A transposable planetary general circulation model (PGCM) and its preliminary application to Titan

We present in this work an application to Titan, Saturnʹs satellite of the transposable planetary general circulation model (PGCM), which was developed based on the second version of the Community Atmosphere Model (CAM2) of NCAR. The PGCM is a spectral model with the sigma coordinate (where σ is the pressure normalized to its surface value, commonly used as a vertical coordinate in general circulation models) and is integrated in time using the semi-implicit leapfrog scheme. The horizontal resolutions of the model are based on 128 points in longitude and 64 points in latitude, and the vertical discretization is of 26 σ-levels. In Titanʹs conditions we apply the PGCM to simulate Titanʹs general circulation in this study. Some interesting phenomena such as equatorial superrotation, vertical meridional circulations, vertical structure, etc. are well replicated. This demonstrates the good performance and applicability to Titan of our model and provides a foundation for further studies on simulating and understanding Titanʹs general circulation and its variability by coupling the physical processes. The features of Titanʹs circulation under the condition of the Earthʹs rotation rate are also investigated. The results suggest that different rotation rates can significantly affect the dynamical structure of Titanʹs circulation.