Cloud Structure Under Suppressed Conditions in DYNAMO

During the DYNAMO field campaign, the S-Pol radar observed three multi-week active periods of the MJO, characterized by deep, organized convection and enhanced precipitation. Between these periods, shallower convection populated the domain under suppressed conditions, with early echo exhibiting distinct polarimetric signatures detected by S-Pol. Early in these suppressed periods, shallow clouds organized into lines oriented parallel to the flow, attributed to convectively driven rolls in the boundary layer. As the shallow clouds started to precipitate, these lines were no longer observed as cold pools began to dominate the scene. This development of and the interaction between cold pools led to new convective initiation, which allowed for deeper, more numerous convective cells as the MJO phase neared the active period. This study describes this transition and highlights the importance of boundary layer features during suppressed conditions in understanding the build up of the active MJO period.