Is the MJO Signature a Continuum? The Statistics of Global Observations of Multi-day Cloud Systems

Geosynchronous infrared satellite tracking of convective clusters (T cloud < 245 K) was used to capture global lifecycle statistics of clouds in 4 zones: Tropical land and ocean, and Mid-latitude land and ocean. The ISCCP tracking dataset from 1984-2006 was used for this study, the largest dataset of its kind. Only systems with lifetimes > 1 day that were moving predominantly eastwards or westwards were retained. The lifecycle variables of lifetime, maximum area, and minimum cloud top temperature were compared to each other and to the meridional propagation velocity. Velocity distributions were mono-modal with tails slightly skewed in the direction of the prevailing wind, shifting to an almost pure eastwards distribution in the mid-latitudes, and a nearly centered distribution with a westward bias in the tropics. No distinct clustering corresponding to the MJO signal was evident; instead the upstream propogation signature seems to exist as part of a continuum.