A vertically resolved analysis of the budget equation for the spatial variance of moist static energy (MSE) is used to diagnose processes associated with the development of tropical cyclones (TCs) in a high-resolution general circulation model (GCM) under realistic boundary conditions. Previous studies have shown that radiation provides an important feedback which enhances TC development. Here we examine the vertical contributions to this feedback by performing a series of mechanism-denial experiments in which synoptic-scale radiative interactions are suppressed either in the boundary layer or in the free troposphere. Although the boundary layer makes up a much smaller proportion of the atmospheric column than the free troposphere, the two experiments result in similar magnitude of reduction in global TC frequency, indicating that radiative interactions in the boundary layer and those in the free troposphere are of comparable importance in modulating TC frequency. Using instantaneous 6-houly outputs, an explicit computation reveals spatial patterns of the advection term during different TC stages. Instead of damping the spatial variance of MSE as noted in previous idealized studies, the advection term is found to promote the development of TCs. We attribute this result primarily to the explicit calculation of the advection term, however the influence of SST gradients cannot be ruled out. While the vertical component of the advection term is prominent in the middle troposphere, the horizontal component dominates in the boundary layer. These results provide additional insight of how different physical processes contribute to TC development in GCMs under realistic boundary conditions.