On the relationship between surface pressure, terrain elevation, and air temperature. Part I: The large diurnal surface pressure range at Gale Crater, Mars and its origin due to lateral hydrostatic adjustment

Abstract

The daily variation of surface pressure observed by the Curiosity Rover Environmental Monitoring Station (REMS) is both significantly larger than observed at other landing sites on Mars and larger than simulated for the Curiosity site by global circulation models (GCM). Mesoscale numerical models are able to simulate the large REMS daily pressure range, but only if they possess sufficiently high horizontal resolution (grid spacing <5 km); low resolution (120–500 km) GCM simulations typically generate daily ranges of about half the observed value. The pressure range in low resolution simulations corresponds to the large-scale thermal tides and the augmentation of this range in high resolution models is associable with mesoscale topographic and surface property variations in the Gale Crater region. We show that the augmentation is due to the lateral redistribution of mass required for the surface pressure distribution over topographic relief to remain approximately hydrostatic as the near-surface air temperature varies through the diurnal cycle. The physical origin and nature of this adjustment flow is explored. We provide a means of predicting the daily surface pressure due to lateral hydrostatic adjustment for any location and further show that this range is slightly reduced by the inability of the atmosphere to completely achieve hydrostaticity and by the thermal effects of induced flows.