The thermosphere of Titan simulated by a global three-dimensional time-dependent model

We present three-dimensional numerical simulations for dynamics and energet ics of Titan's thermosphere. In so doing, we distinguish between the dynami cs driven by solar insolation and those driven by vertical coupling to wind s in Titan's middle atmosphere. Our calculations reveal that the solar-driv en thermospheric dynamics are characterized by the balance between pressure gradients and viscosity, while the super-rotating zonal winds detected in Titan's stratosphere set up a balance between the pressure gradients, curva ture and Coriolis forces. The day to night temperature gradients in the upp er thermosphere (around 1300 km) typically lie around 20 (10) K for solar m aximum (minimum), with peak solar-driven winds of around 60 (30) m/s. This difference decreases with height and virtually disappears below 1000 km as a result of dayside adiabatic cooling and nightside adiabatic heating. The model highlights unique features about the thermosphere on Titan, such as t he important nighttime heating from mid-latitudes to high-latitudes caused by the relatively small size of the planet's shadow, leading to features in the wind profiles which are not found on Earth. Although the lack of measu rement constraints prevents us from making predictions of actual wind profi les on Titan, the model does illustrate the physical processes driving the dynamics and suggests that anticipated thermospheric measurements from the Cassini spacecraft may provide constraints also for the dynamics at lower a ltitudes.