From introduction: Jupiter is the largest planet in the solar system. Its distance from the Sun is five times that of the Earth and its mass is nearly two and a half times that of all the other planets added together. Jupiter turns about its own axis rather rapidly, once in just under ten hours, and it completes one revolution about the Sun in just under twelve years. Thus Earth has to pass almost directly between the Sun and Jupiter once every thirteen months. When this happens Jupiter is said to be in "opposition", as its position is then opposite to that of the Sun, when viewed from Earth. Around this time the planet will be most favourably placed for observations, as it is at its closest to Earth and up in the sky for a large part of the night. During the day observations on radio frequencies are more difficult, as the Sun is a source of great interference. Besides being an emitter of thermal electromagnetic radiation, as one would expect, Jupiter also emits two kinds of non-thermal radiation, one in the decimetre wavelength range and the other in the decametre wavelength range. A large number of scientists have worked on the problems of decimetre and decametre radiation. This thesis deals with some aspects of decametre radiation.

Master of Engineering

The Cassini mission provided wonderful tools to explore Saturn, its satellites and its rings system. The UVIS instrument allowed stellar occultation observations of structures in the rings with the best resolution available (around 10 meters depending on geometry and navigation), bringing our understanding of the physics of the rings to the next level. In particular, we have been able to observe, dissect, model and test the interactions between the satellites and the rings. We first looked at kilometer-wide structures generated by resonances with satellites orbiting outside the main rings. The observation of structures in the C ring and their association with a few new resonances allowed us to estimate some constraints on the physical characteristics of the rings. However, most of our observed structures could not be explained with simple resonances with external satellites and some other mechanism has to be involved. We located four density waves associated with the Mimas 4:1, the Atlas 2:1, the Mimas 6:2 and the Pandora 4:2 Inner Lindblad Resonances and one bending wave excited by the Titan -1:0 Inner Vertical Resonance. We could estimate a range of surface mass density from 0.22 ([plus or minus]0.03) to 1.42 ([plus or minus]0.21) g cm[super-2] and mass extinction coefficient from 0.13 ([plus or minus]0.03) to 0.28 ([plus or minus]0.06) cm[super2] g[super-1]. These mass extinction coefficient values are higher than those found in the A ring (0.01 - 0.02 cm[super2] g[super-1]) and in the Cassini Division (0.07 - 0.12 cm[super2] g[super-1] from Colwell et al. (2009), implying smaller particle sizes in the C ring. We can therefore imagine that the particles composing these different rings have either different origins or that their size distributions are not primordial and have evolved differently.; Using numerical simulations for the propeller formation, we estimate that our observed moonlets belong to a population of bigger particles than the one we thought was composing the rings: Zebker et al. (1985) described the ring particles population as following a power-law size distribution with cumulative index around 1.75 in the Cassini Division and 2.1 in the C ring. We believe propeller boulders follow a power-law with a cumulative index of 0.6 in the C ring and 0.8 in the Cassini Division. The question of whether these boulders are young, ephemeral and accreted inside the Roche limit or long-lived and maybe formed outisde by fragmentation of a larger body before migrating inward in the disk, remains a mystery. Accretion and fragmentation process are not yet well constrained and we can hope that Cassini extended mission will still provide a lot of information about it.; We also estimate the mass of the C ring to be between 3.7 ([plus or minus]0.9) x 10[super16] kg and 7.9 ([plus or minus]2.0) x 10[super16] kg, equivalent to a moon of 28.0 ([plus or minus]2.3) km to 36.2 ([plus or minus]3.0) km radius (a little larger than Pan or Atlas) with a density comparable to the two moons (400 kg m[super-3]). From the wave damping length and the ring viscosity, we also estimate the vertical thickness of the C ring to be between 1.9 ([plus or minus]0.4) m and 5.6 ([plus or minus]1.4) m, which is consistent with the vertical thickness of the Cassini Division (2 - 20 m) from Tiscareno et al. (2007) and Colwell et al. (2009). Conducting similar analysis in the A, B rings and in the Cassini Division, we were able to estimate consistent masses with previous works for the these rings. We then investigated possible interactions between the rings and potential embedded satellites. Looking for satellite footprints, we estimated the possibility that some observed features in the Huygens Ringlet could be wakes of an embedded moon in the Huygens gap. We discredited the idea that these structures could actually be satellite wakes by estimating the possible position of such a satellite. Finally, we observed a whole population of narrow and clear holes in the C ring and the Cassini Division. Modeling these holes as depletion zones opened by the interaction of a moonlet inside the disk material (this signature is called a "propeller"), we could estimate a distribution of the meter-sized to house-sized objects in these rings. Similar objects, though an order of magnitude larger, have been visually identified in the A ring. In the C ring, we have signatures of boulders which sizes are estimated between 1.5 and 14.5 m, whereas similar measures in the Cassini Division provide moonlet sizes between 0.36 and 58.1 m.

A long-standing question in planet formation is the origin of planetesimals, the kilometre-sized precursors to protoplanets. Asteroids and distant Kuiper Belt objects are believed to be remnant planetesimals from the beginnings of our Solar system. A leading mechanism for explaining the formation of these bodies directly from centimetre-sized dust pebbles is the streaming instability (SI). Using high resolution numerical simulations of protoplanetary discs, we probe the behavior of the non-linear SI and planetesimal formation in previously unexplored configurations. Small variations in initial state of the disc can lead to different macroscopic outcomes such as the total mass converted to planetesimals, or the distribution of planetesimal masses. These properties can vary considerably within large simulations, or across smaller simulations re-run with different initial perturbations. However, there is a similar spread in outcomes between multiple smaller simulations and between smaller sub-regions in larger simulations. In small simulations, filaments preferentially form rings while in larger simulations they are truncated. Larger domains permit dynamics on length scales inaccessible to the smaller domains. However, the overall mass concentrated in filaments across various length scales is consistent in all simulations. Small simulations in our suite struggle to resolve dynamics at the natural filament separation length scale, which restricts the possible filament configurations in these simulations. We also model discs with multiple grain species, sampling a size distribution predicted from theories of grain coagulation and fragmentation. The smallest grains do not participate in the formation of planetesimals or filaments, even while they co-exist with dust that readily forms such dense features. For both single-grain and multiple-grain models, we show that the clumping of dust into dense features results in saturated thermal emission, requiring an observational mass correction factor that can be as large as 20-80\%. Finally, we present preliminary work showing that the critical dust-to-gas mass ratio required to trigger the SI can vary between 3D and 2D simulations. / Thesis / Doctor of Philosophy (PhD)

It is well established that a vast majority of the Earth's surface is inaccessible to conventional vehicles. Furthernore, projects alluding to the exploration of Mar's conclude that its surface is too rough for conventional wheeled vehicles. Man and cursorial animals, however, are capable of traversing virtually all types of terrain. These reasons, among others, have focused almost all development on walking vehicles having fixed torsos and articulated legs which emulate the locomotion of man and animals. Insects such as the caterpillar move with fixed legs and an articulated torso. They too can traverse rough terrain but do so with greater stability than bipeds or quadrupeds. This thesis presents a design for a caterpillar-like crawling vehicle. An overview of the effort to develop walking vehicles is included to show the depth of interest in developing a vehicle capable of traversing rough terrain. A general overview of crawling vehicle objectives and the control problems hampering the realization of a crawling vehicle are then described. Finally, this thesis provides a detailed mechanical design with the kinematic and mechanical considerations governing that design. / Master of Science

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No description available.

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