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 L[subscript s]=l20 and L[subscript s]=l50. At L[subscript s]=l20 transient circulations are seen primarily along the NPRC margin, consistently producing strong flow over the residual cap (~l5 m/s). By L[subscript s]=135, transient eddies form a "storm track" between the northern slopes of Tharsis and the NPRC. By L[subscript s]=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. / Graduation date: 2005

No description available.

Mariner 9 and Viking spacecraft observations during the 1970's have provided evidence for planetary-scale wave-like disturbances in the Mars atmosphere. It has been suggested that possible sources of the wave activity are dynamical instabilities (e.g., barotropic and/or baroclinic instabilities). An other candidate source is forced, quasi-stationary planetary waves. In connection with Mars' enormous relief, both mechanical forcing and large-scale thermal contrasts due to spatially varying surface thermal-inertia and albedo patterns should provide a strong source for planetary-wave activity. In this thesis, we attempt to model aspects of the observed wave activity, focusing on forced planetary waves in the wintertime atmosphere of Mars. Our approach is to apply two dynamical models: a linear primitive equations model and a quasi-linear 'wave, mean-flow' model. Both models have spherical geometry and represent deviations from zonal symmetry in terms of Fourier modes. The former model permits a separation of responses to different elements that make up the total forcing mechanism, whereas the latter is used principally to investigate the role forced planetary waves may play in the Mars polar warming phenomenon. Basic states representing relatively 'non-dusty' and 'highly dusty' conditions near winter solstice allow wavenumber-1 and -2 disturbances to propagate meridionally and vertically into the winter jet. Higher wavenumbers are strongly vertically trapped. Stationary waves in the northern and southern extratropics differ strongly in amplitude, phase and horizontal wave pattern. The possibility for near-resonant, long-period modes in Mars' winter atmosphere is also examined. For several wave-amplitude measures and dissipation strengths, dusty low-frequency responses are an order of magnitude larger than non-dusty ones. Wave, mean-flow simulations using wavenumber-1 or -2 forcings indicate north polar warmings can occur for the dusty basic states. The sensitivity (magnitude, location, and time scale) of a simulated warming to the wave forcing and the dissipation strength is investigated. / Graduation date: 1993

A variety of general circulation model experiments are performed to investigate the influence of seasonality and topography on the strength of baroclinic eddies in the Martian atmosphere. Three different models are used: a full physics model, a simplified physics model, and a zonally symmetric simplified physics model. All three models are sigma coordinate, finite difference global atmospheric circulation models that have been adapted to the Martian regime. The full physics model has previously been tested extensively by researchers at the NASA Ames Research Center. The simplified physics model replaces many of the atmospheric physics routines with simple parameterizations; most importantly, the radiation code is replaced by Newtonian cooling. A Newtonian cooling code with a radiative time constant that varies in height and latitude produces superior results to one with a radiative time constant that is the same everywhere throughout the atmosphere. It is found that baroclinic eddy activity is extremely sensitive to the mean meridional temperature gradient in the simplified model. A power law fit gives an exponent of approximately six. The baroclinic eddy activity is also sensitive to the maximum growth rate in the Eady model of baroclinic activity. This is due to the close connection between the meridional temperature gradient and the maximum growth rate. Baroclinic adjustment theory, which predicts how baroclinic eddies will react to changes in the mean circulation, does not appear to be valid in the Martian regime, according to the simplified model. This finding may be related to the differences in the relative strengths of the baroclinic eddies and the mean circulation on Earth and Mars. The simplified model indicates that seasonality is more important than topography in creating stronger eddies in the northern hemisphere winter than in the southern hemisphere winter. However, the effects of topography in the simplified model may not be adequately matching the effects of topography in the full physics model, particularly in the southern hemisphere. / Graduation date: 2001

This paper investigates the atmospheric circulation and transport characteristics of the Martian atmosphere (as modeled by a Mars GCM) for three sets of conditions. The conditions are based on a combination of season and dust loading (as parameterized by the optical depth, τ). The first experiment is for the Northern Spring Equinox with no dust loading (τ=0). Experiment 2 is for Northern Hemisphere Winter Solstice with no dust loading. Experiment 3 is for Northern Hemisphere Winter Solstice under moderately dusty conditions (τ=1.0). These cases allow a comparison between seasons and a look at the effects of dust in the atmosphere on the circulation and transport processes. After presenting some of the theoretical and mathematical background pertinent to atmospheric transport and circulation the results of the study are given. These include analyses of the zonal-mean winds, the time-evolution of the mean tracer field, the mean meridional circulation, and the effective transport circulation [Plumb and Mahlman, 1987]. In addition we estimate the time scales for "stratospheric" overturning and calculate a set of eddy diffusion, coefficients (K[subscript yy] and K[subscript zz]) for each case. These coefficients are a means of parameterizing the strength of eddy mixing. Others [Conrath, 1971; Zurek, 1976; Kong and McElroy, 1977; Toon et al., 1977; Anderson and Leovy, 1987] have estimated, using various methods, values for the vertical diffusion coefficient K[subscript zz] of the order of 10³ m²/s. The results here show that there is no "typical" value of K[subscript zz] (or K[subscript yy]) which can be used to characterize the atmosphere globally, and K[subscript zz] seldom reaches 10³ m²/s except in isolated regions and/or under dusty conditions. Both K[subscript yy] and K[subscript zz] are dependent upon season, dust loading, and location in the atmosphere. In addition to identifying the regions of strong mixing, probable sources of the eddy activity which is responsible for the mixing are discussed. In all three cases the effective transport circulation (which includes both advection and diffusion) is structurally similar to the mean meridional circulation but somewhat more intense. The Martian equinox circulation is structurally similar to Earth's circulation; both are characterized by a dual Hadley cell system with rising branch over the equator, poleward flow aloft, and return flow at low levels. The mean zonal winds are westerly in both hemispheres with easterlies near the ground and at high altitudes over the equator. The jet stream in the northern hemisphere peaks at 45 m/s at equinox. Unlike the Earth, Mars' circulation changes dramatically with the seasons. For solstice conditions the mean meridional circulation is characterized by a large, intense cross-equatorial Hadley cell which dominates the circulation pattern. The mean zonal winds are now predominately westerly in the northern winter hemisphere and easterly in the southern hemisphere. The westerly jet reaches 95 m/s while the easterly jet reaches 30 m/s. There is a band of westerlies (up to 10 m/s) found in low southern latitudes near the ground. Dust in the atmosphere acts to intensify the strength of the circulation (while having little effect on the structure); there is a two- to three-fold increase in the strength of the mean winds between the two winter solstice experiments. / Graduation date: 1995

The Mars Pathfinder (MPF) arrived on the Martian surface on 4 July 1997 to become only the third successful landed mission to Mars, recording surface meteorological data intermittently over a period of 83 Martian days ("sols"). The in situ observations made by the MPF meteorology (MET) experiment were recorded at much greater precision than those of the previous missions, Viking Landers 1 and 2. These observations have been analyzed, focusing primarily upon the four so-called "Presidential" sessions, which each covered a complete diurnal cycle. The signature of very strong convective activity was seen in the temperature data, beginning soon after sunrise with temperatures changing as much as 14.39 K over the four-second interval between observations, and ceasing in late afternoon at the collapse of the boundary layer. Less extreme variability occurred at most other times of day and night. Examination of the first ten tidal pressure harmonic amplitudes for each Presidential session revealed strong diurnal and semidiurnal amplitudes and smaller, yet significant, amplitudes at the higher tidal frequencies. The normalized diurnal amplitude was slightly more than 1.7% for one session and averaged ~2.5% for the other three sessions. The semidiurnal amplitude averaged ~1.3%. A pattern in the tidal pressure harmonic amplitudes exists, in which odd-numbered harmonics (excluding the diurnal frequency) have smaller amplitudes than those of the next lower and next higher, even-numbered harmonics. Wind direction data for one Presidential session show very high variability throughout most of the diurnal cycle, the most intense activity occurring during the daytime convective period. A generally clockwise rotation of the mean wind direction was observed throughout the session. Temperature and wind data were examined closely for evidence of contamination of the temperature data by thermal effects of the lander itself. No evidence was found for such "lander interference" in the morning, but lander interference may have occurred in the afternoon of the session examined. A study of a numerical simulation by the NASA Ames Mars General Circulation Model (MGCM) showed prominent minima and maxima, resembling those observed by MPF, in the diurnal pressure cycles of simulated sols corresponding to the Presidential sessions. Also well simulated in each sol is the very rapid increase in surface pressure immediately after the daily minimum. Maps of diurnal and semidiurnal tidal amplitudes for the simulated Presidential sols show that tidal harmonic amplitudes are very spatially dependent, and that large changes in the harmonic amplitudes at any given location are likely to result if the global amplitude pattern for one or more frequencies undergoes small shifts in areographic location. Simulated temperature has a classic "red" power spectrum, while simulated pressure power is concentrated in the tidal frequency range. These spectral shapes are roughly consistent with those computed from the MPF Presidential sessions. The ratios of simulated to observed temperature power spectral estimates for frequencies from 1 to 50 cycles/sol show that the MGCM's simulated temperature variability is too low at all frequencies and especially so at higher frequencies. / Graduation date: 2003

A numerical model for inductive plasma wind tunnels is developed. This model provides the flow conditions at the edge of a boundary layer in front of a thermal protection material placed in the plasma jet stream at the outlet of an inductive torch. The governing equations for the hydrodynamic field are derided from the kinetic theory. The electromagnetic field is deduced from the Maxwell equations. The transport properties of partially ionized and unmagnetized plasma in weak thermal nonequilibrium are derived from the Boltzmann equation. A kinetic data base of transport collision integrals is given for the Martian atmosphere. Multicomponent transport algorithms based upon Krylov subspaces are compared to mixture rules in terms of accuracy and computational cost. The composition and thermodynamic properties in local thermodynamic<p>equilibrium are computed from the semi-classical statistical mechanics.<p>The electromagnetic and hydrodynamic fields of an inductive wind tunnel is presented. A total pressure measurement technique is thoroughly investigated by means of numerical simulations.<p> / Doctorat en sciences appliquées / info:eu-repo/semantics/nonPublished