Electrostatic Ion Cyclotron Turbulence Research Articles

Origin of ion-cyclotron turbulence in the downward Birkeland current region

Linear stability analysis of the electron velocity distributions, which are observed in the FAST satellite measurements in the downward Birkeland current region of the magnetosphere, is presented. The satellite-measured particle (electrons and protons) velocity distributions are fitted with analytic functions and the dispersion relation is derived in terms of the plasma dispersion functions associated with those distribution functions. Numerical solutions of the dispersion relation show that the bump-on-tail structure of the electron velocity distribution can excite electrostatic ion-cyclotron instabilities by the Landau resonance mechanism. Nonlinear evolution of these instabilities may explain the observed electrostatic ion-cyclotron turbulence in the Birkeland current region. Excitation of other types of instabilities by the fitted electron velocity distributions and their relevance are also discussed.

Anomalous transport effects on the parallelEfield in downward auroral current regions of the Earth's magnetosphere

[1] The physical processes that determine the fluid quantities and the self-consistent electric field (E∥) parallel to the magnetic field have been an unresolved problem in magnetospheric physics for over 40 years. We review a recently developed kinetic and multimoment fluid theory for inhomogeneous, nonuniformly magnetized plasma with temperature anisotropy in the guiding-center and gyrotropic approximation and apply the theory to solve for the quasi steady state in the long-range potential region of a downward Birkeland current sheet when electrostatic ion cyclotron turbulence is dominant. We find that an electron, bump-on-tail-driven ion cyclotron instability produces the turbulence and that a large enhancement in ∣E∥∣ by nearly a factor of 40 occurs when the turbulence is present compared to the case when it is absent. Anomalous momentum transfer (anomalous resistivity) by itself has a very small effect on E∥; however, the presence of the turbulence and the anomalous energy transfers (anomalous heating and cooling) that result have a very large effect on the entire solution. In the electron and ion momentum balance equations for E∥, the turbulence enhances the magnitude of E∥ by reducing the effect of the generalized parallel pressure gradients and thereby enhancing the effect of the mirror forces. A new, nonlinear formula for the current-voltage relationship in downward Birkeland current regions is also given.

Anomalous momentum and energy transfer rates for electrostatic ion-cyclotron turbulence in downward auroral-current regions of the Earth’s magnetosphere. III

Recently, a new multimoment fluid theory was developed for inhomogeneous, nonuniformly magnetized plasma in the guiding-center and gyrotropic approximation that includes the effect of electrostatic, turbulent, wave-particle interactions (see Jasperse et al. [Phys. Plasmas 13, 072903 (2006); Jasperse et al., Phys. Plasmas13, 112902 (2006)]). In the present paper, which is intended as a sequel, it is concluded from FAST satellite data that the electrostatic ion-cyclotron turbulence that appears is due to the operation of an electron, bump-on-tail-driven ion-cyclotron instability for downward currents in the long-range potential region of the Earth’s magnetosphere. Approximate closed-form expressions for the anomalous momentum and energy transfer rates for the ion-cyclotron turbulence are obtained. The turbulent, inhomogeneous, nonuniformly magnetized, multimoment fluid theory given above, in the limit of a turbulent, homogeneous, uniformly magnetized, quasisteady plasma, yields the well-known formula for the anomalous resistivity given by Gary and Paul [Phys. Rev. Lett. 26, 1097 (1971)] and Tange and Ichimaru [J. Phys. Soc. Jpn. 36, 1437 (1974)].

The self-consistent parallel electric field due to electrostatic ion-cyclotron turbulence in downward auroral-current regions of the Earth’s magnetosphere. IV

The physical processes that determine the self-consistent electric field (E∥) parallel to the magnetic field have been an unresolved problem in magnetospheric physics for over 40 years. Recently, a new multimoment fluid theory was developed for inhomogeneous, nonuniformly magnetized plasma in the guiding-center and gyrotropic approximation that includes the effect of electrostatic, turbulent, wave-particle interactions (see Jasperse et al. [Phys. Plasmas 13, 072903 (2006); Jasperse et al., Phys. Plasmas13, 112902 (2006)]). In the present paper and its companion paper [Jasperse et al., Phys. Plasmas 17, 062903 (2010)], which are intended as sequels to the earlier work, a fundamental model for downward, magnetic field-aligned (Birkeland) currents for quasisteady conditions is presented. The model includes the production of electrostatic ion-cyclotron turbulence in the long-range potential region by an electron, bump-on-tail-driven ion-cyclotron instability. Anomalous momentum transfer (anomalous resistivity) by itself is found to produce a very small contribution to E∥; however, the presence of electrostatic, ion-cyclotron turbulence has a very large effect on the altitude dependence of the entire quasisteady solution. Anomalous energy transfer (anomalous heating and cooling) modifies the density, drift, and temperature altitude profiles and hence the generalized parallel-pressure gradients and mirror forces in the electron and ion momentum-balance equations. As a result, |E∥| is enhanced by nearly a factor of 40 compared to its value when turbulence is absent. The space-averaged potential increase associated with the strong double layer at the bottom of the downward-current sheet is estimated using the FAST satellite data and the multimoment fluid theory.

Transport of thermal plasma above the auroral ionosphere in the presence of electrostatic ion-cyclotron turbulence

Abstract. The electron component of intensive electric currents flowing along the geomagnetic field lines excites turbulence in the thermal magnetospheric plasma. The protons are then scattered by the excited electromagnetic waves, and as a result the plasma is stable. As the electron and ion temperatures of the background plasma are approximately equal each other, here electrostatic ion-cyclotron (EIC) turbulence is considered. In the nonisothermal plasma the ion-acoustic turbulence may occur additionally. The anomalous resistivity of the plasma causes large-scale differences of the electrostatic potential along the magnetic field lines. The presence of these differences provides heating and acceleration of the thermal and energetic auroral plasma. The investigation of the energy and momentum balance of the plasma and waves in the turbulent region is performed numerically, taking the magnetospheric convection and thermal conductivity of the plasma into account. As shown for the quasi-steady state, EIC turbulence may provide differences of the electric potential of ΔV≈1–10 kV at altitudes of 500 < h < 10 000 km above the Earth's surface. In the turbulent region, the temperatures of the electrons and protons increase only a few times in comparison with the background values.Key words. Magnetospheric physics (electric fields; plasma waves and instabilities)

Effect of double layers on magnetosphere–ionosphere coupling

The earth's auroral zone contains dynamic processes occurring on scales from the length of an auroral zone field line (about 10RE) which characterizes Alfven wave propagation to the scale of microscopic processes which occur over a few Debye lengths (less than 1 km). These processes interact in a time-dependent fashion since the current carried by the Alfven waves can excite microscopic turbulence which can in turn provide dissipation of the Alfven wave energy. This review will first describe the dynamic aspects of auroral current structures with emphasis on consequences for models of microscopic turbulence. In the second part of the paper a number of models of microscopic turbulence will be introduced into a large scale model of Alfven wave propagation to determine the effect of various models on the overall structure of auroral currents. In particular, we will compare the effect of a double layer electric field which scales with the plasma temperature and Debye length with the effect of anomalous resistivity due to electrostatic ion cyclotron turbulence in which the electric field scales with the magnetic field strength. It is found that the double layer model is less diffusive than the resistive model leading to the possibility of narrow, intense current structures.

On the Theory of Auroral Kilometric Radiation

The induced bremsstrahlung interaction between the auroral electrons and electrostatic ion cyclotron turbulence or double layer is effective for the generation of the auroral kilometric radiation. The theory explains the close correlation between the double layer or the electrostatic shocks and AKR.

Turbulent heating of heavy ions on auroral field lines

Electrostatic ion cyclotron turbulence and the associated acceleration of ions on auroral field lines are investigated analytically and by plasma simulations. The auroral plasma is assumed to consist of drifting electrons and stationary hydrogen and oxygen ions. It is found that for a given critical drift, the maximum ion perpendicular heating is generally larger for oxygen ions than for hydrogen ions. Simulation results show that unless the oxygen ions are a minority species, oxygen transverse heating generally exceeds that of hydrogen ions. Theory and numerical simulations are in good agreement.

Generation of auroral arc elements in an inverted‐V arc due to ion cyclotron turbulence

By using a two‐dimensional particle simulation it is shown that the electrostatic ion cyclotron turbulence driven by the field‐aligned current on auroral field lines can lead to striations of the current into east–west aligned current sheets of ion gyroradius scale (La ∼ ρi). Physical mechanism for the striation can be identified with nonlinear mode couplings of ion cyclotron waves resulting in condensation of the wave energy into a zero‐frequency mode. It is proposed that the auroral arc elements (La ∼ ρi), which collectively give rise to the inverted‐V arc (Lυ ≫ ρi), can be produced by the east–west aligned striations of the field‐aligned current on inverted‐V field lines.

Acceleration of hydrogen ions and conic formation along auroral field lines

Electrostatic ion cyclotron turbulence and the formation of ion conics at low altitudes (≈ 1500 km) along auroral field lines have been investigated analytically and by plasma numerical simulations. Ion cyclotron waves are assumed to be driven unstable by the upgoing cold ionospheric electrons associated with the downward auroral current. When the electron drift speed is comparable to the electron thermal speed, it was found that the large‐amplitude (eϕ/Te ≈ 1) coherent (ω = Ωi) ion cyclotron waves should exist along auroral field lines at low altitudes extending a few hundred kilometers. Ion conics are associated with ion cyclotron turbulence, and the ion bulk temperature is found to increase by a factor of 10 from the initial ionospheric temperature, while the temperature of the high‐energy tail can be as much as 100 times the ionospheric temperature. Theory and simulations are in good agreement.

Ion heating by strong electrostatic ion cyclotron turbulence

A theory of the ion heating due to electrostatic ion cyclotron (EIC) waves in the auroral zone is presented. Due to the slowly convecting nature of the EIC mode, quasi‐linear plateau formation cannot stabilize the waves, and growth occurs until the nonlinear mechanisms of ion resonance broadening and electron trapping provide saturation. The large amplitude and coherent nature of the resulting wave imply that quasi‐linear theory provides only a lower limit to the ion heating. An upper bound on the heating rate is derived using a time‐average model of ion dynamics in the coherent waves. The effects of ion heating in the presence of the magnetic gradient force and parallel electric fields are considered, with the result that perpendicular energies over 100 eV are easily attainable from a 1 eV source plasma. Perpendicular heating in the absence of a parallel electric field yields conical ion distributions, which in the presence of an electric field become field‐aligned beams.

Coherent anomalous resistivity in the region of electrostatic shocks

Evidence from the S3‐3 satellite indicates that parallel electric fields occur above 5,000 km altitude where electron drift velocity is highest for a current carrying plasma. Electrostatic ion cyclotron (EIC) turbulence is also observed in this altitude range. Previous models of current‐supported potential drops have neglected the role of turbulence. Large amplitude Alfvén waves can carry a current which drives the electrostatic ion cyclotron (EIC) mode unstable above 5,000 km. Anomalous resistivity associated with coherent EIC waves can support parallel electric fields in excess of 1 mV/m and may set up particle populations necessary to support oblique electrostatic shocks.

The rapid heating of coronal plasma during solar flares - Nonequilibrium ionization diagnostics and reverse currents

view Abstract Citations (12) References (29) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The rapid heating of coronal plasma during solar flares: nonequilibrium ionization diagnostics and reverse currents. Shapiro, P. R. ; Knight, J. W. Abstract A simple method is presented for diagnosing the electron temperature and density of a rapidly heated, coronal-type plasma from observable, nonequilibrium enhancements of X-ray line emission. This method, it is argued, is applicable to the study of solar flares. Accordingly, theoretically predicted line enhancements are given for a representative selection of X-ray lines prominent in the prefiare coronal emission spectrum. Some of these predicted line enhancements should soon be observable with instruments aboard the Solar Maximum Mission. Mechanisms, involving energetic electron beams and reverse currents, for the heating of coronal flare plasma rapidly enough to produce these nonequilibrium effects are examined. A timedependent calculation of Joule heating by the reverse current is presented for two illustrative electron beam strengths. For the first, classical Coulomb resistivity is assumed for the ambient plasma; for the second, anomalous resistivity is assumed to result from the onset of electrostatic ion-cyclotron turbulence. The results suggest that rapid heating can occur by a variety of mechanisms. Subject headings: plasmas - Sun: corona - Sun: flares - Sun: X-rays Publication: The Astrophysical Journal Pub Date: September 1978 DOI: 10.1086/156453 Bibcode: 1978ApJ...224.1028S Keywords: Gas Ionization; Plasma Diagnostics; Plasma Heating; Solar Corona; Solar Flares; Electron Beams; Electron Density (Concentration); Electron Energy; Fine Structure; Ion Acoustic Waves; Line Spectra; Ohmic Dissipation; Resistance Heating; Solar X-Rays; Stellar Models; Solar Physics; Plasma:Solar Corona; Plasma:Solar Flares; Solar Corona:Heating; Solar Flares:X Rays full text sources ADS |

Magnetic field‐aligned potential drops due to electrostatic ion cyclotron turbulence

Measurements of DC and AC electric fields and plasma densities on the S3‐3 satellite have shown that electrostatic ion cyclotron (EIC) turbulence is associated with significant DC electric fields parallel to auroral field lines. The EIC mode has been identified in regions of strong DC electric fields and magnetic field aligned currents by AC electric field and density fluctuations with frequency components between the local hydrogen gyrofrequency and its harmonics, and by wave vector polarization primarily perpendicular to the magnetic field at wavelengths of an ion gyroradius. The anomalous resistivity has been computed for measured AC electric fields of 50 mV/m in the EIC mode, yielding ∼1 mV/m DC parallel electric fields for measured currents of ∼10 µA/m². This theoretical result implies that several kV potential drops will occur if the anomalous resistivity region extends over several thousand kilometers along auroral field lines. This is adequate to accelerate auroral particles to observed energies and consistent with the scale height over which parallel electric fields and EIC turbulence are statistically observed on S3‐3.

Saturation of the cyclotron decay instability

The cyclotron decay instability results from the nonlinear interaction of a magnetosonic wave with two electrostatic ion-cyclotron waves in a multispecies plasma. A saturation mechanism for the instability is the nonlinear ion-cyclotron damping process involving the interaction of electrostatic ion-cyclotron and hydromagnetic-acoustic turbulence with a nonlinear plasma response near an ion-cyclotron frequency. Strong nonlinear ion heating can be a consequence of the saturation particularly if electron Landau damping is reduced by quasi-linear diffusion or trapping.

Anomalous resistivity of the auroral plasma in the top‐side ionosphere

Using plasma parameters from a stormtime ionospheric energy balance model, we have investigated a steady state level of electrostatic ion cyclotron turbulence. It has been determined that ion temperature anisotropy is responsible for the saturation rather than one‐dimensional ion heating. Both the electrical resistivity and ion anisotropy are evaluated as functions of altitude and field aligned Birkeland current.

Anomalous resistivity resulting from electrostatic ion cyclotron turbulence

An expression is found for the collisionless electrical resistivity resulting from a current driven electrostatic ion cyclotron instability.

Topside ionosphere ion heating due to electrostatic ion cyclotron turbulence

We have performed a model calculation of the ion heating rate due to electrostatic ion cyclotron turbulence in the topside ionosphere, with the assumption that the formation of a plateau on the electron velocity distribution is inhibited. Ion temperature profiles are obtained and the implications of the heating effect on anomalous resistivity calculations are discussed.