A Composite Whole-atmosphere Circulation Model for Titan

We develop a novel approach to simulating the general circulation of Titan’s whole atmosphere from the surface to the thermopause (~1400 km) by combining two general circulation models in different regions: the TitanWRF model, developed at Aeolis Research (formerly Ashima Research) for the stratosphere below ~400 km, and the Titan Thermospheric General Circulation Model (TGCM) developed at Imperial College London for the thermosphere above ~600 km. The two models are coupled by extending the lower boundary of the TGCM dynamically down to 400km, then driving this lower boundary using the dynamical outputs at the upper boundary of TitanWRF. The whole-atmospheric circulation simulated by this coupled model is used to derive the residual circulation, which is then used to drive a two-dimensional chemistry transport model developed at the California Institute of Technology. The implications for the tracer distribution is examined through the age of air.