AMIE/DYNAMO observations of clouds during the transition from suppressed to active MJO conditions
Authors
Robert Houze — University of Washington
Angela K Rowe — University of Wisconsin
Category
MJO: Madden-Julian Oscillation
Description
A schematic showing (1) the organization of nonprecipitating clouds, (b) the production of cold pools from precipitating cells, (c) the secondary initiation of deeper convection along intersecting cold pool boundaries, and (d) the eventual upscale growth to MCSs overnight during the later suppressed periods.
During the AMIE/DYNAMO field campaign in the Indian Ocean, the sensitivities of the KAZR and S-Pol radars allowed for investigation of the initiation and organization of both nonprecipitating and precipitating clouds. Early in the suppressed MJO periods, shallow nonprecipitating clouds organized along inferred horizontal convective boundary layer rolls during the morning hours. Once some of the clouds began to precipitate, small cold pools formed, and, by afternoon, the cold pools dominated the scene, serving as focal points for new convective initiation. Over time, the atmosphere moistened, as characterized by the AMIE sounding network, and deeper, more numerous clusters of convective cells were observed along intersecting cold pool boundaries. Increased cloud depth and spatial organization were noted in the AMIE/DYNAMO observations as the suppressed periods transitioned into active MJO phases, including a secondary peak in convection observed overnight reflecting upscale growth into MCSs during the latter part of the suppressed periods. This study therefore emphasizes the need for models to accurately represent the timing and organization of boundary features that produce the initial nonprecipitating clouds.
