Large-scale organization of tropical convection in two-dimensional explicit numerical simulations

The large-scale organization of tropical deep convection is investigated in idealized two-dimensional cloud-resolving simulations. A 20 000 km periodic computational domain allows interactions among moist convection, mesoscale organization, and surface exchange on a wide range of scales. A uniform 10 m s(-1) easterly wind and a uniform sea surface temperature of 30 C are assumed. A prescribed temperature tendency mimicking the mean radiative cooling of the tropical troposphere is used in this pilot study. The large-scale organization of convection resembles the observed tropical atmosphere as well as results from some previous numerical studies using parametrized convection. The simulation highlights mesoscale convective systems with horizontal scales of several hundred kilometres moving east to west with speeds similar to the mean flow, and an envelope of convection with a horizontal extent of a few thousand kilometres and propagating west to east. The propagation speed of the large-scale envelope compares well with the phase velocitites of convectively coupled Kelvin waves observed in the equatorial waveguide. Convective momentum transport and the impact of convective systems on temperature and moisture near the surface are key processes responsible for the large-scale organization of convection. These results are discussed in the context of recent observations and numerical studies of convection organization in the tropics.