Gravity-Wave Dynamics of the Hierarchical Structure of Super Cloud Clusters

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  • Numaguti Atusi
    Center for Climate System Research, University of Tokyo Present affiliation: Graduate School of Environmental Earth Science, Hokkaido University
  • Hayashi Yoshikazu
    Geophysical Fluid Dynamics Laboratory/NOAA, Princeton University

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Other Title
  • スーパークラウドクラスターの階層構造にかかわる重力波の力学

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The hierarchical structures of eastward-moving tropical super cloud clusters (SCC) and embedded westward-moving quasi-periodic cloud clusters (QPCC) are successfully simulated by a simple longitude-height two-dimensional model with simple moist processes.<br>The model results clearly show a life cycle of cloud activity. The cloud area starts as a low-level shallow cloud, develops into deep convection, becomes a top-heavy cloud, and decays. Gravity-wave packets are excited by the growth and decay of this cloud and propagate both eastward and westward. The westward-propagating gravity waves are coupled with cloud activity and form westward-moving QPCC. On the other hand, the eastward propagating waves are not immediately coupled with deep convective activity. A deep convective cloud develops only after the low and middle troposphere is sufficiently moistened and cooled. The quasi-periodic emergence of the new convective cloud to the east results in the eastward movement of the envelope of QPCC, forming an eastward-moving SCC.<br>It is suggested that the excitation of gravity waves of two vertical modes by grow and decay of the heating with top-heavy vertical profile is essential to this hierarchical structure. Especially, the net upward parcel displacement due to the shallow gravity-wave cell have a important role in the generation of new QPCC. Although both eastward-moving SCC and westward-moving SCC are possible in a non-rotating atmosphere with no external origins of east-west asymmetry, eastward-moving SCC can be selected under existence of some external asymmetry, such as the beta effect, mean zonal wind shear, or asymmetry of latent heat flux due to WISHE (wind-induced surface heat exchange) effect.

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