Studies of the Martian atmospheric boundary layer and global circulation from combined use of spacecraft data and numerical circulation models

In this thesis, the near-surface environment on Mars is studied in connection to the general atmospheric circulation. Well-established methods for modelling Earth's atmosphere were invoked, such as embedding a regional mesoscale model into a global atmospheric circulation model, and driving the atmospheric states from the global model, by assimilation of orbital spacecraft data. Embedding a regional model inside a global one for Mars is innovative. But the novelty of our work comes with the assimilation of spacecraft data into such an assembly of numerical models, to produce a regional (GCM+mesoscale model) reanalysis. This achievement is unique in the studies of the Martian atmosphere. However, performing this for the atmosphere of another Solar System planet, came with a collection of challenges. We first proved the viability of our terrestrial model configuration for Mars' atmosphere, by quantifying the direction of energy transfer (potential and kinetic) between scales from both free-running simulations and assimilated reanalyses. We thus produced the first systematic study of the spectral energy budget of the Martian atmosphere, and concluded that energy flows from large scales to small scales. This can be interpreted as suggesting that information flow also goes from large to small scales, to justify using unidirectional information flow from global to embedded model via boundary conditions. Moreover, we discovered that Mars is missing an enstrophy-dominated energy inertial range (i.e. the k-3 range in kinetic energy) that is present in Earth's spectral energetics.
The embedded simulations were carried out for 4 typical Martian seasons around Gale Crater, at a resolution of 80 × 80 × 60 grid-boxes of 5km side-lengths, covering a 400km × 400km region surrounding the crater. Ulteriorly, the assimilated analysis was interpolated to the location of the Curiosity rover (situated in the crater floor) for comparison with in situ measurements. Different methods of decomposing the measured variability into various time-dependent components were employed. Given that atmospheric tides are directly forced in models and reality, the correlations from the diurnal and semidiurnal atmospheric tides show almost perfect matching between our analysis and observations. The differences come from uncorrelative effects added by the crater topography and incorrect atmospheric dust and aerosol loading in the models. We finalized our pursuit by explaining both datasets (model and observations) from the superposition of correlations. We concluded that atmospheric dust and aerosol loading is responsible for the underlying shape in the data, with perturbations from superimposing the local meteorology. The tidal components that are not well-matched are important because they can lead to improved models and/or analyses.

Keywords: Mars Modelling
Mesoscale Modelling
Singular Spectrum Analysis
General Circluation Modelling
Data Assimilation
"Regional" Reanalysis
Curiosity REMS
Mars Climate Sounder
Spectral Energy Budget
Advisor: Read, P