Abstract
<title>Abstract</title> <p>Titan's middle atmosphere has a well-observed north-south haze asymmetry (NSA), with a mysteriously sharp boundary that migrates seasonally across the equator. Several stratospheric trace species display similarly steep latitudinal gradients near the equator, yet the origin of these abrupt transitions is not well understood. Here we map the distributions of multiple trace species between 40°S and 40°N using observations from Cassini's Composite Infrared Spectrometer spanning almost half a Titan year, providing the highest-latitudinal-resolution view of Titan’s equatorial stratosphere to date. The measurements provide unique insight into the dynamics of Titan's equatorial region, which cannot be constrained using conventional thermal wind balance techniques. We show that composition boundaries near the equator follow a strikingly similar migration to Titan's haze NSA boundary, suggesting the NSA boundary is driven primarily by dynamics rather than chemistry or haze microphysics. Comparison with the Titan Atmospheric Model (TAM) general circulation model shows that the steep equatorial gradients are established primarily by vertical transport associated with the meridional overturning circulation. The observed offset of the boundary from the equator is explained by horizontal transport of enriched air, driven predominantly by horizontal eddies rather than mean-flow advection. These results reveal the dynamical origin of Titan’s enigmatic equatorial boundary and constrain the seasonal evolution of its global circulation.</p>