Electromagnetic radiation from plasma oscillations
Electromagnetic radiation from plasma oscillations and type iii solar radio bursts
PLASMA OSCILLATION↗
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Locations of termination shock and heliopause based on Voyager plasma and magnetic field data
The locations of the termination shock and the heliopause are studied taking into account the effects of pickup protons. The study uses available plasma and magnetic field data from Voyagers over a 14-year period (1978-1991) and Voyager observation of the 1992-93 radio emission event. Outside 30 AU, pickup protons have a significant influence on dynamical structures of the outer heliosphere. The solar wind is treated as a mixture of electrons, solar wind protons, and interstellar pickup protons. If the magnitude of the interstellar magnetic field B(sub int) is given, one can quantitatively study the motion and location of the termination shock. The location is anti-correlated with the sun spot number and the shock has an average speed of approx. 24 km/s. Because B(sub int) is poorly known, additional information is needed in studying the termination shock. Cummings, et al. have used observations of anomalous cosmic rays to estimate the location of the shock. The observations of the 1991 GMIR and GMIR shock and the 1992-93 radio emission event provide another handle for the study of the termination shock and the heliopause. After its penetration through the termination shock, the GMIR shock continued to propagate in the subsonic region of the solar wind and eventually interacted with the heliopause. This interaction produces a transmitted shock propagating outward in the interstellar medium and a reflected shock propagating inward toward the sun in the subsonic solar wind. The plasma frequencies behind the reflected and the transmitted shock can be, respectively, responsible for the 2- and 3-kHz radio emissions. Taking into account the effects of pickup protons we found that the average locations of the termination shock and the heliopause in 1991-92 are at approximately 66 AU and 150 AU, respectively.
Whang, Y. C.↗
Structure and Dynamics of Coronal Plasmas
During the past year this grant has funded research in the interaction between magnetic fields and the hot plasma in the solar outer atmosphere. The following is a brief summary of the published papers, abstracts and talks which have been supported. The paper 'Coronal Structures Observed in X-rays and H-alpha Structures' was published in the Kofu Symposium proceedings. The study analyzes cool and hot behavior of two x-ray events, a small flare and a surge. We find that a large H-alpha surge appears in x-rays as a very weak event, while a weak H-alpha feature corresponds to the brightest x-ray emission on the disk at the time of the observation. Calculations of the heating necessary to produce these signatures, and implications for the driving and heating mechanisms of flares vs. surges are presented. A copy of the paper is appended to this report. The paper 'Differential Magnetic Field Shear in an Active Region' has been published in The Astrophysical Journal. We have compared the 3D extrapolation of magnetic fields with the observed coronal structure in an active region. Based on the fit between observed coronal structure throughout the volume of the region and the calculated magnetic field configurations, we propose a differential magnetic field shear model for this active region. The decreasing field shear in the outer portions of the AR may indicate a continual relaxation of the magnetic field with time, corresponding to a net transport of helicity outward. The paper 'Difficulties in Observing Coronal Structure' has been accepted for publication in the journal Solar Physics. In this paper we discuss the evidence that the temperature and density structure of the corona are far more complicated than had previously been thought. The discussion is based on five studies carried out by our group on coronal plasma properties, showing that any one x-ray instrument does see all of the plasma present in the corona, that hot and cool material may appear to be co-spatial at a given location in the corona, and that simple magnetic field extrapolations provide only a poor fit to the observed structure. A copy of the paper is appended to this report.
Golub, Leon↗
Determination of Non-Thermal Velocity Distributions from SERTS Linewidth Observations
Non-thermal velocities obtained from the measurement of coronal Extreme Ultraviolet (EUV) linewidths have been consistently observed in solar EUV spectral observations and have been theorized to result fro m many plausible scenarios including wave motions, turbulence, or magnetic reconnection. Constraining these velocities can provide a physical limit for the available energy resulting from unresolved motions in the corona. We statistically determine a series of non-thermal velocity distributions from linewidth measurements of 390 emission lines from a wide array of elements and ionization states observed during the Solar Extreme Ultraviolet Research Telescope and Spectrograph 1991-1997 flights covering the spectral range 174-418 A and a temperature range from 80,000 K to 12.6 MK. This sample includes 248 lines from active regions, 101 lines from quiet-Sun regions, and 41 lines were observed from plasma off the solar limb. We find a strongly peaked distribution corresponding to a non-thermal velocity of 19-22 km/s in all three of the quiet-Sun, active region, and off-limb distributions. For the possibility of Alfven wave resonance heating, we find thai velocities in the core of these distributions do not provide sufficient energy, given typical densities and magnetic field strengths for the coronal plasma, to overcome the estimated coronal energy losses required to maintain the corona at the typical temperatures working as the sole mechanism. We find that at perfect efficiency 50%-60% of the needed energy flux can be produced from the non-thermal velocities measured.
Coyner, Aaron J.↗
The radial gradients and collisional properties of solar wind electrons
The plasma electron detector on Mariner 10 is used to obtain measurements of electron density and temperature in the interplanetary medium between heliocentric distances of 0.85 and 0.45 AU. The observations show quantitatively that the core of the electron distribution function can be described as collisional at least for radial distances within 1 AU, since with a very few well-marked exceptions associated with high-speed streams, the Coulomb collisional momentum relaxation length is less than the density scale height at all times and all radial distances at which data were obtained. It is found that the Coulomb energy exchange collisions between the core and the (test) halo population are negligible. The power law exponent of the core temperature is about -0.3, whereas the halo temperature is almost independent of heliocentric distance.
Ogilvie, K. W.↗
Corotating energetic particle and fast plasma streams in the inner and outer solar system: Radial dependence and energy spectra
Interplanetary acceleration processes are shown as the most plausible explanation for the observed corotating energetic particle events. The relation between the energetic particle events and the properties of the high speed solar wind streams observed at 1 AU were investigated along with the form of the energy spectrum of the corotating energetic particle streams and its variation with respect to CIR boundaries and with radial distance. It is shown that: (1) at 1 AU a correlation exists between the j particle intensity and the solar wind velocity measured during the rising part of the event, of the form I is proportional to exp (V sub sw/V sub o); and (2) the energy spectra from .5 to 20 MeV are well represented by an exponential in momentum of the form dJ/dP = C exp (-P/P sub o). This representation is found to apply from .45 AU to beyond 5 AU. The variation of P sub o with respect to the CIR boundaries was studied using a method of superposed epoch analysis. It is shown that at 1 AU the spectrum remains constant during the first two days and then progressively flattens; between 3-4AU.
Vanhollebeke, M. A. I.↗
Research on solar-wind and magnetospheric electric fields and plasmas
The phenomena of particle preciptation and ion convection at high latitudes and their response to variations in the interplanetary magnetic field. Data from the low energy electron experiment and the retarding potential analyzer drift meter on Atmosphere Explorers C and D were analyzed. Additional data from the spacecraft Imp-J were utilized.
Burch, J. L.↗
Coronal and Prominence Plasmas
Various aspects of solar prominences and the solar corona are discussed. The formation of prominences, prominence diagnostics and structure, prominence dissappearance, large scale coronal structure, coronal diagnostics, small scale coronal structure, and non-equilibrium/coronal heating are among the topics covered.
Poland, Arthur I.↗
Particle and Field Signatures of Coronal Mass Ejections in the Solar Wind
When CME plasma passes over a spacecraft in interplanetary space, it can often be recognized by a number of characteristic signatures in the properties of the plasma and magnetic field. Those signature are briefly summarized.
interplanetary signatures CME coronal mass ejectio↗
Ulysses Field and Plasma Observations of Magnetic Holes in the Solar Wind and Their Relation to Mirror-Mode Structures
Data obtained by the Ulysses magnetometer and solar wind analyzer have been combined to study the properties of such magnetic holes in the solar wind between 1 AU and 5.4 AU and to 23° south latitude.
magnetic↗
AXIOM: Advanced X-Ray Imaging of the Magnetosphere
Planetary plasma and magnetic field environments can be studied in two complementary ways by in situ measurements, or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Some parts of the Earth's magnetosphere have been remotely sensed, but the majority remains unexplored by this type of measurements. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques, which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth's magnetosphere. In this article we describe how an appropriately designed and located X-ray telescope, supported by simultaneous in situ measurements of the solar wind, can be used to image the dayside magnetosphere, magnetosheath and bow shock, with a temporal and spatial resolution sufficient to address several key outstanding questions concerning how the solar wind interacts with the Earth's magnetosphere on a global level. Global images of the dayside magnetospheric boundaries require vantage points well outside the magnetosphere. Our studies have led us to propose AXIOM: Advanced X-ray Imaging Of the Magnetosphere, a concept mission using a Vega launcher with a LISA Pathfinder-type Propulsion Module to place the spacecraft in a Lissajous orbit around the Earth Moon L1 point. The model payload consists of an X-ray Wide Field Imager, capable of both imaging and spectroscopy, and an in situ plasma and magnetic field measurement package. This package comprises a Proton-Alpha Sensor, designed to measure the bulk properties of the solar wind, an Ion Composition Analyser, to characterize the minor ion populations in the solar wind that cause charge exchange emission, and a Magnetometer, designed to measure the strength and direction of the solar wind magnetic field. We also show simulations that demonstrate how the proposed X-ray telescope design is capable of imaging the predicted emission from the dayside magnetosphere with the sensitivity and cadence required to achieve the science goals of the mission.
Branduardi-Raymont, G.↗
AXIOM: Advanced X-ray Imaging of the Magnetosphere
Planetary plasma and magnetic field environments can be studied in two complementary ways - by in situ measurements, or by remote sensing. While the former provide precise information about plasma behaviour, instabilities and dynamics on local scales, the latter offers the global view necessary to understand the overall interaction of the magnetospheric plasma with the solar wind. Some parts of the Earth's magnetosphere have been remotely sensed, but the majority remains unexplored by this type of measurements. Here we propose a novel and more elegant approach employing remote X-ray imaging techniques. which are now possible thanks to the relatively recent discovery of solar wind charge exchange X-ray emissions in the vicinity of the Earth's magnetosphere. In this article we describe how an appropriately designed and located. X-ray telescope, supported by simultaneous in situ measurements of the solar wind, can be used to image the dayside magnetosphere, magnetosheath and bow shock. with a temporal and spatial resolution sufficient to address several key outstanding questions concerning how the solar wind interacts with the Earth's magnetosphere on a global level. Global images of the dayside magnetospheric boundaries require vantage points well outside the magnetosphere. Our studies have led us to propose 'AXIOM: Advanced X-ray Imaging Of the Magnetosphere', a concept mission using a Vega launcher with a LISA Pathfinder-type Propulsion Module to place the spacecraft in a Lissajous orbit around the Earth - Moon Ll point. The model payload consists of an X-ray Wide Field Imager, capable of both imaging and spectroscopy, and an in situ plasma and magnetic field measurement package. This package comprises a Proton-Alpha Sensor, designed to measure the bulk properties of the solar wind, an Ion Composition Analyser, to characterize the minor ion populations in the solar wind that cause charge exchange emission, and a Magnetometer, designed to measure the strength and direction of the solar wind magnetic field. We also show simulations that demonstrate how the proposed X-ray telescope design is capable of imaging the predicted emission from the dayside magnetosphere with the sensitivity and cadence required to achieve the science goals of the mission.
Branduardi-Raymont, G.↗
Geomagnetic storm particles in the high-latitude magnetotail.
Nearly monoenergetic positive ions flowing outward along magnetic-field lines in the high-latitude magnetotail, outside the plasma sheet, have been observed with Vela satellites. These ions, probably mainly protons, are detected only during geomagnetic storms. The ?storm particles' have average energies per charge ranging from about 0.3 to 3 kV, but at any instant the energy distribution is quite narrow, sometimes less than 10%. Their angular distribution is usually narrow, sometimes about 6 deg. Particles with storm-particle characteristics are not observed in the plasma sheet. Possible sources of the storm particles are considered, including the solar wind, magnetosheath, polar cusps, polar wind, or ionosphere, plasma sheet, solar neutral hydrogen streams, reconnection transfer of plasma into the magnetotail from the polar cusps, polar wind, or polar ionosphere, and parallel electric-field acceleration of the polar wind or ionosphere ions along the polar-cap magnetic-field lines. Of these possibilities, the electric-field acceleration is favored.
Bame, S. J.↗
Interaction of the solar wind with the moon.
During its orbit about the earth, the moon is located in the interplanetary medium or in the geomagnetosheath-geomagnetotail formed by the solar wind interaction with earth. In the tail, no evidence is found for a lunar magnetic field. In the interplanetary medium, no evidence exists for a bow shock or a trailing shock, although a well defined plasma wake region is observed in the anti-solar wind direction. The moon absorbs the solar wind plasma that strikes its surface and creates a void region or cavity in the flow. The observed lunar Mach cone gives evidence for the anisotropic propagation of waves in the magnetized collisionless warm plasma of the solar wind. The transmission of microstructural discontinuities in the interplanetary medium past the moon shows little distortion, indicating a low effective electrical conductivity of the lunar body. Fluctuations of the interplanetary magnetic field upstream from the plasma wake are stimulated by the disturbed conditions in that region. The moon behaves like a cold, nonmagnetic, fully absorbing dielectric sphere in the solar wind flow.
Ness, N. F.↗
Space environments and their effects on space automation and robotics
Automated and robotic systems will be exposed to a variety of environmental anomalies as a result of adverse interactions with the space environment. As an example, the coupling of electrical transients into control systems, due to EMI from plasma interactions and solar array arcing, may cause spurious commands that could be difficult to detect and correct in time to prevent damage during critical operations. Spacecraft glow and space debris could introduce false imaging information into optical sensor systems. The presentation provides a brief overview of the primary environments (plasma, neutral atmosphere, magnetic and electric fields, and solid particulates) that cause such adverse interactions. The descriptions, while brief, are intended to provide a basis for the other papers presented at this conference which detail the key interactions with automated and robotic systems. Given the growing complexity and sensitivity of automated and robotic space systems, an understanding of adverse space environments will be crucial to mitigating their effects.
Garrett, Henry B.↗
Analysis of plasma measurements for the Geotail mission
The first phase of the Geotail mission, an exploration of the distant magnetotail, was successfully concluded in October 1994. Geotail is currently engaged in a survey of plasmas at distances from Earth approximately 10 to 30 R(sub E). Throughout the mission the Comprehensive Plasma Instrumentation has functioned well with successful return of data. The analysis of the CPI measurements has resulted in a series of publications, and research efforts are ongoing. Research topics include interaction of the magnetotail with the fields and plasmas of the solar wind, steady-state magnetic reconnection in the distant magnetotail at a neutral line bounded by a pair of slow-mode magnetohydrodynamic shocks, development and evolution of plasmoids in magnetotail and magnetospheric substorms, and cold ion beams coexisting as distinct components in the presence of hot plasma-sheet plasmas.
Frank, Louis A.↗
Electron acceleration and plasma instabilities in the transition region.
Solar wind magnetosphere interface, examining effect of ion acoustic wave instabilities on plasma sheath
IONIC WAVE↗
Effect of Solar Array Plume Interactions on Hall Thruster Cathode Common Potentials
In typical implementations of spacecraft electric propulsion (EP) systems the electrical ground of the EP power processing units are resistively isolated from the main spacecraft electrical ground. Telemetry measuring the potential difference between EP power processing unit and the spacecraft electrical ground is usually referred to as the “cathode common” potential. In this paper we review flight and laboratory data on natural and EP generated plasma interactions with solar arrays, present the theory of spacecraft floating potentials, show how this theory is consistent with flight data, and extend this theory to spacecraft with high power Hall effect thrusters.
Katz, Ira↗