GCM simulations of Titan's middle and lower atmosphere and comparison to observations

TL;DR

This paper presents a new GCM for Titan that accurately simulates its atmospheric temperature, superrotation, and cloud activity, validated against recent Cassini-Huygens data, enhancing understanding of Titan's climate dynamics.

Contribution

Introduction of the Titan Atmospheric Model (TAM) with advanced physics modules, providing realistic simulations of Titan's atmospheric structure and dynamics, validated against observations.

Findings

Realistic temperature profiles from surface to mesosphere.

Successful simulation of superrotation dependent on angular momentum buildup.

Polar cloud activity well represented, mid-latitude clouds remain puzzling.

Abstract

Simulation results are presented from a new general circulation model (GCM) of Titan, the Titan Atmospheric Model (TAM), which couples the Flexible Modeling System (FMS) spectral dynamical core to a suite of external/sub-grid-scale physics. These include a new non-gray radiative transfer module that takes advantage of recent data from Cassini-Huygens, large-scale condensation and quasi-equilibrium moist convection schemes, a surface model with "bucket" hydrology, and boundary layer turbulent diffusion. The model produces a realistic temperature structure from the surface to the lower mesosphere, including a stratopause, as well as satisfactory superrotation. The latter is shown to depend on the dynamical core's ability to build up angular momentum from surface torques. Simulated latitudinal temperature contrasts are adequate, compared to observations, and polar temperature anomalies agree with observations. In the lower atmosphere, the insolation distribution is shown to strongly impact turbulent fluxes, and surface heating is maximum at mid-latitudes. Surface liquids are unstable at mid- and low-latitudes, and quickly migrate poleward. The simulated humidity profile and distribution of surface temperatures, compared to observations, corroborate the prevalence of dry conditions at low latitudes. Polar cloud activity is well represented, though the observed mid-latitude clouds remain somewhat puzzling, and some formation alternatives are suggested.