Energetic Composition Research Articles

Ulysses observations of energetic H 3+ ions in Jupiter's magnetosphere

Ulysses was the fifth spacecraft to visit Jupiter. In this paper measurements of energetic H 3 +-ions in the Jovian magnetosphere made by the EPAC (Energetic Particle Composition) instrument onboard Ulysses are presented and compared with formerly published findings from the HI-SCALE instrument also onboard Ulysses.

First Composition Measurements of Energetic Neutral Atoms

Energetic neutral atoms (ENAs) were detected by the Energetic Particles and Ion Composition (EPIC) instrument on the Geotail spacecraft during a magnetic storm on October 29–30, 1994. The energetic particles could be identified as neutrals because the direction of the particle flux steadily tracked the direction of the Earth and was uncorrelated with the changing orientation of the ambient magnetic field as the spacecraft viewed the dayside magnetosphere for ∼16 hours. These observations provide the first composition measurements of ENAs, yielding the storm‐time evolution of ENA fluxes of hydrogen, helium, and oxygen separately as well as their energy spectra. ENA fluxes and the rate of recovery of Dst are both roughly steady, consistent with charge exchange being a significant energy loss process for the storm‐time ring current. For total energies above 200 keV, the intensity of ENA oxygen is the highest, followed by hydrogen, and then by helium. These observations enable us to deduce the line‐of‐sight (LOS) integrals of the products nHjion and nHfion, where nH=hydrogen geocorona density, jion=differential ion flux, and fion=phase space density (PSD), for ion species H+, He+ and O+ at energies between ∼60 and ∼600 keV. A ∼50–60 keV Maxwellian fits the O+ LOS PSD fairly well but fits the He+ and the H+ only poorly.

ULYSSES observations of energetic particle acceleration and the superposed CME and CIR events of November 1992

Abstract. During November 1992, a series of forward and reverse shocks passed the ULYSSES spacecraft. Spectral and anisotropy measurements are reported for protons and alpha particles between 0.28 and 6 MeV observed by the Energetic Particle Composition Experiment, data recorded by the Magnetometer Experiment and the high-energy (2.7–300 MeV) proton data from the Kiel Electron Telescope. An analysis of energetic particle, plasma and magnetometer data from ULYSSES has allowed a unique study of the corresponding arrival of fare particles, particles within a corotating interaction region and particles transported with a coronal mass ejection. We present an analysis of these data in terms of possible diffusive shock acceleration but conclude that this is likely to be incompatible with the short transit time of the particles. Shock drift acceleration of particles with energies 0.3 MeV/nucleon or solar acceleration followed by particle trapping behind the shock front are alternative possibilities.

ULYSSES observations of energetic particle acceleration and the superposed CME and CIR events of November 1992

During November 1992, a series of forward and reverse shocks passed the ULYSSES spacecraft. Spectral and anisotropy measurements are reported for protons and alpha particles between 0.28 and 6 MeV observed by the Energetic Particle Composition Experiment, data recorded by the Magnetometer Experiment and the high-energy (2.7–300 MeV) proton data from the Kiel Electron Telescope. An analysis of energetic particle, plasma and magnetometer data from ULYSSES has allowed a unique study of the corresponding arrival of fare particles, particles within a corotating interaction region and particles transported with a coronal mass ejection. We present an analysis of these data in terms of possible diffusive shock acceleration but conclude that this is likely to be incompatible with the short transit time of the particles. Shock drift acceleration of particles with energies 0.3 MeV/nucleon or solar acceleration followed by particle trapping behind the shock front are alternative possibilities.

The Downtail Distance Variation of Energetic Ions in Earth's Magnetotail Region: Geotail Measurements at X>-208RE

We report on the downtail distance, x, variation of energetic ions observed on Geotail in the spatial region dominated by the magnetotail plasma sheet antisunward of Earth, 0 < x < 208RE. The energy-integrated ∼9.4-210 keV/e ion fluxes presented herein were measured by the Supra-Thermal Ion Composition Spectrometer (STICS) of the Energetic Particles and Ion Composition experiment. H+ is the dominant energetic ion species observed. When averaged over geomagnetic activity, the overall x variations of the major ion species are qualitatively similar in that the energy-integrated flux levels decrease with increasing x Earthward of ∼70-100RE. In this x range tailward, sunward, duskward, and dawnward fluxes are of roughly comparable intensity, although tailward fluxes are slightly more intense. Beyond x ∼ 100RE, tailward fluxes dominate and their levels do not decrease appreciably, if at all, out to ∼208RE. Fluxes in the other directions generally continue to decrease with increasing x, albeit with a smaller gradient than closer to Earth. An exception to this exists for high-mass, singly-charged atomic and molecular ions predominantly from the ionosphere, which we group together and call I(O+1). Tailward and duskward I(O+1) fluxes are higher relative to sunward and dawnward I(O+1) fluxes than such intercomparisons for other species. The x variations of H+ and He+2 fluxes are very similar throughout the magnetosphere. We find that the solar wind is the dominant source for H+ by intercomparing the x gradient of H+ flux to those of: 1) the I(O+1) flux; 2) ion flux consisting of high-mass, high charge state ions from the solar wind, which we call SW(O+6) flux; and 3) He+2 flux. He+2 and O+6 are the second and third most abundant solar wind species next to H+, respectively. At these energies and during the decline to solar activity minimum, the solar epoch of these measurements, the I(O+1) flux is less than He+2 flux but greater than SW(O+6) flux. The difference between x gradients of the solar wind and ionospheric origin ion flux increases as geomagnetic activity increases, corresponding to the well-known geomagnetic activity related production of O+1 in the ionosphere. We suggest that the overall difference between H+ and I(O+1) x gradients may be explained in part by spatial/temporal differences of the two different respective sources: one extended and steady, the solar wind, the other localized and transient, Earth's ionosphere.

Looking for the FIP Effect in EUV Spectra: Examining the Solar Case

Systematic differences between elemental abundances in the corona and in the photosphere have been found in the Sun. The abundance anomalies are correlated with the first ionization potentials (FIP) of the elements. The overall pattern is that low-FIP elements are preferentially enhanced relative to high-FIP elements by about a factor of four; the transition occurs at about 10 eV. This phenomenon has been measured in the solar wind and solar energetic particle composition, and in EUV and X-ray spectra of the corona and flares. The FIP effect should eventually offer valuable clues into the process of heating, ionization and injection of material into coronal and flaring loops for the Sun and other stars. The situation for the Sun is remarkably complex: substantial abundance differences occur between different types of coronal structures, and variations occur over time in the same region and from flare to flare. Anomalies such as enhanced Ne/O ratios, distinctly at odds with the basic FIP pattern, have been reported for some flares. Are the high-FIP elements underabundant or the low-FIP elements overabundant with respect to hydrogen? This issue, which has a significant impact in physical interpretation of coronal spectra, is still a subject of controversy and an area of vigorous research.

Observations of energetic particles with EPAC on Ulysses in polar latitudes of the heliosphere

Measurements with the Energetic Particle Composition instrument (EPAC) aboard Ulysses show particles from near the ecliptic that were apparently accelerated by shocks associated with a corotating interaction region. The particles were detected together with the shocks and even when shocks no longer arrived at Ulysses up to -65 degrees of heliographic latitude but not beyond. Particles could have reached these latitudes along magnetic fields; such connections to the outer lower latitude heliosphere evidently do not exist above that latitude. The accelerated streams have composition similar to solar wind abundances, no dispersion, and a net inward anisotropy. The underlying composition between the recurrent stream is similar to the anomalous component of cosmic rays. The channel sensitive to high-energy protons (> 230 megaelectron volts) shows a 26-day variation of the flux superimposed on the heliospheric modulation of galactic ions.

A preliminary assessment of energetic ion species in flux ropes/plasmoids in the distant tail

Measurements of the Energetic Particles and Ion Composition (EPIC) instrument on the Geotail satellite are used to investigate at high‐time resolution the relative intensity enhancements of different ion species at energies ∼10 keV‐3 MeV during encounters of magnetic field structures attributed to flux ropes or plasmoids in the distant tail. An examination of six events reveals the new result that the composition varies considerably within the interval of the encounter of each structure as well as among different encounters. There is no consistent trend for enhancement nor reduction of energetic ions from the ionospheric source relative to that from the solar wind source during intervals of flux ropes or plasmoids. A possible interpretation is that these plasma structures are connected to a particle source or sources actively modifying their compositional content while they are being ejected downstream beyond ∼100 REE.

Tail lobe ion composition at energies of 0.1 to 16 keV/e: Evidence for mass‐dependent density gradients

A large set of energetic (0.1‐ to 16‐keV/e) ion composition data from the central magnetotail, obtained by the ISEE 1 spacecraft between 10 and 23 RE from Earth, is sorted according to measured total ion beta value, in order to investigate whether bulk properties of different ions vary in different ways between plasma sheet and lobes, as suggested by a comparison of certain experimental and theoretical results in the literature. Despite inevitable difficulties with extracting statistically valid data at very low beta (10−2 or lower), the results seem to support a recent theoretical model suggesting that lighter ions have a steeper density gradient than heavier ions, especially when comparing H+ ions with O+ ions. The results also indicate that ion velocity distributions are fairly isotropic even at low beta, at least those of H+ ions, although field‐aligned flows are common. The results are evaluated in the context of plasma transport and are found to lend some support to the notion that tail lobe convection may be directed inward from the dawn and dusk flanks.

GEOTAIL Energetic Particles and Ion Composition Instrument.

The Energetic Particles and Ion Composition (EPIC) instrument, flown onboard the GEOTAIL satellite, is designed to measure the characteristics of particle populations important to understanding the make-up and dynamics of the earth's geomagnetic tail. To do this, EPIC, a joint endeavor between the Technical University of Braunschweig (TUB), the University of Maryland (UM), and The Johns Hopkins University Applied Physics Laboratory (JHU/APL), is made up of five subassemblies: the Supra-Thermal Ion Composition Spectrometer (STICS) sensor, the STICS analog electronics, the Ion Composition System (ICS) sensor, the ICS analog electronics, and the Data Processing Unit (DPU). The STICS sensor provides ∼4π angular coverage, composition and spectral observations, with charge state determination for all ions from 30 keV to 230 keV/e, and mass per charge measurements ≥7.5 keV/e. The ICS sensor provides flux, composition, spectra, and angular distributions over two polar angles of the elemental species protons through iron from ≥50 keV to 3 MeV along with angular distributions in one plane of electron fluxes >32 keV and >110 keV. The DPU provides the capability of numerous operating modes from which a small number will be selected to optimize data collection throughout the many phases of the GEOTAIL mission. To date the EPIC instrument performance has been very successful. In this paper we describe the instrument, its operation, and show some of our early results.

Three-dimensional particle anisotropies in and near the plasma sheet of Jupiter observed by the EPAC experiment onboard the Ulysses spacecraft

During its inbound journey into Jupiter's magnetosphere, Ulysses had several encounters with the Jovian plasma sheet near the magnetic equator, which were related with intensity maxima in the energetic particles. We show for the first time anisotropies in three dimensions of three ion species (protons, helium and oxygen) in the energy range 0.24 < E < 0.77 [MeV/nucleon]. The data, obtained with the Energetic Particle Composition Experiment (EPAC) onboard Ulysses have been analysed by using spherical harmonics in three dimensions. We show that the first-order anisotropies of ions in or near the plasma sheet are strongest in a plane parallel to the ecliptic plane and more or less azimuthal with respect to the rotation of Jupiter. We show that the first-order anisotropy amplitude is larger for helium and oxygen ions than for protons in nearly the same energy per nucleon range. We find flow velocities for helium ions which are not consistent with corotation, but are larger by a factor of 2 in and near the Jovian plasma sheet on the dayside magnetosphere. In contrast for protons we observe nearly corotation. Far from the plasma sheet, at high magnetic latitudes, the flow velocities are less than corotation for protons, as well as for helium and oxygen. The azimuthal particle anisotropies are explained by intensity gradients perpendicular to the centre of the plasma sheet, by E × B particle drifts, and by nonadiabatic orbits of the particles near the Jovian plasma sheet. All of the three phenomena act in the same azimuthal direction, perpendicular to the mainly radial magnetic field direction. Each of them can be estimated, but their individual effects cannot be distinguished from each other. In addition, we find a radial component of the anisotropy which apparently is stronger for protons than for heavier ions. This radial anisotropy component is interpreted as a result of the radial outward displacement of ions in an azimuthally swept back magnetic field.

Simultaneous observations of H+ and O+; ions at two altitudes by the Akebono and Dynamics Explorer 1 satellites

We report simultaneous observations of H+ and O+ ions from the suprathermal ion mass spectrometer (SMS) on Akebono and the energetic ion composition spectrometer (EICS) on Dynamics Explorer 1. These observations were made simultaneously above and below regions of ion acceleration on auroral and polar cap magnetic field lines. The evening auroral zone data reported here directly confirm the existence of an ionospheric preenergization mechanism for oxygen ions. The preenergized oxygen ions have characteristic energies of the order of 10 eV and are transported to altitudes of several thousand kilometers where they acquire significant additional energy. Nearly simultaneous observations of O+ ions on polar cap field lines near the cusp/cleft region reveal two distinct populations. The first population is energized at altitudes of a few thousand kilometers and transported up and into the polar cap by the combination of the effects of the gradient in the magnetic field and the prevailing magnetospheric convection field. The second population has significantly more energy than the first. This second population could arise through several mechanisms, which are identified and discussed. The data presented illustrate that the creation (energization) and transport of streams of upflowing ions in the polar cap is more complex than previously anticipated and point to the importance and our limited knowledge of ionospheric processes responsible for the pre‐energization of oxygen ions.

O+ and He+ restricted and extended (BI‐modal) ion conic distributions

We have developed an automated procedure using standard image processing techniques that finds and characterizes energetic ion conic events in the data acquired by the Energetic Ion Composition Spectrometer on DE‐1 in the altitude range 8,000 to 24,000 km. The algorithm discriminates between the two types of ion conic distribution, those restricted to a narrow angular range and those extended in angle. Extended (bi‐modal) ion conic distributions also have a significant flux of field‐aligned energetic ions. Extended ion conies constitute more than one third of the ion conics found. The two types of ion conic distribution have different altitude dependences. The average properties of energetic conic distributions suggest that conic formation by localized, explosive, transverse energization is not the dominant mechanism responsible for producing energetic conic distributions above 8,000 km.

Energetic particle composition variations during the March 1991 events measured with the Ulysses EPAC instrument

We report on energetic particle measurements obtained with the EPAC instrument on board the Ulysses spacecraft during March 1991, when a series of important flares occurred at the Sun. The EPAC instrument measures electrons (0.1–0.38 MeV), protons (0.3–1.5 MeV) and heavy ions (0.2–6.0 MeV/N). We discuss the time interval March 22 through March 29 (DOY 81 through 88) and divide this interval in three periods with different ion compositions. At a quasi‐perpendicular shock on March 23, shock drift acceleration of protons, helium and electrons was observed. Thirteen hours after this shock the energetic ion composition changed dramatically by almost two orders of magnitude, signalling the arrival of a coronal mass ejection (CME) or driver gas. This driver gas was still present at the spacecraft when a second quasi‐perpendicular shock passed the spacecraft. The ratio Fe/O increased from 0.6 to 1.0 indicative of a connection to solar particles for about 6 hours after the second shock. The second shock did not accelerate ions as well and electrons not at all. Six hours after this shock the same oxygen and iron composition was observed as before, indicating that the second shock did not alter the energetic ion composition. A third ion composition was observed before the driver gas disappeared which was significantly different from those observed before the first and between the two shocks.

Chemical defense, biochemical composition and energy content of three shallow-water Antarctic gastropods

Aqueous extracts of the mantle tissues of the opisthobranchs Austrodoris kerguelensis and Tritoniella belli and the lamellarid gastropod Marseniopsis mollis were cytotoxic to the sperm of the antarctic sea urchin Sterechinus neumayeri, and caused behavioral responses (sustained terminal sensory tube-feet retractions) in five species of antarctic sea stars. Pieces of mantle tissue of all three species were noxious to two species of antarctic fish. Primary body components (mantle, foot, viscera) of the three gastropod species contained high levels (% dry wt) of NaOH-insoluble protein (40–59%), moderate levels of NaOH-soluble protein (7–25%) and lipid (6–18%), and low levels of carbohydrate (< 1%). The energetic composition of the tissues reflected their organic make-up, with most energy (11–17 kJg−1 dry wt) associated with protein. Total energy contents of representative adult individuals were 192,26 and 69 kJ for A. kerguelensis (93 g wet wt), T. belli (22 g wet wt) and M. mollis (114 g wet wt), respectively. Although these sluggish gastropods lack an external shell and are nutrient-and energy-rich and therefore high quality prey, like many of their temperate and tropical counterparts, they appear to be protected by chemicals.

Energetic composition, biomass, and chemical defense in the common antarctic nemertean Parborlasia corrugatus McIntosh

Parborlasia corrugatus McIntosh is a large, abundant, epibenthic antarctic nemertean which represents a considerable source of nutrition for predators. The energetic composition of adult body tissues (kJ·g −1 dry wt) is comprised primarily of energy derived from protein (11.4 kJ NaOH-insoluble, 6 kJ NaOH-soluble). Energy units associated with lipid (4.3 kJ) and carbohydrate (0.2 kJ) are much lower. Based on calculations of the energetic composition of whole body tissues, and a density of 0.3 ind·m −2, mean population energetic density is estimated to be 65 kJ·m −2. These values are often significantly higher as P. corrugatus aggregates when feeding. Despite their high abundance, nemerteans are not preyed upon and appear to be chemically defended. Sperm of the antarctic sea urchin Sterechinus neumeyeri (Meissner) were killed when exposed to a 3% aqueous extract of whole nemertean body tissues. In laboratory feeding experiments, two common species of antarctic fish showed significant rejection of nemerteans. Its toxic and feeding-deterrent characteristics are probably the result of the epithelial production of copious acidic mucus (pH = 3.5), although other toxic or noxious metabolites may be present. These results indicate that P. corrugatus, an important scavenger in antarctic benthic systems, is abundant, high in nutrients and energy content, and could be judged on this basis as a high-quality prey item. Nonetheless, due to its chemical defense, potential predators may avoid ingestion of this species.

Biochemical and energetic composition, population biology, and chemical defense of the antarctic ascidian Cnemidocarpa verrucosa lesson

The biochemical and energetic composition, population biology (size-weight relationship, abundance and size-frequency distribution) and chemical defense of the antarctic ascidian Cnemidocarpa verrucosa Lesson was investigated at McMurdo Sound, Antarctica, during the austral summer of 1989. The organic content (% organic material · g −1 dry tissue wt) of individual body components (tunic, body wall, endocarps, intestines, mature ovitestes and branchial basket) was generally high, with values ranging from 44.5% in the endocarps to 83.9% in the gonads. Most of this material was in the form of NaOH-soluble and insoluble protein. Tissue energy values ranged from 15.1 (tunic) to 22.4 (gonad) kJ · g −1 dry wt. Body height (cm) was positively related to body weight (g dry wt) by an exponential function. A representative individual (14 cm height, 550 g wet wt) contained a total of 493 kJ with most (75%) of this energy attributable to the body wall and tunic. The gonadal index [(kJ ovitestes · total kJ −1) x 100] for sexually mature individuals collected in November was 17.2 ± 4.7 ( n = 6). Population densities of C. verrucosa at depths of 20–30 m were 0.4 ind · m −2 at a site 3 km north of McMurdo Station. Energetic densities were estimated to be 197 kJ · m −2. Size-frequency analysis revealed four modal peaks that probably represent distinct age cohorts, and may indicate predictable, annual recruitment events. Bioassays revealed that the tunic was noxious to sympatric pelagic and benthic fish, as well as an allopatric model fish. However, aqueous tunic extracts did not cause mortality in sea urchin sperm indicating the noxious compound(s) is not cytotoxic. pH values for body components were weakly acidic or neutral (5.86–6.93). Mature ovitestes were rejected by sympatric pelagic fish suggesting that gametes may be chemically defended. Although this common antarctic ascidian represents a significant resource of materials and energy, its tunic is tough and noxious, and probably provides an effective means of defense against potential predators.

Energetic particle composition measurements from Phobos 2: Results of the LET experiment

The Low Energy Telescope (LET) experiment carried on board the Phobos spacecraft measured the flux, spectra and elemental composition of nuclei from hydrogen up to iron, in the energy range ∼ 1–75 MeV nucleon −1. Isotope separation for helium was also achieved. We present the results of a study of solar energetic particle (SEP) composition using LET data acquired during the period July 1988 to March 1989. The set of particle events selected for study comprises six large solar flare events, two 3He-rich events and two energetic storm particle increases associated with interplanetary shocks. Three of the six large flare events occurred during a period of unusually high solar activity in March 1989. In two of these events, large Fe/O ratios were measured (0.44 ± 0.05 and 0.95 ± 0.24). The Fe/O ratios determined for the complete set of large flare events show an inverse correlation with the spectral index of oxygen, suggesting that the acceleration mechanism that produces events showing enhanced heavy-ion abundances is different from that responsible for lower Fe/O ratios. Our results in the case of the 3He-rich events are in agreement with earlier work, showing an enrichment in heavy ions relative to the average SEP composition. The abundances measured for the shock-associated increases are consistent with the acceleration of the ambient population of solar flare particles.

Statistical analysis of upflowing ion beam and conic distributions at DE 1 altitudes

Statistical analyses of energetic (0.01–17 keV) upflowing ions (UFI), beams, conies, and hybrid pitch angle distributions, have been made using the energetic ion composition spectrometer (EICS) data on the DE 1 satellite for the 8000‐km to 23,300‐km altitude range over a 5‐year period from September 1981 to June 1986. Hybrid types are defined here as combinations of lower‐energy beams and higher‐energy conics at three different energies (0.01–1, 1–4, and 4–17 keV). In general, it is found that (1) the source and transport mechanisms confine UFI mostly to auroral field lines; (2) although field‐aligned currents and UFI events have similar frequencies of occurrence, no obvious (one‐to‐one) relationship between current direction and UFI source characteristics was found; (3) although H+ and O+ UFI spatial (latitude, local time, and altitude) distributions are similar, O+ is more efficiently accelerated than H+ at higher values of Kp; and (4) the electric potential drop along auroral field lines, which would accelerate ions away from the ionosphere, is small (&lt;1 kV) except perhaps in the dusk to midnight sectors where on occasion large values (1–10 kV) may be present.

Biochemical and energetic composition of bathyal echinoids and an asteroid, holothuroid and crinoid from the Bahamas

The biochemical and energetic composition of body components of ten species of bathyal echinoids, and an asteroid, a holothuroid and a stalked crinoid were determined from individuals sampled from a variety of deep-water sites near the Bahamas (north Caribbean Sea) in October 1988. When compared with other studies of echinoderms, no geographic- or depth-related differences in biochemical or energetic composition were found. Body-wall tissues were composed primarily of skeletal material (mineral ash), but were comparatively high in organic material in the echinothuriid echinoids, and the asteroid and holothuroid. Gut tissues and pyloric cecae had high levels of lipid and protein, indicating their potential role in nutrient storage. Body-wall tissues were generally low in energy, but were highest in the echinoidsAraeosoma belli (7.7 kJ g−1 dry wt) andSperosoma antillense (8.0 kJ g−1 dry wt), the asteroidOphidiaster alexandri (8.9 kJ g−1 dry wt), and the holothuroidEostichopus regalis (13.1 kJ g−1 dry wt). Energy levels of gut and pyloric cecal tissues were two to three times higher than those of body-wall tissues. Total somatic tissue energy values varied greatly among species, ranging from 1.5 kJ in the echinoidAspidodiadema jacobyi to 142.1 kJ inE. regalis. As the bathyal echinoderms examined in this study occur in great abundance, they represent a significant reservoir of organic and inorganic materials and energy in deep-water benthic systems.