Mechanisms of large-scale wave organization in cloud resolving models

Stefan Tulich

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Tropical deep convection is often found to be organized into large-scale [O(1000 km)] waves satisfying linear dispersion relations. In cloud-resolving models (CRMs) driven by uniform radiative cooling and lower boundary conditions, such large-scale waves develop spontaneously from random initial convection fields. This supports theories of large-scale moist instability and is inconsistent with theories of moist convective damping. These simulations may provide a useful arena for clean diagnosis of candidate mechanisms of instability.

One useful framework for considering linear wave-convection interactions is via superposition of the linear response of the stratified atmosphere to localized heat sources (like convective cloud systems). With this framework in mind, a discrete vertical spectral decomposition has been performed of large-scale dynamical fields in a 2D CRM, as well as heating profiles associated with objectively defined shallow convective, deep convective, and stratiform anvil cloud types. Just a few vertical wavelengths are dominant, suggesting low-order governing dynamics. The upscale development of large-scale waves from random initial convection fields is seen to involve a cooperative interaction between delayed stratiform heating in deep convective cloud systems and large-scale wave disturbances with short vertical wavelengths (near 10 km). This interaction requires that convection be especially sensitive to low-level conditions, which such short waves preferentially enhance.

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9 November 2005
2 PM/ DSRC 1D 403
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