Zonal winds in Titan's middle atmosphere from a stellar occultation observed with Keck adaptive optics

Abstract

We present spatially resolved Keck/NIRC2 images of a stellar occultation by Titan on September 5, 2022 and compare them to predictions from concurrent ALMA observations and a suite of General Circulation Model (GCM) simulations. ALMA data and GCM simulations can predict middle atmosphere zonal wind distributions, which in turn produce diagnostic occultation image sequences. We construct an occultation forward model using the temperature profile measured by the Huygens Atmospheric Structure Instrument, which is then distorted using latitudinal zonal wind profiles from the ALMA data or GCM simulations. The occultation forward model yields simulated light distributions around Titan's limb, which we compare directly to the light distributions observed during the occultation. The GCM zonal wind profile corresponding to slightly before the time of the stellar occultation provides the best overall match to the data. The ALMA wind profile provides the best match to the occultation data when only the ingress data were considered, but is not the best match when data from ingress and egress are combined. Our data support the presence of stronger winds in the southern hemisphere during late northern summer.