Large-Scale Precipitation Systems: Essential Elements of the Madden-Julian Oscillation

Possible roles of large-scale precipitation on model simulations of the Madden-Julian Oscillation (MJO) were investigated using the Large-scale Precipitation Tracking (LPT) method. Individual LPT systems and eastward propagating MJO LPT systems were identified in both observations and 25 general circulation model (GCM) simulations. LPT systems show dominant eastward propagation over the Indian Ocean in the observation, whereas LPT systems are too stationary in GCM simulations. The MJO statistical signals in the model simulations are represented by the occurence frequencies of LPT systems with a size of similar to 4-9 x 10(6) km(2) (similar to 20-30 degrees in longitude and latitude) and a strength of similar to 15-18 mm d(-1). Growth rate in size of LPT systems in early stage determines the size of LPT systems, which differentiates the MJO statistical signals among the GCM simulations. Comprehensive diagnostics of MJO simulations in GCMs should include both individual LPT systems as essential elements and the MJO statistical signals.