization of the large scale envelope. Therefore the metrics describing the evolution of MJO in regional models are needed. To achieve this goal we constructed an index based on EOF of regional precipitation anomaly using the TRMM precipitation. This approach allows us to determine which precipitation patterns are essential for MJO a how well are these patterns predicted in a limited area model. We identified first two modes of eastward moving precipitation . Each of the modes explains about 8% of the variance. The first mode illustrates the Indian Ocean /Western Pacific seesaw, with the maximum precipitation near the DYNAMO IOP area; the second shows the convective maximum near west of Sumatra that develops before MJO crosses the Maritime continent. We analyze the behavior of this “mesoscale MJO index” during the field phase of DYNAMO in TRMM observations and in coupled COAMPS forecasts.