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A real time International Sun Earth Explorer (ISEE) data system directed toward the prediction of geomagnetic substorms and storms is discussed in detail. Such a system may allow up to 60 minutes or more, advance warning of magnetospheric substorms and up to 30 minute warnings of geomagnetic storms induced by high speed streams and solar flares. The proposed system utilizes existing capabilities of several agencies thereby minimizing costs.
Many of the scientifically interesting phenomena that occur in the Jovian system are strongly time variable. Some are episodic (e.g., Io volcanism); some are periodic (wave transport in Jupiters atmosphere); and some are exceedingly complex (magnetosphere - Io - Torus-Auroral interactions) and possibly unstable. To investigate this class of phenomena utilizing Voyager data and, in the future, Galileo results, a coherent program of ground based and earth-orbital observations, and of theory that spans the time between the missions, is required. To stimulate and help define the basis of such a scientific program researchers organized an International Workshop on the subject with the intent of publishing the proceedings which would represent the state of knowledge in 1987.
The various regions of the magnetosphere-ionosphere system are coupled by flows of charged particle beams and electromagnetic waves. This coupling gives rise to processes that affect both technical and non-technical aspects of life on Earth. The CRRES Program sponsored experiments which were designed to produce controlled and known input to the space environment and the effects were measured with arrays of diagnostic instruments. Large amounts of material were used to modify and perturb the environment in a controlled manner, and response to this was studied. The CRRES and PEGSAT satellites were dual-mission spacecraft with a NASA mission to perform active chemical-release experiments, grouped into categories of tracer, modification, and simulation experiments. Two sounding rocket chemical release campaigns completed the study.
The Twin Electric Magnetospheric Probes Exploring on Spiral Trajectories mission concept was proposed as a Middle Explorer class mission. A pre-phase-A design was developed which utilizes the advantages of electric propulsion for Earth scientific spacecraft use. This paper presents propulsion system analyses performed for the proposal. The proposed mission required two spacecraft to explore near circular orbits 0.1 to 15 Earth radii in both high and low inclination orbits. Since the use of chemical propulsion would require launch vehicles outside the Middle Explorer class a reduction in launch mass was sought using ion, Hall, and arcjet electric propulsion system. Xenon ion technology proved to be the best propulsion option for the mission requirements requiring only two Pegasus XL launchers. The Hall thruster provided an alternative solution but required two larger, Taurus launch vehicles. Arcjet thrusters did not allow for significant launch vehicle reduction in the Middle Explorer class.
In order to examine the self-consistent formation of large-scale quasi-static parallel electric fields in the auroral zone on a micro/meso scale, a particle in cell simulation has been developed. The code resolves electron Debye length scales so that electron micro-processes are included and a variable grid scheme is used such that the overall length scale of the simulation is of the order of an Earth radii along the magnetic field. The simulation is electrostatic and includes the magnetic mirror force, as well as two types of plasmas, a cold dense ionospheric plasma and a warm tenuous magnetospheric plasma. In order to study the formation of parallel electric fields in the auroral zone, different magnetospheric ion and electron inflow boundary conditions are used to drive the system. It has been found that for conditions in the primary (upward) current region an upward directed quasi-static electric field can form across the system due to magnetic mirroring of the magnetospheric ions and electrons at different altitudes. For conditions in the return (downward) current region it is shown that a quasi-static parallel electric field in the opposite sense of that in the primary current region is formed, i.e., the parallel electric field is directed earthward. The conditions for how these different electric fields can be formed are discussed using satellite observations and numerical simulations.
Plasma pressure data from the ISEE 2 fast plasma experiment (FPE) are statistically analyzed to determine the plasma sheet pressure versus distance in the midnight local time sector of the near-earth (12-35 earth radii) magnetotail plasma sheet. In regions where the bulk of the plasma pressure is contributed by particles in the energy range of the FPE (70 eV to 40 keV for ions), the statistically determined peak plasma pressures vary with distance similarly to previously determined lobe magnetic pressures. Estimates of plasma pressures in the 'transition' region (7-12 earth radii), where the magnetic field topology changes rapidly from a dipolar to a taillike configuration, are compared with the observed pressure profiles. Quiet time observations and estimates are combined to provide profiles of the equatorial plasma pressure along the midnight meridian between 2.5 and 35 earth radii.
The observation of one of the largest magnetic clouds ever observed at a distance of 1 AU, with a diameter of greater than about 0.4 AU, is reported. The cloud is shown to be almost unchanged structurally by interaction with the earth bow shock. The first observations are reported of an auroral activity response to the passage of a magnetic cloud, with a nearly immediate increase in auroral activity when the IMF theta(B) angle reversed polarity to negative near the cloud center. The results provide strong evidence that turbulent magnetic fields behind interplanetary shocks are a possible cause of Forbush decreases, but contest the idea that relatively smooth, strong fields in clouds are a cause of such decreases. The cloud field modeling supports the existence of magnetic force-free fields in describing cloud structure.
The Galileo spacecraft has executed nine close flybys of Jupiter's moon Europa for which plasma wave observations were obtained. This paper presents an analysis of the observations from these flybys taking into consideration the variable geometry of the trajectories in an attempt to characterize the general plasma-wave environment associated with the interaction of the Jovian magnetosphere with the moon. A wide variety of plasma-wave phenomena are found to be associated with this interaction. While there are apparently temporal variations which complicate the analysis, a crude model of the distribution of these phenomena around Europa is derived. Primarily on the upstream side of Europa, and working inward to the moon, electron-cyclotron harmonics are first observed, followed by a region within about two Europa radii of the moon with whistler-mode hiss or chorus, and culminating in a region closest to the moon where a band at the upper hybrid resonance frequency is sometimes enhanced over its ambient intensity. The wake region is approximately two Europa radii across and comprises a broadband, highly variable, and bursty electrostatic phenomenon. Upon closer inspection, these bursty emissions appear as solitary structures similar to those in Earth's auroral zone and plasma sheet boundary layer. In addition to the survey of wave phenomena in the vicinity of Europa, we provide density profiles derived primarily from the upper hybrid resonance frequency which is readily apparent throughout most of each of the flybys. Finally, we suggest that the whistler mode, electron cyclotron harmonic, and upper hybrid resonance emissions are driven by some combination of factors including variations in the magnetic field near Europa and the loss and production of plasma at Europa as a result of the interaction of the Jovian magnetosphere with the moon. By analogy with studies of the ion and electron holes and broadband electrostatic noise at Earth and Jupiter, we argue that the electrostatic solitary structures in the wake are associated with currents and beams coupling Europa to Jupiter's ionosphere.
Mercury is the least explored terrestrial planet, and the one subjected to the highest flux of solar radiation in the heliosphere. Its highly dynamic, miniature magnetosphere contains ions from the exosphere and solar wind, and at times may allow solar wind ions to directly impact the planet's surface. Together these features create a plasma environment that shares many features with, but is nonetheless very different from, that of Earth. The first in situ measurements of plasma ions in the Mercury space environment were made only recently, by the Fast Imaging Plasma Spectrometer (FIPS) during the MESSENGER spacecraft's three flybys of the planet in 2008-2009 as the probe was en route to insertion into orbit about Mercury earlier this year. Here. we present analysis of flyby and early orbital mission data with novel techniques that address the particular challenges inherent in these measurements. First. spacecraft structures and sensor orientation limit the FIPS field of view and allow only partial sampling of velocity distribution functions. We use a software model of FIPS sampling in velocity space to explore these effects and recover bulk parameters under certain assumptions. Second, the low densities found in the Mercury magnetosphere result in a relatively low signal-to-noise ratio for many ions. To address this issue, we apply a kernel density spread function to guide removal of background counts according to a background-signature probability map. We then assign individual counts to particular ion species with a time-of-flight forward model, taking into account energy losses in the carbon foil and other physical behavior of ions within the instrument. Using these methods, we have derived bulk plasma properties and heavy ion composition and evaluated them in the context of the Mercury magnetosphere.
When the angle of the IMF to the earth sun line is 15 deg or less, the occurrence rate of dayside Pc 3,4 pulsations in 7-8 times the average at L values of 2.4-2.8, and 2.2-3.5 times the average at L of 4-4.3. These waves disappear when the IMF is nearly at right angles to the sun-earth line. Such observations are consistent with a source originating in the waves upstream of the subsolar bow shock, which are transported by convection to the magnetopause. There, they couple to oscillations of magnetospheric field lines. Because the magnetospheric plasma's index of refraction decreases with radial distance except at the plasmapause, inwardly propagating waves should be refracted away from the radial direction. To reach low L values, the waves should therefore couple near the stagnation point and propagate nearly radially inwards. The streamline geometry and its connection to the foreshock region is illustrated for various IMF orientations, using a simple approximation to the magnetosheath flow field.
The polar wind represents the outflow of light ions from the polar regions of the earth's ionosphere. Tne present investigation is concerned with the results of detailed modeling of steady state outflow of H(+) and He(+) ions from the polar ionosphere into the tail regions of the magnetosphere. Theoretical models of the polar wind are examined, taking into account H(+) outflow, He(+) outflow, and the collisionless polar wind. Experimental observations are discussed, giving attention to direct measurements of plasma flow parallel to the geomagnetic field, and measurements of ionospheric plasma parameters indirectly related to the effects of outflow. It is concluded that at the present time the bulk of the information on the polar wind derives from theoretical models.
The CRRES plasma wave experiment is designed to provide information on the plasma wave environment and the total plasma density in the Earth's radiation belts and throughout the CRRES orbit. This information is valuable both for studying the naturally occurring wave-particle interactions affecting the plasma and particle environment in the plasmasphere and magnetosphere as well as for studying the chemical releases. The electric field sensors for this instrument consist of two long electric dipole antennas (about 100 m tip-to-tip), and the magnetic field sensor is a search coil magnetometer mounted at the end of a 6-m boom. The instrument has a 14-channel spectrum analyzer covering the frequency range from 5.6 Hz to 10 kHz, and a 128-step sweep frequency receiver covering the frequency range from 100 Hz to 400 kHz.
This paper presents a conceptual design for the attitude control and determination (ACAD) system for the Magnetosphere Imager (Ml) spacecraft. The MI is a small spin-stabilized spacecraft that has been proposed for launch on a Taurus-S expendable launch vehicle into a highly-ellipdcal polar Earth orbit. Presently, launch is projected for 1999. The paper describes the MI mission and ACAD requirements and then proposes an ACAD system for meeting these requirements. The proposed design is low-power, low-mass, very simple conceptually, highly passive, and consistent with the overall MI design philosophy, which is faster-better-cheaper. Still, the MI ACAD system is extremely robust and can handle a number of unexpected, adverse situations on orbit without impacting the mission as a whole. Simulation results are presented that support the soundness of the design approach.
Energy-principle analysis performed on two-dimensional, self-consistent solutions for magnetospheric convection indicates that the magnetosphere is unstable to isobaric (yet still frozen-in) fluctuations of plasma-sheet flux tubes. Normally, pdV work associated with compression maintains stability of the inward/outward oscillating normal mode. However, if Earth's ionosphere can provide sufficient mass flux, isobaric expansion of flux tubes can occur. The growth of a field-aligned potential drop in the near-Earth, midnight portion of the plasma sheet, associated with upward field-aligned currents responsible for the Harang discontinuity, redistributes plasma along field lines in a manner that destabilizes the normal mode. The growth of this unstable mode results in an out-of-equilibrium situation near the inner edge. When this occurs over a downtail extent comparable to the half-thickness of the plasma sheet, collapse ensues and forces thinning of the plasma sheet whereby conditions favorable to reconnection occur. This scenario for substorm onset is consistent with observed upward fluxes of ions, parallel potential drops, and observations of substorm onset. These observations include near Earth onset, pseudobreakups, the substorm current wedge, and local variations of plasma-sheet thickness.
This final report describes activities under NASA grant NAGW-4049 to Lockheed Missiles and Space Company. The report covers the entire period of the grant from 15 August 1994 to 31 January 1998. The original grant was for 3 years ending in August 1997; however the grant was extended 6 months to accomodate additional data analysis that added significantly to the scientific results. This is a grant under the NASA Supporting Research and Technology Program for the analysis and interpretation of the combined scientific data from the ISEE-1 Plasma Composition Experiment and the AMPTE/CCE Hot Plasma Composition Experiment. These combined data sets were used in a study of the Earth's magnetopause to develop a fundamental understanding of plasma entry and dynamics at the boundary and formation and maintenance of the low latitude boundary layer under a variety of solar wind and magnetospheric conditions and at a wide range of local times.
This NASA JPL (Jet Propulsion Laboratory) video production is a compilation of the best short movies and computer simulation/animations of the Galileo spacecraft's journey to Jupiter. A limited number of actual shots are presented of Jupiter and its natural satellites. Most of the video is comprised of computer animations of the spacecraft's trajectory, encounters with the Galilean satellites Io, Europa and Ganymede, as well as their atmospheric and surface structures. Computer animations of plasma wave observations of Ganymede's magnetosphere, a surface gravity map of Io, the Galileo/Io flyby, the Galileo space probe orbit insertion around Jupiter, and actual shots of Jupiter's Great Red Spot are presented. Panoramic views of our Earth (from orbit) and moon (from orbit) as seen from Galileo as well as actual footage of the Space Shuttle/Galileo liftoff and Galileo's space probe separation are also included.
Large scale imaging of Geospace has played a significant role in the recent advances in the comprehension of the coupled Solar-Terrestrial System. The Earth's ionospheric far ultraviolet emissions provide a rich tapestry of observations that play a key role in sorting out the dominant mechanisms and phenomena associated with the coupling of the ionosphere and magnetosphere (MI). The MI coupling is an integral part of the Solar-Terrestrial and as such, future observations in this region should focus on understanding the coupling and the impact of solar variability. This talk will focus on the outstanding problems associated with the coupled Solar-Terrestrial system that can be best addressed using far ultraviolet imaging of the Earthls ionosphere. Challenges of global scale imaging and high-resolution imaging will be discussed and how these are driven by unresolved compelling science questions of magnetospheric configuration, and auroral dynamics.
The Defense Meteorological Satellite Program (DMSP) spacecraft are a series of low-earth orbit (LEO) satellites whose mission is to observe the space environment using the precipitating energetic particle spectrometer (SSJ/4-5). DMSP satellites fly in a geosynchronous orbit at approx.840 km altitude which passes through Earth s ionosphere. The ionosphere is a region of partially ionized gas (plasma) formed by the photoionization of neutral atoms and molecules in the upper atmosphere of Earth. For satellites in LEO, such as DMSP, the plasma density is usually high and the main contributors to the currents to the spacecraft are the precipitating auroral electrons and ions from the magnetosphere as well as the cold plasma that constitutes the ionosphere. It is important to understand how the ionosphere and auroral electrons can accumulate surface charges on satellites because spacecraft charging has been the cause of a number of significant anomalies for on-board instrumentation on high altitude spacecraft. These range from limiting the sensitivity of measurements to instrument malfunction depending on the magnitude of the potential difference over the spacecraft surface. Interactive Data Language (IDL) software was developed to process SSJ/4-5 electron and ion data and to create a spectrogram of the particles number and energy fluxes. The purpose of this study is to identify DMSP spacecraft charging events and to present a preliminary statistical analysis. Nomenclature