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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS2011

Detection of Ionospheric Alfven Resonator Signatures Onboard C/NOFS: Implications for IRI Modeling

The 2008-2009 long-lasting solar minimum activity has been the one of its kind since the dawn of space age, offering exceptional conditions for investigating space weather in the near-Earth environment. First ever detection of Ionospheric Alfven Resonator (IAR) signatures in orbit offers new means for investigating ionospheric electrodynamics, namely MHD (MagnetoHydroDynamics) wave propagation, aeronomy processes, ionospheric dynamics, and Sun-Earth connection mechanisms at a local scale. Local and global plasma density heterogeneities in the ionosphere and magnetosphere allow for formation of waveguides and resonators where magnetosonic and shear Alfven waves propagate. The ionospheric magnetosonic waveguide results from complete magnetosonic wave reflection about the ionospheric F-region peak, where the Alfven index of refraction presents a maximum. MHD waves can also be partially trapped in the vertical direction between the lower boundary of the ionosphere and the magnetosphere, a resonance mechanism known as IAR. In this work we present C/NOFS (Communications/Navigation Outage Forecasting System) Extremely Low Frequency (ELF) electric field measurements related to IAR signatures, discuss the resonance and wave propagation mechanisms in the ionosphere, and address the electromagnetic inverse problem from which electron/ion distributions can be derived. These peculiar IAR electric field measurements provide new, complementary methodologies for inferring ionospheric electron and ion density profiles, and also contribute for the investigation of ionosphere dynamics and space weather monitoring. Specifically, IAR spectral signatures measured by C/NOFS contribute for improving the International Reference Ionosphere (IRI) model, namely electron density and ion composition.

Simoes, F.↗
NASA NTRS1994

Growing 'Alfvenic' modes in the upstream region of Saturn

Recent studies of low-frequency electromagnetic waves upstream of the Saturn bow shock have shown that these waves, in contrast to those at Earth, are observed not in one, but in at least two, distinct frequency bands. The results of wave mode identification based on the Hall-magnetohydrodynamic (MHD) model of plasma and observed wave polarization suggested that these waves propagate in the high beta intermediate mode. However, the underlying instability was not unambiguously determined. In the present paper we use the full electromagnetic dispersion relation derived from linear Vlasov theory in order to examine which of the plasma modes, with observed properties, are unstable in an isotropic Maxwellian plasma in the presence of backstreaming proton beams consistent with Voyager 2 observations at Saturn. As a result we find that the unstable 'Alfvenic' beam mode, as well as resonant and non-resonant fast magnetosonic modes have properties consistent with the data. Moreover, we find that in contrast to the Earth's upstream waves, at Saturn no 'kinetic' normal mode can account for the observed magnetic polarization.

Orlowski, D. S.↗
NASA NTRS1992

Nonlinear magnetosonic waves and mirror mode structures in the March 1991 Ulysses interplanetary event

In examining the March 23-25, 1991 Ulysses (2.2 AU) high speed solar wind events, two distinct plasma wave modes are found: steepened magnetosonic waves with whistler precursors and mirror mode structures. These two modes are locally generated by plasma instabilities, presumably associated with anisotropies existing in the energetic shock particles and solar wind plasma, respectively. The magnetosonic waves are generated by a right-hand resonant instability associated with an about 40 keV ion beam. By an extrapolation of the results presented here, assuming microflares and nanoflares at the sun generate shocks in the lower corona and these shocks accelerate energetic ions, it is suggested that the ions, via the right-hand resonant instability, generate magnetosonic waves which steepened to form 'microshocks'. These shocks could, in turn, accelerate more energetic ions, leading to a shock/energetic ion/magnetosonic wave cascade. These newly formed magnetosonic waves and shocks presumably could propagate in a broad range of directions, leading to energy dissipation over a large region of the outer corona.

Tsurutani, Bruce T.↗
NASA NTRS1984

Relationship between the IMF magnitude and Pc 3 magnetic pulsations in the magnetosphere

The relationships between the IMF magnitude and pulsation frequencies in the Pc 3-4 range simultaneously observed both at synchronous orbit and at low latitudes on the ground are statistically described. A theoretical discussion is given on how these observations can be interpreted in terms of the characteristic frequency of compressional Pc 3-4 magnetic pulsations in the magnetosphere, based on the well-established ion cyclotron resonance mechanism between magnetosonic mode of low-frequency upstream waves and narrowly reflected ion beams in the earth's foreshock.

Yumoto, K.↗
NASA NTRS1989

Test particle simulation study of whistler wave packets observed near Comet Giacobini-Zinner

Nonlinear interactions of water group ions with large-amplitude whistler wave packets detected at the leading edge of steepened magnetosonic waves observed near Comet Giacobini-Zinner (GZ) are studied using test particle simulations of water-ion interactions with a model wave based on GZ data. Some of the water ions are found to be decelerated in the steepened portion of the magnetosonic wave to the resonance velocity with the whistler wave packets. Through resonance and related nonlinear interaction with the large-amplitude whistler waves, the water ions become trapped by the packet. An energy balance calculation demonstrates that the trapped ions lose their kinetic energy during the trapped motion in the packet. Thus, the nonlinear trapping motion in the wave structure leads to effective energy transfer from the water group ions to the whistler wave packets in the leading edge of the steepened MHD waves.

Kaya, N.↗
NASA NTRS1992

Relativistic magnetosonic shock waves in synchrotron sources - Shock structure and nonthermal acceleration of positrons

The theoretical properties of relativistic, transverse, magnetosonic collisionless shock waves in electron-positron-heavy ion plasmas of relevance to astrophysical sources of synchrotron radiation are investigated. Both 1D electromagnetic particle-in-cell simulations and quasi-linear theory are used to examine the spatial and kinetic structure of these nonlinear flows. A new process of shock acceleration of nonthermal positrons, in which the gyrating reflected heavy ions dissipate their energy in the form of collectively emitted, left-handed magnetosonic waves which are resonantly absorbed by the positrons immediately behind the ion reflection region, is described. Applications of the results to the termination shocks of pulsar winds and to the termination shocks of jets emanating from the AGN are outlined.

Hoshino, Masahiro↗
NASA NTRS1991

Magnetohydrodynamic turbulence dissipation and stochastic proton acceleration in solar flares

The Alfven and fast magnetosonic wave MHD modes can stochastically accelerate protons from super-Alfvenic to ultrarelativistic energies in solar flares. It is the Landau resonance, however, which generates most of the magnetosonic wave energy being dissipated on electron heating rather than on stochastic proton acceleration. Alfven waves are also subject to a nonlinear wave-particle interaction, and nonlinear Landau damping can selectively and efficiently heat the ambient protons to preaccelerate many to super-Alfvenic speeds. A spectrum of Alfven waves can therefore energize protons from low-temperature thermal to ultrarelativistic energies through a combination of linear and nonlinear particle-wave interactions.

Miller, James A.↗
DOE OSTI2025

Dependence of ion-cyclotron range of frequencies instabilities on species mix and fast-ion distribution: I. Stability

Ion cyclotron emission (ICE) driven by fast ions has the potential to be a reactor relevant diagnostic of confined and escaping fast ions; moreover, controlled experiments in magnetic fusion devices can shed light on similar magnetospheric instabilities below and above the ion cyclotron frequency f ci . Dedicated DIII-D experiments studied instabilities below f ci and at cyclotron harmonics l f ci by injecting thirteen different neutral beam populations into plasmas with different thermal compositions of H, D, and 3He at five different values of toroidal field. High-frequency magnetic loops diagnose mode properties. Each beam type is individually injected for an approximate slowing-down time (~100 ms), resulting in a database of 2529 conditions that are analyzed in frequency bands corresponding to ICE harmonics and < f ci global Alfvén eigenmodes. The sub-cyclotron modes are more unstable at low field and in plasmas with large H concentration. For D injection, first harmonic ICE at f cD is more unstable in hydrogen plasmas but, for H injection, the converse is true (ICE at f cH is more unstable in D), suggesting that thermal same-species ions damp fundamental ICE. ICE stability also depends upon the pitch-angle anisotropy gradient and upon the ‘bump-on-tail’ gradient ∂f/∂v. Although the frequency of unstable ICE in these plasmas always occurs near the central cyclotron frequency, the precise value also depends on the Alfvén speed and beam direction, consistent with the idea that instability occurs for modes that simultaneously satisfy ω ≃ 2πlf ci , the magnetosonic dispersion relation, and the Doppler-shifted resonance condition.

electromagnetic ion cyclotron instabilities↗
NASA NTRS1983

Plasma rest frame frequencies and polarizations of the low-frequency upstream waves - ISEE 1 and 2 observations

The plasma rest frame frequencies and polarizations of the large amplitude low frequency (0.03 Hz) upstream waves are investigated using magnetic field data from the dual ISEE 1 and 2 spacecraft. The monochromatic sinusoidal waves associated with intermediate ion fluxes are propagating in both the Alfven and magnetosonic modes, in both cases with typical frequencies approximately 0.1 times the local proton gyrofrequency and wavelengths of approximately 1 R(E). It is shown that the generation of the magnetosonic mode can be explained by the cyclotron resonance mechanism driven by narrow reflected ion beams, but the concurrent observation of Alfven mode waves appears to require wave generation by the more isotropic diffuse ion distributions as well.

Hoppe, M. M.↗
NASA NTRS1978

Excitation of low frequency waves by streaming ions via anomalous cyclotron resonance

The effect of a small population of streaming ions on low-frequency waves with frequencies below the ion cyclotron frequency is analyzed for three modes of interest: Alfven waves, magnetosonic waves, and ion-cyclotron waves. The instability mechanism is the anomalous cyclotron resonance of the waves with the streaming ions. Conditions for excitation of the three types of waves are derived and expressions for the growth rates are obtained. Excitation of Alfven waves is possible even if the ratio of the densities of the streaming ions to the thermal ions is very small. For magnetosonic waves, excitation can easily occur if waves are propagating parallel or nearly parallel to the ambient magnetic field. As for ion-cyclotron waves, it is found that for the ion-whistler branch the excitation is suppressed over a broader range of wave frequencies than for the fast magnetosonic branch.

Wu, C. S.↗
NASA NTRS1993

Acceleration of Cometary H 2 0 Group Pickup Ions by Obliquely Propagating Nonlinear Magnetosonic Waves

The observations made during the encounter with comet Giacobini Zinner show that the character of MHD turbulence is governed by the magnetosonic (MS) waves generated by the pickup ions via a resonant cyclotron instability. We have performed the test particle calculations to study wave particle interactions via cyclotron resonance of water group cometary ions with (1) linearly polarized monochromatic MS waves, (2) circularly polarized monochromatic MS waves, and (3) magnetic fluctuations consisting of MS waves with a power spectrum which varies as 1 / k 2 .

magnetosonic↗