Browsing by Author "Cloutier, Paul A."
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Item A global magnetic potential model for Venus' ionosphere(1999) Walker, Peter Wykoff, II; Cloutier, Paul A.Venus represents the prototype for a class of objects whose interaction with the solar wind is characterized by the dominance of an ionospheric obstacle to the magnetized plasma. Though the interaction region between the bow shock and the ionopause boundary of Venus has been extensively studied and successfully modeled, the ionosphere itself, especially on the night side, has only been the subject of piecemeal models. These models either restrict themselves to two dimensions, or treat only one ionospheric phenomenon at a time. However, it is possible to combine the information from these models of the ionosphere into a coherent three dimensional model of the large-scale fields of the Venerean ionosphere. The model, which makes use of magnetic potentials to insure the proper continuity relations of field across boundaries and to insure the magnetic field is globally divergenceless, is developed by breaking the field into altitude-independent toroidal, poloidal, and flow-parallel components. These components are fit to terminator characteristics that can be specified by a very few number of parameters, and to an approximate adherence to Newtonian pressure balance at the dayside ionopause. Finally, the altitude profiles of the field are inserted into the model as the potentials are renormalized and fit to a more exacting ionopause boundary condition on the dayside determined by a gasdynamic treatment of the magnetosheath. In addition, methods of applying the model to similar objects are discussed.Item A magnetic potential model for the interface of vertical-field tail-lobes with Venus' nightside ionosphere(1998) Walker, Peter Wykoff; Cloutier, Paul A.Venus' nightside ionosphere may be characterized by two general magnetic field geometries. Most of the ionosphere is characterized by largely horizontal fields carried over across the terminator from the dayside. However, regions of mostly vertical fields, associated with the nightside ionospheric 'holes' and connected to regions in the ionosheath where there are strong tailward fields, are also present. A magnetic potential model has been developed to describe the interface of the ionosphere, represented as an infinite slab bounded by two magnetically impermeable planes, with the tail lobes idealized as semi-infinite solenoids terminating at the ionopause. From this model, ionospheric boundary currents are generated to confine all field lines in either the flat ionosphere or the vertical tail lobe, and the field geometries are explored. Techniques for mapping this solution to a sphere and approximating it at long ranges from the transition region are discussed, and a preliminary global nightside model is offered.Item A modified flow/field model of the solar wind interaction with Mars(1992) Stewart, Brian K.; Cloutier, Paul A.A modified steady state flow/field model is applied to the direct interaction of the solar wind with the Martian ionosphere. The original flow/field model (Cloutier et al., 1987) is a one-dimensional, self-consistent derivation of differentials in vertical velocity, magnetic field, and ion densities from the coupled MHD equations. While successful in reproducing features of the ionosphere of Venus (Cloutier et al., 1987; McGary, 1987) and of Mars (Stewart, 1989), the flow/field model required an independently specified heating term (Q). The requirement of this term implies the presence of an energy source not accounted for in conventional calculations. This source was previously simulated with the inclusion of Q, but an unrecognized momentum or pressure term may also provide the coupling with the solar wind without the need of the free parameter Q. An in-depth analysis of Pioneer Venus data in relation to the total conservation of momentum of the system led to the discovery that the total momentum was in most cases not entirely accounted for, and that this "missing" term was correlated with solar wind dynamic pressure. By including this missing pressure, a new set of differential equations, which were also extended to include horizontal velocity terms, was derived. Extrapolation of the missing pressure to Mars gave results that faithfully reproduced the ionospheric features associated with previous flow/field models while maintaining agreement with Viking 1 and 2 observations. Finally, we suggest that the source of P$\sb{\rm missing}$ could be a population of suprathermal particles within the ionosphere. The missing pressures in the Viking simulations are consistent with measured suprathermal pressures at Mars (Hanson and Mantas, 1988).Item A steady state flow/field model of solar wind interaction with Mars(1989) Stewart, Brian Keith; Cloutier, Paul A.A steady state flow/field model is applied to the direct interaction of the solar wind with the Martian ionosphere. We have coupled observational data with the kinetic theory plasma equations within a single self-consistent framework. We do not imply that the interaction is purely ionospheric, but rather we show that a self-consistent, direct ionospheric interaction is feasible. The model demonstrates how the dynamic solar wind pressure is transferred to the ultimate obstacle, the planet itself, without the requirement of an intrinsic Martian magnetic field. The results of the model are in agreement with Viking observations, and hence make possible predictions of quantities as yet unmeasured within the Martian ionosphere. We predict that the magnetic field configuration of the Martian ionosphere may be similar to the "Venusian dip" structure observed by Pioneer Venus. (Abstract shortened with permission of author.)Item A two-dimensional model of the Venus ionosphere(1988) McGary, John Edward; Cloutier, Paul A.The Pioneer Venus observations show a peak in the O$\sb2\sp+$ concentration at $\sim$170 km altitude in the dayside ionosphere of Venus. In this thesis, the 2-dimensional MHD equations are solved in a self-consistent manner, as an extension to the 1-dimensional model by Cloutier et al. (1987), to present a global model of the Venus dayside ionosphere for solar zenith angles (SZA) $\leq$ 60$\sp\circ$. The model describes, by calculating vertical profiles at different SZA, ion densities, magnetic field magnitudes, and ion velocities. The model shows that the O$\sb2\sp+$ peak, at $\sim$170 km altitude, occurs throughout the dayside ionosphere as observed by the Orbiter Ion Mass Spectrometer (OIMS). The velocity field, which affects the ion distributions, is mainly tangential near the ionopause and radial for altitudes below 200 km. The downward flow accelerates, near 170 km altitude, due to collisional interactions with the neutral atmosphere, and removes the O$\sb2\sp+$ densities to lower altitudes, thus, producing the bump observed in the altitude profile.Item Accuracy of the vector magnetometer as an attitude sensing device for auroral sounding rockets(1979) Robinson, Robert M.; Cloutier, Paul A.; Clayton, Donald W.; Reiff, Patricia H.A Terrier-Malemute sounding rocket was launched over a stable auroral arc from Poker Flat, Alaska on March 9, 1978 U. T. Among the instruments carried by the payload were a cesium vapor magnetometer and a solid-state star sensor. The star sensor, designed and built at INIK, Lulea, Sweden, measured the time and magnitude of individual star transits during the flight. These data were used to determine the attitude and rotational dynamics of the payload to very high accuracy. Similar information was not available for previous Rice University payloads so that attitude reconstruction for these flights was done using magnetometer data alone. However, the procedure for extracting spin and coning parameters from magnetometer data requires certain assumptions about the direction of the geomagnetic field. Since independent attitude information was available for the present flight, it was possible to test the accuracy of the magnetometer as an attitude sensing device. The following errors were discovered. First, the direction of the rocket coning center as measured by the magnetometer was in error by about 3 degrees of arc. Second, the payload spin frequency computed from the magnetometer data differed by as much as .1 degrees per second from that measured by the star sensor. With regard to the detection of ionospheric currents for this and the previous flights, these errors suggest that (1) unless the rocket coning center is in the plane of the trajectory the orientation of the inferred current system may be uncertain by as much as 15 degrees, and (2) the effects of large scale field-aligned currents may be misinterpreted as a gradual variation in the spin rate of the payload.Item Analysis of low frequency whistler wave occurrences in the night-side Venus ionosphere(2008) White, Harold Glenn; Cloutier, Paul A.This body of work deals with a detailed analysis of plasma, magnetic, and electric field data from Pioneer Venus Orbiter (PVO) to determine if the data are consistent with the possibility of lightning on Venus. This has been a strong topic of debate in the planetary physics community. In a recent Nature article [Ingersoll, 2007], Ingersoll provides a synopsis of the case against lightning on Venus. He states that there should not be lightning on Venus, whose clouds, at roughly 55-60km above the surface, are like terrestrial smog clouds, which do not produce lightning. Ingersoll then goes on to recount that no visible evidence (flashes) has been detected on the night or day-side of Venus. An article published by Gurnett [ Gurnett, et al., 2001] details the non-detection of high frequency radio waves characteristic of terrestrial lightning (0.125 to 16MHz) during Cassini's two fly-bys of Venus, contrasted with the definite detection of RF waves during Cassini's later earth fly-by. However, the detection of low frequency whistler waves by Venus Express has revived claims that the source of these whistler waves is lightning in the lower atmosphere of Venus [ Russell, et al., 2007]. Numerous other papers have been published on different aspects of the debate, such as a paper addressing telemetry interference being incorrectly interpreted as evidence for lightning [Taylor, et al., 1988], another paper suggesting the detected events are a local phenomenon [Taylor, et al., 1983], and a paper documenting some of the optical searches for Venusian lightning [Taylor, et al. , 1994]. This work is a comprehensive reconsideration of 14 years of PVO plasma data on a season by season basis, as the spacecraft goes to low altitudes on the night-side of Venus. In this effort, intelligent software filters have been developed to find, sort, and analyze the frequency of occurrence of low frequency whistler waves. The results of this investigation show that the source cannot be in the lower atmosphere of Venus, since at the lowest altitudes (140-156km), the signals disappear. Therefore, an ionospheric source for these whistler waves must be considered.Item Currents and magnetic field structures in the dayside solar wind interaction with Venus and Mars(1996) Law, Colin Christian; Cloutier, Paul A.The solar wind interaction with the non-magnetic Venerean ionospheric obstacle is unique. Ionospheric models of this interaction have primarily been in two dimensions that do not allow for changes in the orientation of the solar wind magnetic field near the obstacle. Analysis of high resolution magnetic field data from the Pioneer Venus Orbiter spacecraft has revealed field rotations that are observed to occur in conjunction with the dayside ionopause. These rotations are a result of the velocity shear at the ionopause and indicate the alignment of the magnetic field with the radial day to night flow of ionospheric plasma. A new configuration of the dayside magnetic field draping has been derived from these results. In addition, a new current system to account for this changing field orientation has been determined and is discussed in relation to current systems derived from previous models. These new aspects of the dayside solar wind interaction at Venus can be applied to other similar solar system objects. Assuming Mars also represents a non-magnetic obstacle to the flow, as past experimental observations indicate, the field diagnostics discovered here make it possible to probe the structure of the Martian ionosphere using magnetometer data in the absence of ion mass spectrometer data. These results will play a major role in predictive modeling and data analysis for future Mars missions.Item Effects of the charge exchange of solar wind with the Martian exosphere(2003) Chen, Yue; Cloutier, Paul A.Charge exchange of solar wind with the Martian exosphere is shown to have two-fold consequences. From the solar wind perspective, the thermal pressure is removed by charge exchange with Martian neutral particles. To maintain a constant total pressure in the flow, increase of magnetic field occurs and therefore accounts for the formation of the magnetic pileup boundary observed by the Mars Global Surveyor Magnetometer. To simulate this a fluid model is constructed and results from it are shown to successfully fit observations. On the other hand, the Martian exosphere is affected by the charge exchange, too. Compared to Venus, Mars has an ionosphere that is so dilute that charge exchange of solar wind should play an important role in the formation of a nonthermal Martian hydrogen exosphere component. In order to study quantitatively how the Martian exosphere is influenced by it, we develop a 3-dimensional Monte Carlo exosphere model in which effects of charge exchange with solar wind are isolated. Simulation results show the existence of that hot population does change the exospheric temperature structure greatly, and we also investigate the simulation results by calculating the contribution of the hot component to Ly-alpha emission and comparing it with data acquired by Mariners' ultraviolet spectrometers. Finally, it is concluded that charge exchange is important in the interaction between solar wind and Martian exosphere. Output of our models can be used in future modeling and data analysis for the coming Mars missions.Item Evidence of electron impact ionization in the magnetic pileup boundary of Mars: Observations and modeling results(1999) Crider, Dana Hurley; Cloutier, Paul A.We analyze the solar wind interaction with Mars through examination of Mars Global Surveyor Magnetometer/Electron Reflectometer (MGS MAG/ER) data. We focus on data in the postshock, dayside plasma flow, especially the Magnetic Pileup Boundary (MPB). First, we present the data to characterize the features of the MPB. Next, we argue the evidence that the MPB is formed through a series of processes, beginning with electron impact ionization of planetary neutrals in the exosphere of Mars. These new ions form an unstable population of energetic ions in the post-shock flow. Ion cyclotron waves are established to scatter the ion distribution into one more stable. This removes thermal pressure from the ions. In order to maintain a constant total pressure in the flow, the magnetic field intensifies, transferring the lost ion thermal pressure into magnetic energy. Also, we develop a model of the electron impact ionization process in the martian exosphere. This model calculates the evolution of the electron distribution function as the flow encounters exospheric planetary neutrals. It reproduces the electron spectrum observed by the ER in the MPB very well. Therefore, we conclude that electron impact ionization is the process responsible for the onset of magnetic pileup in the postshock flow at Mars.Item Experimental Characterization of Plasma Detachment from Magnetic Nozzles(2013-09-16) Olsen, Christopher; Cloutier, Paul A.; Chang-Diaz, Franklin R.; Alexander, David; Tittel, Frank K.Magnetic nozzles, like Laval nozzles, are observed in several natural systems and have application in areas such as electric propulsion and plasma processing. Plasma flowing through these nozzles is inherently tied to the field lines and must separate for momentum redirection or particle transport to occur. Plasma detachment and associated mechanisms from a magnetic nozzle are investigated. Experimental results are presented from the plume of the VASIMR® VX-200 device flowing along an axisymmetric magnetic nozzle and operated at two ion energies to explore momentum dependent detachment. The argon plume expanded into a 150m3 vacuum chamber where the background pressure was low enough that charge-exchange mean-free-paths were longer than experiment scale lengths. This magnetic nozzle system is demonstrated to hydrodynamically scale up to astrophysical plasmas, particularly the solar chromosphere, implying general relevance to all systems. Plasma parameters were mapped over a large spatial range using measurements from multiple plasma diagnostics. The data show that the plume does not follow the magnetic field lines. A mapped integration of the ion flux shows the plume may be divided into three regions where 1) the plume briefly follows the magnetic flux, 2) diverges quadratically before 3) expanding with linear trajectories. Transitioning from region 1→2, the ion flux departs from the magnetic flux suggesting ion detachment. An instability forms in region 2 driving an oscillating electric field that causes ions to expand before enhancing electron cross-field transport through anomalous resistivity. Transitioning from region 2→3 the electric field dissipates, the trajectories linearize, and the plume effectively detaches. A delineation of sub-to-super Alfvénic flow aligns well with the inflection points of the linearization without a change in magnetic topology. The detachment process is best described as a two part process: First, ions detach by a breakdown of the magnetic moment when the quantity |v/fcLB| becomes of order unity. Second, the turbulent electric field enhances electron transport up to a factor of 4±1 above collisional diffusion; electron cross-field velocities approximate that of the ions and depart on more centralized field lines. Electrons are believed to detach by breakdown of magnetic moment further downstream in the weaker magnetic field.Item Flow/field model of a hot magnetized plasma interacting with a cold neutral atmosphere(1993) Hoogeveen, Gary; Cloutier, Paul A.Solar wind interactions with planets that possess neither an intrinsic magnetic field nor a significant ionosphere have not been well studied. We have constructed a model to simulate the interaction between a hot magnetized plasma and a planet containing only a neutral atmosphere. Examination of the boundary conditions that yield a physically valid solution shows that the interaction is similar to the solar wind interaction with Venus. We show that most (97%) of the incident flow is deflected around the atmosphere, and the small fraction that enters interacts in such a way as to transfer the flowing momentum through the neutral atmosphere to the planetary body. This demonstrates that the true barrier to a flowing plasma, such as the solar wind, is neither its ionosphere nor its intrinsic magnetic field, but rather the planetary body itself.Item Ion flux maps and helicon source efficiency in the VASIMR VX-100 experiment using a moving Langmuir probe array(2009) Olsen, Christopher Scott; Cloutier, Paul A.This research paper describes the design, setup, and application of a moving multi-Langmuir probe array that measured and mapped ion flux and plasma source efficiency in a flowing plasma with large (∼1.5 T) external magnetic fields in the VASIMR (Variable Specific Impulse Magnetoplasma Rocket) VX-100 experiment. The probe array was swung through an argon plasma revealing a detailed 2-dimensional cross section. Neutral input flow and probe collector bias voltage were scanned from pulse to pulse in an effort to find optimal settings. Secondary electron emission was found to be an important factor that artificially enhanced the measured flux at large negative bias voltages. The most accurate bias voltages were found to be around -20 volts where the flux enhancing effects were minimized. Variations of this probe will be used in more advanced plasma rocket study.Item Low frequency plasma waves at Mars(2005) Espley, Jared R.; Cloutier, Paul A.Mars Global Surveyor's magnetometer/electron reflectometer (MAG/ER) experiment has returned over eight years of observations of low frequency plasma waves produced in the interaction of the solar wind with the Martian ionosphere. Using the MAG/ER data, I identify the properties and physical origins of the waves in the magnetosheath, magnetic pileup region, and ionosphere. I find that the waves in the dayside magnetosheath are predominately mirror mode instabilities produced by plasma temperature anisotropies arising from the draping of the solar wind magnetic field around the ionosphere. The nightside magnetosheath shows evidence for resonant ion instabilities arising from the interaction of the solar wind plasma with the ionospheric plasma. These waves are therefore an indirect observation of ongoing atmospheric loss at Mars. During the large solar storm of October 2003, dramatic changes were observed in the plasma waves present; even the normally placid tail region showed signs of significant wave activity. Coherent oscillations are observed in the ionosphere and are presumably driven by solar wind fluctuations or are associated with field line resonances along crustal fields.Item Magnetic perturbations due to current structural variations(1974) Teng, Yuan-Cheng; Cloutier, Paul A.Study of the magnetic perturbations caused by auroral currents has been conducted by rocket-borne magnetometer measurements for years. Since the horizontal auroral currents were usually found to be confined near the visible auroral arcs, as determined by Heppner [1954], Davis [1961], and Davis and Kimball [1962], a number of current models have been established in order to explain observed data by rockets or satellite measurements. In those models, the requirement that the current be continuous across the highly conducting arc results in either polarization electric fields to reduce the current in the highly conducting region or Birkeland currents to provide return current to the outer part of the magnetosphere. Bostrom found two basic solutions, one in which a horizontal electrojet connects two filamentary Birkeland currents, and the other in which broad Birkeland sheet currents (Fig. 2) flow to the edges of the arc, with a transverse closing current and a Hall electrojet. In this thesis, we adopted a model similar to the second solution and assumed that the arc was bombarded by energetic precipitating electrons. In this thesis, the effect of a spatial fold on the magnetic vector field in the vicinity of the arc is examined. Fig. 1 shows the current model used in the initial calculations. It has a displacement of thickness of 3 km from its center and is composed of two current parts. One part is the two oppositely directed Birkeland sheet currents having an equal current density of .5 amp/m and an equal thickness of 3 km for each sheet, in which the downward current sheet is on the south side of the arc and the upward on the north. And the 3 other part is an electrojet having a magnitude of 5 x 1 amp flowing eastward at an altitude of 1 km. Model computations were performed with the Rice IBM 37/155 computer. The variations of the vector components as well as the directions of the magnetic fields due to the following three cases, such as the electrojet, the sheet currents and the combination of the two along a path of rocket flight were individually included in details. For the electrojet current which was a kinked line current at the center, we get more details from a comparison with a straight line current in Chapter 2.Item Model of superthermal ions in the dayside Venus ionosphere(1993) Kramer, Leonard; Cloutier, Paul A.A model is presented which simulates the behavior of superthermal ions previously reported in the dayside ionosphere of Venus. The model considers effects of E $\times$ B and gradient drifts, charge exchange and collisions with the ambient neutral atmosphere and the possible effects of a wave-particle (anomalous) scattering process. Results indicate that scattering processes are required if superthermal ions are the explanation for the observed "missing pressure" component in the dayside Venus ionosphere. The scattering scale length required to match the "missing pressure" distribution is similar to the scale length previously predicted for growth of a lower hybrid beam instability.Item Model of superthermal ions in the postshock flow field at Venus(1992) Kramer, Leonard; Cloutier, Paul A.The role of the superthermal ions in the dayside postshock ionospheric flow field at Venus is investigated in a 2-D model by integrating the equation of motion of a superthermal population of O$\sp+$ test particles and statistically examining their contribution to the altitude variation of number density and horizontal current distribution. The model reveals superthermal ions $\vec {\rm E} \times \vec {\rm B}$ drifting downward and gradient drifting horizontally with attendant currents. Regions of "wrapped up" plasma known as fluxropes and identified previously as resulting from Kelvin-Helmholtz instability in the ionosphere are found to significantly scatter ions and limit the horizontal currents. Monte-Carlo simulation of charge exchange and subsequent neutral-on-neutral collision processes produce a substantial vertical flux of ballistic neutrals with hyperbolic trajectories possibly representing a heretofore unrecognized atmospheric loss mechanism at Venus. Modeled altitude profiles of superthermal density superficially agree with empirical analysis by Stewart (1991) for a "missing" pressure term in the momentum balance requirements. (Abstract shortened with permission of author.)Item Model of Venus ionopause formation(1992) Matney, Mark John; Cloutier, Paul A.A model is presented that simulates the physics of the Venus mantle plasma. A modified magnetohydrodynamic (MHD) fluid picture is assumed where the post-shock solar wind plasma is mass-loaded by photoionizations and other atomic interactions with exospheric neutral atoms. By assuming Newtonian pressure profiles and draped magnetic field geometry in the mantle, the three-dimensional steady-state flow problem is reduced to a one-dimensional calculation along the stagnation (subsolar) flowline. In addition, the validity of the model assumptions and questions about the plasma thermodynamics are addressed. When the resulting model is run using various solar wind conditions, the computed magnetic field features correspond with those measured by the Pioneer Venus spacecraft. The model reproduces the observed region of sharp ion density gradients, known as the ionopause, that separates the mantle plasma from the denser ionospheric plasma below. The straightforward application of the model reproduces the shape and location of the low-altitude ionopause cases well, but for solar wind conditions that correlate with high-altitude ionopauses, the computed ionopauses tend to be lower than those observed. The addition of anomalous heating terms to the model, however, raises the computed ionopause to locations consistent with the medium altitude cases. The inability of the model to adequately describe the high altitude cases may indicate that they are transient events and thus cannot be simulated in steady state. While the source of the anomalous heating is not specified, the presence of hyperthermal ions or plasma-wave interactions are suggested as possible heating mechanisms.Item Observations of magnetic signatures and structure in the dayside ionosphere of Venus(1993) Law, Colin Christian; Cloutier, Paul A.Present models of the Venus solar wind interaction do not allow for changes in the orientation of the field as you approach the planet. Analysis of high resolution magnetic field data from the Pioneer Venus Orbiter spacecraft has revealed two distinct field rotations that are observed to occur in conjunction with the dayside ionosphere and ionopause. These rotations are a result of the velocity shear at the ionopause and indicate an alignment of the magnetic field with the day to night ionospheric plasma flow. From these results a new configuration of the dayside field draping has been determined. In addition, the field diagnostics discovered here can be used to probe the ionosphere of Mars which may otherwise go unobserved due to a lack of ion instrumentation onboard the Mars Observer spacecraft.Item Observations of selected Perseus Arm H II regions(1979) Talent, David Leroy; Dufour, Reginald J.; Talbot, Raymond J.; Cloutier, Paul A.The results of an investigation of the optical spectra of four galactic H II regions: NGC 7635, NGC 7538, NGC 2359, and NGC 1624 are presented. The nebulae, located in the Perseus Arm of the Galaxy at distances ranging from 11 to 14 kpc from the galactic center (3.5 to 5. kpc from the sun), were examined using the Intensified Image Dissector Scanner (IIDS) on the 2.1-meter telescope at Kitt Peak National Observatory (KPNO). From the measurement of selected emission-line strengths in the XX37-41 and XA46-74 spectral ranges, the relative abundances of He, N, O, Ne, S, and Ar are calculated with respect to H (log(H) = 12.) for each nebula. Electron densities are derived for the H II regions from the ratio of the [S II] line intensities, I (6716)/I (6731) , while their temperatures are obtained from the ratio of the [N II] line intensities, 1(5759/1(6583). The effects of temperature fluctuations on the abundance calculations are also discussed. The derived chemical abundances are examined in the context of possible chemical abundance gradients in the Galaxy. Significant radial gradients are found for oxygen and nitrogen: dlog(/H)/dR = -.12+.3 kpc-1 and dlog(N/H)/dR = -.16+.3 kpc-1. In each nebula several positions were observed. In this paper particular attention is given to an examination of the condensations in NGC 7635, while an overabundance of nitrogen in NGC 2359 is discussed in the context of its association with the Wolf-Rayet star HD 56925 (WN5).