Dynamics of Titan's thermosphere

We estimate the wind speeds in Titan's thermosphere by considering the vari ous terms of the wind equation, without actually solving it, with a view to anticipating what might be observed by the Cassini spacecraft in 2004. The winds, which are driven by horizontal pressure gradients produced by solar heating, are controlled in the Earth's thermosphere by ion-drag and coriol is force, but in Titan's thermosphere they are mainly controlled by the non linear advection and curvature forces. Assuming a day-night temperature dif ference of 20 K, we find that Titan's thermospheric wind speed is typically 60 m s(-1). In contrast, the Earth's thermospheric winds, of order 50 m s( -1), do not equalize day and night temperatures. We speculate on other fact ors, such as the electrodynamics of Titan's thermosphere and the tides due to Saturn. (C) 1999 Elsevier Science Ltd. All rights reserved.