Magnetospheric Particle Populations Research Articles

A system science methodology develops a new composite highly predictable index of magnetospheric activity for the community: the whole-Earth index E(1)

For community use, a new composite whole-Earth index E(1) and its matching composite solar wind driving function S(1) are derived. A system science methodology is used based on a time-dependent magnetospheric state vector and a solar wind state vector, with canonical correlation analysis (CCA) used to reduce the two state vectors to the two time-dependent scalars E(1)(t) and S(1)(t). The whole-Earth index E(1) is based on a diversity of measures via six diverse geomagnetic indices that will be readily available in the future: SML, SMU, Ap60, SYMH, ASYM, and PCC. The CCA-derived composite index has several advantages: 1) the new “canonical” geomagnetic index E(1) will provide a more powerful description of magnetospheric activity, a description of the collective behavior of the magnetosphere–ionosphere system. 2) The new index E(1) is much more accurately predictable from upstream solar wind measurements on Earth. 3) Indications are that the new canonical geomagnetic index E(1) will be accurately predictable even when as-yet-unseen extreme solar wind conditions occur. The composite solar wind driver S(1) can also be used as a universal driver function for individual geomagnetic indices or for magnetospheric particle populations. To familiarize the use of the new index E(1), its behavior is examined in different phases of the solar cycle, in different types of solar wind plasma, during high-speed stream-driven storms, during CME sheath-driven storms, and during superstorms. It is suggested that the definition of storms are the times when E(1) >1.

Local Heating of Oxygen Ions in the Presence of Magnetosonic Waves: Possible Source for the Warm Plasma Cloak?

AbstractIn the energy regime between the plasmasphere (a few eV) and the ring current (greater than 1 keV), there exists another magnetospheric particle population with energies from a few eV to a few keV, the origins of which are debated. Studies explore generation mechanisms for warm plasma energies in the inner magnetosphere through two observed phenomena: the warm plasma cloak and the oxygen torus. The relations between these two populations are unclear. Recent data reveal local heating of cold H+ and He+ ions to warm plasma energies by magnetosonic waves. In this study, we report first observations of thermal O+ heating by magnetosonic waves and link the heating to a possible formation mechanism for the warm plasma cloak. The O+ heating is observed by different plasmaspheric density profiles, including density channels. We observe that O+ heating always occurs with thermal H+ and He+ heating. We investigate the harmonic structure of the observed magnetosonic waves and find intense O+ heating is accompanied by discrete heavy ion gyroharmonics. We suggest that locally heated thermal ions to 100s eV by magnetosonic waves along the plasmapause could provide a possible mechanism for warm plasma cloak generation.

Large‐scale jets in the magnetosheath and plasma penetration across the magnetopause: THEMIS observations

AbstractTime History of Events and Macroscale Interactions during Substorms multipoint observation of the plasma and magnetic fields, conducted simultaneously in the dayside magnetosheath and magnetosphere, were used to collect 646 large‐scale magnetosheath plasma jets interacting with the magnetopause. The jets were identified as dense and fast streams of the magnetosheath plasma whose energy density is higher than that of the upstream solar wind. The jet interaction with the magnetopause was revealed from sudden inward motion of the magnetopause and an enhancement in the geomagnetic field. The penetration was determined as appearance of the magnetosheath plasma against the background of the hot magnetospheric particle population. We found that almost 60% of the jets penetrated through the magnetopause. Vast majority of the penetrating jets was characterized by high velocities V > 220 km/s and kinetic βk > 1 that corresponded to a combination of finite Larmor radius effect with a mechanism of impulsive penetration. The average plasma flux in the penetrating jets was found to be 1.5 times larger than the average plasma flux of the solar wind. The average rate of jet‐related penetration of the magnetosheath plasma into the dayside magnetosphere was estimated to be ~1029 particles/d. The rate varies highly with time and can achieve values of 1.5 × 1029 particles/h that is comparable with estimates of the total amount of plasma entering the dayside magnetosphere.

Remote sensing the plasmasphere, plasmapause, plumes and other features using ground-based magnetometers

The plasmapause is a highly dynamic boundary between different magnetospheric particle populations and convection regimes. Some of the most important space weather processes involve wave-particle interactions in this region, but wave properties may also be used to remote sense the plasmasphere and plasmapause, contributing to plasmasphere models. This paper discusses the use of existing ground magnetometer arrays for such remote sensing. Using case studies we illustrate measurement of plasmapause location, shape and movement during storms; refilling of flux tubes within and outside the plasmasphere; storm-time increase in heavy ion concentration near the plasmapause; and detection and mapping of density irregularities near the plasmapause, including drainage plumes, biteouts and bulges. We also use a 2D MHD model of wave propagation through the magnetosphere, incorporating a realistic ionosphere boundary and Alfven speed profile, to simulate ground array observations of power and cross-phase spectra, hence confirming the signatures of plumes and other density structures.

On the coupling between unstable magnetospheric particle populations and resonant high <i>m</i> ULF wave signatures in the ionosphere

Abstract. Many theories state that Ultra Low Frequency (ULF) waves with a high azimuthal wave number (m) have their energy source in wave-particle interactions, yet this assumption has been rarely tested numerically and thus many questions still remain as to the waves' exact generation mechanism. For the first time, this paper investigates the cause and effect relationship between the driving magnetospheric particle populations and the ULF wave signatures as observed in the conjugate ionosphere by quantitatively examining the energy exchange that occurs. Firstly, a Monte Carlo method is used to demonstrate statistically that the particle populations observed during conjugate ionospheric high m wave events have more free energy available than populations extracted at random. Secondly, this paper quantifies the energy transferred on a case study basis, for two classes of high m waves, by examining magnetospheric Ion Distribution Functions, (IDFs) and directly comparing these with the calculated wave energy dissipated into the conjugate ionosphere. Estimates of the wave energy at the source and the sink are in excellent agreement, with both being of the order of 1010J for a typical high m wave. Ten times more energy (1011J) is transferred from the magnetospheric particle population and dissipated in the ionosphere when considering a subset of high m waves known as giant pulsations (Pgs). Previous work has demonstrated that 1010J is frequently available from non - Maxwellian IDFs at L=6, whereas 1011J is not. The combination of these studies thus provides an explanation for both the rarity of Pgs and the ubiquity of other high m waves in this region.

CRRES/Ground-based multi-instrument observations of an interval of substorm activity

Abstract. Observations are presented of data taken during a 3-h interval in which five clear substorm onsets/intensifications took place. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were recorded. In addition data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation, are available. The locations and movements of the substorm current system in latitude and longitude, determined from ground and spacecraft magnetic field data, have been correlated with the locations and propagation of increased particle precipitation in the E-region at EISCAT, increased particle fluxes measured by CRRES and DMSP, with auroral luminosity and with ionospheric convection velocities. The onsets and propagation of the injection of magnetospheric particle populations and auroral luminosity have been compared. CRRES was within or very close to the substorm expansion phase onset sector during the interval. The onset region was observed at low latitudes on the ground, and has been confirmed to map back to within L=7 in the magnetotail. The active region was then observed to propagate tailward and poleward. Delays between the magnetic signature of the substorm field aligned currents and field dipolarisation have been measured. The observations support a near-Earth plasma instability mechanism for substorm expansion phase onset.

CRRES/Ground-based multi-instrument observations of an interval of substorm activity

Abstract. Observations are presented of data taken during a 3-h interval in which five clear substorm onsets/intensifications took place. During this interval ground-based data from the EISCAT incoherent scatter radar, a digital CCD all sky camera, and an extensive array of magnetometers were recorded. In addition data from the CRRES and DMSP spacecraft, whose footprints passed over Scandinavia very close to most of the ground-based instrumentation, are available. The locations and movements of the substorm current system in latitude and longitude, determined from ground and spacecraft magnetic field data, have been correlated with the locations and propagation of increased particle precipitation in the E-region at EISCAT, increased particle fluxes measured by CRRES and DMSP, with auroral luminosity and with ionospheric convection velocities. The onsets and propagation of the injection of magnetospheric particle populations and auroral luminosity have been compared. CRRES was within or very close to the substorm expansion phase onset sector during the interval. The onset region was observed at low latitudes on the ground, and has been confirmed to map back to within L =7 in the magnetotail. The active region was then observed to propagate tailward and poleward. Delays between the magnetic signature of the substorm field aligned currents and field dipolarisation have been measured. The observations support a near-Earth plasma instability mechanism for substorm expansion phase onset.

Theoretical structure of a magnetospheric plasma boundary: Application to the formation of discrete auroral arcs

In the framework of a kinetic theory for tangential discontinuities we modeled the electrical structure of the sheath that separates magnetospheric particle populations of different densities and temperatures. The model can equally be applied to the plasma sheet boundary layer in the tail or to the boundary of some plasma sheet cloud immersed in the central plasma sheet. With plasma parameters typical of the Earth's outer magnetosphere and plasma sheet, we obtain results bearing many features pertinent to magnetospheric processes, specifically the origin of discrete auroral arcs. Creation of a space‐charge separation electrostatic potential in a direction normal to the magnetic field results from the contact of the two plasma populations. When the large‐scale solar wind potential difference is further imposed across the transition layer, the potential gradients are locally much enhanced, to give rise to large electric fields (several hundreds millivolts per meter) appearing over small distances perpendicular to the magnetic field—just the situation needed for the creation of an auroral arc. The transition itself is characterized by two scale lengths of the plasma and fields variables: the average electron Larmor radius ϱe (or some multiple of ϱe) for thin embedded electron‐dominated layers which generate the sharpest potential gradients, and the ion gyroradius ρp (or some multiple of ρp) for the broader ion‐dominated layers located at the outer edges of the transition. The larger‐scale sizes are appropriate to auroral arcs dimensions. The generated electric potential differences, consistent with the energy acquired by the precipitated electrons associated with discrete aurora, are identified with the source of the electromotive force (EMF) required for the auroral current circuit. Wave particle interactions are likely to scatter the electrons into the atmospheric loss cone, establishing the current system threading both the EMF and the ionosphere by means of field‐aligned currents. The half lifetime of the transition is at least of the order of 1000 s. This is also the time interval during which dissipative processes will not alter significantly the available potential gradients of the initially unloaded EMF.

The magnetosphere as a sufficient source for upstream ions on November 1, 1984

We consider 10 tests which distinguish the source of energetic particles in upstream ion events. Some tests are definitive, and others inadequate. In particular, we note that the Fermi model requires a finite time of magnetic field line connection to the bow shock before energetic ions appear and inverse velocity dispersion when the interplanetary magnetic field rotates to a more radial direction but that these features are also expected for the leakage model under certain conditions. We present simultaneous magnetospheric, magnetosheath, and upstream energetic particle observations during two well‐documented upstream events on November 1, 1984, and apply the 10 tests. The events are unusual in that they occurred during a period when the magnetosphere was greatly compressed, providing for an increase in the energetic magnetospheric particle population and a decrease in the magnetosheath thickness. Magnetospheric leakage satisfactorily explains our observations on this day, but in situ Fermi acceleration does not. Consequently, we consider magnetospheric leakage a sufficient source for upstream particles during these two events.

The terrestrial plasma source: A new perspective in solar‐terrestrial processes from Dynamics Explorer

The geospace environment has been viewed as a mixing bowl for plasmas of both solar and terrestrial origin. Our perspective on the nature of the supply mechanisms has undergone a radical evolution over the past decade, particularly during the 5 years of the Dynamics Explorer mission. During this period, the terrestrial source has increased in importance in both magnitude and character of ionospheric outflow. These outflows include the classical polar wind, the cleft ion fountain, the auroral ion fountain, and the polar cap. The Earth can be envisioned as a multifaceted fountain which ejects particles from different spatial locations spread around the globe. These particles exhibit a range of masses from 1 to 32 amu and a range of energies from 1 eV to 10 keV. The total flux of this ionospheric outflow is very large: adequate to supply the entire magnetospheric particle population. And the implications of the outflow are significant across a broad spectrum of solar‐terrestrial processes ranging from sources of magnetospheric plasmas, to influences on ionospheric density and temperature structure, to energy transfer in phenomena such as stable auroral red arcs. The Dynamics Explorer mission has made a major contribution in the characterization of the terrestrial plasma source.

The Magnetosphere of Uranus: Hot Plasma and Radiation Environment

The low-energy charged-particle (LECP) instrument on Voyager 2 measured lowenergy electrons and ions near and within the magnetosphere of Uranus. Initial analysis of the LECP measurements has revealed the following. (i) The magnetospheric particle population consists principally of protons and electrons having energies to at least 4 and 1.2 megaelectron volts, respectively, with electron intensities substantially excceding proton intensities at a given energy. (ii) The intensity profile for both particle species shows evidence that the particles were swept by planetry satellites out to at least the orbit of Titania. (iii) The ion and electron spectra may be described by a Maxwellian core at low energies (less than about 200 kiloelectron volts) and a power law at high energies (greater than about 590 kiloelectron volts; exponentmicro, 3 to 10) except inside the orbit of Miranda, where power-law spectra (micro approximately 1.1 and 3.1 for electrons and protons, respectively) are observed. (iv) At ion energies between 0.6 and 1 megaelectron volt per nucleon, the composition is dominated by protons with a minor fraction (about 10(-3)) of molecular hydrogen; the lower limit for the ratio of hydrogen to helium is greater than 10(4). (v) The proton population is sufficiently intense that fluences greater than 10(16) per square centimeter can accumulate in 10(4) to 10(') years; such fluences are sufficient to polymerize carbon monoxide and methane ice surfaces. The overall morphology of Uranus' magnetosphere resembles that of Jupiter, as evidenced by the fact that the spacecraft crossed the plasma sheet through the dawn magnetosheath twice per planetary rotation period (17.3 hours). Uranus' magnetosphere differs from that of Jupiter and of Saturn in that the plasma 1 is at most 0.1 rather than 1. Therefore, little distortion ofthe field is expected from particle loading at distances less than about 15 Uranus radii.

The Medium-Energy Particle Analyzer (MEPA) on the AMPTE CCE Spacecraft

The medium-energy particle analyzer (MEPA) was designed to measure the spectra and composition of magnetospheric particle populations from 10 keV per nucleon (for oxygen) to more than 6 MeV The instrument provides for high background rejection and a geometry tactor large enougn (10-2 cm2 * sr) to be sensitive to rare natural species and tracer ions beyond geosynchronous orbit, while having the ability to operate without saturation in the very high flux regions of the inner magnetosphere. The MEPA telescope measures time of flight and thus velocity of energetic ions from a thin front foil to a rear solid-state total-energy detector, determining the incident ion mass. The telescope is capable of isotopic resolution of hydrogen and helium, of elemental resolution up through oxygen, and can resolve major species and groups to beyond iron with 32-sector angular resolution and temporal resolution of 0.2-24 s. MEPA represents a new and extremely promising technology for space-particle instrumentation in that it has the capability of measuring low-energy heavy ions with high efficiency while discriminating against high natural fluxes of protons.

The active magnetospheric particle tracer explorers (AMPTE) program

The Active Magnetospheric Particle Tracer Explorers (AMPTE) will carry out the release and monitoring of tracer ions (lithium and barium) in the solar wind and within the distant magnetosphere in order to study access of solar wind ions to the magnetosphere and the convective‐diffusive transport and energization of magnetospheric particles. In addition, a single massive release of barium in the dawn magnetosheath will create a visible artificial comet in the flowing solar wind plasma within which studies of diamagnetic effects, ionization, momentum exchange, ion transport, and visible phenomena will be made. The AMPTE spacecraft will also obtain comprehensive measurements of the composition and dynamics of the ambient Z≥2 magnetospheric particle populations at the geomagnetic equator, including the energy interval (˜20 to ˜200 keV) of importance to the ring current. Implementation of these objectives utilizes two primary spacecraft, the Ion Release Module (IRM) and the Charge Composition Explorer (CCE), launched into elliptical orbits of apogee 19.5 RE and 9.0 RE, respectively. A supporting instrumented spacecraft, the United Kingdom Subsatellite, positioned a few hundred kilometers from the IRM, provides two‐point in situ plasma diagnostic measurements. All three spacecraft are currently scheduled for launch on a Delta 3924 vehicle in August 1984. The AMPTE program is a collaborative effort between the United States and the Federal Republic of Germany (FRG) and between Germany and the United Kingdom (UK).

A subauroral and mid-latitude view of substorm activity

Experimental observations from a variety of sources made during a substorm period near 0900 UT on January 2, 1971 have provided evidence confirming mid-latitude and subauroral phenomena associated with magnetic substorm activity. A review of these observations, including ground and balloon observations made near L=4 at the conjugate stations Siple, Antarctica and Roberval, Canada and data obtained from the synchronous-orbit satellite ATS 5 positioned about 2 hours west of the Siple, Roberval meridian, is presented. During the hour before the reported correlated bursts of X rays and VLF noise (Rosenberg et al., 1971), the plasmapause appears to be displaced towards the equator from Siple; resonance conditions along the field lines at Siple were favorable for the observation of results of magnetospheric wave-particle interactions involving electrons with energies exceeding 30 keV. The correlated observations are a potential source of information concerning the relationship of ULF and VHF noise activity to the magnetospheric particle population at middle latitudes; the injection and subsequent drift of low and medium energy electrons during substorms; and enhanced particle precipitation deep within the plasmasphere during substorms.

Relation between geomagnetic sudden impulses and solar wind pressure changes-An experimental investigation

Theoretically the relation between the size of a geomagnetic sudden impulse si and the associated change in the solar wind stagnation pressure Ps is given by where (1) and (2) refer to pressures before and after the event and k is a proportionality constant. We have determined k experimentally using the M.I.T. solar wind measurements on Pioneer 6. The results support the general functional relation given above; however, the experimental value for k is approximately ½ that expected theoretically. This discrepancy was also found in a direct comparison of geomagnetic field strength and different solar wind pressures on quiet days. Several factors might contribute to the difference, such as the seasonal inclination of the dipole axis, the solar wind magnetic field, and the magnetospheric particle population.