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Mauk, B. H.

Publications and source records attributed to Mauk, B. H..

50 records · Page 3
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NASA NTRS1986

Quantitative modeling of the 'convection surge' mechanism of ion acceleration

To explore the properties of the 'convection surge' mechanism postulated by Quinn and Southwood (1982), a quantitative computer model of the mechanism is constructed. The model incorporates the dipolarization of the field line shapes as well as the results of recent transient electric field measurements by the AST-6 satellite. The computer model numerically integrates the equations of motion of ensembles of ions populating a single flux tube that goes through the convection surge or 'dipolarization' transformation. The numerical results confirm that the mechanism easily generates the bounce-phase-bunched ion distributions in question, and show that the convection surge can generate dramatically field-aligned ion distributions. It is hypothesized that the convection surge mechanism is fundamentally associated with the processes responsible for transporting tail ion populations to the geosynchronous regions of the earth's magnetosphere.

Mauk, B. H.↗
NASA NTRS1986

Macroscopic ion acceleration associated with the formation of the ring current in the earth's magnetosphere

As an illustration of the operation of macroscopic ion acceleration processes within the earth's magnetosphere, the paper reviews processes thought to be associated with the formation of the earth's ring-current populations. Arguing that the process of global, quasi-curl-free convection cannot explain particle characteristics observed in the middle (geosynchronous) to outer regions, it is concluded that the transport and energization of the seed populations that give rise to the ring-current populations come about in two distinct stages involving distinct processes. Near and outside the geostationary region, the energization and transport are always associated with highly impulsive and relatively localized processes driven by inductive electric fields. The subsequent adiabatic earthward transport is driven principally by enhanced, curl-free global convection fields.

Mauk, B. H.↗
NASA NTRS1985

Low-frequency waves and associated energetic ions downstram of Saturn

Examples of highly coherent, low-frequency waves that were observed by Voyager 2 in the IMF during several months following the Saturn encounter in 1981 are presented. It is shown that the detection of these events was due to a favorably oriented IMF. These events are discussed in terms of correlated ion and magnetic field data, and the evolution of their properties with incresing distance from Saturn is addressed. The spectral and eigenfunction characteristics of the observed waves are shown, and the mode of the waves and their possible excitation mechanisms are considered, including an instability analysis. The results are compared with those obtained in the foreshock regions of other planets, especially the earth.

Behannon, K. W.↗
NASA NTRS1985

Particle and field stress balance within a planetary magnetosphere

A technique is developed for experimentally estimating the local tensor stresses within a planetary magnetic field configuration characterized by local spacecraft measurements. Key to the technique is the determination of the shapes of field lines using the symmetry properties of the system coupled with local and instantaneous measurements of the field line inclination angles. The technique is applied here to the inner and middle Saturnian magnetosphere using data returned by the Magnetic Field Experiment on the Voyager 1 spacecraft. It is concluded that the ring current has substantial radial structure, heretofore not shown. Outside about 13 R(s) the newly derived field stresses match remarkably well the funtional variation of the centrifugal corotation stresses of the cool particle population measured previously by the Plasma Science Experiment. Inside about 13 R(s) the key structure in the derived field stresses, a prominent local maximum, matches the approximate position of an apparent strong pressure gradient in the energetic particles characterized by the Low-Energy Charged Particle detectors.

Mauk, B. H.↗
NASA NTRS1985

Ion and electron energy dispersion features detected by ISEE 1

An energy dispersion feature observed by the ISEE 1 medium energy particle instrument is reported. This feature is characterized by enhancements in both electron and ion fluxes which occur in the 20-200 keV energy range and at radial distances from 5 to 13.5 earth radii. There is a strong energy dependence in the onset times of the enhancements. The time period between the first appearance of an enhancement at high energy to its eventual disappearance in the 20 keV channel can be as much as an hour. The duration of the enhancement in a given energy channel decreases with increasing energy. The species and pitch angle of particles in which the feature is most marked depend on local time. It is shown that the feature is a new manifestation of an old phenomenon, the drift dispersion that frequently produces signatures in particle data from geosynchronous satellites.

Greenspan, M. E.↗
NASA NTRS1983

Dynamical injections as the source of near geostationary quiet time particle spatial boundaries

The question whether the noon-dusk feature is a manifestation of the spatial structures that should arise from quasi-stationary convection is examined. The key consideration here is whether the energy dispersion of the feature can be explained. It is shown that the observed energy dispersion cannot be attributed to the standard stationary convection configurations, either perturbed or unperturbed. It is also demonstrated, using a detailed computer simulation, that the nighttime, double-spiral-shaped injection boundary (used previously to reproduce the fast changing nighttime features) is successful at reproducing the noon-dusk feature by allowing the particles to evolve for periods of 12 to 36 hours after the injection. It is stressed that the portion of the injection boundary responsible for the feature looks very different from the standard convection boundaries configuration. Conclusions are offered concerning the importance of quasi-stationary convection as the mechanism by which the near geostationary regions are populated.

Mauk, B. H.↗
NASA NTRS1983

Corotation anisotropies in Saturn's magnetosphere

Ion data from the Voyager 1 and 2 low-energy charged particle (LECP) experiment are fit to a second-order harmonic expansion to determine anisotropies within the Saturnian magnetosphere. Anisotropies from the low-energy channels (28-130 keV) are often consistent with those expected from corotation (generally with a small radial component on the dayside) but are at times distinctly different from corotation. On the dayside, near the noon meridian, first-order anisotropies often depart significantly from the corotation direction. On the nightside, amplitudes are consistent with full corotation but begin to drop below corotation values at a dipole L of approximately 27 Saturn radii (corresponding to a velocity of approximately 265 km/s). Second-order anisotropies are significant, even dominant at times, on the dayside where a relatively broad range of pitch angles is sampled by the instrument. In all cases there is a departure of approximately 180 deg from the first-order anisotropies expected due to corotation beginning outside the Rhea L shell and continuing through at least the orbit of Dione. This is the region where the cold and hot plasma tori have been observed. The anisotropies expected from rigid corotation of the observed flux distributions are computed, and it is concluded that parts of the Saturnian magnetosphere are not rigidly corotating. Calculations based on the combined effects of corotation plus solar wind generated convective electric fields appear to provide insights into the anisotropies along the dawn meridian. However, on the dayside near noon, turbulence and/or time variations seem necessary to explain the departure from simple convection models.

Carbary, J. F.↗
NASA NTRS1983

Characterization of geostationary particle signatures based on the 'injection boundary' model

A simplified analytical procedure is used to characterize the details of geostationary particle signatures, in order to lend support to the 'injection boundary' concept. The signatures are generated by the time-of-flight effects evolving from an initial sharply defined, double spiraled boundary configuration. Complex and highly variable dispersion patterns often observed by geostationary satellites are successfully reproduced through the exclusive use of the most fundamental convection configuration characteristics. Many of the details of the patterns have not been previously presented. It is concluded that most of the dynamical dispersion features can be mapped to the double spiral boundary without further ad hoc assumptions, and that predicted and observed dispersion patterns exhibit symmetries distinct from those associated with the quasi-stationary particle convection patterns.

Mauk, B. H.↗
NASA NTRS1981

Non-E x B ordered ion beams upstream of the earth's bow shock

The unexpected appearance of spin modulations in the fixed voltage electrostatic analyzer detectors on ISEE 1 and 2 has made it possible to study the plasma properties of the upstream ions in high time resolution. Using an isotropic flowing Maxwellian distribution to model the count rate modulations, estimates have been obtained of the local plasma temperature and three-dimensional flow velocity of the observed upstream ion population. It is found that in almost all of the observations of upstream particles there exist beam-like ions with temperatures in the range 5-80 eV. Their flow velocities cannot be ordered by E x B. This last point separates these observations from the previously reported reflected and diffuse populations of upstream ions. Mechanisms that can gyrophase bunch the ions reflected at the bow shock are discussed as a method of explaining the data.

Gurgiolo, C.↗
NASA NTRS1981

Helium cyclotron resonance within the earth's magnetosphere

A histogram of electromagnetic Alfven/ion cyclotron wave frequencies, sampled within the geostationary environment and normalized by the equatorial proton cyclotron frequency, shows a dramatic gap centered near the helium (He +) cyclotron frequency. Also, strongly cyclotron phase bunched helium ions (20-200 eV) have been observed directly within the vicinity of wave environments. These observations are interpreted as resulting from the absorption of the waves through cyclotron resonance by cool ambient populations of helium ions.

Mauk, B. H.↗
NASA NTRS1980

An experimental test of the electromagnetic ion cyclotron instability within the earth's magnetosphere

Examples of propagating electromagnetic Alfven/ion cyclotron waves in plasma particle and magnetic field data observed by the ATS-6 geostationary satellite are discussed. These waves were viewed mainly near the afternoon and dusk regions of the earth's magnetosphere with normalized frequencies in the 0.05 to 0.5 range. Two wave events were analyzed: both appeared coincidentally with the encounter of cool plasma populations which joined the hot populations already present. An electromagnetic ion cyclotron instability was proposed as the wave generation mechanism; this theory was tested by evaluating the linear growth integrals under the measured anisotropic hot ion distribution.

Mauk, B. H.↗
NASA NTRS1975

ATS-6 - UCSD auroral particles experiment

The University of California at San Diego Auroral Particles Experiment aboard Applications Technology Satellite-6 (ATS-6) is discussed. The experiment is designed to investigate the time development of geomagnetic substorm particles, the confinement and loss of such particles, and the roles of plasma wave instabilities and characteristic system periodicities in substorm and general magnetospheric processes. The instrumentation includes a complement of five electrostatic charged particle detectors. Two detector assemblies are capable of rotation through 220 deg. The electrostatic curved plate energy/unit charge analyzers are ovoid, requiring particles to be bent only 55 deg to obtain azimuthal focusing. The inside of the plates is serrated to eliminate particles striking the sides. A post-analysis electrostatic lens consisting of two wire grids, one at the potential of the inner plate and one at the potential of ground, focuses particles strongly upon the center of the sensor. A spiraltron particle sensor detects the charged particles. The system has an energy range of five orders of magnitude with a lower extreme of less than 1 eV. Preliminary data are presented to illustrate phenomena which are observed as a result of the novel features described.

Mauk, B. H.↗
NASA NTRS1974

Correlation of Kp with the substorm-injected plasma boundary

The local time position of the low-energy substorm-injected plasma boundary in the dusk to midnight region of the magnetosphere as observed by the geostationary satellite ATS 5 is found to be correlated with the interpolated Kp index. Considering the time resolution of Kp, the correlation is found to be quite close but dependent on season. An estimate of the overall shape and position of the low-energy boundary within this region of the magnetosphere as a function of Kp is found by using a fit to the authors' winter data correlation in conjunction with a fit of data presented by Carpenter (1967) concerning the Kp-related radial positioning of the plasmapause boundary in the postmidnight region. This analysis results in a spiral structure, the scale of which depends on Kp.

Mauk, B. H.↗