The Third ARM Mobile Facility (AMF3) deployment to the Southeastern US (SEUS) provides exciting opportunities to improve understanding and model representation of aerosol, cloud, and land-surface processes and their couplings, as the deployment will provide long-term observations in an environment strongly driven by local atmospheric conditions.  The initial research themes consist of five cross-cutting topics: i) onset of convective clouds, ii) deep convective cloud processes and properties, iii) aerosol properties and processes that control cloud condensation nuclei, iv) aerosol direct impacts on radiation, and v) land-atmosphere two-way interactions.  The Brookhaven National Laboratory-led team will develop a science plan and perform initial research activities for a multi-year deployment of the AMF3 in the SEUS.  These activities will: (1) inform AMF3 deployment and science strategies by conducting modeling studies, observation system simulation experiments and analysis of existing measurements, (2) identify potential deployment locations, (3) provide scientific input on site layout and instrumentation needs, (4) develop new analysis algorithms, datasets, and software tools, (5) identify and develop collaborations with partners in the southeastern US, (6) lead outreach within the broader research community for location, site design, and use-promotion, and (7) coordinate and conduct initial process-based research activities.