13.4 Horizontal scale selection associated with mesoscale gravity wave - convection coupling

Friday, 12 June 2009: 9:00 AM
Pinnacle BC (Stoweflake Resort and Confernce Center)
Todd P. Lane, The University of Melbourne, Melbourne, VIC, Australia; and F. Zhang

Observations and cloud-resolving model simulations often show the emergence of deep convective clouds or cloud bands with regular spacings of order 100 km. Such regular spacing is a key component of cloud organization and is likely a contributor to the processes controlling the upscale growth of convective systems. We argue that this spacing is the result of a coupling between the deep convection and the tropospheric gravity waves it generates.

It is already known that deep bore-like modes generated by pre-existing (long-lived) convection can induce vertical displacements that destabilize the surrounding atmosphere, making it prone to further convective development and clustering. Yet, such modes do not explain the regular spacing of the cloud field. In this presentation a combination of cloud-resolving and idealized model simulations, and theory will be used to show that the emergence of these scales is a result of a coupling between the deep convective clouds and the mesoscale gravity waves that they generate. An important component of the coupling is the transience of the wave source that allows a set of gravity waves with discrete horizontal wavelengths to emerge. The horizontal wavelength of these waves exceeds the size of individual cloud elements and matches the cloud spacing identified from cloud model simulations. The physical characteristics of the convection that control this selected scale will be discussed.

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