A mesoscale model study of atmospheric circulations for the northern hemisphere summer on Mars

The Penn-State/NCAR MM5 mesoscale model was adapted for mesoscale simulations of the Martian atmosphere (the OSU MMM5). The NASA Ames Mars GCM provides initial and boundary conditions. High-resolution maps for albedo, thermal inertia and topography were developed from Mars Global Surveyor (MGS) data; these baseline maps are processed to appropriate resolutions for use in the GCM and the mesoscale model. The OSU MMM5 is validated in Chapter 2 by comparing with surface meteorology observed at the Viking Lander 1 (VL1) and Mars Pathfinder (MPF) landing sites. How the diurnal cycle of surface pressure (the surface pressure tide) is affected by boundaries, domain/nest choices and the resolution of surface properties (topography, albedo and thermal inertia) is examined. Chapter 2 additionally shows the influence of regional slope flows in the diurnal surface pressure cycle for certain locations on Mars. Building on the methods of Chapter 2, Chapter 3 describes the northern midsummer polar circulation and the circulations (both large and small scale) that influence it. Improvements to the model for these studies include: the topographical gradient is now considered when computing surface insolation, and the thermal inertia maps and model initialization are improved for high latitudes; this yields a realistic simulation of surface temperatures for the North Pole Residual Cap (NPRC) and the surrounding region. The midsummer polar circulation is vigorous, with abundant and dynamically important transient eddies. The preferred locations of transients varies significantly during this study, between Ls = 120 and Ls = 150. At Ls = 120 transient circulations are seen primarily along the NPRC margin, consistently producing strong flow over the residual cap (∼15 m/s). By Ls = 135, transient eddies form a "storm track" between the northern slopes of Tharsis and the NPRC. By Ls = 150, the circulation is becoming strong and winter-like. These transient eddies may be important in the Martian annual water cycle; many of the observed circulations are poorly (or not) simulated in present day Mars GCMs. Increased resolution and polar stereographic domains provide improvement over GCMs for high latitude studies of atmospheric circulations. These results are in agreement with recent observations. Future work includes model refinements and water vapor transport studies.