General circulation models of the dynamics of Pluto’s volatile transport on the eve of the New Horizons encounter

•Developed a Pluto GCM using 1D and 2D models for initial and boundary conditions.•Applied the GCM to previously published volatile transport models.•Thermal profiles are mostly isothermal with a strong inversion at the surface.•Sublimation winds are important in seasons with an appreciable atmosphere.•Predicted zonal winds mostly in gradient wind or angular momentum conservation balance. Pluto’s atmospheric dynamics occupy an interesting regime in which the radiative time constant is quite long, the combined effects of high obliquity and a highly eccentric orbit can produce strong seasonal variations in atmospheric pressure, and the strong coupling between the atmosphere and volatile transport on the surface results in atmospheric flows that are quite sensitive to surface and subsurface properties that at present are poorly constrained by direct observations. In anticipation of the New Horizons encounter with the Pluto system in July 2015, we present a Pluto-specific three-dimensional general circulation model (GCM), PlutoWRF, incorporating the most accurate current radiative transfer models of Pluto’s atmosphere, a physically robust treatment of nitrogen volatile transport, and the flexibility to accommodate richly detailed information about the surface and subsurface conditions as new data become available. We solve for a physically self-consistent, equilibrated combination of surface, subsurface, and atmospheric conditions to specify the boundary conditions and initial state values for each GCM run. This is accomplished using two reduced versions of PlutoWRF: a two-dimensional surface volatile exchange model to specify the properties of surface nitrogen ice and the initial atmospheric surface pressure, and a one-dimensional radiative–conductive–convective model that uses the two-dimensional model predictions to determine the corresponding global-mean atmospheric thermal profile. We illustrate the capabilities of PlutoWRF in predicting Pluto’s general circulation, thermal state, and volatile transport of nitrogen by calculating the dynamical response of Pluto’s atmosphere, based on four different idealized models of Pluto’s surface ice distribution from Young (Young, L.A. [2013]. Astrophys. J. 766, L22) and Hansen et al. (Hansen, C.J., Paige, D.A., Young, L.A. [2015]. Icarus 246, 183). Our GCM runs typically span 30years, from 1985 to 2015, covering the period from the discovery of Pluto’s atmosphere to present. For most periods simulated, zonal winds a