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

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 nongray 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.

Modeling of Seasonal Lake Level Fluctuations of Titan's Seas/Lakes

“…The results presented in this study rely on the precipitation input data taken from one particular global climate model. Other GCMs (Faulk et al, ; Lora et al, ; Newman et al, ; Schneider et al, ) run without topography and the uniform geography version of Tokano () predicts a global precipitation pattern, which is more symmetric about the equator than the nonuniform geography version of Tokano () used in this study. If the precipitation output from other GCMs were used, the lake level variation and composition in Ontario Lacus would have been more similar to those in the northern maria.…”

Surface Temperatures on Titan During Northern Winter and Spring

“…Seas account for 10% the surface area at 55-90 N (Hayes et al 2011). Le Gall et al (2015), from 2.18 cm radiometry, report a slower than expected rise in temperature in Ligeia Mare in 2014-2015, possibly revealing the cooling effect of the northern seas. Cooling due to methane evaporation, which may be stronger in the spring as precipitation enhances methane concentrations, will depress sea surface temperatures during early spring (Tokano & Lorenz 2015b).…”

Seasonal Variations of Titan's Brightness

“…Numerical modeling is becoming more detailed and some experiments now are carried out with inclusion of quite elaborate mechanisms, such as methane thermodynamics, precipitation, and seasonal cycle (Dowling et al, 2006;Friedson et al, 2009;Lebonnois et al, 2012;Lora et al, 2015;Mitchell et al, 2009;Newman et al, 2011;Tokano et al, 1999). Numerical modeling is becoming more detailed and some experiments now are carried out with inclusion of quite elaborate mechanisms, such as methane thermodynamics, precipitation, and seasonal cycle (Dowling et al, 2006;Friedson et al, 2009;Lebonnois et al, 2012;Lora et al, 2015;Mitchell et al, 2009;Newman et al, 2011;Tokano et al, 1999).…”