The Multiscale Impacts of Organized Convection in Global 2-D Cloud-Resolving Models

This paper studies the mechanisms behind the multiscale organization of tropical moist convection using a trio of cloud-resolving atmospheric simulations performed in a periodic two-dimensional 32,000-km domain. A simulation with interactive surface fluxes and long-wave radiation over a constant sea surface temperature of 300.15 K produces a planetary-scale self-aggregated patch of convection after 80 days of simulation. Fixing the surface fluxes and radiative cooling at a constant value suppresses this planetary-scale organization. However, increasing the stability at the tropopause by adding stratospheric heating produces a simulation, which generates a planetary-scale wave after just 30 days. This planetary-scale wave modulates eastward propagating synoptic-scale waves, which in turn modulate westward propagating mesoscale convective system. Low-pass filters are used to diagnose the feedbacks, which produce large-scale variance of zonal velocity, buoyancy, and humidity. The planetary-scale buoyancy variance and zonal velocity variance are related to the available potential energy (APE) and kinetic energy (KE) budgets, respectively. In the simulation with stratospheric heating, planetary-scale KE is created by vertical fluxes of zonal momentum, converted to APE, and then dissipated by latent heating, mixing, and other buoyancy sources. Without stratospheric heating, the KE produced by these feedbacks is strongly damped in the stratosphere. The mesoscale eddy flux convergence of zonal momentum dominates the total vertical flux feedback on the planetary-scale KE, and its vertical structure is consistent with the westward propagating mesoscale convective systems. Overall, these results demonstrate that these eddy fluxes can organize two-dimensional deep convection on planetary scales in the absence of other diabatic feedbacks.