bluuebunny/crossref_metadata_2025 huggingface dataset:
Contributions of the high‐degree multipoles of Neptune's magnetic field: An Euler potentials approach
Authors: Ho C. W. , Huang T. S. , Gao S.
Published: February 2004

A new technique of calculating the Euler potentials α and β based on the geometrical relations between the magnetic field structure and Euler potentials [Huang and Yu, 1995] was used to determine the α and β coordinates of Neptune's magnetic field. The result is a mathematical definable coordinate system for a field of which the nondipole terms are nonnegligible. A framework is thus established for future studying of plasma dynamics such as particle drifts and plasma convection. The magnetic field model used is the Goddard Space Flight Center/Bartol Research Institute's I8E1 model. The full I8E1 model was used to investigate the significance of the higher‐degree multipoles beyond the octupole (up to the eighth degree in the spherical harmonic expansions), particularly near the planet's surface. The results were compared to those of the O8 model, which is a simplified version of the I8E1. We found that the higher‐degree terms do not change significantly the overall results of the O8. However, on the planet's surface, footprints of inner drift shells fall into a few concentrated areas, opening more regions into which no particle from these drift shells can precipitate. Close examination of these “open” regions indicates that they are isolated magnetic field systems that may trap particles locally. Our results entail new interpretation of the Voyager 2 UV spectrometer measurements on the planet's nightside surface emissions. Particle precipitation emissions are found to be concentrated on the areas into which the drift shells collapse. These areas of high concentration of drift shell footprints and emissions indicate that the strong emissions are due to high particle downflux into these regions of high magnetic field intensity. Our results suggest that magnetic moments higher than the octupole may constitute nonnegligible components of the magnetic field of planets that have high nondipole terms, such as Neptune and Uranus. For Neptune the high‐degree terms should be included for studying plasma processes within two planetary radii.
Features observed in the trailing regions of interplanetary clouds from coronal mass ejections
Authors: Neugebauer M. , Goldstein R. , Goldstein B. E.
Published: February 2004

ISEE 3 plasma and magnetic field data are used to study features in the trailing regions of interplanetary plasma clouds resulting from coronal mass ejections (CMEs). Approximately one fifth of these events contain periods ≥6 hours for which the interplanetary magnetic field is quiet and nearly radial (|Bx|/B > 0.9). Arguments are presented that the association of quiet radial fields with CMEs is a causal relation, rather than coincidence. The quiet radial fields occur in the trailing, rather than the leading, regions of the CMEs, and they coincide with periods of declining solar wind speed. In some cases the radial field period overlaps periods with other CME signatures, while in other cases the radial field interval follows the disappearance of those signatures. Another trailing‐region feature exhibited by approximately half the CMEs detected by ISEE 3 is a period of outward propagating Alfvén waves. Possible causes of these signatures are discussed.
The temporal and spatial development of MeV proton acceleration at interplanetary shocks
Authors: Kallenrode May‐Britt
Published: February 2004

Particle events observed in association with interplanetary shocks exhibit a wide variety of different features. In this paper we will demonstrate how these features can be understood in terms of a spatially and temporally varying shock efficiency and the subsequent interplanetary propagation. The examples presented here will show that while the location of the observer relative to the shock is an important factor in determining the event properties, the radial and temporal evolution of the shock also plays an important role. In particular, there are shocks which in a given energy range predominately accelerate particles close to the Sun, while in others the shock efficiency increases as they propagate outward. Another goal of this paper is to demonstrate that the black box model used here is able to fit the data.
Core ion flux bursts within solitary kinetic Alfvén waves
Authors: Knudsen David J. , Wahlund Jan‐Erik
Published: February 2004

The Freja cold plasma analyzer (CPA) makes high time resolution measurements of the angle‐ and energy‐integrated core ion velocity distribution (< 20 eV) with spatial resolutions of ∼10 m. In a preliminary study, Knudsen et al. [1994] reported that in the most intense core ion heating regions, integral ion flux becomes bursty on timescales of tens of milliseconds, implying spatial scales of hundreds of meters. The present study demonstrates that these flux bursts are associated with solitary kinetic Alfvén waves (SKAW), and we show examples of a one‐to‐one correspondence between SKAW and ion flux bursts. In principle, the measured flux bursts can result from variations in ion temperature, drift, density, composition, or changes in the functional form of the velocity distribution (e.g., Maxwellian versus conical), or some combination thereof. By modeling the dependence of integral flux on various combinations of these parameters, we calculate the amount of variation needed to explain ion flux bursts, which can have amplitudes in excess of 109 cm−2s−1. This value is comparable in magnitude to the ram flux of cold ions in a 103 cm−3 plasma and is also comparable to the peak ion flux in ion outflow regions measured on previous spacecraft missions. In most cases, flux bursts can be explained either by localized heating to several eV or by bulk drifts of the order of 1–2 km/s; however, it is not possible to distinguish between these two possibilities from the CPA data alone. Plasma wave data show that SKAW are associated with broadband ELF waves extending from dc up to and beyond the proton cyclotron frequency ƒH+. Wave power above ƒH+ and below the oxygen cyclotron frequency ƒO+ is localized within SKAW and could in principle lead to localized ion heating. The region of the spectrum between ƒH+ and ƒO+ appears less localized and could produce a more uniform background of heated ions, depending on the relative contributions to total heating of the different spectral regimes.
High‐speed ion flow, substorm current wedge, and multiple Pi 2 pulsations
Authors: Shiokawa K. , Baumjohann W. , Haerendel G. , Paschmann G. , Fennell J. F. , Friis‐Christensen E. , Lühr H. , Reeves G. D. , Russell C. T. , Sutcliffe P. R. , Takahashi K.
Published: February 2004

We have studied the onset timing of earthward high‐speed ion flow observed by the AMPTE/IRM satellite at 12.3 Earth radii (RE) and 0100 MLT in the central plasma sheet during an isolated substorm event on March 1, 1985. The timing of this onset is compared with that of the substorm current wedge and Pi 2 magnetic pulsations observed by a large number of ground‐based stations and the AMPTE/CCE, GOES 5, and ISEE 1 satellites and with that of high‐energy particle injection observed at Los Alamos geosynchronous satellite 1982‐019. The onset of earthward high‐speed flow is observed 3 min before the onset of the global current wedge formation and 6 min before the onset of high‐energy particle injection. The three bursts of the high‐speed flow observed at AMPTE/IRM are likely to correspond to three compressional pulses observed at AMPTE/CCE at 6 RE and three Pi 2 wave packets observed at midlatitude ground stations. On the basis of these observations we conclude that the substorm current wedge is caused by inertia current and the current due to flow shear at the braking point of the earthward high‐speed flow during the initial stage of the substorm expansion phase. The braking point is well separated from the near‐Earth neutral line. It is also suggested that the compressional pulses and fluctuations of field‐aligned currents generated at the flow braking point can be the initial cause of the Pi 2 magnetic pulsations in the inner magnetosphere.
Decaying equatorial F region plasma depletions
Authors: Hysell D. L. , Kelley M. C.
Published: February 2004

We analyze plasma density data from the AE‐E satellite to determine how F region irregularities decay. This satellite had a low inclination orbit that was ultimately circular at an altitude of 434 km. It frequently observed plasma depletions in the postsunset regime during spread F conditions, sometimes along a trajectory affording a “horizontal cut” perspective through the field‐aligned irregularities. On one occasion, the satellite passed through nearly the same region of depleted flux tubes on sequential orbits. Data from these orbits imply that the irregularities decay at a constant rate over a broad range of horizontal scale sizes. We introduce a statistical model of the intermediate‐scale (10 km – 100 m) plasma irregularities and use it to infer a value for the perpendicular ambipolar diffusion coefficient from the measured decay rate. The value we estimate (2 m2/s) is close to the expected classical value. The uniform decay rate and the quasi‐universal nature of the intermediate‐scale spectra hint that the irregularities themselves maintain a characteristic shape as they decay. High‐resolution satellite density measurements show that irregularities have the form of kilometer‐scale quasi‐periodic depletions. We propose a one‐dimensional, nonlinear model of the collisional interchange instability which admits a closed‐form, steady state solution predicting the shape of the depletions. Computer simulations of the model produce kilometer‐scale waves that resemble the in situ observations.
Electron precipitation associated with geomagnetic activity: Balloon observation of X ray flux in South Atlantic anomaly
Authors: Jayanthi U. B. , Pereira M. G. , Martin I. M. , Stozkov Y. , D'Amico F. , Villela T.
Published: February 2004

A stratospheric balloon experiment was conducted on December 20, 1994, with an X ray detector to measure fluxes of precipitation electrons in the South Atlantic anomaly (SAA) region of Brazil. For the first time in the SAA, this detector system of high sensitivity monitored three events of increases in X ray fluxes which axe associated with simultaneous decreases in geomagnetic H field component. The most prominent event with an X ray emission equivalent to ≈1/4 of the diffuse cosmic X ray flux permitted the determination of the spectrum in the energy range of 18.6 to 120 keV. The inferred electron spectrum showed a steep low‐energy component below 150 keV (E0=16 keV). The electron flux estimates are lower compared to earlier balloon results obtained at the time of a severe magnetic storm. The inferred fluxes from our balloon experiment are consistent with the electron fluxes observed by the S3–2 satellite and are lower than the OGO 5 satellite measurements, both obtained in the SAA at L= 1.3. Further, the estimates are compatible with the P78‐1 satellite fluxes present in the drift loss cone at L = 1.25. The presence of sufficient electron fluxes at L = 1.3 region in the SAA, and the similarity between the electron spectrum observed by the satellite experiments and that inferred in our balloon experiment, prompted us to investigate the possibility of the access of these electrons present at satellite altitudes into L = 1.13 regions during a mild storm. Interestingly, this prominent X ray flux event is associated with two succesive southward turnings of Bz component of the interplanetary magnetic field (IMF). Precipitation of essentially low‐energy electrons below 150 keV occurred at the first northward reversal of IMF Bz and after the latter northward reversal higher energy electrons (> 150 keV) also precipitated. We suggest the diffusion of particles from higher L regions into flux tubes connected to the SAA region, due to electric field fluctuations associated with succession of substorms, in a process similar to the “enhanced radial diffusion” proposed by Lyons and Schulz [1989]. To compare or to relate the inferred fluxes from the balloon experiment with the satellite measurements and for a better understanding of the precipitation of electrons during magnetic disturbances, it is necessary to have additional experimental investigations in the SAA.
Large‐scale structures and multiple neutral lines associated with coronal mass ejections
Authors: Webb D. F. , Kahler S. W. , McIntosh P. S. , Klimchuck J. A.
Published: February 2004

We use Yohkoh soft X‐ray telescope (SXT) images of eruptive events visible against the solar disk to examine the coronal structures and the boundaries of the large‐scale magnetic fields considered to be involved in coronal mass ejections (CMEs). From an initial list of about 100 large‐scale events we selected five for detailed study. The transient X‐ray structures in these events spanned distances across the solar surface ranging from 35 to >100 heliographic degrees, comparable to the spans of white light CMEs observed at the limb. The widths of the coronal loop arcades spanned two or three neutral lines, or a single, highly convoluted neutral line. Our interpretation of these results is that multipolar magnetic systems are a common configuration of the source fields of many CMEs, contrary to the first‐order approximation that CMEs involve the eruption of simple, bipolar structures.
An estimate of large‐scale solar wind density and velocity profiles in a coronal hole and the coronal streamer belt
Authors: Pätzold Martin , Tsurutani Bruce T. , Bird Michael K.
Published: February 2004

With the use of the total electron content data obtained by the Ulysses Solar Corona Experiment (SCE) during the first solar conjunction in summer 1991, two data sets were selected, one associated with a coronal hole and the other associated with coronal streamer belt crossings. To determine a large‐scale coronal streamer belt density profile, the electron content of the tracking passes embedded in the coronal streamer belt were corrected for the contributions from coronal hole densities. The inferred large‐scale streamer belt electron density profile has a radial falloff exponent of −2.4 for distances greater than 7 Rs implying the acceleration of the slow solar wind according to υ(r) ∼ r0.4, in qualitative agreement with SOHO results. The acceleration terminates beyond 60 Rs in agreement with Helios in situ observations. All radial electron density profiles inferred from coronal radio sounding observations, particularly during times of high solar activity, are dominated by coronal streamer contributions. They are applicable to coronal streamers, confined to a limited latitude range about the heliospheric current sheet, and they are not representative of a large‐scale mean coronal electron density profile. Because of a lack of data, similar analysis of the coronal hole electron content data was not unequivocally feasible. The coronal hole tracking passes corrected for contributions from coronal streamer areas display large electron content and density fluctuations inconsisting with the plume interpretation by Woo [1996]. Assuming that the lowest densities represent typical hole densities and comparing these with streamer densities at the same distance, we found the streamer‐to‐hole density ratio to be a factor of 10, which agrees with white light coronagraph results.
Latitudinal distribution of >106 MeV protons and its relation to the ambient solar wind in the inner southern and northern heliosphere: Ulysses Cosmic and Solar Particle Investigation Kiel Electron Telescope Results
Authors: Heber B. , Bothmer V. , Dröge W. , Kunow H. , Müller‐Mellin R. , Sierks H. , Wibberenz G. , Ferrando P. , Raviart A. , Paizis C. , Potgieter M. S. , Burger R. A. , Hattingh M. , Haasbroek L. J. , McComas D.
Published: February 2004

We present observations and model calculations of the modulated intensities of galactic cosmic ray protons above 106 MeV/n along the Ulysses trajectory. Data are taken by the Cosmic and Solar Particle Investigation (COSPIN) Kiel Electron Telescope (KET) from spring 1993 to fall 1996. During this time period solar activity decreased and galactic cosmic rays recovered. To separate spatial from temporal variations we used the University of Chicago measurements from IMP 8 near Earth and compare the residual spatial variation with time independent modulation models. According to standard drift dominated modulation model, one would expect a radial gradient of ≈2%/AU and a latitudinal gradient of ≈1.2%/degree in both hemispheres. The measured mean radial gradient of «3%/AU is within the uncertainties in good agreement with the model predictions. However, the measured mean latitudinal gradient has a value of (0.33 ± 0.04)%/degree in both hemispheres at intermediate latitudes and is by a factor of 4 lower than expected. In the modified models the latitudinal gradient is in agreement with the measured ones when we increase the diffusion coefficient κθθ perpendicular to the magnetic field in polar direction to a value of 15% of the diffusion coefficient parallel to the magnetic field. The latitudinal gradients >106 MeV protons calculated by modified modulation models are in very good agreement with the measured ones at intermediate latitudes. At lower latitudes, when Ulysses is embedded in the streamer belt, the models predict approximately the same latitudinal gradient than at intermediate latitudes, whereas the measured ones are significant smaller, or even vanishing. The observations support the previous conclusion from Paizis et al. [1995] that a significant latitudinal gradient is only observed when Ulysses is outside the streamer belt. Another remarkable observation is the difference of the radial gradient Gr at ∼3.5 AU in the southern (Gr≈3.5%/AU) and in the northern hemisphere (Gr≈2.3%/AU). Probable reasons for the significantly lower radial gradient in the northern hemisphere can be either a spatial asymmetry of the heliosphere or temporal variations.
Alfvénic fluctuations in fast and slow solar winds
Authors: Orlando S. , Lou Y.‐Q. , Peres G. , Rosner R.
Published: February 2004

We compute properties of Alfvénic fluctuations within a wide frequency range (i.e., 10−6 s−1 ≲ ƒ ≲ 10−2 s−1) in both high‐ and low‐speed magnetized radial solar winds. In particular, the radial and frequency variations of the normalized cross helicity σc, the Alfvén ratio RA, and other relevant quantities associated with Alfvénic fluctuations are presented and analyzed. Because of the existence of the Alfvén critical radius rA and a characteristic frequency ƒc for a given magnetized solar wind profile, continuous reflection effects are clearly manifest at frequencies lower than several times ƒc. Since outward propagating fluctuations which many authors consider Alfvénic fluctuations have been detected in the high‐latitude solar wind (which is fast and steady), such continuous reflection effects in the low‐frequency end of the fluctuation spectrum may be found in the Ulysses data. In order to strengthen our case, comparisons are carried out between our theoretical results and previous data analyses of observations from the Helios 1 and 2 spacecraft in the radial range of 0.29 AU ≲ r ≲ 1.0 AU. Stronger evidence for continuous reflection effects of low‐frequency Alfvénic fluctuations is found in the high‐speed solar wind close to the Sun than in the low‐speed solar wind in general.
On the stability of stationary nongyrotropic distribution functions: Coupling and purely growing waves
Authors: Brinca Armando L. , Romeiras Filipe J.
Published: February 2004

Unperturbed particle distributions exhibiting gyrophase bunching can linearly couple the eigenmodes of parallel propagation and destabilize otherwise stable magnetoplasmas. Previous research on the parallel stability of nongyrotropic populations has either considered homogeneous but time‐varying distributions (TNG) associated with closed phase spaces (solutions of the homogeneous Vlasov equation) or homogeneous, stationary distributions (SNG) arising from open phase spaces (solutions of the Vlasov, or transport equation with source and sink terms). Destabilization of otherwise stable media in the TNG case was only reported when the unperturbed gyrophase bunching generated a finite perpendicular current that coupled the electrostatic and electromagnetic parallel eigenmodes at frequencies shifted by multiples of the cyclotron frequency of the TNG species. Here we demonstrate that introduction of SNG in a particle population of an otherwise stable magnetoplasma can (1) bring about unstable linear mode coupling among the parallel eigenmodes for finite perpendicular currents (as was the case for TNG distributions) albeit now without the frequency shifts, and (2) stimulate nonoscillatory purely growing waves (zero real frequency within a finite wavenumber band) in nongyrotropic environments that only couple parallel electromagnetic waves (zero unperturbed perpendicular current), behavior not encountered in TNG media.
Density depletions and current singularities observed by Freja
Authors: Stasiewicz K. , Holmgren G. , Zanetti L.
Published: February 2004

High time resolution data collected by the Freja spacecraft in the topside ionosphere (h ∼ 1500 km) reveal that the “low‐frequency turbulence” observed commonly below the ion gyrofrequency consists of a large number of coherent plasma structures which represent intense field‐aligned currents (j‖ ∼ 30 − 300 μAm−2) accompanied by plasma density depletions (cavities). The electromagnetic fluctuations are identified with inertial electron Alfvén waves (IEAW) at perpendicular wavelengths ≲6 km. The coherent structures with singularly strong j‖ are consistent with being the resonance cones of IEAW generated by localized sources at h > 1 RE. The density cavities are observed to be directly related to the magnetic field gradient, i.e., intensity of field‐aligned current. Using multiresolution wavelet analysis we have investigated also the wave impedance and the polarization of the electromagnetic structures at different scales. The polarization records show phase discontinuities at small‐scale electromagnetic structures which is consistent with the hypothesis that they represent resonance cones or interference patterns of IEAW.
The effect of electron‐neutral energy exchange on the fluid Farley‐Buneman instability threshold
Authors: Kissack R. S. , St.‐Maurice J.‐P. , Moorcroft D. R.
Published: February 2004

The traditional equation for the linear instability threshold phase speed υph of Farley‐Buneman waves in terms of electron and ion temperatures is υph2 = (γeTe0 + γiTi0)/mi, with γe and/or γi taken to be identically unity or 5/3, depending on whether the electrons/ions are assumed to behave isothermally or adiabatically. A generalized fluid treatment of Farley‐Buneman waves, using Grad's 8‐moment method for the electrons with isothermal ions, has allowed us to investigate systematically the influence of two classes of electron thermal effects on the threshold phase speed not normally considered in fluid approaches. The first class is associated with the electron temperature dependence of the electron‐neutral momentum transfer collision frequency, which leads to coupling between momentum and heat flow (thermal force and thermoelectric effects). The second class is electron‐neutral collisional energy exchange and, in particular, the contribution of inelastic processes to electron energetics. A dispersion relation is presented in a form that makes manifest its consistency with earlier, less general treatments. From this dispersion relation an equation for υph2 is obtained, and in turn, an equation for an “effective γe” is presented. Our analysis of this equation leads to simple criteria that indicate when electron‐neutral collisional energy exchange becomes important, as well as when departures from isothermality become significant. While our formalism is valid for Farley‐Buneman waves in both the equatorial and auroral electrojets, our computed results focus on the auroral situation, allowing for background electron temperatures Te0 ranging from the neutral background to 1000 K.
Ionization mechanisms in CRRES chemical releases: 2. Strontium photoionization and Ba+/Sr+ collisional ionization cross‐section calculations
Authors: Wolf Paul J. , Hunton Donald E.
Published: February 2004

Two particular collision processes involving electron transfer are investigated that may have impact on the analyses of ion flux data obtained in the CRRES G‐1 and G‐11b, upper atmospheric chemical release experiments. Ion pair production (σIP) and charge exchange ionization (σCE) cross sections are calculated as a function of collision energy for reactions between Ba/Sr atoms and O atoms and O+ ions, respectively, using two‐state approximation theories. The cross sections for each process are calculated for both the ground and metastable states of the metal atoms. At a collision energy of 9.5 eV attained in the G‐1 and G‐11b CRRES releases, the calculations indicate that σIP = 1.3 × 10−16 cm2 and σCE = 2–6 × 10−16 cm2 for reactions involving Ba(1S0). The cross sections for the analogous Sr reactions are approximately 1.2 × 10−16 cm2 and 2–8 × 10−17 cm2, respectively. In addition, Sr photoionization from 3PJ metastable states is investigated. Although we calculate a 29‐s photoionization time constant from these states, a kinetic analysis indicates the metastable states cannot accumulate an appreciable equilibrium population in full solar exposure. Thus photoionization from the Sr 3PJ levels does not significantly contribute to the total ion inventory.
Particle drift and loss rates under strong pitch angle diffusion in Dungey's model magnetosphere
Authors: Schulz Michael
Published: February 2004

Strong pitch angle diffusion so thoroughly randomizes the first two adiabatic invariants of charged‐particle motion that it conserves (as a first approximation) the surrounded phase space volume Λ ≡ p3Ψ0, where Ψ0 = ∮(ds/B) is the flux tube volume per unit magnetic flux and p is the common scalar momentum of the particles involved. (This conservation law is widely used in plasma physics. Its nonrelativistic form is usually derived from the adiabatic gas law but is not really a “fluid” result. Since the conservation law does not couple particles with different energies in the same flux tube, such particles can have different values of Λ.) Here the flux tube volume Ψ is computed for selected field lines in Dungey's model magnetosphere (dipole moment μE ≈ −30.2 μT−RE3 plus uniform southward ΔBz ≈ −9.0 COS6Λ* μT, Λ* being the invariant latitude of the quiet time auroral oval, which maps outward to a circular neutral line at radial distance b = (μE/ΔBz)1/3 in the equatorial plane). The integral ∮(ds/B) is fitted within 0.2% at all L values by the expression Ψ0 ≈ (L4a4/μE){(32/35) − [2.045 + 1.045(r0/b)3 + 0.095(r0/b)6 + 0.075(r0/b)9] ln [1−(r0/b)3]}, where r0 (equatorial radius of the field line) is obtained by solving the cubic equation (r0/b) = (La/b)[1 + (1/2)(r0/b)3]. The particle lifetime τ against strong pitch angle diffusion is given in turn by τ ≈ [4ΨBnBs/(Bn + Bs)(1 – η)](m/p), where Bn and Bs (which can differ in an offset‐dipole field model) are the field intensities at the northern and southern foot points of the field line, m is the relativistic mass, and η is the backscatter coefficient. The same expression for Ψ thus enters both the quasi‐adiabatic Hamiltonian (to whose derivative with respect to 1/L the ensemble‐averaged gradient‐curvature drift rate is directly proportional) and the particle loss rate 1/τ (by which the phase space density ƒ = J4π/4πp2 is exponentially attenuated along the ensemble averaged drift trajectory). This construction provides a means of numerically simulating kinematical aspects of electron motion in the outer magnetosphere and precipitation in the diffuse aurora, as well as ion motion in part of the plasma sheet (regarded as a source of the ring current). Its use in magnetospheric plasma simulations should save computer time and reveal analytical structure relevant to magnetospheric dynamics.
Spectrum of hot O at the exobases of the terrestrial planets
Authors: Fox J. L. , Hać Aleksander
Published: February 2004

The distribution of energetic O produced in dissociative recombination of O2+ at the exobases of the terrestrial planets is important in determining the structure of the outer hot O coronas and for the escape flux of O from Mars. Using recently measured values for the branching ratios of the energetically allowed channels in O2+ dissociative recombination, along with models of the vibrational distribution of O2+, we compute the velocity distribution of hot O atoms produced at the exobases of Mars, Venus, and Earth. We take into account the effects of the ion and electron temperatures, the rotational energy of the ions, and the decrease of the dissociative recombination cross section with relative velocity of the ion and electron. We find that distinct peaks appear at the energies associated with the various channels in the Martian spectrum but that for Venus, the features are less distinct, and for Earth, the distribution appears as a single, but broad and asymmetrical peak. For Mars, we compute the fractions of atoms produced with speeds greater than the escape velocity for 16O, 17O, and 18O of 0.68, 0.64, and 0.58, respectively. Thus there is a small isotope effect inherent in the dissociative recombination mechanism that has not been taken into account in models of Martian atmospheric evolution or in estimates of the total inventory of oxygen that is implied by the observed lack of enhancement of the heavier isotopes relative to the terrestrial values.
A redefinition of Jupiter's rotation period
Authors: Higgins Charles A. , Carr Thomas D. , Reyes Francisco , Greenman Wes B. , Lebo George R.
Published: February 2004

We measured the rotation period of Jupiter's inner magnetosphere with precision previously unattainable, using 35 years of observations of the Jovian decametric radiation at the University of Florida Radio Observatory at frequencies between 18 and 22.2 MHz. The new rotation period is the weighted mean of 13 independent 24‐year average determinations. Each of these was found by measuring the drift of the histogram of occurrence probability versus System III (1965) central meridian longitude over an interval of approximately 24 years. The measured drift was used to correct the System III (1965) period to obtain the new value. Our weighted mean is 9 hours 55 min 29.6854 s, with a standard deviation of the weighted mean (σ) of 0.0035 s. This new rotation period is 7.4σ shorter than that of the System III (1965), indicating that the latter is in need of revision. Our measurements indicate an upper limit of about 4 ms/year on any possible Jovian rotation period drift.
Current sheet measurements within a flapping plasma sheet
Authors: Sergeev V. , Angelopoulos V. , Carlson C. , Sutcliffe P.
Published: February 2004

Slow plasma flows perpendicular to the magnetotail neutral sheet and associated with flapping motions of the plasma sheet can occasionally exceed the sensitivity threshold of plasma instruments. This is the case in several events selected from 3 months of magnetotail observations by the three‐dimensional plasma instrument on the AMPTE/IRM satellite. By comparing the ion flow in the ZGSM direction and the correlated changes of the XGSM‐directed magnetic field, we estimate the current sheet flapping velocity to range from a few tens to a few hundreds of kilometers per second. Our measurements of the current sheet thickness (0.1 – 1 RE) and current density (10–30 nA/m2) were significantly different from estimates of these parameters based on magnetospheric models, suggesting a stretched field configuration. The observed events took place during geomagnetically disturbed periods. One of those periods was a 2‐hour‐long convection bay interval. The largest flapping flows were observed during the few events which also exhibited high‐speed Earthward flows, but the flapping velocity was smaller during the more common, slow convection intervals. This observation, as well as the unexpectedly large flapping velocities seen as close as 12 RE (i.e., close to the hinge point), suggests that flapping motions originate near the current sheet. Plasma sheet flapping tends to occur in conjunction with ground Pi2 bursts, but the exact onset times and the dominant periods of the two phenomena are generally different. Thus, although a common energy source of both phenomena may be intermittent current disruption/reconnection, the two phenomena are likely to couple differently to that free‐energy source. We discuss the vertical structure of the plasma sheet parameters during flapping plasma sheet episodes.
ISTP observations of plasmoid ejection: IMP 8 and Geotail
Authors: Slavin J. A. , Fairfield D. H. , Kuznetsova M. M. , Owen C. J. , Lepping R. P. , Taguchi S. , Mukai T. , Saito Y. , Yamamoto T. , Kokubun S. , Lui A. T. Y. , Reeves G. D.
Published: February 2004

IMP 8 and Geotail observations of traveling compression regions (TCRs) and plasmoids, respectively, are used to investigate plasmoid formation and ejection. One year of IMP 8 magnetometer measurements taken during the distant tail phase of the Geotail mission were searched for TCRs, which signal the release of plasmoids down the tail. A total of 10 such intervals were identified. Examination of the Geotail measurements showed that this spacecraft was in the magnetotail for only three of the events. However, in all three cases, clear plasmoid signatures were observed at Geotail. These plasmoids were observed at distances of X = −170 to −197 RE. The in situ plasma velocities in these plasmoids are found to exceed the time‐of‐flight speeds between IMP 8 and Geotail suggesting that some further acceleration may have taken place following release. The inferred lengths of these plasmoids, ∼27–40 RE, are comparable to the downtail distance of IMP 8. This indicates that TCR at IMP 8 can be caused by plasmoids forming not only earthward but also adjacent to or just tailward of the spacecraft. The closeness of IMP 8 to the point of plasmoid formation is confirmed by the small, ∼0–3 min, time delays between the TCR perturbation and substorm onset. In two of the plasmoid events, high‐speed earthward plasma flows and streaming energetic particles were measured in the plasma sheet boundary layer surrounding the plasmoid along with large positive Bz at the leading edge of the plasmoid suggesting that the core of the plasmoid was “snow plowing” into flux tubes recently closed at an active distant neutral line. In summary, these unique two‐point measurements clearly show plasmoid ejection near substorm onset, their rapid movement to the distant tail and their further evolution as they encounter preexisting X lines in the distant tail.
Heliospheric tomography using interplanetary scintillation observations: 2. Latitude and heliocentric distance dependence of solar wind structure at 0.1–1 AU
Authors: Kojima M. , Tokumaru M. , Watanabe H. , Yokobe A. , Asai K. , Jackson B. V. , Hick P. L.
Published: February 2004

Interplanetary scintillation is a useful means to measure the solar wind in regions inaccessible to in situ observation. However, interplanetary scintillation measurements involve a line‐of‐sight integration, which relates contributions from all locations along the line of sight to the actual observation. We have developed a computer assisted tomography (CAT) program to reduce the adverse effects of the line‐of‐sight integration. The program uses solar rotation and solar wind motion to provide three‐dimensional perspective views of each point in space accessible to the interplanetary scintillation observations and optimizes a three‐dimensional solar wind speed distribution to fit the observations. We analyzed IPS speeds observed at the Solar‐Terrestrial Environment Laboratory and confirmed that (1) the solar wind during the solar minimum phase has a dominant polar high‐speed solar wind region with speeds of about 800 km s−1 and within 30° of the solar equator speeds decrease to 400 km s−1 as observed by Ulysses, and (2) high‐speed winds get their final speed of 750–900 km s−1 within 0.1 AU, and consequently, that acceleration of the solar wind is small above 0.1 AU.
Magnetotail reconnection rate during magnetospheric substorms
Authors: Blanchard G. T. , Lyons L. R. , de la Beaujardière O.
Published: February 2004

The magnetotail reconnection rate during substorms is studied using data taken by the Sondrestrom incoherent scatter radar during an ensemble of 24 substorms. A superposed epoch analysis indicates that magnetotail reconnection increases marginally significantly above its average level near the time of substorm expansion phase onset. Our data set shows this increase with 87% confidence within ±5 min of onset and with greater than 99% confidence at 10 ± 5 min after onset. However, the median reconnection rate measurement does not begin to increase until 20 min after onset. This effect is shown to be due to a spatial variation in the development of magnetotail reconnection during substorms; magnetotail reconnection increases very soon after onset in a small magnetic local time sector near midnight, while over most of the separatrix, the increase in the reconnection rate is delayed. The average delay in the local time sectors greater that 1.5 hours from midnight is approximately 20 min. We assign functional forms to the average dependence of the magnetotail reconnection rate on magnetic local time, on the interplanetary magnetic field, and on substorm activity, and analyze the generalized linear combination of these functions. The resulting expression consists of the sum of the average interplanetary magnetic field and substorm dependence of the reconnection rate gated by the average spatial variation and accounts for 36% of the variance in the reconnection rate (0.55 linear correlation), which is most of the low‐frequency (ƒ< 0.5 h−1) variation. The residual variance in the reconnection rate is mostly noise at a level consistent with the reconnection rate measurement uncertainty.
Empirical models of storm time equatorial zonal electric fields
Authors: Fejer Bela G. , Scherliess Ludger
Published: February 2004

Ionospheric plasma drifts often show highly complex and variable signatures during geomagnetically active periods due to the effects of different disturbance processes. We describe initially a methodology for the study of storm time dependent ionospheric electric fields. We present empirical models of equatorial disturbance zonal electric fields obtained using extensive F region vertical plasma drift measurements from the Jicamarca Observatory and auroral electrojet indices. These models determine the plasma drift perturbations due to the combined effects of short‐lived prompt penetration and longer lasting disturbance dynamo electric fields. We show that the prompt penetration drifts obtained from a high time resolution empirical model are in excellent agreement with results from the Rice Convection Model for comparable changes in the polar cap potential drop. We also present several case studies comparing observations with results obtained by adding model disturbance drifts and season and solar cycle dependent average quiet time drift patterns. When the disturbance drifts are largely due to changes in magnetospheric convection and to disturbance dynamo effects, the measured and modeled drift velocities are generally in good agreement. However, our results indicate that the equatorial disturbance electric field pattern can be strongly affected by variations in the shielding efficiency, and in the high‐latitude potential and energy deposition patterns which are not accounted for in the model. These case studies and earlier results also suggest the possible importance of additional sources of plasmaspheric disturbance electric fields.
Resonators for hydromagnetic waves in the magnetosphere
Authors: Klimushkin D. Yu.
Published: February 2004

This paper is concerned with the structure of hydromagnetic waves with respect to finite plasma pressure and the curvature of field lines in those magnetospheric regions where magnetospheric parameters (Alfvén velocity, the quantity β, and equilibrium current) have extrema (the region of plasmapause and partial ring current). It is shown that hydromagnetic waves in these regions they can have the structure of a standing wave not only in the geomagnetic field direction but also across magnetic shells (such a structure is called the “MHD resonator”). It is hypothesized that radially polarized Pc4 pulsations as observed in the magnetosphere represent resonator‐enclosed waves in the region of partial ring current.
Oxygen 16 to oxygen 18 abundance ratio in the solar wind observed by Wind/MASS
Authors: Collier Michael R. , Hamilton D. C. , Gloeckler G. , Ho G. , Bochsler P. , Bodmer R. , Sheldon R.
Published: February 2004

Measurements of the 16O and 18O distribution functions in the solar wind at low to average solar wind speeds from the MASS instrument on the Wind spacecraft are reported. The 16O/18O density ratio is 450 ± 130, a value consistent with terrestrial, solar photospheric, solar energetic particle, and galactic cosmic ray 16O/18O isotopic ratios. This study constitutes the first reported spacecraft measurement of the isotope 18O in the core solar wind and may represent the best determination of the solar 16O/18O density ratio to date.
Propagation of a spheromak: 1. Some comparisons of cylindrical and spherical magnetic clouds
Authors: Vandas M. , Fischer S. , Pelant P. , Dryer M. , Smith Z. , Detman T.
Published: February 2004

A series of our papers in the Journal of Geophysical Research, 1995–1996, was devoted to simulations of propagation of cylindrical magnetic clouds (flux ropes) having different orientation of their axes to the ecliptic plane and initial parameters. In this paper we supplement our study with the case of detached spherical plasmoids. By varying the velocity, density, temperature, and the magnetic field strength inside clouds, we simulate a number of plasmoid scenarios that can be compared with observations and with existing models and simulations of flux ropes. Initially, the spherical clouds have a poloidal magnetic field configuration within a sphere. During the propagation they evolve into toroids (i.e., closed flux ropes). Radial profiles of magnetic field and plasma quantities in these toroids are similar to cylindrical magnetic clouds. However, they are different in the central (now external) part of the cloud, where the poloidal axis was originally situated, that is, in the toroid's hole. Here the magnetic field is greatly enhanced but does not rotate, and the temperature decrease is absent. The deceleration and transit time to 1 AU is comparable between spherical and cylindrical clouds. The shock wave ahead of a spherical cloud is about 2 times closer than for a corresponding cylindrical cloud.
Freja and ground‐based analysis of inverted‐V events
Authors: Frey H. U. , Haerendel G. , Clemmons J. H. , Boehm M. H. , Vogt J. , Bauer O. H. , Wallis D. D. , Blomberg L. , Lühr H.
Published: February 2004

During two campaigns, ground‐based auroral observations were performed in coordination with Freja. The high temporal and spatial resolution of the satellite instruments as well as the real‐time recording with a stereoscopic camera system from the ground enabled detailed comparison of small‐ and large‐scale optical phenomena with particle and field data measured by the satellite. Three passes of the satellite over inverted‐V auroral arcs and over precipitation regions with strong field‐aligned electron spectra are investigated. Brightness modulations within auroral arcs coincide with modulations of primary electron fluxes. The dynamics of small‐scale structures within arcs as well as the proper motion of arcs are analyzed and compared with electric fields measured by the satellite and with BARS radar measurements. Energy fluxes independently determined from the ground and from the satellite are used to calculate the field‐aligned conductance. The results agree with predictions of the kinetic theory of the mirror force, if we allow for variations of the density and thermal energy of the electrons in the source region of the magnetosphere. Detailed comparison of electron spectra and electric and magnetic field perturbations provide evidence of different acceleration mechanisms for the electrons, electrostatic acceleration inside inverted‐V's, and wave acceleration in transient regions.
First‐year continuous solar EUV irradiance from SOHO by the CELIAS/SEM during 1996 solar minimum
Authors: Ogawa H. S. , Judge D. L. , McMullin D. R. , Gangopadhyay P. , Galvin A. B.
Published: February 2004

The CELIAS/SEM photodiode spectrometer aboard SOHO continuously monitors the full‐disk EUV solar irradiance in an 8‐nm wavelength band centered at 30.4 nm (first order), and in a broad wavelength band between 0.1 and 77 nm (central order). We present the absolute solar EUV irradiances for the 1996 solar EUV minimum year at 1 AU. The uncertainty in absolute flux for each channel is approximately ± 14%. The accuracy and stability of the instrument make the data extremely useful in modeling the upper terrestrial atmosphere during this period of “low” solar activity. The data show evidence of persistent solar EUV/soft X ray active regions throughout this solar minimum period which give rise to both 27‐day and short‐term (minutes to hours) solar EUV irradiance variations. The lowest value of solar flux in the first order 30.4‐nm band occurred on November 6, 1996, with a photon flux of 9.8 × 109 cm−2 s−1. Using previously obtained solar spectra, we infer a photon flux of 4.7 × 109 cm−2 s−1 within a 1‐nm bandpass centered on the solar He II 30.4‐nm emission line at this time. The irradiance variation of the first order channel was between +15% and −10% as measured from a smoothed quadratic least squares fit to the entire first‐order channel database for 1996. The lowest central‐order EUV photon flux occurred on the same day (November 6, 1996) with an absolute flux of 2.2 × 1010 cm−2 s−1. When sharp increases of short‐term flux variability are ignored, a variation between +45% and −30% from the smoothed least squares fit to the central‐order database is obtained. The long‐term solar cycle valuation during the 12‐month smoothed data in both channels indicates that the solar EUV minimum was reached during mid 1996. Large short‐term sudden increases monitored by both channels correspond to solar flares observed from the ground and from the GOES satellites. New data for two isolated flares obtained from both CELIAS/SEM channels are also presented and compared with GOES 0.1 to 0.8‐nm soft X ray data.