Cloud resolving modeling of tropical circulations driven by large-scale SST gradients

This paper considers interactions between the moist atmospheric convection and the large-scale flow driven by the large-scale gradient of sea surface temperature. A two-dimensional computational framework is used with the hor izontal domain size of 4000 km in which both the convective dynamics and th e large-scale flow are resolved. Rotational effects are not considered. Sim ulations are performed using either a prescribed temperature tendency mimic king the effects of radiative processes or a fully interactive radiation tr ansfer model. The simulations are performed for a period of 60 days with qu asi-equilibrium conditions attained after about a month. The time-mean large-scale Row in the simulations features an ascending bran ch occupied by moist convection over a warm ocean and a cloud-free descendi ng branch over a cold ocean. The time-mean flow for the prescribed radiatio n case features a complex vertical structure characterized by two somewhat decoupled circulations in the lower and upper troposphere. This is in stark contrast with the predominant first-baroclinic-mode structure typical of t he observed large-scale tropical circulations, which is characterized by a single cell. An idealized dry model featuring prescribed convective heat so urce suggests that the complex vertical structure is directly related to th e deviation of the model temperature profile from the climatology. Quasi-tw o-day oscillations are a major transient feature of the simulations. The os cillations are associated with radiation of gravity waves from the convecti ve branch into the descending branch. Inclusion of the interactive radiation results in a significant modificatio n of the large-scale flow and has a dramatic impact on the strength and hor izontal extent of convection. Water vapor and cloud condensate strongly int eract with radiative precesses to induce these paramount effects on the tro pical large-scale circulations.