Hadley cell
Simulations of global wind patterns based on wind speed data taken by "Huygens" during its descent have suggested that Titan's atmosphere circulates in a single enormous Hadley cell. Warm gas rises in Titan's southern hemisphere—which was experiencing summer during "Huygens" descent—and sinks in the northern hemisphere, resulting in high-altitude gas flow from south to north and low-altitude gas flow from north to south. Such a large Hadley cell is only possible on a slowly rotating world such as Titan. The pole-to-pole wind circulation cell appears to be centered on the stratosphere; simulations suggest it ought to change every twelve years, with a three-year transition period, over the course of Titan's year (30 terrestrial years). This cell creates a global band of low pressure—what is in effect a variation of Earth's Intertropical Convergence Zone (ITCZ). Unlike on Earth, however, where the oceans confine the ITCZ to the tropics, on Titan, the zone wanders from one pole to the other, taking methane rainclouds with it. This means that Titan, despite its frigid temperatures, can be said to have a tropical climate.