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At least 325 records · Page 18

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NASA NTRS2011

Large-Amplitude Transmitter-Associated and Lightning-Associated Whistler Waves in the Earth's Inner Plasmasphere at L less than 2

We report observations of very large amplitude whistler mode waves in the Earth fs nightside inner radiation belt enabled by the STEREO Time Domain Sampler. Amplitudes range from 30.110 mV/m (zero ]peak), 2 to 3 orders of magnitude larger than previously observed in this region. Measurements from the peak electric field detector (TDSMax) indicate that these large ]amplitude waves are prevalent throughout the plasmasphere. A detailed examination of high time resolution electric field waveforms is undertaken on a subset of these whistlers at L < 2, associated with pump waves from lightning flashes and the naval transmitter NPM in Hawaii, that become unstable after propagation through the ionosphere and grow to large amplitudes. Many of the waveforms undergo periodic polarization reversals near the lower hybrid and NPM naval transmitter frequencies. The reversals may be related to finite plasma temperature and gradients in density induced by ion cyclotron heating of the plasma at 200 Hz, the modulation frequency of the continuous ]mode NPM naval transmitter signal. Test particle simulations using the amplitudes and durations of the waves observed herein suggest that they can interact strongly with high ]energy (>100 keV) electrons on a time scale of <1 s and thus may be an important previously unaccounted for source of energization or pitch ]angle scattering in the inner radiation belt.

Breneman, A.↗

NASA NTRSDate not supplied

Decoding the energy inputs that drive the upper atmosphere with NASA’s Geospace Dynamics Constellation (GDC)

NASA’s Geospace Dynamics Constellation (GDC) mission will study the effect of space weather phenomena on Earth’s upper atmosphere ion and neutral gases and, in turn, their impact on human assets. GDC will provide multi-point observations to determine how the Earth’s upper atmosphere is driven to dynamic changes and extremes by the solar wind. Magnetospheric energy input, both kinetic and electromagnetic, will be captured by the Comprehensive Auroral Precipitation Experiment (CAPE), the Thermal Plasma Sensor (TPS), and the Near Earth Magnetometer Instrument in a Small Integrated System (NEMISIS). CAPE captures the complete kinetic energy inputs with observations of the precipitating and upgoing electrons and precipitating ions. TPS captures part of the electromagnetic energy inputs with observations of the thermal plasma velocity that map E-field inputs, and NEMISIS captures the other part of the electromagnetic energy input with measurements of magnetic field variations due to field aligned currents. We use similar observations from the Defense Meteorological Space Platform (DMSP) satellites to demonstrate the balance between the different energy inputs (electron and ion Joule heating and Poynting flux) during the different phases of storms. We explore the local time and spatial structure and the impact they have on atmospheric density and winds with simulations of the Global Ionosphere and Thermosphere Model (GITM) and demonstrate how GDC will enable us to reconstruct those energy inputs locally and regionally

Eftyhia Zesta↗

NASA NTRS1995

Plasmasphere Modeling with Ring Current Heating

Coulomb collisions between ring current ions and the thermal plasma in the plasmasphere will heat the plasmaspheric electrons and ions. During a storm such heating would lead to significant changes in the temperature and density of the thermal plasma. This was modeled using a time- dependent, one-stream hydrodynamic model for plasmaspheric flows, in which the model flux tube is connected to the ionosphere. The model simultaneously solves the coupled continuity, momentum, and energy equations of a two-ion (H(+) and O(+) quasineutral, currentless plasma. Heating rates due to collisions with ring current ions were calculated along the field line using a kinetic ring current model. First, diurnally reproducible results were found assuming only photoelectron heating of the thermal electrons. Then results were found with heating of the H(+) ions by the ring current during the recovery phase of a magnetic storm.

Guiter, S. M.↗

NASA NTRS1989

An RF heated tandem mirror plasma propulsion study

Experimental results on a tandem mirror hybrid plume rocket involving a three-stage system of plasma injection, heating, and subsequent injection through a magnetic nozzle are presented. In the experiments, a plasma is created by breaking down the gas with electron cyclotron resonance heating at 2 kW in the central cell, and the ion species is then heated to high temperatures with ion cyclotron resonance heating at 10 kW in the end cell. A Langmuir probe measured an electron density of 2.5 x 10 to the 16th/cu m and a temperature of 100 eV in the central cell and an ion density of 1.25 x 10 to the 17th/cu m and a temperature of 500 eV in the end cell.

Yang, T. F.↗

NASA NTRS1996

Analysis of EUV Dayglow Spectra of Triton, Titan and Earth

We have constructed a coupled ion and neutral chemical model of the ionosphere and thermosphere of Titan. Along with density profiles of ions and minor neutrals, we have computed the heating rates and heating efficiencies for the neutrals and chemical heating rates and efficiencies for the ions. We find that the neutral heating efficiency in our standard model varies from about 30% near 800 km to 22% near 2000 km. The most important heating processes are neutral-neutral reactions and photodissociation. The ion chemical heating rates maximize at about 10 eV cm(sup -3) s(sup -1), and the corresponding ion heating efficiencies peak near 1000 km at about 0.6%.

Fox, Jane L.↗

NASA NTRS1994

Acceleration efficiency in line-driven flows

We reexamine the physics of flow driving by line scattering of a continuum radiation source to determine the degree to which such line scattering can heat as well as accelerate the flow. Within the framework of the Sobolev theory for line transfer, we argue that the finite thermal width of the line scattering profile can lead to a significant 'Doppler heating' via photon frequency redistribution within a Sobolev resonance layer. Quantitative computation of this heating shows, however, that it is largely canceled by a corresponding cooling by the diffuse radiation. The resulting reduction in net Doppler heating or cooling means that the overall effect is only of limited importance in the energy balance of line-driven stellar winds. Through simple scaling relations, we compare the effect to other competing heating or cooling terms, including the ion-drag frictional heating recently discussed by Springmann and Pauldrach. We also provide a physical explanation of the unexpected cooling effect, and comment that its near cancellation of the anticipated heating provides another example of the tendency for ideal Sobolev theory to apply to a higher order than expected.

Gayley, Kenneth G.↗

NASA NTRS1982

Erosion of frozen sulfur dioxide by ion bombardment - Applications to Io

The erosion of frozen SO2 due to bombardment by both light and heavy ions (He and F) was measured for bombarding energies of 0.08 to 1.3 MeV/amu. The number of SO2 molecules ejected from the target per incident ion (i.e., the sputtering yield) was 50 for 1.5 MeV He ions and 7300 for 6 MeV F ions. Ion bombardment followed by heating produced an oxygen/sulfur residue which was much more stable against subsequent ion bombardment than the initial frozen SO2. The erosion rate of SO2 frost on Jupiter's moon Io depends strongly on the elemental composition and energy spectra of the magnetospheric ion flux which bombards the surface. The combined effects of ion bombardment and heating which produced residues on the target substrates may also occur on Io from magnetospheric ion bombardment and heating by volcanism. The experimental results compare favorably with a new model of the sputtering process which considers the energy loss of the incident ion to electronic excitation in the target.

Melcher, C. L.↗

NASA NTRS2010

Atypical Particle Heating at a Supercritical Interplanetary Shock

We present the first observations at an interplanetary shock of large amplitude (> 100 mV/m pk-pk) solitary waves and large amplitude (approx.30 mV/m pk-pk) waves exhibiting characteristics consistent with electron Bernstein waves. The Bernstein-like waves show enhanced power at integer and half-integer harmonics of the cyclotron frequency with a broadened power spectrum at higher frequencies, consistent with the electron cyclotron drift instability. The Bernstein-like waves are obliquely polarized with respect to the magnetic field but parallel to the shock normal direction. Strong particle heating is observed in both the electrons and ions. The observed heating and waveforms are likely due to instabilities driven by the free energy provided by reflected ions at this supercritical interplanetary shock. These results offer new insights into collisionless shock dissipation and wave-particle interactions in the solar wind.

Wilson, Lynn B., III↗

NASA NTRS2010

Large-Amplitude Electrostatic Waves Observed at a Supercritical Interplanetary Shock

We present the first observations at an interplanetary shock of large-amplitude (> 100 mV/m pk-pk) solitary waves and large-amplitude (approx.30 mV/m pk-pk) waves exhibiting characteristics consistent with electron Bernstein waves. The Bernstein-like waves show enhanced power at integer and half-integer harmonics of the cyclotron frequency with a broadened power spectrum at higher frequencies, consistent with the electron cyclotron drift instability. The Bernstein-like waves are obliquely polarized with respect to the magnetic field but parallel to the shock normal direction. Strong particle heating is observed in both the electrons and ions. The observed heating and waveforms are likely due to instabilities driven by the free energy provided by reflected ions at this supercritical interplanetary shock. These results offer new insights into collisionless shock dissipation and wave-particle interactions in the solar wind.

Wilson, L. B., III↗

NASA NTRS1983

Turbulent heating in solar cosmic ray theory

The heating of minor ions in solar flares by wave-wave-particle interaction with Langmuir waves, or ion acoustic waves, can be described by a diffusion equation in velocity-space for the particle distribution function. The dependence of the heating on the ion charge and mass, and on the composition of the plasma, is examined in detail. It is found that the heating mechanisms proposed by Ibragimov and Kocharov cannot account for the enhanced abundances of heavy elements in the solar cosmic rays.

Weatherall, J.↗

NASA NTRS1984

Turbulent heating in solar cosmic-ray theory

The heating of minor ions in solar flares by wave-wave-particle interaction with Langmuir waves, or ion acoustic waves, can be described by a diffusion equation in velocity-space for the particle distribution function. The dependence of the heating on the ion charge and mass, and on the composition of the plasma, is examined in detail. It is found that the heat mechanisms proposed by Ibragimov and Kocharov cannot account for the enhanced abundances of heavy elements in the solar cosmic rays.

Weatherall, J.↗

NASA NTRS1983

Radial evolution of ion distribution functions

A survey of solar wind ion velocity distributions and derived parameters (temperature, ion differential speed, heat flux, adiabatic invariants) is presented with emphasis on the heliocentric distance range between 0.3 and 1 AU traversed by the Helios solar probe. The radial evolution of nonthermal features are discussed which are observed to be most pronounced at perihelion. Within the framework of quasilinear plasma theory, wave particle interactions that may shape the ion distributions are considered. Some results of a self consistent model calculation are presented accounting for ion acceleration and heating by resonant momentum and energy exchange with ion cyclotron and magnetosonic waves propagating away from the Sun along the interplanetary magnetic field. Another tentative explanation for the occurrence of large perpendicular proton temperatures is offered in terms of heating by Landau damping of lower hybrid waves.

Marsch, E.↗

NASA NTRS1995

Magnetospheric space plasma investigations

Topics and investigations covering this period of this semiannual report period (August 1994 - January 1995) are as follows: (1) Generalized SemiKinetic (GSK) modeling of the synergistic interaction of transverse heating of ionospheric ions and magnetospheric plasma-driven electric potentials on the auroral plasma transport. Also, presentations of GSK modeling of auroral electron precipitation effects on ionospheric plasma outflows, of ExB effects on such outflow, and on warm plasma thermalization and other effects during refilling with pre-existing warm plasmas; (2) Referees' reports received on the statistical study of the latitudinal distributions of core plasmas along the L = 4.6 field line using DE-1/RIMS data. Other work is concerned in the same field, field-aligned flows and trapped ion distributions; and (3) A short study has been carried out on heating processes in low density flux tubes in the outer plasmasphere. The purpose was to determine whether the high ion temperatures observed in these flux tubes were due to heat sources operating through the thermal electrons or directly to the ions. Other investigations center along the same area of plasmasphere-ionosphere coupling. The empirical techniques and model, the listing of hardware calibrated, and/or tested, and a description of notable meetings attended is included in this report, along with a list of all present publication in submission or accepted and those reference papers that have resulted from this work thus far.

Comfort, Richard H.↗

NASA NTRS1987

Ion energetics in the inner coma of Comet Halley

The cometary plasma in the magnetic barrier just outside the diamagnetic cavity which surrounds the nucleus of Comet Halley is virtually stagnant. The outflowing neutral gas exerts an outward ion-neutral drag force on this plasma, which balances the inward magnetic pressure gradient force in the vicinity of the contact surface. The cometary ions are frictionally heated due to the relative motion of the ion and neutral gases. The ion flow velocity must have a few km/s nonradial component in order to explain the ion temperatures measured by the ion mass spectrometer on Giotto.

Cravens, T. E.↗

NASA NTRS1991

Fountain-Like Flow of Heavy Oxygen Ions From the Earth's Ionosphere in Response to Transverse Heating

Normally the gravitationally bound heavy O(+) ions in the Earth's ionosphere are in a diffusive equilibrium. However, when energized to superthermal energies of a few eV transverse to the geomagnetic field, the combined effects of the downward gravitational and the upward electric and mirror forces produce interesting flow patterns in the vertical direction like in a pulsating fountain. This flow pattern is studied by means of a particle-in-cell code.

Singh, Nagendra↗

NASA NTRS1983

On the equation of state of solar wind ions derived from Helios measurements

The radial evolution of such adiabatic invariants as the ion magnetic moments are studied on the basis of solar wind ion velocity distribution observations made by the Helios spacecraft between 0.3 and 1 AU. Significant differences between proton and alpha-particle parameters in wind velocity dependence are noted, and adiabaticity is on the average found to be violated. This violation is interpreted as evidence that protons are heated perpendicular to the field in fast streams. The contribution of the differential streaming energy to the total internal energy of the ions is also considered, and average heliocentric radial profiles for the ion heat fluxes are presented together with an examination of a possible ion heat flux role in the supply of thermal energy during the winds radial expansion. The present findings suggest that wave-particle interactions, and/or Coulomb collisions, are required to explain solar wind ion thermal energy states and radial temperature profiles.

Marsch, E.↗

NASA NTRS1994

Magnetospheric space plasma investigations

A time dependent semi-kinetic model that includes self collisions and ion-neutral collisions and chemistry was developed. Light ion outflow in the polar cap transition region was modeled and compared with data results. A model study of wave heating of O+ ions in the topside transition region was carried out using a code which does local calculations that include ion-neutral and Coulomb self collisions as well as production and loss of O+. Another project is a statistical study of hydrogen spin curve characteristics in the polar cap. A statistical study of the latitudinal distribution of core plasmas along the L=4.6 field line using DE-1/RIMS data was completed. A short paper on dual spacecraft estimates of ion temperature profiles and heat flows in the plasmasphere ionosphere system was prepared. An automated processing code was used to process RIMS data from 1981 to 1984.

Comfort, Richard H.↗

NASA NTRS1991

'Self-consistent' production of ion conics on return current region auroral field lines - A time-dependent, semi-kinetic model

We describe initial results from a time-dependent, semi-kinetic model of plasma outflow incorporating wave-particle interactions along current-carrying auroral field lines. Electrostatic waves are generated by the current driven ion cyclotron instability (CDICI), causing perpendicular velocity diffusion of ions plus electron heating via anomalous resistivity when and where the relative drift between electrons and ions exceeds certain critical velocities. Using the local bulk parameters we calculate these critical velocities, and so are able to self-consistently switch on and off the heating of the various particle species. Due to the dependence of these critical velocities on the bulk parameters of the species the heating effects exhibit quite complex spatial and temporal variations. A wide range of ion distribution functions are observed in these simulations, including conics with energies of a few electron volts and 'ring' distributions. The rings are seen to be a natural result of transverse heating and velocity filter effects and do not require coherent acceleration processes. We also observe the formation of a density depletion in hydrogen and enhanced oxygen densities at high altitudes.

Brown, David G.↗