Mesoscale gravity wave - convection coupling

Observations and cloud-resolving model simulations often show the emergence of long-lived deep convective clouds or cloud bands that form in the tropics with regular spacing of order 100 km. Such regular spacing is a key component of cloud self-organization, a process by which clouds generate circulations that promote their upscale growth and longevity. In the tropics such organization cannot be adequately explained using arguments based on background wind shear and therefore another process must be at play. In this presentation it is argued that the coupling between deep convection and the tropospheric gravity waves it generates is responsible for the regular cloud spacing and the longevity of individual systems. In particular, an idealized cloud-system resolving model is used to show that populations of clouds can generate a set of tropospheric mesoscale gravity waves with discrete horizontal wavelengths. The cloud field can become coupled to those waves, which define preferred regions of convective initiation. It is also shown that adjacent clouds can form a mutually beneficial partnership; waves emitted from one cloud promote bursts of convective activity in the adjacent cloud, hence encouraging longevity of the pair.