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Krimigis, S. M.

Publications and source records attributed to Krimigis, S. M..

At least 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Low-energy charged particles in Saturn's magnetosphere - Results from Voyager 1

The Voyager 1 low-energy charged particle instrument measured electrons and ions with energies below 26 and 40 kiloelectron volts, respectively, in the Saturn magnetosphere. Spectra of all ion species were found to have an energy cutoff at levels greater than 2 million electron volts. In contrast to the magnetospheres of Jupiter and earth, there are no lobe regions essentially devoid of particles in Saturn's nighttime magnetosphere. One novel feature of the Saturn magnetosphere is a pervasive population of energetic molecular hydrogen.

Krimigis, S. M.↗
NASA NTRS1981

Relationship between energetic particles and plasmas in the distant plasma sheet

Measurements of ions from three different instruments on the IMP-7 and 8 spacecraft are combined to yield the differential energy spectra of ions over the entire energy range of 100 eV to 4 MeV in the earth's distant (30 to 40 earth radii) plasma sheet. These spectra, obtained during times of relatively small bulk flow velocities, span the intensity range from 10 to the -5th to 10 to the 5th per sq cm-sec-sr-keV, varying smoothly over the entire energy range both when the plasma is cold (about 1 keV) and hot (about 9 keV). Overall, the shape of the spectrum resembles a Maxwellian but with a high energy (not less than 50 keV) tail described well by a power law. The high energy tail is displaced in a parallel fashion to higher or lower intensities when the plasma is hot or cold, respectively. It is found that the energetic particle populations in the plasma sheet appear to be directly related to the mean thermal energies of the corresponding plasmas.

Sarris, E. T.↗
NASA NTRS1981

Upper limits for X-ray and energetic neutral particle emission from Jupiter - Voyager-1 results

The X-ray sensitivity of the low energy proton channels in the Low Energy Charged Particle (LECP) experiment and its directional measurements determined whether X-rays from Jupiter can be recognized as additional flux above background as Voyager 1 approached the planet. Between about 230 and about 100 R(J), a statistically significant count rate was detected interpreted as X-rays and/or neutral particles. Such an X-ray flux leads to estimates of precipitating electrons over the Jovian polar caps which are 200 times larger than over observed electron fluxes in the Io plasma torus.

Kirsch, E.↗
NASA NTRS1980

Intensity variations in plasma flow at the dawn magnetopause

Observations of plasma flows in the region of the dawn magnetopause obtained by the outbound Voyager 1 spacecraft, at a velocity of 11 km/sec, are discussed. Magnetic field and ion data obtained for the period surrounding four magnetopause crossings are presented which reveal energetic anti-sunward flowing ions outside the boundary with a time variability on the order of 400 millisec. These particle intensity variations, observed to vary with frequency, are most likely associated with the particle energization process or with the leakage of magnetospheric protons. The ion flows are considered to have originated sunward of the dawn meridian and were observed to penetrate approximately an ion gyroradius inside the dawn magnetopause.

Lanzerotti, L. J.↗
NASA NTRS1980

Detection of energetic hydrogen molecules in Jupiter's magnetosphere by Voyager 2 - Evidence for an ionospheric plasma source

The discovery of energetic (approximately 1 MeV/nuc) H3 and H2 molecules in Jupiter's magnetosphere is reported. The data, obtained with the LECP instrument on Voyager 2, showed these molecules to be present throughout the magnetosphere and as far as 180 Jupiter radii from the planet, in the 'magnetospheric wind' region. Although the relative abundances of H3 and H2 do not show a monotonic trend with distance from Jupiter, the intervals of highest abundance were found in the outer magnetosphere. As an example, in the radial range 51-56 Jupiter radii, of the dayside magnetosphere, the abundances of H3 and H2 (0.60-0.95 MeV/nuc) were about 20 and 13-25% that of He, respectively, and the He abundance was about 1-2% that of H. Since H3(+) is expected to be an important constituent of Jupiter's ionosphere, the data provide strong evidence that, in addition to Io, the ionosphere may be an important local plasma source for the Jovian energetic particles. The measurements reported may represent the first detection in nature of molecules at energies as high as 1 MeV/nucleon.

Hamilton, D. C.↗
NASA NTRS1980

Statics of the nightside Jovian plasma sheet

Data are analyzed from the low energy charged particle (LECP) and magnetic field (MAG) experiments on the Voyager 2 spacecraft that demonstrate that the configuration of the Jovian plasma sheet at distances of about .80 to about 120 Jupiter radii is determined by ions (protons and heavier nuclei) of energies greater than approximately 30 keV. The energy densities of these ions are sufficient to provide the diamagnetic depressions in the magnetic field strengths observed as the spacecraft crossed the Jovian plasma sheet. The particle bulk direction of motion is predominantly across the local magnetic field, consistent with that expected from corotation of the planetary magnetic field.

Lanzerotti, L. J.↗
NASA NTRS1980

Ions of Jovian origin observed by Voyager 1 and 2 in interplanetary space

Burst-like and long-lived ion fluxes (E greater than 30 keV) of Jovian origin have been observed in interplanetary space by the LECP instrument on the Voyager 1 and 2 spacecraft. Burst (few minute duration) events are observed at distances greater than 0.6 AU from Jupiter. These events are highly anisotropic and possess steep energy spectra, while long-lived (greater than 8 hour duration) events have relatively steady fluxes at low energies, strong anisotropies that decay with time, and a variable high energy component. Both types of events usually display simultaneous onsets and sharp cutoffs for all energies, an excess of atomic number Z not less than 6 particles compared to solar and interplanetary events, and particle flow directions pointed away from Jupiter along the local interplanetary magnetic field. The origin for the long-lived events appears to be inside the bow shock of the planet.

Zwickl, R. D.↗
NASA NTRS1980

Variability of plasma sheet dynamics

IMP 7 observations of plasma sheet structure and dynamics made during a 24-h period in which the satellite traversed the tail plasma sheet at a radial distance of 35 earth radii and remained within 2 earth radii of the expected position at the neutral sheet and in which at least five substorms occured on the ground are presented. High-time-resolution measurements of the magnetic field, plasma flow and greater than 50-keV protons obtained by the satellite and ground-based magnetic measurements are discussed for a 4-hr interval in which two small substorms occurred, a 6-hr geomagnetically quiet interval in which moderate variable plasma flows were observed, a very rapid, smooth neutral sheet crossing and earthward plasma flow during the expansion phase of a small substorm, a moderate-size substorm in which a prolonged interval of field-aligned tailward flow commenced at onset, a strong tailward and dawnward flow burst in an interval between substorms and a large substorm in which strong tailward flow was observed. Observations indicate the significant distortion of the tail field, possibly by plasma flow stresses, a neutral sheet structure occasionally resembling the hydromagnetic rotational discontinuity and a high level of magnetic turbulence during an earthward plasma flow which may contribute towards plasma sheet dissipation.

Coroniti, F. V.↗
NASA NTRS1980

Encounters with Jupiter - The Low Energy Charged Particle results of Voyager

Results of the Low Energy Charged Particle (LECP) experiments on board the Voyager spacecraft, designed to measure the fluxes and compositions of ions of energies 28 keV or greater and electrons of energies 15 keV or greater, during Jupiter encounter are presented. Observations of intense particle bursts coming from Jupiter several weeks before Jovian magnetosphere entry, magnetopause crossings, a hot corotating outer magnetospheric plasma, decreases in particle fluxes at the orbits of the Galilean satellites 10-hr particle flux periodicities and a magnetospheric wind are discussed. A new model of the Jovian magnetosphere based on the Voyager results is presented, and areas of continuing LECP Jovian data analysis are indicated.

Carbary, J. F.↗
NASA NTRS1980

Energetic /approximately 100-keV/ tailward-directed ion beam outside the Jovian plasma boundary

The hot plasma instrument on the Voyager-2 spacecraft measured a nearly monoenergetic (100 keV) ion beam several hours after crossing the Jovian plasma boundary on the nightside of the planet. The beam, deduced to consist primarily of heavy ions, persisted for about four hours and originated from the general direction of Jupiter. The energy density of the beam was about several times the energy density of the magnetic field (beta greater than 1). This beam, a product of an as yet not understood Jovian plasma acceleration mechanism, provides a dramatic example of the energetic dynamics of Jupiter's magnetosphere.

Krimigis, S. M.↗
NASA NTRS1980

Energetic particle bursts in the earth's magnetotail

The present review of observations of energetic particle bursts lead to the following conclusions: the time scales of acceleration range from less than 10 seconds to several tens of minutes; the energy extent of bursts ranges from less than 50 keV to 2 MeV; for impulsive highly anisotropic field-aligned bursts, inverse velocity dispersion has been observed; the source dimension along the x axis is less than 1 earth radius, and even as small as 2400 km; source movement is approximately 30 to 80 km/sec, while source size in the y direction can reach several earth radii; particle anisotropies are primarily directed earthward or tailward with a strong dawn-dusk component for protons.

Krimigis, S. M.↗
NASA NTRS1980

Recurrent energetic particle events associated with forward/reverse shock pairs near 4 AU in 1978

The elemental composition at energies near 1 MeV/nucleon has been studied for three recurrent energetic particle events during the period August-October, 1978, with the low-energy-charged-particle instruments on Voyager 1/2 near 4 AU. These events are associated with forward/reverse shock pairs in the solar wind as identified by the MIT plasma experiments on Voyager. In all three events, the flux increases associated with the reverse shocks showed enhancements in the He/H and CNO/H ratios compared to typical solar flare composition. The average C/O ratio for the three events was 0.68 which is larger than for normal solar flares but somewhat smaller than the average value found for corotating events at 1 AU during the previous solar minimum (1974-1976).

Hamilton, D. C.↗
NASA NTRS1979

Energetic particle activity at 5-min and 10-s time resolution in the magnetotail and its relation to auroral activity

The paper examines several energetic particle bursts associated with substorm events in the magnetotail using data from the Imp 7 and 8 spacecraft experiments. Individual proton and electron bursts observed by the spacecraft do not always coincide nor does magnetotail activity correlate strongly with auroral activity on time scales less than 1 hr. The pitch angle distributions were determined with a time resolution of 10 s by combining magnetic field and particle measurements on Imp 8; during intense particle bursts the 0.3-MeV protons exhibit unidirectional or bidirectional anisotropies along the magnetic field. The data suggest the presence of small localized acceleration regions in the magnetotail observable when magnetically connected to the spacecraft; little evidence is found for a single neutral line extending across the width of the magnetotail.

Carbary, J. F.↗
NASA NTRS1979

Hot plasma environment at Jupiter - Voyager 2 results

Preliminary results are reported from measurements made with the low-energy charged particle (LECP) instrument on Voyager 2 as it approached and traversed the Jovian magnetosphere. The primary objectives of the LECP instrument were to make measurements of the hot plasma (no less than about 20 keV and no less than about 28 keV for electrons and ions, respectively), to characterize the composition of the hot plasma and energetic-particle population, and to determine the particle flows and spatial distributions. In addition, the effects associated with the possible wake of Ganymede are discussed. Attention is given to inbound and outbound passes, along with Jovian plasma characteristics. The results suggest that the Jovian magnetosphere is confined by a plasma boundary rather than a conventional magnetopause. Inside the plasma boundary there exists a discontinuity at about 50-60 Jupiter radii, and the region inside this discontinuity is termed the 'inner plasmasphere'.

Krimigis, S. M.↗
NASA NTRS1979

Measurements of plasma flow at the dawn magnetopause by Voyager 1

Measurements are presented showing strong tailward flow of ions along the dawn magnetopause as the Voyager 1 spacecraft crossed the earth's magnetosphere boundary following launch on September 5, 1977. With one exception all of the observed flows occur outside the magnetopause. The particle flux measurements at energies of at least about 30 keV, together with the observed magnetic-field signatures of the boundary crossing, are consistent with a minimum tailward ion energy flow of about (2-7) x 10 to the 17th erg/s at the time of observation. High-time-resolution particle data indicate that the ion flow can vary on a time scale of about 400 ms. These results, together with recent results from several other spacecraft, show conclusively that a source of energetic particles exists sunward of the dawn-dusk meridian

Lanzerotti, L. J.↗
NASA NTRS1979

Low-energy charged particle environment at Jupiter - A first look

Preliminary results of measurements obtained by the low energy charged particle instrument on board the Voyager 1 spacecraft during its traversal of the Jovian magnetosphere are reported. The instrument consists of the low energy particle telescope and the low energy magnetospheric particle analyzer, designed to perform measurements in the inner and outer magnetosphere respectively. Ions and electrons comprising the Jovian magnetosphere were first detected at a distance of about 600 Jupiter radii from the planet, with the first bow shock crossing at 85.6 Jupiter radii. Upon crossing the magnetopause at about 67 Jupiter radii, the flows of electrons and ions were observed to change direction from away from the planet to the corotational direction. The hot plasma near the magnetosphere boundary is comprised predominantly of protons, sulfur and oxygen. Selective particle absorption near the Io flux tube indicates some form of particle deflection by Io. Fluxes in the outbound region were found to be enhanced from 90 to 160 deg longitude, and 5- and 10-hour low energy particle flux periodicities were observed.

Krimigis, S. M.↗
NASA NTRS1979

Hydrogen over helium enhancement in successive solar flare particle events from the same active region

An analysis of all of the identified solar-flare-associated energetic particle events in the 1972-1975 period observed with instruments aboard the IMP 7 and IMP 8 satellites has revealed at least eight occasions when more than one particle-producing flare occurred within the same McMath active plage region during its transit of the visible solar disk. A strong tendency for second flares to produce hydrogen over helium (p/alpha) enhanced energetic particle fluxes when compared with the first flare in the 1.8-10.0 MeV per nucleon range emerged in these multiflare regions. The p/alpha enhancement is apparently transient, and for flares separated by at least about 100 hours the p/alpha ratio tends toward its preflare value. It is suggested that the substrate plasma in an active region may be enriched prior to a flare in elements heavier than hydrogen and the composition may not be significantly altered during subsequent acceleration, escape, and propagation. Thus, the preflare history of the active region must be added to the list of factors influencing observed solar-particle-event composition.

Briggs, P. R.↗