In this project directed by Dr. Stephen Bougher, the thermosphere and ionosphere of Titan will be examined in great detail,making use of in-situ and remote observations provided by the Cassini Orbiter. In preparation for these observations, fundamental progress can be made in understanding the thermal, compositional and dynamical processes at work in the Titan upper atmosphere by making use of multi-dimensional thermospheric models. The present research effort is devoted to the development, testing, running, and processing of outputs from a detailed 3-D thermospheric general circulation model (TGCM) for Titan's upper atmosphere. This Titan TGCM will incorporate a self-consistent treatment of energetics, dynamics, composition, plus external forcings (from the Sun and Saturn's magnetosphere). The objectives for developing this Titan TGCM are to: (1) construct a 3-D model framework sufficient to capture the feedbacks that link the temperature, composition, and wind structures of the Titan upper atmosphere above 600-700 km, (2) generate a prediction tool that can be used later for Cassini Mission thermosphere-ionosphere data analysis, (3) compare Titan thermospheric energetic and dynamical processes with those of other non-magnetic planets (especially Venus), and (4) provide diagnostic interpretation of the underlying processes giving rise to the Titan thermospheric features simulated. In particular, both solar extreme ultraviolet-ultraviolet (EUV-UV) and Saturn magnetospheric forcing (ionization and neutral heating) will be incorporated into the Titan TGCM and the thermospheric responses examined over the solar cycle, Titan seasons, and Titan's orbital position within Saturn's magnetosphere. An expanded understanding of the feedbacks of these Titan thermospheric processes will be achieved as detailed comparisons are made with similar processes in the Venus upper atmosphere. The addition of this new Titan TGCM (with its combined solar plus magnetospheric forcing) will complement the existing Titan TGCM, and provide extended capability. This research activity will make a significant advance in the characterization of the Titan upper atmosphere itself, as well as providing another thermospheric environment for detailed comparison to the structure and dynamics of the Venus, Earth, and Mars thermosheres. The team assembled on this project has many years of experience developing and running TGCM models as well as constructing the detailed inputs that are required to drive the energetics and dynamics of these planetary upper atmospheres. Prior TGCM simulations for Venus, Earth, and Mars have been used extensively in comparative studies, forecasting campaigns, and spacecraft and ground-based data analysis activities. For the proposed Titan and Venus TGCM studies, the research tasks are distributed across senior personnel and a graduate student at the University of Michigan. This approach broadens the impact of the present research by training new planetary scientists for the future. Finally, the results from this research will be disseminated through planned publications as well as the distribution of archival TGCM products through an existing public website at the University of Michigan. In this manner, the exploration and understanding of our solar system will be advanced. ***
