Browsing by Author "Reiff, Patricia H."
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Item A Dynamic Coupled Magnetosphere-Ionosphere-Ring Current Model(2013-09-16) Pembroke, Asher; Toffoletto, Frank R.; Warren, Joe; Reiff, Patricia H.In this thesis we describe a coupled model of Earth's magnetosphere that consists of the Lyon-Fedder-Mobarry (LFM) global magnetohydrodynamics (MHD) simulation, the MIX ionosphere solver and the Rice Convection Model (RCM). We report some results of the coupled model using idealized inputs and model parameters. The algorithmic and physical components of the model are described, including the transfer of magnetic field information and plasma boundary conditions to the RCM and the return of ring current plasma properties to the LFM. Crucial aspects of the coupling include the restriction of RCM to regions where field-line averaged plasma-beta <=1, the use of a plasmasphere model, and the MIX ionosphere model. Compared to stand-alone MHD, the coupled model produces a substantial increase in ring current pressure and reduction of the magnetic field near the Earth. In the ionosphere, stronger region-1 and region-2 Birkeland currents are seen in the coupled model but with no significant change in the cross polar cap potential drop, while the region-2 currents shielded the low-latitude convection potential. In addition, oscillations in the magnetic field are produced at geosynchronous orbit with the coupled code. The diagnostics of entropy and mass content indicate that these oscillations are associated with low-entropy flow channels moving in from the tail and may be related to bursty bulk flows and bubbles seen in observations. As with most complex numerical models, there is the ongoing challenge of untangling numerical artifacts and physics, and we find that while there is still much room for improvement, the results presented here are encouraging. Finally, we introduce several new methods for magnetospheric visualization and analysis, including a fluid-spatial volume for RCM and a field-aligned analysis mesh for the LFM. The latter allows us to construct novel visualizations of flux tubes, drift surfaces, topological boundaries, and bursty-bulk flows.Item A study of high-latitude auroral arcs using radar, optical, and in situ techniques(1992) Weiss, Loretta A.; Reiff, Patricia H.Two experimental campaigns designed to study high-latitude auroral arcs have been conducted in Sonde Stromfjord, Greenland. The Polar Acceleration Regions and Convection Study (Polar ARCS) on February 26, 1987, consisted of a coordinated set of ground-based and sounding rocket measurements of a weak, sun-aligned arc within the duskside polar cap, while the Rodeo I and II experiments, conducted during December, 1988 and October, 1989, involved uniquely coordinated optical and radar measurements of high-latitude arcs occurring at the poleward boundary of the auroral oval. Analysis of the large-scale Polar ARCS data indicate anti-sunward convection in the region between the duskside auroral oval and the sun-aligned arc. This convection signature is consistent with either a model in which the sun-aligned arcs formed on open field lines over the polar cap or on closed field lines threading an expanded low-latitude boundary layer, but not a model in which the polar cap arc field lines map to an expanded plasma sheet. Electron measurements indicate that the rocket passed through three narrow ($\le$20 km) regions of low-energy ($\le$100 eV) electron precipitation. An electrodynamic analysis has shown the electric and magnetic field perturbations in these regions to be well correlated and associated with small-scale upward and downward field-aligned currents of 1-2 $\mu$A/m$\sp2.$ The Rodeo measurements have been used to examine the aeronomic and electrodynamic characteristics of two optically stable arcs occurring at different magnetic local times and exhibiting different relationships to the polar cap/convection reversal boundary. The first case study is associated with a reversal from antisunward to sunward flow and also the boundary between open and closed field lines. In contrast, the second case study involved an arc with a much greater average precipitation energy and a significant cross-arc flow, evidenced by the radar measurements as well as the convective motion of a polar cap patch directly across the arc. Owing to the relative motion between the F-layer plasma and the arc precipitation, this arc is interpreted as forming across the nightside merging gap on field lines which map to a region of stable reconnection in the tail.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 Unknown Aggregation of grains in a turbulent presolar disk(1983) Wieneke, Bernhard; Clayton, Donald W.; Michel, F. Curtis; Reiff, Patricia H.The growth and evolution of grains in the protostellar nebula is investigated within the context of turbulent-low mass disk models developed by previous investigators. Because of grain collisions promoted by the turbulent velocities, particles aggregate to millimeter size in times of order 1^3 yrs. During the growth the particles acquire a large inward radial velocity due to gas drag (Weidenschilling, 1977) and spiral into the sun. The calculations indicate that the final size of the particles does not exceed a few centimeters. This result is not very sensitive to the specific nebula parameters. For all conditions investigated it seems impossible to grow meter- or kilometer-sized bodies which could decouple from the gas motion. An additional argument is given which shows that only particles smaller than centimeter size can survive drift into the growing sun by being transported radially outwards by turbulent mixing. This agrees well with the maximum size of inclusions and chondrules. Since sedimentation of grains and subsequent dust disk instability is effectively inhibited by turbulent stirring, the formation of planetesimals and planets can not be explained in the above scenario without further assumptions.Item Unknown An open magnetosphere model for Mercury(2000) Sarantos, Menelaos; Reiff, Patricia H.The access of incident solar wind plasma to the surface of Mercury is dependent on the magnetic fields in the vicinity of the planet. We present the structure of the Hermean magnetosphere obtained by the Toffoletto-Hill (1993) model of a magnetically interconnected ("open") magnetosphere modified for the strength of the magnetic field of Mercury and scaled to account for the difference in planetary radii between Mercury and the Earth. We calculate open regions for the access of incident particles to the surface as a function of the interplanetary magnetic field (IMF) direction and of the solar wind pressure. Predictions are also made for cases of limited field penetration. These results are compared with existing sodium data. Although quantitatively crude, the model gives a good qualitative approach on how to interpret the sodium emission. We predict emission is stronger in the southern hemisphere for a positive Bx component, and in the north for a negative Bx. The Bz component regulates the size and position of the open field line region, with more negative Bz's corresponding to more equatorial open flux regions.Item Unknown Artificially produced field-aligned short-scale striations(1980) Frey, Alfred; Gordon, William E.; Chamberlain, Joseph W.; Reiff, Patricia H.HF-radiowaves propagating in the ordinary mode and incident on an overdense ionosphere ( fHF < foF2 ) are known to excite parametric instabilities. Recent experiments showed that under the same conditions short-scale field-aligned striations are formed. The question concerning the interrelation of these two effects is not yet settled. An experiment was performed at the Arecibo Observatory during June 1977 with a 5 MHz radar installed on Guadeloupe island. The Guadeloupe radar had a line of sight perpendicular to the magnetic field lines in the F-region above Arecibo. The 5 MHz radar backscatter measurements from the region where these artificially produced field-aligned striations (AFAS) occur are used to get some insight into the geometry and the temporal behavior of AFAS. The energy density of the HF-field required to produce AFAS is estimated from the experimental data. Plasma-line data on the parametric instability obtained by the 43 MHz incoherent backscatter from the Arecibo Observatory is compared with the Guadeloupe 5 MHz radar data. Several mechanisms which were proposed to produce AFAS are discussed in the light of present and past experimental results.Item Unknown Auroral electrodynamics from simultaneous measurements at high and low altitudes(1991) Lu, Gang; Reiff, Patricia H.Two auroras sampled nearly simultaneously at high and low altitudes along a field line by the Dynamics Explorer (DE) spacecraft have been used to study auroral electrodynamics. Electric fields plotted as a function of invariant latitude show that the large-scale features are essentially the same at high and low altitudes outside the auroral acceleration region. Parallel electric fields associated with parallel currents are such as to filter out the small-scale structure in the high-altitude electric field pattern. From the magnetic field measurements, we find that there is a return current region embedded between two auroral arc structures. The latitude shift between the high-altitude and low-altitude return current regions indicates that the auroral arcs are moving equatorward with a velocity of about 250 m/s. Collisionless plasma kinetic theory (Knight, 1973) has been used to predict the relationship between the upward parallel current and the parallel potential drop. The DE 1/DE 2 pair offers a unique Opportunity to test this relationship because the DE 1 spacecraft can measure high altitude plasma parameters without contamination from auroral heating. Using measured values of J$\sb{\Vert}$ (mapped to the surface) and $\Phi\sb{\Vert}$, the ratio of J$\sb{\Vert}$/e$\Phi\sb{\Vert}$ varies considerably but with a mean value about 0.5$\sim$2.2 $\times$ 10$\sp{-9}$ mho/m$\sp2$. Suprathermal electron bursts are also observed in the diffuse aurora at the same invariant latitudes, both at high and at low altitudes. Thus we suggest that these "bursts" are more properly described as a spatial rather than temporal phenomenon. Observations of upflowing ionospheric ions are obtained by both DE 1 and DE 2 over the nightside auroral regions. At low altitudes, the mean value of the net upward ion number flux is of the order of 10$\sp9$ cm$\sp{-2}$ s$\sp{-1}$. The ionosphere is predominantly O$\sp+$, and the ions with energies greater than 5 eV are a only very small fraction (less than 1%) of the total ion population. At high altitudes, the upflowing ions are accelerated and heated (with characteristic energies of hundreds of eV). Comparing upflowing fluxes at high and low altitudes yields an estimated height of the bottom of the auroral acceleration region of 1100-1400 km.Item Unknown Chemical abundances in planetary nebulae in NGG 6822(1984) Kirsch, Russell Gary; Dufour, Reginald J.; Reiff, Patricia H.; Stebbings, Ronald F.; O'Dell, Charles R.The results of an investigation of the optical spectra of five planetary nebulae and two H II regions are presented. The nebulae, located in NGC 6822, a Local Group Irregular Galaxy at a distance of .557 Mpcs, were examined using the Richey-Cretien spectrograph and the Silicon Intensified (SIT) Vidicon, on the 4-meter telescope at the Cerro Tololo Interamerican Observatory. From the measurement of selected emission line strengths in the XX37 - XX71 spectral ranges, the relative abundances of He, N, , Ne, S are calculated with respect to H (Log (H) = 12.) for each nebula. Electron densities are derived for the planetary nebulae from the ratio of the Cs IlU line intensities, I(6716)/I(6731), while their temperatures are obtained from theiatio of the Co IIlH line intensities, 1(4363), 1(4959), 1(57). The derived chemical abundances are examined in the context of possible Nitrogen enrichment of the Interstellar Medium and the possible age of the galaxy. Type I planetaries exhibited a He and N enrichment of factors of up to 2 and 31, respectively. The high N enrichment indicates it is a product of Primary Nucleosynthesis, and Type I planetaries are probably significant in N enrichment of the ISM. Type II planetaries exhibit a He and N enrichment of a lesser magnitude than Type I; factors of 1.4 and 5, respectively. This lower enrichment indicates N is a product of Secondary Nucleosynthesis. The age of NGC 6822 is probably similar to that of the Milky Way Galaxy, about 1^1 years, whereas the Magellanic Clouds are younger, a few 1^9 years.Item Unknown Cusp particle detection and ion injection source oscillations(1984) Frahm, Rudy Allan; Reiff, Patricia H.; Dunning, F. Barry; Freeman, John W.The magnetic merging process has been suggested as a means for particle injection into the cusp regions of the earth's magnetosphere. If this process occurs, the injected plasma should reveal a characteristic signature. Electrostatic analyzers are used to detect this plasma. This thesis discusses the design of the electrostatic analyzers which are the central components of the High Altitude Plasma Instrument (HAPI) and Low Altitude Plasma Instrument (LAPI) flown on DE-A and DEHB (Dynamics Explorer satellites) respectively. Also discussed is the calibration of the electrostatic analyzers which I was involved in. This includes the co-authored calibration data acquisition program and my Calibration Data Reduction Routine. Typical satellite instrument output is in spectrogram energy-time format with the particle flux intensity indicated by gray shading. This presentation gives a "visual picture" of how the differential energy flux at each energy changes with time. A presentation of this type using the DE-A HAPI data shows the magnetic merging injection signature: multiple ion "V" structures as the satellite passes through the cusp region when the interplanetary magnetic field has a southward component. An alternative output format which I have helped create produces individual line spectra which allows these "V" structures to be examined in finer detail. If one looks at these "V" structure spectrograms, it is easily noticed that they appear to pulsate with time. I have conducted a harmonic analysis of the peak distribution function per spin from several satellite passes- to determine the periodicity of these pulsations, perhaps related to Kelvin-Helmholtz waves at the magnetopause.Item Unknown Design and preliminary evaluation of a baloon-borne instrument for measuring atmospheric electrical profiles(1979) Weinheimer, Andrew John; Few, Arthur A.; Reiff, Patricia H.; Freeman, John W.A balloon-borne instrument has been developed for the purpose of making fair weather atmospheric electrical measurements. The instrument named Balloon Electrical Environment Profiling System (BEEPS), is similar in principle to balloons flown previously into thunderstorms by our group at Rice. It has the capability of measuring the height profiles of the vector electric field, the vertical component of the conduction current, and the polar conductivities. The balloon is designed to make measurements up through the lower polar stratosphere (14 km), and the first two flights of BEEPS were made from Barrow, Alaska, (71°N, 157°W) in conjunction with a solar magnetic sector boundary crossing, with a flight on either side of the boundary. These flights are part of an effort to measure the electrical response of the atmosphere, as a function of altitude, to the solar sector structure. Knowledge gained from flights such as these may prove valuable to developing an understanding of the role atmospheric electricity may play in those aspects of the sun-weather problem that involve the solar sector structure.Item Unknown Development of an ion/electron plasma spectrometer(1999) Keith, Wayne Russell; Reiff, Patricia H.This thesis details the development of the Miniaturized Electrostatic DUal top-hat Spherical Analyzer (MEDUSA) instrument, including calibration, simulation, and data processing software. MEDUSA combines two-species observations with state-of-the-art miniaturization to achieve a low-cost, compact instrument capable of making the measurements that will be required in the future. Calibration of the instrument was performed during November 1997 and July 1998. In order to better understand the characteristics of the instrument, it was also modeled in detail with a modified 2.5 dimensional raytracing code. The production processing software is designed to archive the data into the standard Instrument Data File Set (IDFS) format of the Southwest Data Display and Analysis System (SDDAS). MEDUSA has so far proven itself to be a reliable, low-cost instrument capable of making the scientific measurements required for a better understanding of the behavior of the near-Earth particle environment.Item Unknown Forecasting geomagnetic activity indices using the Boyle index through artificial neural networks(2010) Balasubramanian, Ramkumar; Reiff, Patricia H.Adverse space weather conditions affect various sectors making both human lives and technologies highly susceptible. This dissertation introduces a new set of algorithms suitable for short term space weather forecasts with an enhanced lead-time and better accuracy in predicting Kp, Dst and the AE index over some leading models. Kp is a 3-hour averaged global geomagnetic activity index good for midlatitude regions. The Dst index, an hourly index calculated using four ground based magnetic field measurements near the equator, measures the energy of the Earth's ring current. The Auroral Electrojet indices or AE indices are hourly indices used to characterize the global geomagnetic activity in the auroral zone. Our algorithms can predict these indices purely from the solar wind data with lead times up to 6 hours. We have trained and tested an ANN (Artificial Neural Network) over a complete solar cycle to serve this purpose. Over the last couple of decades, ANNs have been successful for temporal prediction problems amongst other advanced non-linear techniques. Our ANN-based algorithms receive near-real-time inputs either from ACE (Advanced Composition Explorer), located at L1, and a handful of ground-based magnetometers or only from ACE. The Boyle potential, phi = 10-4 &parl0;vkm/sec&parr0;2+ 11.7BnT sin3 (theta/2) kV, or the Boyle Index (BI) is an empirically-derived formula that approximates the Earth's polar cap potential and is easily derivable in real time using the solar wind data from ACE. The logarithms of both 3-hour and 1-hour averages of the Boyle Index correlate well with the subsequent Kp, Dst and AE: Kp = 8.93 log 10<BI> - 12.55. Dst = 0.355<BI> - 6.48, and AE = 5.87<BI> - 83.46. Inputs to our ANN models have greatly benefitted from the BI and its proven record as a forecasting parameter since its initiation in October, 2003. A preconditioning event tunes the magnetosphere to a specific state before an impending geomagnetic storm. The neural net not only improves the predictions but also helps the prediction by capturing the influence of preconditioning. Two of our models have been running in near-real-time forecast mode already, and the BI and Kp predictions can be obtained from http://space.rice.edu/ISTP/wind.html.Item Unknown High-latitude electron density observations from the IMAGE radio plasma imager(2003) Henize, Vance Karl; Reiff, Patricia H.Before the IMAGE mission, electron densities in the high latitude, high altitude region of the magnetosphere were measured exclusively by in situ means. The Radio Plasma Imager instrument onboard IMAGE is capable of remotely observing electron densities between 0.01 and 100,000 e-/cm-3 from distances of several Earth radii or more. This allows a global view of the high latitude region that has a far greater accuracy than was previously possible. Soundings of the terrestrial magnetic cusp provide the first remote observations of the dynamics and poleward density profile of this feature continuously over a 60-minute interval. During steady quiet-time solar wind and interplanetary magnetic field conditions, the cusp is shown to be stable in both position and density structure with only slight variations in both. Peak electron densities within the cusp during this time are found to be somewhat higher than predicted. New procedures for deriving electron densities from radio sounding measurements are developed. The addition of curve fitting algorithms significantly increases the amount of useable data. Incorporating forward modeling techniques greatly reduces the computational time over traditional inversion methods. These methods are described in detail. A large number high latitude observations of ducted right-hand extraordinary mode waves made over the course of one year of the IMAGE mission are used to create a three dimensional model of the electron density profile of the terrestrial polar cap region. The dependence of electron density in the polar cap on average geocentric distance (d) is found to vary as d-6.6. This is a significantly steeper gradient than cited in earlier works such as Persoon et al., although the introduction of an asymptotic term provides for basic agreement in the limited region of their joint validity. Latitudinal and longitudinal variations are found to be insignificant. Both the mean profile power law index of the electron density profile and, to a stronger degree, its variance show dependence with the DST index.Item Unknown Ion trajectories in Mercury's magnetosphere(2005) Sarantos, Menelaos; Reiff, Patricia H.This thesis presents new tracings of ions in Mercury's magnetosphere that model the variability of the solar wind, sodium and potassium surface fluxes. The magnetic field is given from a modified version of the analytic Toffoletto-Hill (TH93) open magnetosphere model, which also gives the electric potential along open field lines. Its applicability is extended into the closed field line region by the Ding (1995) potential solver, which computes the realistic electric potential that is self-consistent with the magnetic field. Three cases of the solar wind and the interplanetary magnetic field (IMF) are tested, two at aphelion and one at perihelion. Photoions are launched from the scale height for each species, while solar wind ions are backtraced from the surface and to the magnetopause. Photoion results reveal that the escape rate to the solar wind responds to external conditions only loosely: between aphelion and perihelion, the escape ratio was seen to range from 30 to just 40 percent. Therefore, impacts dominate. The prediction that recycling reduces by a factor of 1.5 at perihelion could help explain why the sodium atmosphere is denser at aphelion. The flux capable of sputtering varies between 10--15 of the total dayside flux for strongly southward IMF Bz = -10 nT. In addition, tracings of Hermean ions show that differential escape losses do not exist for potassium photoions such that may explain the variable Na/K ratio in the Hermean atmosphere. Solar wind ion tracings confirm that precipitation to Mercury's surface may happen along closed field lines not only at perihelion, but even at aphelion for realistic cases of southward IMF. The computed total sputtering flux increased by a factor of 1.7 from aphelion to perihelion. Most of the flux capable of sputtering is deposited on a region that is extended in longitude but limited in latitude. We conclude that ion sputtering caused by the solar wind can explain the high-latitude variability seen in imaging data of Mercury's sodium atmosphere. This work is relevant to the NASA/Messenger and ESA/BepiColombo missions, both for mission planning and analysis of results.Item Unknown Magnetospheric Model Performance During Conjugate Aurora(2014-04-23) Longley, William; Reiff, Patricia H.; Geurts, Frank; Chan, Anthony ArthurAt 16:40 UT on August 17th, 2001, the IMAGE satellite was in position to view an auroral storm in the Northern Hemisphere, while the POLAR satellite was simultaneously in position to view the storm in the Southern Hemisphere. For many low-latitude auroras, the precipitation maps along field lines from the Southern Hemisphere to the Northern Hemisphere. However, in this case, the IMF had a very strong dawn-dusk component which has been shown to make the polar cap shift towards the dusk in one hemisphere and towards the dawn in the other, but this has not yet been confirmed by simultaneous auroral imaging. Using the satellite images in the 130 nm to 160 nm wavelength range, we have been able to identify the Polar Cap Boundary in both hemispheres throughout the event, and calculated the Dawn-Dusk Offset, ∆L, in both hemispheres. We then found correlations of 0.90 in the Northern Hemisphere and 0.83 in the Southern Hemisphere between ∆L, ranging from 4 to 12 degrees during the event, and By, ranging from 20 to 32 nT during the event. ∆L also correlated well against IMF Clock Angle (ϴC) and the Epsilon parameter (ϵ=vB2sin[ϴC/2]) when using specific time averages of these parameters. The same methods are then applied to the compute Polar Cap Boundaries in the BATSRUS, OpenGGCM, and LFM-MIX models that were run to simulate the event. We find that none of the models accurately describe the observed open-closed field line boundary during this event, with BATSRUS tending to produce boundaries that are too ideal and symmetric, OpenGGCM producing boundaries that are highly distorted and random, and the LFM-MIX model always yielding low correlations between ∆L and the various solar wind parameters.Item Unknown Numerical modeling of the magnetospheric cusp: Ion injection and number density calculations(1997) Xue, Shan; Reiff, Patricia H.The magnetospheric cusp is the principal site of solar wind plasma entry into the magnetosphere, and plasma entry through this region constitutes an important source of plasma in the Earth's magnetosphere. The goal of this dissertation is to understand the dynamics and location of the plasma injection process and the subsequent transport of this plasma throughout the magnetosphere by numerically modeling the cusp in terms of the "zeroth-order" physical processes. A quantitative model of ion injection and number density in the magnetospheric cusp is developed, incorporating mutually consistent electric and magnetic fields. This work extends the method of Onsager et al., who calculated precipitating particle fluxes from quantitative models of magnetosheath flow and ion acceleration at the magnetopause. We have simulated cusp ion energy-latitude spectrograms at mid-altitude. Both the large-scale energy-latitude dispersion and the embedded small-scale energy-pitch-angle V signatures are clearly evident in these simulated spectrograms. Our results show that a much finer V microsignature is obtained when the ion injection source is restricted to a small region. However, the cutoff of the plasma injection at the magnetosheath sonic line also yields relatively narrow V's, even without restricting the injection region to a small locus on the magnetopause. This effect is most noticeable in winter conditions. To explain the frequently observed multiple cusp ion injections that appear to overlap on the same field lines, we present two independent approaches. Our simulations have successfully reproduced the meso-scale cusp ion overlapping structure by firstly incorporating temporal effects of separate bursts of reconnection which last 1.4 min and are 3.6 and 4.6 mins apart; and secondly by introducing a time-dependent magnetosheath plasma density variation along the magnetopause to our cusp model, even with assuming steady interconnection. Our cusp injection model which returns precipitating particle flux also allows us to calculate the number density profile in the cusp. Our result along the noon-meridian cusp demonstrates that the density gradient is sharper on the equatorward edge than the poleward edge, and that the equatorward edge of the density structure shifts to higher latitude at lower altitude.Item Unknown Polar cap response to the 18-21 October 1995 magnetic cloud event(1998) Boyle, C. Benjamin; Reiff, Patricia H.A statistical study of ten years of solar wind particle and magnetic field observations, ionospheric convection measurements, and geomagnetic index data is combined with a case study of the interaction of the 18-21 October 1995 magnetic cloud event to illuminate several aspects of solar-terrestrial coupling. Models of polar cap responses to the solar wind are presented and compared to the observations from the case study. The sudden southward turning of the IMF during the event approximated a step function input to the coupled magnetosphere-ionosphere system. The resulting polar cap size, expansion rate, and polar cap potential are unusually large. This allows a straightforward analysis of effects which have traditionally been difficult to assess. During the event, the polar cap expanded by up to 5$\sp\circ$MLAT/hour, which is roughly the fastest rate of polar cap expansion observed by DMSP in a decade of continuous in-situ measurements. The rapid expansion is used to compare flow observations, estimates of the polar cap potential, and the induced emf which corresponds to the polar cap expansion by Faraday's Law. The analysis also resolves earlier indications that the hypothesized saturation of the polar cap potential drop exists, and confirms the numerical and functional predictions of Hill et al (1976). The implications for high time resolution models of the total polar cap potential are discussed. The statistical analysis includes an expanded set of empirical proxies which relate commonly used magnetospheric parameters. An analysis of the solar wind and ionospheric data also confirms the predictions of Hill (1985) regarding the rate of magnetic flux loss along the length of the magnetotail. In addition, while the ratio of open flux to polar cap potential is often approximated as a constant, the analysis reveals a functional dependence of the ratio which has implications for the length scale of the magnetotail. The ionospheric data used came from six low altitude Defense Meteorological Satellites (DMSP), while WIND and the Interplanetary Monitoring Platform (IMP 8) solar wind monitoring satellites provided solar wind plasma and field data. The data set spans the period from 1987 through 1996.Item Unknown The development of the plasma electron analyzer for the Comet Rendezvous and Asteroid Flyby Mission(1988) Weiss, Loretta Ann; Reiff, Patricia H.The Comet Rendezvous and Asteroid Flyby Mission (CRAF) will include, as one of its complement of thirteen scientific instruments, a plasma electron analyzer capable of providing 3-dimensional measurements of the energy and angular distribution of electrons in the solar wind, asteroidal and cometary environments. After initial instrument selection, mission planners at JPL suggested that an instrument capable of performing angular scanning electronically rather than mechanically be investigated. This thesis describes the development of the redesigned CRAF plasma electron detector, consisting of an electronic scanning component, called the "elevation analyzer", and an energy analyzing component based on the Soft Particle Spectrometer (SPS). The numerical simulation of each component's operation--consisting of ray-tracing particles through the electrostatic field of each analyzer and collecting statistics on those particles successfully transmitted--is used to determine the energy and angular response functions of each component and the design dimensions that optimize these responses.Item Unknown The Water Vapor and Dust Plumes of Enceladus(2014-02-11) Dong, Yaxue; Hill, Thomas W.; Reiff, Patricia H.; Semmes, StephenEnceladus is the most active moon of Saturn. Its south polar plume, composed mostly of water vapor and ice grains, is one of the groundbreaking discoveries made by the Cassini spacecraft. During Cassini’s E2, E3, E5 and E7 encounters with Enceladus, the Ion and Neutral Mass Spectrometer (INMS) measured high neutral water vapor densities up to ~10^9 cm-3 (Waite et al., 2006; Teolis et al., 2010; Dong et al., 2011). We have constructed a physical model for the expected water density in the plumes, based on supersonic radial outflow from one or more of the surface vents. We apply this model to possible surface sources of water vapor associated with the multiple jets observed in the visible dust plumes (Spitale and Porco, 2007). Our model predictions fit well with the INMS measurements of neutral water vapor density along the E3, E5, and E7 trajectories. The fit is optimized by values of outflow velocity in the range ~550–750 m/s and values of total source rate in the range ~1.5 − 3.5 10^28 H2O molecules/s ~ 450 – 1050 kg/s. The model can be extended to incorporate the jet features within the plume observed during the E7 encounter. The dust (ice grain) plumes of Enceladus have been observed by multiple Cassini instruments. We propose a composite ice grain size distribution covering a continuous size range from nanometer to micrometers, by combining the CAPS (Cassini Plasma Spectrometer) nanograin size distributions (Hill et al., 2012) and the CDA (Cosmic Dust Analyzer) and RPWS (Radio and Plasma Wave Science) dust power-law size distribution (Kempf et al., 2008; Ye et al., 2012, 2013). We also study the grain charging process using the RPWS-LP (Langmuir Probe) data (Morooka et al., 2011). Based on the size distribution and charge per grain, the densities, source rate, motion, and currents of the ice grains can be calculated. We found that the grains ~2-20 nm dominate in both charge density and number density. The total grain mass density is likely to be ~ 1- 10 times that of the water vapor, and the grain mass loading rate is ~100 kg/s. The motion of the charged grains in Saturn’s magnetosphere implies a transition from ion-like motion to neutral-like motion as the grain size increases from ~nm to ~μm. The grains carry a total current of ~10^5 A at Enceladus, which leads to a different current system from that of the ion pick-up and associated Birkeland currents. The grain current system may be dominant or at least comparable to the ion pick-up current system in accounting for the magnetic perturbations observed near Enceladus.Item Unknown Topology and convection of a northward interplanetary magnetic field reconnection event(2009) Wendel, Deirdre E.; Reiff, Patricia H.From observations and global MHD simulations, we deduce the local and global magnetic topology and current structure of a northward IMF reconnection event in the dayside magnetopause. The ESA four-satellite Cluster suite crossed the magnetopause at a location mapping along field lines to an ionospheric H-alpha emission observed by the IMAGE spacecraft. Therefore, we seek reconnection signatures in the Cluster data. From the four-point Cluster observations, we develop a superposed epoch method to find the instantaneous x-line, its associated current sheet, and the nature of the reconnecting particle flows. This method is unique in that it removes the motion of the hyperbolic structure and the magnetopause relative to the spacecraft. We detect singular field line reconnection—planar hyperbolic reconnecting fields superposed on an out-of-plane field. We also detect the non-ideal electric field that is required to certify reconnection at locations where the magnetic field does not vanish, and estimate a reconnection electric field of -4 mV/m. The current sheet appears bifurcated, embedding a 30 km current sheet of opposite polarity within a broader current sheet about 130 km thick. Using a resistive MHD simulation and ionospheric satellite data, we examine the same event at global length scales. This gives a 3D picture of where reconnection occurs on the magnetopause for northward IMF with B x and B y components and a tilted dipole field. It also demonstrates that northward IMF 3D reconnection couples the reconnection electric field and field-aligned currents to the ionosphere, driving sunward convection in a manner that agrees with satellite measurements of sunward flows. We find singular field line reconnection of the IMF with both open and closed field lines near nulls in both hemispheres. The reconnection in turn produces both open and closed field lines. We discuss for the first time how line-tying in the ionosphere and draping of open and IMF field lines produce a torsion of the reconnecting singular magnetic field lines within the magnetopause. The simulation and data show that magnetopause reconnection topology is three-dimensional in a way that challenges accepted models of neutral lines and x-lines with guide fields.