bluuebunny/crossref_metadata_2025 huggingface dataset:
Populating of the cusp and boundary layers by energetic (hundreds of keV) equatorial particles
Authors: Delcourt D. C. , Sauvaud J.‐A.
Published: September 2002

We examine the dynamics of charged particles in the frontside magnetosphere. We show that the existence of a magnetic field minimum in the outer cusp region has significant implications for the large‐scale transport of energetic (a few hundreds of keV) particles that are trapped near the equator. Upon approach (within a few Earth radii) of the magnetopause in the day side sector, these particles are subjected to a mirror force pointing away from the equator and may escape toward high latitudes. We demonstrate that via this process, energetic electrons and ions from the outer radiation belts and ring current may leak into the outer cusp and be scattered back into the nightside plasma sheet. During transport, the particle behavior critically depends upon gradient drift timescale as compared with convection timescale. We show that by diverting energetic equatorial particles toward the frontside magnetopause, dynamical reconfiguration of the magnetospheric field lines during substorms may favor such injections toward high latitudes and loading of the outer cusp. At a given energy, equatorial particles with higher charge state (i.e., larger drift timescale) reside longer in the dayside magnetosphere and are thus more susceptible to transport toward the field minimum.
Thin current sheets and magnetotail dynamics
Authors: Schindler Karl , Birn Joachim
Published: September 2002

We investigate the formation of thin current sheets in Earth's magnetotail and the stability of the resulting plasma sheet structure. In the study of current sheet formation we concentrate on the mechanism based on a large gradient of the magnetic flux tube volume and derive a general expression for maximum current density using quasi‐static magnetotail theory. That expression relates the amount of magnetic flux transferred to the magnetotail to the maximum current density in the near‐Earth tail region. The analysis also includes the effects of varying solar wind plasma pressure and Mach number. The stability analysis addresses the resistive tearing mode, and how the presence of a thin current sheet changes the dispersion relation is investigated. For an infinitely extended double‐structured sheet the tearing dispersion curve has a single peak, similar to the dispersion relation of a sheet with a single scale. A qualitative argument suggests that a thin current sheet of finite length might lead to a double‐peaked dispersion curve. Several possible consequences of these results are discussed.
Comparison of an ionosonde drift model at a single station with polar convection patterns
Authors: Smith Paul R. , Dyson Peter L. , Morris Ray J.
Published: September 2002

A study of convection at a single point in the polar cap is made by comparing vertical incidence ionosonde Doppler drift data with the Weimer 96 (W96) convection model. Four years of data are used to construct a local convection model at Casey, Antarctica (geographic 66.3°S, 110.5°W, geomagnetic 80.8°S). The Casey 97 (C97) model is capable of producing a drift velocity for any time and interplanetary magnetic field (IMF) vector in the By–Bz plane for either summer or winter seasons. The direct comparison of vectors predicted by C97 and W96 shows there is generally very good agreement between them at all IMF angles. Because of this, our findings consequently support the existence of multiple convection cells for IMF angles within 30° of northward (+Z). For all other angles there is a distortion of the two‐cell pattern that becomes a minimum when the IMF is strongly southward with slightly a positive By component. Drawing on an earlier study with the Heppner‐Maynard model [Smith et al., 1998], but now using the C97 model for comparison, we also find their patterns only begin to match the Casey results when |By| ≫ Bz. A significant seasonal dependence also exists within the C97 and W96 models, although the agreement with each other in winter is not as good. The presence of additional summer lobe cells embedded within the merging cells is supported, particularly for a rounder, expanded dusk cell.
Stationary slow shocks in the magnetosheath for solar wind conditions with β < 2/γ: Three‐dimensional MHD simulations
Authors: De Sterck H. , Poedts S.
Published: September 2002

Magnetohydrodynamic simulation results are presented of three‐dimensional bow shock flows around a conducting paraboloid surface. For upstream parameter values for which switch‐on shocks occur, a stationary secondary shock of slow type is formed which follows the leading shock front and is attached to it. These results may have direct implications for the structure of the flow in the Earth's magnetosheath. They offer a physically attractive explanation for the possible observation of stationary slow shocks in the magnetosheath and in the distant magnetotail region.
Continuous tracking of coronal outflows: Two kinds of coronal mass ejections
Authors: Sheeley N. R. , Walters J. H. , Wang Y.‐M. , Howard R. A.
Published: September 2002

We have developed a new technique for tracking white‐light coronal intensity features and have used this technique to construct continuous height/time maps of coronal ejecta as they move outward through the 2–30 Rs field of view of the Large‐Angle Spectrometric Coronagraph (LASCO) on the Solar and Heliospheric Observatory (SOHO) spacecraft. Displayed as gray‐scale images, these height/time maps provide continuous histories of the motions along selected radial paths in the corona and reveal a variety of accelerating and decelerating features, including two principal types of coronal mass ejections (CMEs): (1) Gradual CMEs, apparently formed when prominences and their cavities rise up from below coronal streamers: When seen broadside, these events acquire balloon‐like shapes containing central cores, and their leading edges accelerate gradually to speeds in the range 400–600 km/s before leaving the 2–30 Rs field of view. The cores fall behind with speeds in the range 300–400 km/s. Seen along the line of sight, these events appear as smooth halos around the occulting disk, consistent with head‐on views of optically thin bubbles stretched out from the Sun. At the relatively larger radial distances seen from this “head‐on” perspective, gradually accelerating CMEs fade out sooner and seem to reach a constant speed more quickly than when seen broadside. Some suitably directed gradual CMEs are associated with interplanetary shocks and geomagnetic storms. (2) Impulsive CMEs, often associated with flares and Moreton waves on the visible disk: When seen broadside, these CMEs move uniformly across the 2–30 Rs field of view with speeds typically in excess of 750 km/s. At the relatively larger radial distances seen from a head‐on perspective, impulsive events tend to have a more ragged structure than the gradual CMEs and show clear evidence of deceleration, sometimes reducing their speeds from 1000 to 500 km/s in 1 hour. Such decelerations are too large to represent ballistic motions in the Sun's gravitational field but might be caused by shock waves, sweeping up material far from the Sun.
Magnetospheric MHD response to a localized disturbance in the ionosphere
Authors: Leonovich A. S.
Published: September 2002

A theory has been constructed for standing quasi‐Alfven waves excited in the magnetosphere by a broadband source localized in the ionosphere. Formulas are obtained which describe the oscillation field of individual standing waves excited by a source arbitrarily distributed in the ionosphere and with an arbitrary behavior in time. It is shown that oscillations from an impulsive source that is narrowly localized across geomagnetic field lines can occur in two different regimes. The initial regime is characterized by the fact that the excited standing wave oscillates throughout the space with the same frequency. In the asymptotic regime, the oscillation field of the standing Alfven wave occupies a distinctly delineated region across field lines. At every point of the region the waves are oscillating with their eigenfrequency. A numerical calculation is made of the total field of standing quasi‐Alfven waves excited in the magnetosphere by an impulsive source localized in the ionosphere. It is shown that the fundamental harmonic of standing waves reaches an asymptotic regime already after the first oscillation period. All other harmonics oscillate in the initial regime during many oscillation periods of the fundamental harmonic. Such a picture of the oscillations adequately depicts the MHD disturbances recorded as part of the active MASSAI experiment (at 023100 UT on November 28, 1981) aboard the AUREOLE‐3 satellite. The point at which the leading edge of a strong electromagnetic impulse was recorded is quite well associated with the equatorward boundary of localization of the fundamental harmonic of standing waves. The form and duration of the impulse recorded aboard the satellite is also adequately described.
A synthesis of solar cycle prediction techniques
Authors: Hathaway David H. , Wilson Robert M. , Reichmann Edwin J.
Published: September 2002

A number of techniques currently in use for predicting solar activity on a solar cycle timescale are tested with historical data. Some techniques, e.g., regression and curve fitting, work well as solar activity approaches maximum and provide a month‐by‐month description of future activity, while others, e.g., geomagnetic precursors, work well near solar minimum but only provide an estimate of the amplitude of the cycle. A synthesis of different techniques is shown to provide a more accurate and useful forecast of solar cycle activity levels. A combination of two uncorrelated geomagnetic precursor techniques provides a more accurate prediction for the amplitude of a solar activity cycle at a time well before activity minimum. This combined precursor method gives a smoothed sunspot number maximum of 154 ± 21 at the 95% level of confidence for the next cycle maximum. A mathematical function dependent on the time of cycle initiation and the cycle amplitude is used to describe the level of solar activity month by month for the next cycle. As the time of cycle maximum approaches a better estimate of the cycle activity is obtained by including the fit between previous activity levels and this function. This Combined Solar Cycle Activity Forecast gives, as of January 1999, a smoothed sunspot maximum of 146 ± 20 at the 95% level of confidence for the next cycle maximum.
Electromagnetic heavy‐ion/proton instabilities
Authors: Wang Joseph J. , Gary S. Peter , Liewer Paulett C.
Published: September 2002

Ion/ion instabilities are driven by the relative velocity Vo of two distinct ion components. This manuscript reports linear theory and simulation studies of electro‐magnetic ion/ion instabilities for a warm proton component streaming against a cool, heavy ion component in a homogeneous, magnetized, collisionless plasma in which Vo is parallel or antiparallel to the background magnetic field. Under these conditions linear Vlasov dispersion theory predicts that the fastest growing mode is usually the right‐hand polarized proton resonant instability. Two‐dimensional initial value hybrid simulations of this growing mode are carried out, yielding scaling relations for the maximum fluctuating magnetic field energy density and the proton pickup time. The latter is proportional to the inverse of the maximum growth rate for a wide range of plasma parameters.
Form of the anomalous cosmic ray spectrum at the solar wind termination shock
Authors: Steenberg Conrad D. , Moraal Harm
Published: September 2002

New insights regarding the form of the accelerated anomalous cosmic ray spectrum at the solar wind termination shock, obtained from solutions of the cosmic ray transport equation, are presented. A simple analytical expression for the spectrum on the shock is derived, and its dependence on the acceleration parameters is shown. Particular attention is paid to the high‐energy cutoff of this spectrum. This expression and its parameterization should be applicable for the acceleration of charged particles in any spherical shock.
Nonlinear features of electrostatic ion cyclotron instability driven by counterstreaming ion beams in equatorial outer plasmasphere
Authors: Singh Nagendra , Leung W. C.
Published: September 2002

A commonly observed feature of the field‐aligned flow of ions on closed geomagnetic field lines is that the pitch angle distributions are considerably broadened. Such pitch angle distributions facilitate in trapping ions and thus contribute to the process of plasmaspheric refilling. Since counterstreaming ion beams are a common feature of the early stage refilling as shown by models, we have investigated the role of ion‐beam‐driven instabilities in broadening the pitch angle distribution of the ion beams. The study is performed using a 2.5‐dimensional particle‐in‐cell code. It is shown that for sufficiently fast ion beams as expected in the outer region of the plasmasphere, the ion cyclotron modes, which appear at frequencies less than the ion‐cyclotron frequency Ωi, in the rest frame of the nondrifting electrons, are the dominant unstable wave modes. In the early stage of the instability a nearly purely growing mode dominates, which efficiently mediates in transferring a part of the parallel drift energy into the perpendicular energy, significantly broadening the ion pitch angle distribution. The transfer abruptly saturates when Jn (k⊥ρif) → 0, where Jn ( ) is the Bessel function of an appropriate order n, k⊥ is the perpendicular wave number of the dominant mode, and ρif,y is the maximum value of the Larmor radius of the beam ions in anomalous cyclotron resonance with the wave. This behavior of the dominant mode in conjunction with the conservation of ion energy allows a method for including such wave‐particle interaction effects in mesoscale models for the plasmaspheric refilling. The perpendicular acceleration of ions by this instability reduces the parallel drift only by a relatively small fraction, leaving the counterstreaming intact. However, the perpendicular acceleration produces a pitch angle distribution which is inducive for the trapping of the counterstreaming ions in the plasmaspheric flux tubes.
Drag forces on interplanetary dust grains induced by the interstellar neutral gas
Authors: Scherer K.
Published: September 2002

In the outer region of the heliosphere (> 20 AU) the neutral gas density becomes larger than the solar wind plasma density, which is inversely proportional to the square of the heliocentric distance. Thus the neutral gas drag may play an important role in the evolution of dust grains in this region. The effect is similar to the plasma Poynting‐Robertson effect; the neutral hydrogen gas exerts a drag force on the dust particles. However, the monodirectional velocity of the interstellar gas, connected with the inflow direction of the interstellar material, induces an effect which is very much different from that induced by the radial solar wind velocity. This causes an asymmetric force acting on the dust particles, which forces the eccentricity and semimajor axis to change rapidly. As an effect of that the lifetime of dust grains in the Edgeworth‐Kuiper Belt is not determined by the electromagnetic or plasma Poynting‐Robertson lifetime but by the drag of the neutral gas leading to lifetimes of the order of half a million years for a 10‐μm‐sized particle.
Radial diffusion analysis of outer radiation belt electrons during the October 9, 1990, magnetic storm
Authors: Brautigam D. H. , Albert J. M.
Published: September 2002

The response of outer radiation belt relativistic electrons to the October 9, 1990, magnetic storm is analyzed in detail using a radial diffusion model and data from the Combined Release and Radiation Effects Satellite (CRRES) and the Los Alamos National Laboratory (LANL) geosynchronous satellite 1989‐046. Electron measurements are expressed in terms of phase space density as a function of the three adiabatic invariants determined from CRRES magnetic field data and the Tsyganenko 1989 Kp‐dependent magnetic field model. The radial diffusion model is implemented with a time‐dependent radial diffusion coefficient parameterized by Kp, and a time‐dependent outer boundary condition scaled by geosynchronous electron data. The results show that radial diffusion propagates outer boundary variations into the heart of the outer radiation belt, accounting for both significant decreases and increases in the <1 MeV electron flux throughout that region. It is further shown that the gradual increase throughout the recovery phase of the >1 MeV electrons is inconsistent with the radial diffusion model given the parameter regime chosen for this study. Greatly enhanced whistler chorus waves observed by CRRES throughout the recovery phase suggest that a possible explanation for the inconsistency may be electron acceleration via wave‐particle interaction.
Comparing fluid and particle‐in‐cell solutions for the polar wind
Authors: Demars H. G. , Schunk R. W. , Barakat A. R.
Published: September 2002

Theoretical descriptions of the terrestrial polar wind have taken a variety of forms. Fluid equations have long been used to provide a description of the plasma bulk flow parameters in the polar wind. More recently, particle‐in‐cell (PIC) models have been applied to the polar wind, yielding a description of far‐from‐Maxwellian features of the flow. A global, time‐dependent, fluid model of the coupled ionosphere and polar wind has recently made possible the description of plasma flow along a multitude (>1000) of magnetic flux tubes as they move under the combined influence of convection and corotational electric fields. In this paper, fluid and PIC solutions for the time‐dependent polar wind are compared for a variety of realistic flux‐tube trajectories, with both the trajectories and the PIC boundary conditions supplied by the global model described above. The two formulations are generally seen to be in excellent agreement in their description of the H+ component of the polar wind. For O+ the agreement is good at low altitudes (below 3000 km), but the two descriptions tend to diverge at high altitudes for reasons related to both the fluid and the PIC models. The results of this study indicate that fluid and PIC models of the polar wind are, to a high level of accuracy, interchangeable with regard to their predictions for the behavior of the plasma densities and drift velocities. This is true for a wide range of altitudes and for a broad spectrum of geophysical conditions.
Aspects of the mass distribution of interstellar dust grains in the solar system from in situ measurements
Authors: Landgraf M. , Baggaley W. J. , Grün E. , Krüger H. , Linkert G.
Published: September 2002

The in situ detection of interstellar dust grains in the solar system by the dust instruments on‐board the Ulysses and Galileo spacecraft as well as the recent measurements of hyperbolic radar meteors give information on the properties of the interstellar solid particle population in the solar vicinity. Especially the distribution of grain masses is indicative of growth and destruction mechanisms that govern the grain evolution in the interstellar medium. The mass of an impacting dust grain is derived from its impact velocity and the amount of plasma generated by the impact. Because the initial velocity and the dynamics of interstellar particles in the solar system are well known, we use an approximated theoretical instead of the measured impact velocity to derive the mass of interstellar grains from the Ulysses and Galileo in situ data. The revised mass distributions are steeper and thus contain less large grains than the ones that use measured impact velocities, but large grains still contribute significantly to the overall mass of the detected grains. The flux of interstellar grains with masses > 10−14 kg is determined to be 1 × 10−6 m−2 s−1. The comparison of radar data with the extrapolation of the Ulysses and Galileo mass distribution indicates that the very large (m > 10−10 kg) hyperbolic meteoroids detected by the radar are not kinematically related to the interstellar dust population detected by the spacecraft.
Dynamics of the substorm growth phase as observed using CANOPUS and SuperDARN instruments
Authors: Voronkov I. , Friedrich E. , Samson J. C.
Published: September 2002

The substorm growth phase in four substorm events was studied using ground‐based observations from the Canadian Open Unified Study (CANOPUS) array of meridian scanning photometers and magnetometers, the Gillam all‐sky camera, and two Canadian Super Dual Auroral Radar Network (SuperDARN) radars. The following common features were revealed: A proton aurora that has a latitudinal width of ∼2° moves equatorward remaining near the equatorward boundary of the intense electron precipitation zone. The proton aurora intensifies during the growth phase toward the onset of the substorm intensification. The latitudinal width of the electron precipitation region narrows during the growth phase reaching 2°–5° of latitudinal width just before the substorm intensification, which indicates significant stretching of magnetic field lines and thinning of the plasma sheet. At the beginning of the growth phase, convection is intensified near the proton aurora band, forming a flow with a large‐amplitude westward component. This enhanced westward component of the convection is in agreement with magnetometer observations of the increased eastward electrojet in this region. The maximum of the flow moves equatorward following the proton aurora band. Prior to substorm intensification, the convective flow develops significant latitudinal gradients. All‐sky images available for one event indicate that just before a substorm intensification, a large auroral vortex develops from an auroral arc imbedded in the proton aurora region and then intensifies. These observational constraints are discussed with respect to a possible mechanism which can lead to a large scale auroral vortex at substorm intensification.
Kilometric continuum detected by Geotail
Authors: Hashimoto K. , Calvert W. , Matsumoto H.
Published: September 2002

A new kind of terrestrial continuum that appears to be generated inside the Earth's plasmasphere has been detected by the Geotail satellite at an orbital distance of 10 to 30 RE in the dayside and evening sectors of the magnetosphere. This previously undetected emission, which will be called “kilometric continuum,” is found to consist of slowly drifting narrowband signals at a frequency of 100 to 800 kHz, corresponding to the plasma frequency inside the plasmasphere at an altitude extending down to only a few thousand kilometers in the topside equatorial region of the Earth's ionosphere. Unlike normal continuum, kilometric continuum is found to occur only near the magnetic equator, where it appears to be unrelated to magnetic activity and is emitted within a well‐defined beam within only ∼10° of the magnetic equator.
Oxygen freeze‐in temperatures measured with SOHO/CELIAS/CTOF
Authors: Hefti S. , Grünwaldt H. , Bochsler P. , Aellig M. R.
Published: September 2002

We use the charge time‐of‐flight (CTOF) mass and charge spectrometer of the charge, element, and isotope analysis system (CELIAS) on board the Solar and Heliospheric Observatory (SOHO) to determine the solar wind oxygen freeze‐in temperature T76 from the O7+ and O6+ abundance ratios in the period from days 92 to 229 of 1996 (Carrington Rotations 1908 to 1912). The freeze‐in temperature is a conserved property of the solar wind because the charge states do not change after a distance of a few solar radii. Therefore it is an ideal in situ diagnostic for remote sensing of the inner solar corona. We determine the mean freeze‐in temperature during the selected period to be 1.6 × 106 K. We use it to map coronal regions of different temperatures and to determine the separation between such regions based on our observation of abrupt transitions of the freeze‐in temperature. We find a upper limit for the separation in the inner corona of 1000 km.
Soliton approach to magnetic holes
Authors: Baumgärtel Klaus
Published: September 2002

“Magnetic holes” (MHs), depressions in the magnetic field magnitude associated with enhancements in density and kinetic pressure, have been observed in the solar wind, the magnetosheaths of terrestrial planets and in the environments of comets, suggesting that this phenomenon may be a common occurrence in space plasmas. MHs are usually believed to result from the mirror instability which can develop in high‐beta plasmas with a temperature anisotropy, T⊥/T‖ > 1. Motivated by the fact that solar wind MHs are often observed in a mirror mode stable environment [Winterhalter et al., 1994], this paper proposes a mechanism for the maintainance of MHs in an equilibrium plasma. We suggest an explanation in terms of magnetically rarefactive (“dark”) MHD solitons with anticorrelation of magnetic field and density, which propagate with small velocities at large angles to the ambient magnetic field. This intrinsically nonlinear approach is based on a magnetohydrodynamic plasma description including Hall inertia effects and utilizes the well‐developed soliton theory of the Derivative Nonlinear Schrödinger Equation (DNLS) which appears as a partly adequate approximation to the parent Hall‐MHD system. The approach introduces an alternative mechanism into the discussion over the physical nature of MHs that is not related to an instability and provides an explanation for various aspects of the observations including amplitude, thickness, and spatial structure of MHs.
Auroral proton and electron signatures in the dayside aurora
Authors: Lorentzen D. A. , Moen J.
Published: September 2002

Pulsed proton events (PPEs) were observed in the dayside aurora over Svalbard, December 10, 1997. Ground‐based optical instruments together with satellite instrumentation are used to categorize dayside optical signatures in the time period 0500 UT to 1100 UT (0810–1410 MLT). We find it useful to separate the events into two main regions: regions 1 and 2. Region 1 is the auroral oval containing boundary plasma sheath (BPS) and low‐latitude boundary layer (LLBL)/cusp activities. Region 2 is equatorward of that, with a drizzle of energetic electrons from the central plasma sheath (CPS), producing a green glow. Within region 1 a well‐defined transition from intense green to red‐dominated auroral activity is taken as a signature of the transition between BPS and LLBL. The hydrogen emissions are seen to be associated with both BPS and LLBL. Major PPEs are uniquely related to moving auroral forms identified as being on open LLBL/cusp field lines and are likely stimulated by pulsed reconnection events.
Global Positioning System phase fluctuations and ultraviolet images from the Polar satellite
Authors: Aarons J. , Lin B. , Mendillo M. , Liou K. , Codrescu M.
Published: September 2002

In a study designed to determine the temporal development of ionospheric irregularities in the auroral region in magnetic storm periods, different types of simultaneous observations were compared for the storms of January 10, April 10–11, and May 15, 1997. The data sets consisted of ultraviolet images (UVI) from the Polar satellite, phase fluctuations and total electron content (TEC) from Global Positioning System (GPS) recordings at a large number of sites, magnetometer observations and hemispheric power precipitation. The large‐scale global or macroscale picture of the magnetic storm showed the importance of universal time in the development of irregularities. The hemispheric total power picture and the global indices such as Kp show this macroscale picture of the entire storm period. However, individual sites show differences in localized magnetic field variations and the development of irregularities; this we term the microscale. The storms of January 10 and May 15 show the importance of local magnetic time and local magnetic variations at the sites, while the storm of April 10–11 was dominated by the UT storm development. During the intense activity of the storms, total electron content shows minute‐by‐minute increases with the satellite moving to positions 6 km apart in the minute. The structured precipitation either directly produces irregularities or indirectly sets instability conditions for irregularity development in the auroral region. Good correlation was established for the three storms between UVI intensity and phase fluctuation development. The UVI Lyman‐Birge‐Hopfield‐long (170 nm) emission is sensitive to 100–200 km precipitation. Phase fluctuation development undoubtedly arises from perturbations in the F region as well. Topside and bottomside soundings have shown the high occurrence of spread‐F in the auroral region. The comparison of the data sets from these storms and from other studies indicates that the creation of irregularities develops from conditions existing over a large range of bottomside heights, i.e., at altitudes from 100 km to the F layer.
Laboratory studies of silicate smokes: Analog studies of circumstellar materials
Authors: Nuth Joseph A. , Hallenbeck Susan L. , Rietmeijer Frans J. M.
Published: September 2002

Grains entering our solar system at the heliopause or encountered by an interstellar probe will be dominated by materials formed in carbon‐rich and oxygen‐rich outflows from high mass‐loss‐rate AGB stars with moderate contributions from novae and supernovae. Laboratory studies of the condensation and thermal evolution of silicate grains have greatly increased our understanding of grain formation processes and may provide the basis for theoretical prediction of chemical speciation and spectral evolution of grains produced in specific stellar outflows. These grains will be modified by long‐term exposure to high‐energy cosmic rays, thus rendering them amorphous, and will potentially be coated by one or more layers of refractory carbonaceous material. This coating results when radiation‐damaged organic‐rich water ices are allowed to sublime in vacuum during the transition from the interior of a dense molecular cloud to the warm interstellar medium. Measurement of the chemical compositions of large numbers of individual grains in the local interstellar medium could lead to a better understanding of the life cycle of grains in the general interstellar medium. Such measurements might also serve as a diagnostic indicator of the primary source of interstellar grains: origin in stellar outflows or in the interstellar medium itself. These measurements would be possible using an impact‐ionization, time‐of‐flight, mass spectrometer during the cruise phase of an interstellar probe mission.
An equatorial bubble: Its evolution observed in relation to bottomside spread F and to the Appleton anomaly
Authors: Whalen J. A.
Published: September 2002

This is a case study that undertakes the first comprehensive description of the concurrent evolutions of an isolated equatorial bubble, bottomside spread F (BSSF), and the enhanced Appleton anomaly. A principal focus is the dynamics of the intersection of the bubble with the anomaly crest which is the source of maximum scintillation on transionospheric RF propagation. Conditions are equinox at solar maximum. Measurements were by an array of eight ionospheric sounders in the Western Hemisphere with a collective field of view extending along the dip equator for about 1600 km and to 40° north dip latitude that resolved rapid changes in the phenomena yet encompassed their extent and duration. Viewed locally, the bubble was triggered by an upwelling of the bottomside F layer during E × B upward drift that accelerated upward for 15–20 min before the onset of irregularities seen as range spread F (RSF). Viewed macroscopically, this onset was part of continuous front of RSF onset that coincided with E × B reversal and moved westward at the velocity of the terminator so as to remain at 1920 LT, to the east of the bubble as BSSF; within the bubble during the upwelling of the bottomside crest; at the west wall of the bubble at the onset of its eastward drift; and west of the bubble as BSSF. The bubble drifted eastward at 185 m/s and rose upward at ≤190 m/s intersecting the maximum of the anomaly crest at 2100 LT, 95 min after bubble onset. During this entire period the bubble was in continuous contact with the anomaly profile which was simultaneously increasing but as a function of LT. Thus the intersection was a function of the upward and eastward velocities of the bubble and the westward motion of the anomaly at the velocity of the terminator. The time and place of the intersection is thus dependent on the entire sequence of events and on the differing dependences on UT and LT, and since each can vary, the time and place of maximum scintillation is highly variable. In light of this variability, observations at least as comprehensive as those reported here appear to be necessary to describe the region adequately and therefore to study it further.
Electric field variability associated with the Millstone Hill electric field model
Authors: Codrescu M. V. , Fuller‐Rowell T. J. , Foster J. C. , Holt J. M. , Cariglia S. J.
Published: September 2002

Joule heating that is generated at high latitudes in the thermosphere because of the magnetospherically imposed electric potential is proportional to the average of the square of the electric field (E field). Most theoretical Joule heating computations use only average electric fields, resulting in heating that is proportional to the square of the average E field. The computation of the average of the square of the E field requires knowledge about the statistical characteristics of E field variability associated with the average electric field model. In this paper we present the variability associated with the Millstone Hill bin‐averaged empirical E field model [Foster et al. 1986] and discuss the implications of variability as an upper atmosphere energy source. We rebinned the radar plasma drift measurements from Millstone Hill, Massachusetts, in magnetic latitude and local time as a function of auroral activity and calculated the average electric fields and the variability associated with them as reflected in the bin standard deviations. We present the E field patterns and the associated variability for both quiet and disturbed geomagnetic conditions for the four seasons. We show that for an electric field model with a Gaussian distribution of small‐scale variability around the mean, the average field and the variability have equal contributions to Joule heating generation.
Toward predicting the position of the magnetopause within geosynchronous orbit
Authors: Shue J.‐H. , Song P. , Russell C. T. , Chao J. K. , Yang Y.‐H.
Published: September 2002

Although the average magnetopause is ∼10 RE from the Earth, the magnetopause moves inside the geosynchronous orbit during extreme solar wind conditions. Under these circumstances some geosynchronous satellites suddenly enter the magnetosheath and are exposed to the plasma and fields of the magnetosheath. In this study we evaluate the predictive capabilities of magnetopause location models in forecasting geosynchronous magnetopause crossings. We predict periods during which geosynchronous satellites enter the magnetosheath using the Petrinec and Russell [1996] and Shue et al. [1998] magnetopause location models driven by data from Interplanetary Monitor Platform (IMP) 8. These predictions are then verified with in situ observations from Geosynchronous Operational Environment Satellite (GOES) 5, 6, and 7. We estimate the false alarm rate, probability of detection, and probability of false prediction for the two models. The estimation shows that false alarm rate for a forecast with a 20‐min separation cadence is ∼62% (80%) for the Shue et al. [1998] model (the Petrinec and Russell [1996] model). The probability of detection is very high for both prediction models. These results suggest that both models work well in predicting magnetosheath periods for geosynchronous satellites. Predictions from the models provide a prerequisite condition for geosynchronous magnetopause crossings. Further examination of unsuccessful events indicates that preconditioning by the interplanetary magnetic field BZ needs to be included in the forecasting procedure for a better forecast. This finding provides us with a guide to improving future magnetopause location models.
High‐latitude ionospheric response to a sudden impulse event during northward IMF conditions
Authors: Moretto T. , Ridley A. J. , Engebretson M. J. , Rasmussen O.
Published: September 2002

A high‐density structure under northward interplanetary magnetic field BZ conditions is identified at the Wind and IMP 8 satellites, both in the solar wind on August 22, 1995. A compression of the magnetosphere is observed by the GOES 7 magnetometer within a few minutes of the pressure increase encountering the magnetopause. The response of the high‐latitude ionosphere is analyzed on the basis of ground‐based magnetometer data. A comprehensive description of this response in the Northern Hemisphere is provided by more than 70 ground magnetometers. This data set is interpreted in terms of high‐latitude ionospheric potential patterns by means of the assimilative mapping of ionospheric electrodynamics technique. Convection cells in the polar cap are formed and disappear on minute timescales in accordance with previous results. However, the high‐latitude ionospheric ground magnetic signature does not match the interpretation as events of traveling convection vortices, as has been suggested by past studies.
Effects of reconnection on the coronal mass ejection process
Authors: Lin J. , Forbes T. G.
Published: September 2002

This work investigates how magnetic reconnection affects the acceleration of coronal mass ejections (CMEs) and how the acceleration in turn affects the reconnection process. To model the CME process, we use a two‐dimensional flux rope model, which drives the ejection by means of a catastrophic loss of mechanical equilibrium. Our model provides a method for relating the motion of the ejected material to the reconnection rate in the current sheet created by the erupting field. In the complete absence of reconnection the tension force associated with the current sheet is always strong enough to prevent the flux rope from escaping from the Sun. However, our results imply that even a fairly small reconnection rate is sufficient to allow the flux rope to escape. Specifically, for a coronal density model that decreases exponentially with height we find that average Alfvén Mach number MA for the inflow into the reconnection site can be as small as MA = 0.005 and still be fast enough to give a plausible eruption. The best fit to observations is obtained by assuming an inflow rate on the order of MA ≈ 0.1. With this value the energy output matches the temporal behavior inferred for the long duration events often associated with CMEs. The model also suggests an explanation for the peculiar motion of giant X‐ray arches reported by Svestka et al. [1995, 1997]. X‐ray arches are the large loops associated with CMEs which are similar in form to “post”‐flare loops, but they have an upward motion that is often different. Instead of continually slowing with time, the arches move upward at a rate that remains nearly constant or may even increase with time. Here we show how the difference can be explained by reversal of the gradient of the coronal Alfvén speed with height.
Plasma sounding at the upper hybrid frequency
Authors: Dieckmann M. E. , Chapman S. C. , Ynnerman A. , Rowlands G.
Published: September 2002

A sounder measures the density of plasmas in various parts of the solar system. The sounder emits wave pulses into the ambient plasma and listens to the response. Intensity peaks in the wave response are typically related to two mechanisms. One is provided by waves that are reflected off plasma inhomogeneities and propagate back to the emitting antenna, where they are then detected. The second is provided by waves propagating with the same group velocity as that of the receiving antenna. In the second case the waves stay close to the antenna and thus yield a long‐lasting response. Response peaks to sounding at the upper hybrid (UH) frequency have, in most cases, been related to reflected waves. In this work we examine if accompanying waves can give rise to the UH response peak. We examine quantitatively how the plasma response to sounding at the UH frequency depends on the plasma density, on the electron temperature, and on the emission amplitude. For the first two parameters this is done by solving the linear dispersion relation. The well‐known property of the UH waves to change from having a zero group velocity to propagating waves, depending on how the electron density compares to the electron cyclotron frequency, is applied to Alouette sounder data. It is discussed how the change in the group velocity may affect the spectral profile of the UH resonance. We present results from numerical particle in cell (PIC) simulations which show that in the case of nonpropagating UH waves, energy can be coupled into the plasma even though the vanishing group velocity of the UH waves should not allow this. The PIC simulations and sounder data from the Alouette mission show that in the case of propagating UH waves the response duration to sounding may be used to determine the electron temperature. Emission amplitudes that are typical for plasma sounders are also shown to suppress the generation of certain electron cyclotron harmonic waves.
Plasmaspheric storm time erosion
Authors: Clilverd Mark A. , Jenkins Barbara , Thomson Neil R.
Published: September 2002

Unusually low whistler mode group delay times are observed by VLF Doppler receivers at both Faraday, Antarctica, and Dunedin, New Zealand, following magnetic storms. These are typically caused by plasmaspheric electron concentration depletions near L=2.4 and not by changes in the VLF wave propagation path. Using a data set that is almost continuous since 1986, we find that depletions during storms in the solar minimum of 1995 are significantly deeper than in the minimum of 1986. Event studies at Faraday show that the electron concentration depletions caused by storms were about a factor of 2 in 1986 and a factor of 3–4 in 1995, independent of the time of year. However, the depletions observed by both sites are significantly deeper than those observed in 1958 and 1961 using natural whistlers (i.e., factors of 2–4 compared to 1.3). The Sheffield University Plasmasphere Ionosphere Model (SUPIM) has been used to investigate possible causes of the plasmaspheric electron concentration depletions observed in the whistler mode data. Thermospheric parameters, including a reduction in the concentration of neutral hydrogen and oxygen at all altitudes, were perturbed by a factor of 10 from their normal levels. However, the plasmaspheric depletions produced were only of the order of 10% after 27 hours. It is unlikely therefore that thermospheric modifications alone are responsible for the depletions observed in the data. Additionally, a tube of plasma was moved to higher L shell under the influence of an equatorial meridional E × B drift velocity of 1000 m s−1 and showed levels of depletion of about a factor of 2. Although it is possible to generate plasmaspheric concentration depletions using the drifting tube model, the depletions are smaller than those observed and the outward E × B drift velocity needed is a factor of 2 greater than those reported previously at L=2.4. It is therefore unlikely that the tube drifting mechanism is the principal cause of the observed plasmaspheric electron concentration depletions at L=2.4. Although no mechanism is clearly identified in this study, the ground‐based results presented in this paper indicate erosion levels of similar structure and magnitude to electron concentration profiles from the ISEE 1 satellite in the aftermath of magnetic disturbances during 1983, thus providing a long‐term record of plasmaspheric erosion.
Giant pulsations: A nonlinear phenomenon
Authors: Pokhotelov O. A. , Khabazin Y. G. , Mann I. R. , Milling D. K. , Shukla R. K. , Stenflo L.
Published: September 2002

Previous treatments of the excitation of Alfvén waves by drift‐bounce resonance have been dominated by the linear approximation. We present a nonlinear treatment of the excitation of giant pulsations (Pgs) by drift‐bounce resonance and show that nonlinear behavior becomes important well within the typical lifetimes of Pg wave packets. In particular, we show that the nonlinear phase mixing of the resonant particles trapped in the wave fields is of great importance for Pgs, and hence these nonlinearities must be included in calculations of the growth rates of Pgs. We believe that Pg behavior can be described by monochromatic modes exhibiting strong nonlinear wave‐particle interactions during injections of resonant particles into the magnetosphere and that the observed growth and damping of Pg wave packets may provide an indication of the temporal variations in the driving resonant particle source population.
Magnetic lineations within Shatsky Rise, northwest Pacific Ocean: Implications for hot spot‐triple junction interaction and oceanic plateau formation
Authors: Nakanishi Masao , Sager William W. , Klaus Adam
Published: September 2002

Oceanic plateaus are major ocean features, yet their origins and development are poorly understood. Many are huge piles of basalt, and it is widely accepted that mantle plumes are their source, perhaps from eruptions of the voluminous head of an emerging plume. Shatsky Rise is a basaltic plateau that formed during a period of geomagnetic reversals, unlike many mid‐Cretaceous plateaus, so magnetic data can help us understand its tectonic history. In this study, we analyzed magnetic anomaly data from 131 cruises over and around Shatsky Rise and constructed a magnetic lineation chart for tectonic interpretation. A significant finding is that magnetic lineations are traceable through low parts of the rise between volcanic massifs, indicating nearly normal lithosphere, and between large volcanic edifices. Many lineations form bights near the rise axis and show former locations of the Pacific‐Izanagi‐Farallon triple junction. They indicate that the junction was in a ridge‐ridge‐ridge (RRR) configuration and closely followed the rise axis from chron M20 (146 Ma) to chron M4 (127 Ma). Lineation and bight geometries indicate that the triple junction jumped northeastward at least nine times, often apparently in response to volcanic activity from the mantle plume. Some jumps, however, appear related to ridge reorientations. Numerous features within the rise are parallel to lineations or lineation offsets, implying that the plateau formed near the triple junction and was modified by ridge faulting. Most of our observations support the hypothesis that Shatsky Rise was formed by a mantle plume that captured a triple junction.