Climatology of tropical intraseasonal convective anomalies: 1979-2002

Tropical intraseasonal convective anomalies (TICA) have a central role in subseasonal changes in the coupled ocean-atmosphere system, but the climatology of TICA events has not been properly documented. This study exploits 24 years of outgoing longwave radiation (OLR) data and a tracking algorithm to develop a climatology of eastward propagating TICA events. Three distinct types of TICA occurrences are documented according to their propagation characteristics. The first type (IND) is characterized by events that propagate in the Indian Ocean without significant influence in the western Pacific Ocean. The second and third types are associated with occurrences of the Madden-Julian oscillation during boreal winters (MJO) and summers (ISO). The frequency of occurrence of TICA events is highest in April-June and October-December and lowest in July-September. An analysis of the spatial and temporal characteristics reveals that MJO events tend to have the longest life cycle, greatest intensity, and largest variability inside the contiguous region of OLR anomaly. Given the data record of 24 years, the analysis of interannual occurrences of TICA events does not show statistically significant differences among events that occur in different phases of the El Nino-Southern Oscillation (ENSO). A procedure is developed to identify major MJO events and estimate their frequency of occurrence in the data record.