The Effect of Model Resolution on Wind-stress Dust Lifting within the Lmd/uk Mars Global Circulation Model

Modelling Martian surface dust lifting: This work uses the UK version of the LMD Mars Global Circulation Model (“the MGCM”). The MGCM is a global, multi-level spectral model of the lower and middle regions of the Martian atmosphere. The UK version of the model uses a truncated series of spherical harmonics to represent horizontal variations in atmospheric fields, with the field values stored as coefficients of the spherical harmonic functions (Hoskins and Simmons, 1975; Read and Lewis, 2004). These field values are transformed onto a three-dimensional grid in order to complete calculations involving parameterisations of physical processes. The horizontal resolution of the model is defined by the total wavenumber of the spherical harmonic series: for example, a spectral resolution with a series of wavenumber 31 corresponds roughly to a computational grid of 36 latitude by 72 longitude points. This “T31” spectral resolution results in a physical horizontal resolution of 5° latitude by 5° longitude. T31 is a resolution typically used within Mars global circulation model climate experiments. The highest resolution experiment reported in this work uses a spectral resolution of T85, corresponding to a physical horizontal resolution of 1.88° latitude by 1.88° longitude. All simulations use 25 vertical levels. Higher resolution experiments are underway. Calculations involving surface dust lifting processes are completed within the MGCM’s physical space. Dust lifting by near-surface wind stress occurs when the horizontal frictional drag force of the wind on the surface dust particles is large enough to overcome the forces keeping the particles on the surface. This dust lifting is modelled by calculating the friction velocity of the wind, u, and the threshold friction velocity required to lift particulate matter, ut ∗