As the tropical atmosphere is never far from a state of radiative convective equilibrium (RCE), previous cloud resolving modeling (CRM) studies using such a framework have proven highly successful in experiments focusing on the feedbacks between radiation, clouds, water vapor and convection in the tropics. For the research presented here, large-domain, high-resolution, long-duration three-dimensional CRM simulations have been conducted using the Regional Atmospheric Modeling System (RAMS) under such a RCE framework. The three-dimensional setup allows for a more accurate representation of mesoscale convective systems than is provided by a two-dimensional framework. Such systems play a key role in tropical convective processes. RAMS is a sophisticated CRM that includes the prognosis of aerosol concentrations. The model grid used for these experiments utilizes a horizontal grid spacing of 1km, variable grid spacing in the vertical, and periodic lateral boundary conditions. The lower boundary is an oceanic boundary with a fixed sea surface temperature.
The CRM is first run until RCE is reached, a process that takes approximately 50 simulation days. The model is then restarted at day 50 and aerosols that can potentially serve as cloud condensation nuclei (CCN) are introduced in one half of the domain. No aerosols are introduced into the other half of the domain. The amount of aerosol available for activation is progressively increased from one sensitivity experiment to the next (still within only half of the domain) thus representing a range of aerosol conditions from pristine to polluted atmospheres. The sensitivity tests are run for a further 50 days. The design of these experiments allows us to examine aerosol indirect forcing on the large-scale circulations that develop between the clean and polluted portions of the domain, as well as for side-by side comparisons of the cloud and microphysical characteristics of the tropical convective systems developing in the clean and polluted environments.