bluuebunny/crossref_metadata_2025 huggingface dataset:
Pioneering the swinging 1960s into the 1970s and 1980s
Authors: Ness Norman F.
Published: February 2004

Webster's Third International Dictionary defines pioneer several ways: as a noun, “…one that begins or helps develop something new and prepares a way for others to follow,” or as an active verb “…to open or prepare, as a way or a region, for others to follow, i.e., explore.” It was my good fortune to become part of the pioneering efforts of the U.S. space program at the NASA Goddard Space Flight Center in 1960, soon after the space age began with Sputnik 1 being launched by the USSR on October 4, 1957. This paper will summarize important events of my participation in the exploration of space as they relate to studies of magnetic fields in interplanetary space, of the planets Mercury to Neptune and the Moon, of interactions of the solar wind with the planets, and of corotating magnetospheres with some moons of the giant planets. The most intense period in my career was the decade 1963‐1973, when I was involved in 15 successful spacecraft launches.
A synoptic study of Pc 3, 4 waves using the Air Force Geophysics Laboratory magnetometer array
Authors: Chi P. J. , Russell C. T. , Le G. , Hughes W. J. , Singer H. J.
Published: February 2004

We have studied the Pc 3, 4 wave amplitude recorded at the Air Force Geophysics Laboratory (AFGL) magnetometer network on August 19–20, 1978. During this period of time the wave amplitude was modulated coherently across the magnetometer network. From observations, three important factors affecting the wave amplitude measured on the ground have been determined as follows: (1) the intrinsic or magnetospheric magnitude of the wave events, (2) their local time dependence, and (3) the subsurface conductivity. We present a statistical method to calculate these three factors from the simultaneous observations of a longitudinal array of magnetometers. The intrinsic wave amplitude is found to be bursty. On short timescales the wave amplitudes do not follow our expectations based on long‐term statistical studies. Amplitudes vary rapidly without concomitant changes in the solar wind. We also find that the amplification of the wave amplitude due to the subsurface conductivity is different from station to station. For the northern five AFGL stations it is found that the ratio between the largest amplification and the smallest amplification is close to 2. The local time dependence maximizes approximately at local noon. A possible reason due to the reflection of Alfvén waves in the ionosphere is discussed.
Ionospheric turbulence induced in the lower part of the E region by the turbulence of the neutral atmosphere
Authors: Gurevich A. V. , Borisov N. D. , Zybin K. P.
Published: February 2004

Strong large‐scale oscillations of the electric field and plasma density observed on rockets in the lower part of the ionospheric E layer and the scattering of low‐frequency radar waves (ƒ ≤ 10 MHz) in the same region of ionosphere are not well explained by the existing theories. We explore here a new mechanism of the excitation of plasma turbulence in the lower part of the E region, connected with the turbulent motion of neutral atmosphere. The problem is solved in a fluid approximation. The spectrum of induced fluctuations of electron and ion densities and electric field is determined and analyzed. The cross section for scattering of radio waves from the lower ionosphere is determined.
An empirical model of the solar wind flow around Mars
Authors: Kallio E.
Published: February 2004

An empirical model that describes the proton velocity around Mars has been developed. The analytical axially symmetric model is based on Automatic Space Plasma Experiment with a Rotating Analyzer three‐dimensional (3‐D) proton velocity observations on the Phobos 2 spacecraft near Mars in early 1989. The model includes a bow shock, a magnetopause, and an impenetrable obstacle a few hundred kilometers above the surface of Mars. The flow model can be used to model both an open and a closed magnetosphere. The model velocity values are found to describe rather well the 3‐D proton velocity observations in the Martian magnetosheath and magnetosphere both on the dayside and on the nightside. Characteristics of the velocity field are studied on the basis of an ideal MHD model, assuming that the magnetic field is frozen into the proton flow and that there are no proton sources or sinks. Under these assumptions the velocity field can be used to calculate the proton density and the magnetic field. When the proton density and the magnetic field are compared with the observations, quite good qualitative agreement between the model and the data is found. Our model shows that a relative simple flow model can predict several observed plasma and field features near Mars.
The am annual‐diurnal variations 1959‐1988: A 30‐year evaluation
Authors: de La Sayette P. , Berthelier A.
Published: February 2004

This paper is devoted to a reevaluation of the annual and universal time variations of the geomagnetic activity through a study of the am index over a 30‐year period starting in 1959, taking into account the interplanetary magnetic field polarity. A visualization of the annual diurnal variations, showing the continuous evolution of the times of the diurnal maximum and minimum, is applied both to this extended data set and to the simulation of the main processes invoked to explain these variations. The various contributions of the different processes to the annual‐diurnal variations of the activity are discussed, including the Russell‐McPherron and the McIntosh effects, as well as a third source introduced in this study. One concludes that three contributions, two of which being attached to the Bz southward influence, must be combined to account for the observations.
Solitary kinetic Alfvén waves: A study of the Poynting flux
Authors: Volwerk Martin , Louarn Philippe , Chust Thomas , Roux Alain , de Feraudy Hervé , Holback Bengt
Published: February 2004

Using a particular mode of the FREJA wave experiment (three magnetic and one electric simultaneous measurements), we have investigated the electromagnetic structure of the solitary kinetic Alfven waves observed in the topside ionosphere. It is shown that these strong electromagnetic spikes (ΔE ≈ 100 mV/m and ΔB ≈ 10 nT) have mainly a rotational character with, nevertheless, a tiny compressional component (ΔB‖/ΔB ≈ 10 %). They seem to be associated with small‐scale (100 m) tubular current structures. On the assumption that their electric component is perpendicular to the magnetic one their Poynting flux is estimated. Values of the order of 10−3 W/m2 are measured.
The multi‐instrumented studies of equatorial thermosphere aeronomy scintillation system: Climatology of zonal drifts
Authors: Valladares C. E. , Sheehan R. , Basu S. , Kuenzler H. , Espinoza J.
Published: February 2004

A spaced‐antenna scintillation system was installed at Ancon, Peru, in May 1994 to measure scintillation of 250‐MHz signals from a geostationary satellite by three antennas spaced in the magnetic east‐west direction. These measurements were used to establish the climatology of the zonal drift of the irregularities which cause equatorial scintillations. The major objective of this study is to compare this drift climatology to the climatology of zonal neutral wind which is the driver of the equatorial electrodynamics. A comparison of these two climatologies in conjunction with scintillation statistics may provide some clues regarding factors which help or hinder the formation of equatorial spread‐F (ESF). With these objectives in mind, the first year's drift and scintillation statistics have been presented as a function of local time, season and magnetic activity and compared with the statistics of ion drift published earlier from incoherent scatter radar observations. The scintillation drift is in good agreement with the Jicamarca radar observations except for the fact that the local time dependence of our drift observations exhibit a broader maximum. The broad maximum may be attributed to lower ion drag experienced in the presence of ESF due to sustained uplifting of the ionosphere. During magnetically active periods, the scintillation drift often exhibits east to west reversals presumably because of the disturbance dynamo effects. The westward drifts during such reversals may be as large as 100 m/s. We have also modeled the zonal drifts as a seasonal basis by using Hedin's neutral wind model and Anderson's fully analytical ionospheric model. The modeled zonal drifts present good quantitative agreement with the drifts obtained with the scintillation technique.
IMPs, EGOs, and Skyhooks
Authors: McDonald Prank B.
Published: February 2004

In the October 1994 issue of the Journal of Geophysical Research, J. Simpson, E. Parker, and C. Sonnett wrote of the early history of space physics. Previously, J. Van Allen had written a monogram on the genesis of magnetospheric physics, and H. Newell (“Above the atmosphere”) and J. Naugle (“First among equals”) had given excellent accounts of the initial development of the space sciences within NASA and the broader research community. I write as a member of the second generation or Junior Pioneers who profited greatly from the foundation laid down by the Pioneers of the era. With the second wave it was possible to fully participate in the dramatic expansion of the nation's space science program that occurred in the 1960s. In this brief memoir, I give a personal recollection of this period and try to relate it to some of the current developments in space physics.
Dreicer order ambipolar electric fields at Parker's steady state solar wind sonic critical point
Authors: Scudder Jack D.
Published: February 2004

The time‐independent ambipolar electric field E(r*) at Parker's solar wind sonic critical point r* is analytically shown to range between (0.6–2.0) ED(r*), where ED(r*) is the local Dreicer [1959, 1960] electric field. The ratio of ambipolar to Dreicer field strength scales as (〈T*〉/106° K)3/2 20/ln Λ, where 〈T*〉 is the average of electron and ion temperatures at the critical point. As a million degree corona is nearly certainly required for the wind as we observe it, E(r*) ≃ ED(r*). Since the steady state solar wind is characterized by no parallel currents, these large electric fields require generalizations of Dreicer's discussion of what are the results of such large electric fields. This is clear since even when E = 0.43ED in a homogeneous plasma, the electron fluid drifts at the electron thermal speed with respect to the ions in the absence of collective instabilities. Consequences of such a large current at the critical point are not found at 1 AU. The electric fields at the orbit of earth [Scudder, 1995b] and at the base of the fully ionized layer of the transition region [Scudder, 1995a] are nevertheless comparable to the local Dreicer electric field. From a theoretical point of view, the finding that such large electric fields are required in the plasma points to the need for basic modifications to the macroscopic description of a magnetized plasma that are outside of the Chapman‐Enskog‐Spitzer‐Braginskii closure schemes that assume perturbative corrections to homogeneous solutions as an expansion in the small parameter ε = E‖/ED. It is suggested that the possibility to form gradients, to allow heat to flow, and to allow the bulk plasma to move can short circuit the homogeneous expectations of bulk runaway implicit in the Dreicer discussion. However, the intrinsic bifurcation of the electron distribution reflects the physics of the Coulomb cross section in the presence of the very strong dc field and is suggested as the underlying reason for the omnipresent nonthermal distributions inside and out of the critical point. The ambipolar electric field at the solar wind critical point from two‐fluid theory and the electric field assumed in Spitzer‐Braginskii heat transport are shown to disagree at almost all the possible two‐fluid critical points. This same closure flaw also afflicts the fluid portion of any turbulence description that may be thought relevant for the wind.
Ionospheric electron heating by structured electric fields: Theory and experiment
Authors: Kagan Ludmila M. , Kelley Michael C. , Doe Richard A.
Published: February 2004

Ionospheric electron heating due to structured electric fields is considered herein. In a survey of incoherent scatter (IS) radar data gathered with the Sondrestrom IS radar in Greenland (66.99°N, 50.95°W), we find that such heating takes place at F layer altitudes accompanying intense auroral events in the E layer. Because of competition with heating by precipitating particles this type of heated region can only be observed when it is shifted from the geomagnetic field line penetrating the associated E layer arc. We have detected regions of this sort in which we argue that the temperature is enhanced either by illumination of auroral ionospheric cavities by an Alfvén wave source or by collocation with turbulent electrostatic fields. We have developed a model that predicts the observed Te enhancement in the F layer. We also present a consistent physical picture of auroral activity involving coupling between the magnetosphere and the ionosphere via electrostatic and wave‐ or turbulence‐induced field‐aligned currents. Both can be generated by the region surrounding the electron acceleration zone. Applying our model to the observations allows us to separate electron heating due to structured fields (with a pronounced maximum in the F layer), static field‐aligned currents (with the electron temperature smoothly increasing with altitude from the F layer up to the magnetosphere), and electron impact in the E layer. In turn, the temperature observations give us information on the Alfvén wave impinging on the auroral F layer and/or the turbulent electrostatic fields which map to the ionosphere.
Cosmic ray solar semidiurnal anisotropy: 1. Treatment of experimental data
Authors: Ahluwalia H. S. , Fikani M. M.
Published: February 2004

We have analyzed data obtained with 39 globally distributed detectors, with median primary rigidity of response (Rm) in the range: 10 GV ≤ Rm ≤ 330 GV, for the period 1953 to 1992. The time interval covers several epochs of solar activity maxima, minima, and polar field reversals. Data are sparse for earlier period but adequate after 1970. We have investigated long‐term changes in the parameters applicable to the annual mean solar semidiurnal variation. We show that its dependence on the median asymptotic latitude of viewing (λm) is given by cos2 λm. The data are consistent with a double power law fit in rigidity for the entire period of our study. The power law exponents are given by γ1, = 0.7 ± 0.3 (if R ≤ Rp,) and γ2 = − 0.4 ± 0.2 (if R > Rp), where Rp is the peak primary rigidity. The values of Rp near maximum for even solar activity cycles (20, 22) are quite large (∼125 GV) compared to other periods. These large values lie close to the epochs of magnetic polarity reversals from negative (q A < 0) to positive (q A > 0) in the northern hemisphere of Sun. During these times, the exponent γ2 acquires large negative values. Near solar activity minima, the values of Rp, are among the lowest at about 40 GV. We have also computed the mean limiting primary rigidity (Rc) for each year. The values of Rc lie close to 50 GV for solar activity minima and near 100 G V for maxima. In other words, the values of Rc are very close to those of Rp. Moreover, the correspondence between them is good. Both exhibit solar as well as Hale cycle variations.
Self‐consistent determination of the electrostatic potential barrier due to the photoelectron sheath near a spacecraft
Authors: Zhao Hua , Schmidt R. , Escoubet C. P. , Torkar K. , Riedler W.
Published: February 2004

A series of scientific spacecraft either in orbit or to be launched in the very near future carries ion emitters for active control of the electrostatic surface potential. The ion beam emission changes, via the associated reduction of the positive surface potential, the photoelectron sheath around the spacecraft which may result in the formation of a potential barrier. In this study, a spherically symmetric model of the photoelectron sheath around a spacecraft (with conductive surface) is analyzed. An algebraic equation is set up to describe the current equilibrium between the escaping photoelectrons, incoming ambient plasma electrons, and the artificially emitted charged particles at the surface of the spacecraft. The height of the potential barrier can be given by solving the algebraic equation, if the electrostatic surface potential of the spacecraft, the density and temperature of the ambient plasma electrons are known. The position of the potential barrier is estimated with the assumption that the electrostatic potential distribution is of a Debye form/The method has been applied to the data gained from the Geotail spacecraft at times when the ion emitter was operational. From the calculation, it is shown that the height of the potential barrier grows from 0.27(Tph/e) to 0.91(Tph/e), as the ion emitter current increases from 9.2(μA) to 38.3(μA). The maximum barrier height appears to be about 2 V, when the ion emitter operates at its maximum current about 50 μA.
Atomic hydrogen corona of Uranus
Authors: Herbert Floyd , Hall Doyle T.
Published: February 2004

We have analyzed Voyager 2 ultraviolet spectrometer observations of the H Lyman α emission from the atomic hydrogen corona of Uranus. The resulting estimated hydrogen density distribution has a radial profile ∝ 1/r2. This distribution implies a weakly bound or escaping population of hot (≳2 eV) hydrogen not thermalized with the 0.07 eV thermosphere/exosphere. The hot H density is enhanced on the sunward side of Uranus, with the maximum weakly associated with the dayside magnetic pole. The source of this hot hydrogen is presumably near the position we have found for the density maximum. Therefore we suggest that this source of hot H atoms may be associated either with electroglow or else with the dayside aurora.
A statistical study of UHF auroral backscatter at large magnetic aspect angle: A reanalysis of unpublished results from 1968
Authors: Moorcroft D. R.
Published: February 2004

In 1968 a joint study of radar‐auroral backscatter was carried out by Bell Laboratories, Western Electric, and Lincoln Laboratory using the 448‐MHz radar of the Prince Albert Radar Laboratory. They made observations covering a range of magnetic aspect angles from 4.5° to 16°, but the results were not published in the open literature. These data have been reanalyzed and used to obtain results on the aspect sensitivity, flow angle dependence, absolute scattering cross section, Doppler velocity distributions, and the azimuthal variation of Doppler velocity for large aspect angle auroral backscatter. The average aspect sensitivity was found to be independent of aspect angle and to decrease with increasing backscatter power. Estimates of the largest absolute scattering cross sections were much greater than previous estimates at the same aspect angles, but these cross sections appear to be consistent with previous values once the long duration of the experiment is taken into account. Backscatter power was found to be essentially independent of flow angle.
Detection of localized, plasma‐depleted flux tubes or bubbles in the midtail plasma sheet
Authors: Sergeev V. A. , Angelopoulos V. , Gosling J. T. , Cattell C. A. , Russell C. T.
Published: February 2004

Recent studies have shown that most Earthward transport hi the midtail, high‐beta plasma sheet takes place in the form of short‐lived, high‐speed plasma flow bursts. Bursty bulk flows are observed both when the plasma sheet is thin, such as during substorm expansion, and when it is thick, such as during substorm recovery. We present multi‐instrument observations from the ISEE1 and ISEE 2 spacecraft to argue that when the plasma sheet becomes thick and close to its equilibrium state, the plasma and magnetic field signatures of high‐speed flow events are consistent with the theoretically predicted signatures of plasma‐depleted flux tubes or “bubbles” [Pontius and Wolf, 1990; Chen and Wolf, 1993]. These signatures consist of a decrease in the plasma pressure and an increase in the Bz‐component of the magnetic field accompanying the high speed flow. We show that the Earthward moving bubbles are separated from the plasma ahead of them by a sharp tangential discontinuity. The layer ahead of the bubbles exhibits flow and magnetic field shear consistent with flow around an Earthward moving obstacle. The bubble is in approximate total pressure balance with the surrounding medium. We show that there is a systematic difference in the orientation of the discontinuity measured at ISEE 1 and 2, implying a small (about 1–3 RE) cross‐tail size of the bubbles.
Observations of bow shock motion during times of variable solar wind conditions
Authors: Lepidi Stefania , Villante Umberto , Lazarus Alan J. , Szabo Adam , Paularena Karolen
Published: February 2004

We examine seven periods during which IMP 8 made multiple crossings of Earth's bow shock during times when IMP 7 data were available to monitor external solar wind conditions. The positions of the bow shock encounters are consistent with reference shock shape models normalized to the solar wind conditions. We find that multiple crossings can usually be interpreted as being due to changes in the external solar wind parameters. We also find that inward motion of the shock is accompanied by large magnetosheath densities just before the shock sweeps across the spacecraft. We perform a chi‐square minimization analysis using a limited set of Rankine‐Hugoniot conditions across the bow shocks in order to determine their speeds and normals; we find that the shock velocities are generally consistent with the postulated inward and outward bow shock motions. Whether the crossings are observed on the dawnside or the duskside, most of the bow shock structures are quasi‐perpendicular due to changes in the external field orientation just upstream of the shock. The orientations of the normals are consistent with a model in which effects of changes in external conditions propagate as shock shape deformations which move downstream from the nose to the flanks.
The angular extents of solar/interplanetary disturbances and modulation of galactic cosmic rays
Authors: Cliver E. W. , Cane H. V.
Published: February 2004

From comparisons of solar activity with galactic cosmic ray (GCR) modulation events at 1 AU and in the outer heliosphere, we argue against the suggestion that individual solar eruptions can give rise to major cosmic ray modulation events that span the heliosphere. For the inner heliosphere, we use a sample, covering a ∼30‐year period, of eruptive flares and confidently associated interplanetary shocks to show that the following three parameters, determined at 1 AU, all decrease with increasing longitudinal distance from the flare: probability of detecting a shock, shock transit speed, and magnitude of any associated Forbush decrease (FD). In addition, we associate each of the 18 large (≥10%) FDs observed at Earth from 1958 to 1991 with one or more eruptive flares located near solar central meridian (E47 – W31). For each of the six heliosphere‐wide modulation events that have been associated thus far by other investigators with individual flares we are able to identify multiple powerful flares, with one or more of these eruptive events generally occurring close in ecliptic longitude to each affected spacecraft. Supporting evidence for the limited longitudinal extent of major interplanetary effects from single eruptions is provided by a remarkable outer heliosphere event in late 1989. A large shock (ΔV – 200 km/s) and Forbushlike decrease (18%) at Pioneer 10 at ∼50 AU was not preceded by a commensurate disturbance at Voyager 1/Voyager 2/Pioneer 11 located at ∼30–40 AU on the opposite side of the heliosphere. We conclude that wide‐spread modulation events in the outer heliosphere result from systems of solar/interplanetary disturbances that, only in aggregate, encompass 360° of ecliptic longitude, rather than from azimuthally symmetric shocks associated with single eruptive flares. We point out that the documented preference for coronal mass ejections to occur at low and middle solar latitudes will naturally form the wedge‐shaped barrier proposed by Van Allen and Mihalov to account for the “inside‐out” pattern of recovery of individual modulation events observed at progressively greater distances in the heliosphere.
Nonlocal dynamics of the collisional Rayleigh–Taylor instability: Applications to the equatorial spread F
Authors: Migliuolo Stefano
Published: February 2004

The linear stability and eventual nonlinear saturation of plasma depletions in the high‐altitude, F layer ionosphere are modeled via two‐fluid equations for a plasma consisting of electrons and a single species of ions. Major emphasis is given to the nonlocal properties of the perturbations, permitting the description of relatively long wavelength modes (κ⊥L → 1, where L a characteristic plasma scale length and κ⊥ is the wavevector component perpendicular to the magnetic field), a regime not accessible under the often used “local approximation.” The condition for onset (marginal stability), as well as the spatial structure of strongly growing linear eigenmodes, are derived analytically for an ionosphere that includes a height‐dependent collisional diffusion coefficient. A nonlinear model, comprising both quasilinear and three‐wave coupling, is used to illustrate the dynamics of the depletions, and estimates are given for the saturated amplitudes.
Parametric study of loop‐like magnetic cloud propagation
Authors: Vandas M. , Fischer S. , Dryer M. , Smith Z. , Detman T.
Published: February 2004

Propagation and evolution of loop‐like magnetic clouds in the ambient solar wind flow are studied self‐consistently using ideal MHD equations in the 2½ dimensional approximation. Magnetic clouds, as ideal force‐free objects (cylinders lying in the ecliptic plane), are ejected near the Sun and followed beyond the Earth's orbit. We investigate the influence of various initial parameters, like the injection velocity or different steady states of the solar wind, on their propagation and evolution. Simulation results are compared with an analytical theory of magnetic cloud evolution (expansion) published by Osherovich et al. [1993a, b]; good agreement is found, although no need to use a polytropic index less than 1 (as in the analytical approach) is required.
Coupling of Kelvin‐Helmholtz and current sheet instabilities to the ionosphere: A dynamic theory of auroral spirals
Authors: Lysak Robert L. , Song Yan
Published: February 2004

The Kelvin‐Helmholtz instability has often been invoked to describe transport at the magnetopause. However, recent observations of vortices in the postnoon sector of the auroral zone [Elphinstone et al., 1993] have indicated that structure of these vortices is inconsistent with the evolution of the standard Kelvin‐Helmholtz instability, and is instead consistent with the theory of auroral spirals proposed by Hallinan [1976]. Models of the Kelvin‐Helmholtz instability coupled to the ionosphere have generally neglected the effect of the field‐aligned current which is generated by the velocity shear. This current must close in the ionosphere, and leads to the presence of a magnetic shear in addition to the velocity shear. This magnetic shear is susceptible to a dynamic current sheet instability, which has many of the same properties as the Kelvin‐Helmholtz instability but produces vortices which are wound in a sense consistent with spiral observations. This instability, which may grow much faster than Kelvin‐Helmholtz, may provide a basis for a dynamic theory of auroral spirals.
Does chaos alter the ensemble‐averaged drift equations?
Authors: Usadi A. , Wolf R. A. , Heinemann M. , Horton W.
Published: February 2004

Can the average drift of an ensemble of charged particles in Earth's plasma sheet still be described by adiabatic theory even if many particles in the ensemble execute non adiabatic motion? This is part of a broader spectrum of questions which asks if chaotic microscopic processes can be parameterized as macroscopic ones when ensemble averaged. Through a comparison of numerical test particle simulations with adiabatic theory we show that the average particle drift speed of an appropriately chosen ensemble of nonrelativistic particles, including those executing chaotic and Speiser [1965, 1967] motion, is given correctly by the simple adiabatic guiding‐center drift formula. We further show that the dispersion of particles about the mean drift speed tends to decrease due to the presence of chaotic particle scattering. These conclusions are demonstrated for tail‐like magnetic fields B(x, z), including a non zero y component. The presence of an electric field does not change the conclusions provided that E/B is small compared to the total velocity of an individual particle. Thus we have shown that a standard way of representing particle transport in the middle magnetosphere, namely, the formalism describing average drift in a flux tube filled with an isotropic particle distribution, remains a useful theoretical description for the central plasma sheet, despite the presence of non adiabatic particle motion.
Reconstruction of grand minima of solar activity from Δ14C data: Linear and nonlinear signal analysis
Authors: Voss H. , Kurths J. , Schwarz U.
Published: February 2004

Using a special technique of data analysis, we have found 34 grand minima of solar activity in a 7700‐year‐long Δ14C record. The method used rests on a proper filtering of the Δ14C record and the extrapolation of verifiable results for the later history back in time. Additionally, we have applied a method of nonlinear dynamics, the recurrence rate, to back up the results. Our findings are not contradictory to the record of grand minima by Eddy [1977] but constitute a considerable extension. Hence it has become possible to look closer at the validity of models. This way, we have tested the model of Barnes et al. [1980]. There are hints for that the grand minima might solely be driven by the 209‐year period found in the Δ14C record.
Minor heavy ion electromagnetic beam–plasma interactions in the solar wind
Authors: Gomberoff L. , Gnavi G. , Gratton F. T.
Published: February 2004

It is shown that the velocity threshold of the right‐hand‐polarized ion‐ion resonant instability decreases with decreasing gyrofrequency values of the beam ions, and also, the system can become unstable for very small beam concentrations. In order to illustrate the results, a plasma consisting of a proton background and a very tenuous O+ ion beam is considered. It is shown that for an ion beam of nO+/np = 10−4, the threshold velocity is VO+ ∼ 1.36VA (VA is the Alfvén velocity), and the maximum growth rate is of the order of 10−3Ωp (Ωp is the proton gyrofrequency). We apply these results to high‐speed solar‐wind‐type plasmas consisting of a proton background, an alpha particle beam, and a beam of O+ ions. It is also shown that the presence of alpha particles reduces the velocity instability threshold of the O+‐p resonant instability.
The organized nonlinear dynamics of the magnetosphere
Authors: Klimas A. J. , Vassiliadis D. , Baker D. N. , Roberts D. A.
Published: February 2004

The linear prediction filters computed byBargatze et al.[1985] have resulted in a turning point in the study of solar wind‐magnetosphere coupling. The evolution of the filters with varying activity provides a clear demonstration that the coupling is nonlinear. The filters have thus brought about the end of one era of linear correlative studies and the beginning of a new era of nonlinear dynamical studies. Two separate, but complementary, approaches have emerged in these dynamical studies, analogue modeling and data‐based phase space reconstruction. The reconstruction research has evolved from the original autonomous method studies, which were not conclusive, to the more recent input‐output studies that are more appropriate for the solar wind‐driven magnetosphere and have produced more reliable results. At present it appears that the modeling and reconstruction approaches may be merged in future attempts to produce analogue models directly from the results of the input‐output data‐based methods. If this can be accomplished, it will constitute a major step forward toward the goal of a low‐dimensional analogue model of the magnetospheric dynamics derived directly from data and interpreted in terms of magnetospheric physics. These developments are reviewed in three sections: autonomous data analysis methods, analogue models, and input‐output data analysis methods. The introduction provides sufficient information to read each of these sections independently.
A useful relationship between time‐dependent and steady state solutions of the Boltzmann equation
Authors: Bieber John W.
Published: February 2004

A simple proof shows that, under certain conditions, a solution of the time‐dependent Boltzmann equation integrated over the lifetime of a finite event equals the steady state solution. This is true regardless of the shape of the particle injection function. A key restriction is that the transport parameters remain constant in time on the flux tube or set of flux tubes where the measurements are made, a condition most likely to be satisfied in short‐duration events. The theorem has important practical benefits: it means that steady state analysis techniques can be applied with rigor to certain solar particle events, and at the same time it permits improved statistical accuracy by summing measurements over the whole event.
Linear theory and modeling of the Rayleigh‐Taylor instability leading to the occurrence of equatorial spread F
Authors: Sultan P. J.
Published: February 2004

In a test of the generally accepted Rayleigh‐Taylor (R‐T) instability mechanism for equatorial spread F (ESF), a linear instability growth rate γRT is derived following the formalism of Haerendel (preprint, 1973) which takes into account the variations of physical parameters along geomagnetic flux tubes. The resulting form of γRT extends the results of previous work by including direct dependencies on transequatorial neutral winds, zonal electric fields, vertical and horizontal ionospheric density gradients, the presence of an E region, and chemical recombination. Realistic atmospheric and ionospheric density model inputs are used for the first time to make quantitative calculations of R‐T growth rates for a range of geophysical conditions. The key result of this study is that time/altitude domains having positive calculated instability growth rates are found to coincide with observed time/altitude patterns of ESF occurrence over both a monthly and a yearly time frame. This success in being able to model the climatological occurrence of ESF lends support to the physical model adopted for the instability mechanism and opens up new avenues of research into ESF predictability on a night‐to‐night and even an hour‐to‐hour basis.
An eight‐moment approximation two‐fluid model of the solar wind
Authors: Olsen Espen Lyngdal , Leer Egil
Published: February 2004

In fluid descriptions of the solar wind the heat conductive flux is usually determined by the use of the classical Spitzer‐Härm expression. This expression for the heat flux is derived assuming the gas to be static and collision‐dominated and is therefore strictly not valid in the solar wind. In an effort to improve the treatment of the heat conductive flux and thereby fluid models of the solar wind, we study an eight‐moment approximation two‐fluid model of the corona‐solar wind system. We assume that an energy flux from the Sun heats the coronal plasma, and we solve the conservation equations for mass and momentum, the equations for electron and proton temperature, as well as the equations for heat flux density in the electron and proton fluid. The results are compared with the results of a “classical” model featuring the Spitzer‐Härm expression for the heat conductive flux in the electron and proton gas. In the present study we discuss models with heating of the coronal protons; the electrons are only heated by collisional coupling to the protons. The electron temperature and heat flux are small in these cases. The proton temperature is large. In the classical model the transfer of thermal energy into flow energy is gradual, and the proton heat flux in the solar wind acceleration region is often too large to be carried by a reasonable proton velocity distribution function. In the eight‐moment model we find a higher proton temperature and a more rapid transfer of thermal energy flux into flow energy. The heat fluxes from the corona are small, and the velocity distribution functions, for both the electrons and protons, remain close to shifted Maxwellians in the acceleration region of the solar wind.
Solar wind–driven flows in the Jovian magnetosphere
Authors: Desai M. I. , Simnett G. M.
Published: February 2004

Ion anisotropies in the sub‐MeV/nucleon energy region have been measured during the inbound pass of Ulysses through the Jovian magnetosphere. Azimuthal flows in the direction opposite to corotation were detected at several different times, each lasting approximately hours, in the boundary layer and the outer magnetosphere. Similar flows were also observed in parts of the middle magnetosphere whenever Ulysses was far away from the plasma sheet. Such flows were not detected when the Voyager spacecraft traversed the dayside magnetosphere. This could be explained by the fact that Ulysses found the dayside outer magnetosphere in a greatly extended state, compared with the Voyager encounters. In addition, Ulysses also traversed the dayside middle magnetosphere at higher magnetic latitudes than the Voyager spacecraft. The plasma composition during periods of anticorotational flow was more like that measured during solar energetic particle events rather than that measured during the plasma sheet crossings, implying an external source, i.e., the solar wind. From the ion composition and energy spectra we show that solar wind interaction may be an important factor in determining the plasma flow in many regions of the dayside magnetosphere. Mechanisms such as large‐scale magnetic reconnection, “viscous‐like” interactions, and impulsive penetration of plasmoids were ruled out on the basis of magnetic field measurements and charged particle distribution functions around the time of the outermost magnetopause crossing. Adapting recently formulated models of the situation in the terrestrial magnetosphere to Jupiter, we suggest that the anticorotational flows and solar wind‐like composition are caused by “patchy” reconnection at high latitudes. Plasma from the reconnected flux tube forms a low‐latitude boundary layer, from which the solar wind plasma enters the outer magnetosphere. In this model, anticorotational flows in the middle magnetosphere could also be caused by solar wind plasma entering the high‐latitude regions directly from the reconnection site.
Population of the near‐Earth magnetotail from the auroral zone
Authors: Peroomian Vahé , Ashour‐Abdalla Maha
Published: February 2004

This paper reports the development and performance of a large scale kinetic simulation using a three‐dimensional model of the terrestrial electric and magnetic fields in an effort to reach a better understanding of the ionospheric contribution to the near‐Earth (x < 10 RE) region during quiet and slightly disturbed times. The simulation employed the Tsyganenko [1989] magnetic field model and an electric field derived from the Heppner and Maynard [1987] ionospheric potentials. For the conditions considered in this study (southward interplanetary magnetic field (IMF), ϕXT = 20–40 kV), it was found that the cleft ion fountain plays a relatively minor role in supplying particles to the near‐Earth region. The ionospheric contribution to the near‐Earth proton population is significant during quiet times with the bulk of the O+ ions in the near‐Earth region coming from the auroral zone up welling region. However, the plasma mantle becomes the dominant hot proton source during more active times. Using the nightside auroral zone as a source, we launched distributions of H+, He+, and O+ ions and calculated densities, pressures, and other bulk parameters in the near‐Earth plasma sheet and partial ring current. Because of the static nature of the model, ionospheric ions had very limited access to the trapped ring current, but the ions formed a reservoir of energetic particles just outside this region that in theory could act as a source for the ring current during more active times. The residence time of ions in the model is too short for charge exchange losses to become significant, and the principal loss mechanism is through the dusk flank of the magnetopause, with precipitation into the ionosphere playing a minor role.
On the formation of wave packets in planetary foreshocks
Authors: Muschietti L. , Roth I. , Ergun R. E.
Published: February 2004

Kinetic localization of beam‐driven Langmuir waves is studied for parameters relevant to the electron foreshock environment. Particle‐in‐cell simulations of the interaction occurring between energetic electrons and Langmuir waves are performed. It is shown that the nonlinearities in the resonant electrons lead to the formation of packets growing out of the noise. The characteristic spatial scale depends upon the beam velocity and has a weak dependence on the wave amplitude. The mechanism takes place within shorter timescales and for smaller amplitudes than the classic nonlinearities due to bulk electrons and ions. As an example, we apply the results to observations made in the Earth and Jovian foreshocks.
An “in situ” investigation of early time multi‐ion expansion processes in an F region chemical release
Authors: Szuszczewicz E. P. , Earle G. , Bateman T. , Klos Z. , Kiraga A. , Schunk R. W.
Published: February 2004

We present the results of a controlled rocket‐borne experiment designed to study the very early time expansion characteristics (t < 1.0 s) of an artificially created ion cloud in the F region ionosphere. Using an attitude control system which optimized the investigation of parallel and perpendicular to B expansion properties, we have investigated the ionization and multi‐ion expansion features of the cloud constituents Ba+, Li+, and Ti+ and the relative influences of Saha and solar UV ionization mechanisms, ion‐neutral collisionality, and gyrokinetic orbits. Unique “in situ” diagnostic capabilities provided highly resolved measurements of the plasma structure within the cloud, the variations in mean ion composition, and the distributions of electron temperature. Among the findings we report that (1) the observations can be characterized by an expanding photoionized shell of structured cloud ions, with kinetically snowplowed background O+ ions and appreciable amounts of Li+ ions as forerunners on the leading and trailing edges; (2) a 25% depleted ionosphere is left behind the expanding shell; (3) the density structure within the cloud is created by gyrokinetic motion of individual ion components; and (4) electron temperatures are elevated on the average by 80% above the background levels with the hottest region (at twice the background temperature) in the domain of forerunner ions. The results are in agreement with simple analytical models and large‐scale simulations, corroborating and quantifying issues involving ionization, cycloidal dynamics, snowplow effects, depletion levels, and electron heating; while the unexpected discovery of Ti+ suggests an incomplete understanding of the burning process in the artificial cloud source and the temperatures in its ignition system.
A nonspecialist's guide to kinetic simulations of space plasmas
Authors: Winske D. , Omidi N.
Published: February 2004

The basic concepts involved in formulating and analyzing simulations of kinetic space plasmas are presented for readers with little background in simulation methods. Issues related to choosing the appropriate physics models and numerical algorithms, such as the correct representation for the plasma, proper description of the electromagnetic fields, geometric effects, initial and boundary conditions, and diagnostics, are discussed. Some of the strengths and limitations of the various approaches are also described. Explicit examples involving the simulation of collisionless shocks are presented to illustrate these points. Questions related to numerical accuracy and verification of the results are also examined and again illustrated through appropriate examples.
Motion of the footpoints of heliospheric magnetic field lines at the Sun: Implications for recurrent energetic particle events at high heliographic latitudes
Authors: Fisk L. A.
Published: February 2004

The interplay between the differential rotation of the footpoints of heliospheric magnetic field lines in the photosphere and the subsequent nonradial expansion of these same field lines with the solar wind from rigidly rotating coronal holes can result in extensive excursions of heliospheric magnetic field lines with heliographic latitude. Thus magnetic field lines at high latitudes can be connected directly to corotating interactions regions (CIRs) in the solar wind at low latitudes at larger heliocentric distances. A model is presented which illustrates that this effect can account for the observations from the Ulysses spacecraft that recurrent energetic particle events, which appear to originate in low‐latitude CIRs, occur at the highest latitudes observed. The model also has implications for the observation that the heliospheric magnetic field appears to have a tighter than expected spiral angle at high latitudes over the south solar pole and for the modulation of galactic cosmic rays.
Outflow of He+ from the polar ionosphere: Comparison of hydrodynamic and kinetic descriptions
Authors: Leer Egil , Lie‐Svendsen Øystein , Olsen Espen Lyngdal , Hansteen Viggo H.
Published: February 2004

Singly ionized heliurn, a minor species in the polar ionosphere, is being propelled out along open magnetic field lines by an outward polarization electric field. In the present study we compare the kinetic and hydrodynamic descriptions of this transonic outflow treating the singly ionized helium as a test particle population in a static background of singly ionized oxygen and electrons. We find that the resultant He+ particle fluxes are equal in both the eight‐moment hydrodynamic description and in the kinetic description based on the Fokker‐Planck equation. A five‐moment hydrodynamic description gives a flux that is some 40% lower. The increase of the He+ energy flux with altitude is also equal in the eight‐moment hydrodynamic and in the kinetic descriptions.
On the seasonal dependence of medium‐scale atmospheric gravity waves in the upper atmosphere at high latitudes
Authors: Bristow W. A. , Greenwald R. A. , Villain J. P.
Published: February 2004

Seasonal dependence of medium‐scale atmospheric gravity waves is examined in SuperDARN HF radar data and through analysis of the gravity wave dispersion relation. We found that the probability of gravity wave observation in the HF radar data is highest in winter months and lowest in summer months. The winter probability of observation in a given 2‐hour period with sufficient amounts of ground backscatter peaks at about 0.8, while in the summer the probability remains near 0.4. Examination of the dispersion relation shows that there is a seasonal dependence to the altitude profile of the gravity wave's vertical wavelength that may lead to a seasonally dependent reflection of the waves resulting from the mesospheric temperature gradient. The dispersion relation predicts that for waves of a given horizontal wavelength, the minimum wave period that may be transmitted through the mésosphère is longer in the summer than in the winter; the longer the wavelength, the longer the minimum period. Thus some waves that are transmitted through the mesosphere in the winter may not be transmitted in the summer. This seasonal dependence predicted from the dispersion relation is consistent with the HF radar observations.