Multi-scale Organization of Convection in a Global Numerical Simulation of the December 2006 MJO Event Using Explicit Moist Processes

Multi-scale convective organization in a Madden-Julian Oscillation (MJO) event that occurred during December 2006 and January 2007 was studied by global numerical experiments using explicit moist physics. The simulations successfully reproduced the eastward-propagating (similar to 5 m s(-1)) convective envelope of the MJO with a zonal scale of 5000-10,000 km, which included eastward-propagating (10-15 m s(-1)) disturbances (EPDs) and westward-propagating cloud clusters (CCs) with zonal scales of 1000-2000 km and O (100 km), respectively. The simulated EPDs were composed of CCs, with new clusters growing to the east of older ones. When the large-scale circulation associated with the MJO intensified the EPDs formed well-organized squall-type clusters (rainbands). The dynamical structure of the simulated EPDs was reminiscent of moist Kelvin waves. Relevance of westward-propagating wave disturbances including cross-equatorial flow to convective organization in the EPDs was also suggested.