Convective Population Associated with the Madden-Julian Oscillation Observed by DYNAMO Experiment and TRMM Satellite

This study is motivated to investigate the role of moisture and convective cloud population in the MJO initiation. The evolution of convective population over the Central Indian Ocaen is composited across the MJO life cycle using both shipborne radar observations during DYANMO and long-term TRMM measurements. The same feature-based analysis methodology is applied to both TRMM and shipborne radar data, so that the DYNAMO convective population could be fairly compared to the longer term climatology. Convective variations among different MJO phases are further connected to the changes of atmospheric moisture and sea surface temperature.

Currently, we adopt the global phase definition (Wheeler and Hendon, 2004) to define MJO phases during DYNAMO. We first construct the DYNAMO composite for vertical moisture profile and population of different convective types. In this way, we can objectively link the convective population and structures (on both the feature scale and radar pixel scale) to environment factors of MJO evolution. Convective types are defined by the size or height of defined convective features (i.e., 20-dBZ radar reflectivity). Preliminary DYNAMO results indicates close relations among changes of atmospheric moisture, SST, and the convective population. For example, the moistening of the lower troposphere from the suppressed stage to inactive pre-onset stage coincides with the growth of shallow or isolated convection. Similarly, significant mid-to-upper troposphere moistening occurs after the onset of the MJO when deep convection (most of them with lightning) bursts out during this stage. Upper troposphere becomes the most moist during the most active phases when MCS population, total rainfall, and fraction of stratiform precipitation also reach their peak. At the later portion of active stage, though large MCSs are still prevailing, convection becomes slightly shallower and stratiform precipitation is dominating. These findings are generally consistent to the conceptual model of MJO initiation and those findings in the literature. The convective structures in different MJO phase will be analyzed in more depth using measurements from both DYNAMO and TRMM satellite.