Shallow cloud structure and organization under suppressed conditions in AMIE/DYNAMO

Description

Three multi-week active periods of the Madden-Julian Oscillation (MJO) were observed during the AMIE/DYNAMO 2011-2012 field campaign in the Indian Ocean. Between these periods, suppressed conditions were characterized by generally shallow convection that could be detected by the sensitive S-PolKa radar, with early echo exhibiting distinct polarimetric signatures, in addition to the details about nonprecipitating clouds available from the ARM KAZR radar. Using the radar data in the context of the sounding observations, the organization and structure of the boundary clouds during the build-up phase of the MJO can be described and related to the environmental conditions under this suppressed scenario. The small nonprecipitating clouds often organized into lines parallel to the boundary layer wind before beginning to precipitate. Once precipitation was produced, the development of and interaction between cold pools led to new convective initiation, which occasionally resulted in deeper convection as the MJO phase neared the active period. This study documents these nonprecipitating structures and describes the transition from shallow to deeper convection as the environmental conditions evolved.