Magnetospheric Ion Composition Research Articles

A new, temporarily confined population in the polar cap during the August 27, 1996 geomagnetic field distortion period

On August 27, 1996, a two‐hour energetic heavy ion event (∼1 MeV) was detected at 8:25 UT at apogee (∼9 Re and an invariant latitude of ∼80°), by the Charge and Mass Magnetospheric Ion Composition Experiment onboard POLAR. The event, with a maximum spin averaged peak flux of ∼150 particles/(cm²‐sr‐s‐MeV), showed three local peaks corresponding to three localized regions; the ion pitch angle distributions in the three regions were different from an isotropic distribution and different from each other. No comparable flux was observed by the WIND spacecraft. The appearance of lower energy He++ and O > +2 during the event period indicates a solar source for these particles. From region 1 to 2 to 3, the helium energy spectra softened. A distorted magnetic field with three local minima corresponding to the three He peak fluxes was also observed by POLAR. A possible explanation is that the energetic He ions were energized from lower energy helium by a local acceleration mechanism that preferred smaller rigidity ions in the high altitude polar cusp region.

Dispersive O<sup>+</sup> conics observed in the plasma-sheet boundary layer with CRRES/LOMICS during a magnetic storm

Abstract. We present initial results from the Low-energy magnetospheric ion composition sensor (LOMICS) on the Combined release and radiation effects satellite (CRRES) together with electron, magnetic field, and electric field wave data. LOMICS measures all important magnetospheric ion species (H+, He++, He+, O++, O+) simultaneously in the energy range 60 eV to 45 keV, as well as their pitch-angle distributions, within the time resolution afforded by the spacecraft spin period of 30 s. During the geomagnetic storm of 9 July 1991, over a period of 42 min (0734 UT to 0816 UT) the LOMICS ion mass spectrometer observed an apparent O+ conic flowing away from the southern hemisphere with a bulk velocity that decreased exponentially with time from 300 km/s to 50 km/s, while its temperature also decreased exponentially from 700 to 5 eV. At the onset of the O+ conic, intense low-frequency electromagnetic wave activity and strong pitch-angle scattering were also observed. At the time of the observations the CRRES spacecraft was inbound at L~7.5 near dusk, magnetic local time (MLT), and at a magnetic latitude of –23°. Our analysis using several CRRES instruments suggests that the spacecraft was skimming along the plasma sheet boundary layer (PSBL) when the upward-flowing ion conic arrived. The conic appears to have evolved in time, both slowing and cooling, due to wave-particle interactions. We are unable to conclude whether the conic was causally associated with spatial structures of the PSBL or the central plasma sheet.

CRRES observations of the composition of the ring-current ion populations

The Magnetospheric Ion Composition Spectrometer onboard the CRRES spacecraft provided mass and charge state composition data for positive ions in the energy-per-charge range 10–425 keV/e. The CRRES data is compared to the AMPTE/CCE observations during both geomagnetically quiet and active periods. The CRRES average radial profiles of H +, He +, and He ++ during quiet intervals are remarkably similar to those measured by CCE. The excess of ions measured by CRRES at L < 4 compared to standard ion transport models tends to support the necessity of additional ion radial diffusion by ionospheric electric-field variations. A summary is also given of the measured storm-time variations of the major ion populations during the large storm of March 1991. The results are compared to previous observations by the AMPTE/CCE spacecraft during a large storm. The CRRES data confirm that the rapid initial recovery of the Dst magnetic index is due to a momentary change of the relative ion composition of the ring current to an oxygen-dominated state. A preliminary test of the Dessler-Parker-Sckopke relation between the ion energy and the global magnetic perturbation shows that the observed particle fluxes during the March 1991 storm could account for only 30–50% of the variation of the Dst magnetic index.

Auroral Ionospheric Ion Feeding of the Inner Plasma Sheet during Substorms

During the last decade, satellite observations in the nightside magnetosphere have confirmed the presence of energetic (>20 keV) ionospheric-origin ions in the near-Earth magnetotail. Observations also imply that the feeding of the equatorial magnetosphere with ions from the high-latitude ionosphere can be very fast and intense at times. In the present paper we use observations from the Combined Release and Radiation Effects Satellite (CRRES) to investigate the characteristics of ion energy density variations. Multispecies studies of the energy density give important clues on the coupling of the different plasma sources and their participation in the substorm energization. The measurements, coming from the Magnetospheric Ion Composition Spectrometer (MICS), confirm previous results obtained from the AMPTE/CCE-CHEM spectrometer, with regard to the timing of the high-latitude ionosphere response to the equatorial magnetosphere disturbances. The energy density profile of the ionospheric-origin O+ follows the intensity enhancements of the westward electrojet very closely in time, exhibiting a continuing increase, contrary to the behaviour of the other major ion species H+ and He++. This feature, which is consistent with statistical studies of AMPTE/CCE observations, points towards a fast activation of an extraction/acceleration mechanism which feeds the inner plasma sheet with ions of ionospheric origin during the substorm expansion.

Origin of energetic ions in the polar cusp inferred from ion composition measurements by the Viking satellite

Abstract. The magnetospheric ion composition spectrometer MICS on the Swedish Viking satellite provided measurements of the ion composition in the energy range 10.1 keV/e\\leqE/Q\\leq326.0 keV/e. Data obtained during orbit 842 were used to investigate the ion distribution in the northern polar cusp and its vicinity. The satellite traversed the outer ring current, boundary region, cusp proper and plasma mantle during its poleward movement. H+ and He++ ions were encountered in all of these regions. He+ ions were present only in the ring current. The number of O+ and O++ ions was very small. Heavy high-charge state ions typical for the solar wind were observed for the first time, most of them in the poleward part of the boundary region and in the cusp proper. The H+ ions exhibited two periods with high intensities. One of them, called the BR/CP event, appeared at energies up to 50 keV. It started at the equatorward limit of the boundary region and continued into the cusp proper. Energy spectra indicate a ring current origin for the BR/CP event. Pitch angle distributions show downward streaming of H+ ions at its equatorward limit and upward streaming on the poleward side. This event is interpreted as the result of pitch angle scattering of ring current ions by fluctuations in the magnetopause current layer in combination with poleward convection. The other of the two periods with high H+ ion intensities, called the accelerated ion event, was superimposed on the BR/CP event. It was restricted to energies \\leq15 keV and occurred in the poleward part of the boundary region. This event is regarded as the high-energy tail of magnetosheath ions that were accelerated while penetrating into the magnetosphere. The cusp region thus contains ions of magnetospheric as well as of magnetosheath origin. The appearance of the ions depends, in addition to the ion source, on the magnetic field configuration and dynamic processes inside and close to the cusp.

Data processing algorithms for on-board satellite event analysis

The authors describe the data analysis and reduction schemes employed by the data processing unit (DPU) supporting the magnetospheric ion composition spectrometer sensor aboard the CRRES satellite. One method of reducing output telemetry requirements is to partition the underlying event parameter spaces into disjoint classes, and to downlink statistics based on these classes rather than individual events. The DPUs utilize a hardware implemented binary search algorithm to classify each valid event into one of several mass and mass per charge-state groups, using lookup tables written under software control. The tables contain discrete approximation to polynomial curves which separate adjacent groups. The curves were derived from extensive preflight sensor calibration data using a novel curve-fitting and extrapolation algorithm combining local and global least-squares approximations. Both the onboard table writing software and the techniques employed to derive the boundary curves are described. >

Magnetospheric ion composition spectrometer onboard the CRRES spacecraft

The magnetospheric ion composition spectrometer (MICS) in the CRRES scientific payload utilizes time-offlight and energy spectroscopy in combination with an electrostatic entrance filter to measure the mass A , energy E, and ionic charge Q of particles with energies between 1 keV/charge and 430 keV/charge. An advanced ogive design of the electrostatic filter system provides a narrow angle of acceptance and high sensitivity. Incident particles are postaccelerated prior to entering the detection segment in order to improve the resolution at the lower end of the useful energy range. The principle features of the MICS spectrometer are described in some detail. Selected data gathered in-flight are shown as an illustration of the instrument performance in the operational orbit. I. Introduction T HE magnetospheric ion composition spectrometer (MICS) in the payload of the Combined Release and Radiation Effects Satellite (CRRES) belongs to a class of advanced instruments which provide full characterization of incident ions by determining their mass A (in amu), charge Q, and velocity V (magnitude and direction) as independent parameters. The particle's identity is derived from a time-offlight Tand energy E measurement, and the ionic charge Q is obtained from an electrostatic energy per charge E/Q filter which serves as the entry element of the spectrometer. Upon leaving the E/Q filter the ion's energy is increased by a postaccelerating voltage to improve the instrument resolution at low particle energies. The MICS energy range extends from 1.2 keV/charge up to 426.5 keV/charge, and ion species are identified from hydrogen to iron. The obtainable mass resolution A/dA is a complex function of the particle mass and energy. For a given ion species the mass resolution increases as a function of the energy per mass ratio E/A. A typical ratio A /cL4 = 8 is obtained for oxygen ions with energies above 100 keV. Despite this only moderate mass resolution, atoms and molecules, even isobaric structures, can be discriminated by a peculiarity of the MICS detection technique: Fragmentation of swift molecules in the thin START foil of the TIE spectrometer leads to groups of particles which travel with the original velocity but each fragment's energy is apportioned to its mass. The resulting statistical distribution in (E, T) space can be used to identify the presence of molecules.

The May 2‐3, 1986 magnetic storm: First energetic ion composition observations with the Mics instrument on Viking

Measurements with the Magnetospheric Ion Composition Spectrometer (MICS) onboard the polar orbiting Swedish satellite VIKING clearly show a strong asymmetry between the dusk‐ and dawnside ion distributions obtained after the onset of a magnetic storm on May 2‐3, 1986. The eveningside of the inner ring current region is quickly filled by protons with energies of some tens of keV. The morningside continues for several hours to show the quiet‐time inner ring current proton spectra in which protons below ∼100 keV have been removed due to charge‐exchange processes. The data obtained at high latitudes will be compared with measurements of the CHEM instrument on the AMPTE/CCE spacecraft near the equatorial plane. The observations are discussed in context of the convection of injected ions into the inner magnetosphere during magnetically active periods.

Correlations of magnetospheric ion composition with geomagnetic and solar activity

A large ion composition data set consisting of 1‐month averages has been assembled for the energy per charge range 0.9–15.9 keV/e. It includes 48 months of data taken by the Ion Composition Experiments on the ESA/GEOS 1 and 2 satellites at or near geostationary orbit. Data were obtained during the rising and maximum phases of the current solar cycle from May 1977 through November 1981 inclusive. Five ion species are routinely identifiable: H+, He++, He+, O++, and O+, above a limiting density ∼10−3 ions cm−3. Ion densities exhibit a number of very striking statistical correlations with one another and with both Kp and solar EUV as measured by F10.7. One principal result is that increases in the densities of magnetospheric He+, O++, and O+ are observed that are apparently due entirely to increased solar EUV fluxes associated with the rising phase of the current solar cycle. There is a marked rise in O+ density by a factor of ∼8 with increasing geomagnetic activity, but no corresponding increase in either He+ or O++ and only a small increase in H+. The He++/H+ ratio is found to be remarkably constant at ≈0.01. Contrary to ion density results, little or no variation is found in mean energy. These observations are interpreted in terms of the composition and dynamics of two sources of magnetospheric plasma: the solar wind and the high‐latitude topside ionosphere.

The plasma mantle: Composition and other characteristics observed by means of the PROGNOZ-7 satellite

A brief summary of the main results of magnetospheric ion composition measurements in general is first presented. PROGNOZ-7 measurements in the nightside plasma mantle are then described and analyzed. Some of the results are the following: In the nightside mantle not too far from midnight the properties of the mantle are sometimes consistent with the open magnetosphere model. However during most magnetic storm situations O+ ions appear in the mantle in large proportions and with high energies. The acceleration process affecting the ions has been found in several cases to give equal amounts of energy to all ions independent of mass. Along the flanks of the magnetosphere the flow of the plasma is often low or absent. The O+ content is high (up to 20%) and the energy spectrum of both ions and electrons may be very hot, even up to the level of the ring current plasma in the keV range.

Observed increase in the abundance of kilovolt O + in the magnetosphere due to solar cycle effects

Since May 1977 the Ion Composition Experiments on board GEOS-1 and 2 have measured the abudance of magnetospheric ions in the energy per charge range from a few eV to 16 keV. Long term averages of a subset of this data, restricted to magnetic quiet (Kp ≦ 2) and the energy range 0.9 to 13.9 keV, reveal striking trends in magnetospheric ion composition over a period of nearly 3 years. These include a 10-fold increase in the average magnetospheric O +/H + ratio which is well correlated with increased solar activity as measured by the 10.7 cm solar radio flux. No comparable trend was found, for example, in the magnetospheric He ++/H + ratio which had an average value of (7.7 ±3.4) × 10 −.

Dynamics of magnetospheric ion Composition as observed by the GEOS mass spectrometer

Dynamics of magnetospheric ion Composition as observed by the GEOS mass spectrometer