Mechanisms of large-scale wave organization in a two-dimensional cloud resolving model

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. These simulations may provide a useful arena for 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 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.