Convective characteristics of tropical synoptic-scale disturbances and their contributions to the ITCZ are examined by applying a cloud pattern tracking method to a 20-year daily OLR dataset. This method isolates and tracks deep convective signals which propagate zonally. Time-mean OLR is decomposed into five components: westward-moving, eastward-moving, and random (non-propagating) deep convective clouds, non-deep convective clouds, and clear-sky background.

Contributions of the four cloud components to the total time-mean ITCZ are quantitatively, although crudely, estimated. The results indicate that westward-propagating synoptic-scale disturbances are an important component of the ITCZ. 20-40 percent of the total deep convection (10-20 percent of total cloud) within the ITCZ can be ascribed to these disturbances. However, the random deep convection is found to be mainly responsible for the spatial (and even temporal) variations of the ITCZ.