Search NASA⌕ Search

SEARCH · Search NASA

Results for “Ulysses”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Solar wind thermal electrons from 1.15 to 5.34 AU - Ulysses observations

Using unique 3-d velocity space measurements by the Ulysses solar wind plasma experiment from 1.15 to 5.34 AU, we assess the radial gradient in thermal electron temperature. Until 3.8 AU, the gradient was steeper than previously reported but flatter than adiabatic; after 3.8 AU the gradient flattened. Trends in the observed electron distribution shapes qualitatively support predictions for regulation by Coulomb collisions and by expansion in a spiral IMF.

Phillips, J. L.↗
NASA NTRS1993

Solar wind composition measurements by the Ulysses SWICS experiment during transient solar wind flows

For the March/April 1991 time period, the alpha/proton abundance ratio, the proton kinetic temperature and speed distributions, and the relative abundance of O(+7) to O(+6) is determined over each 13-minute duty cycle of the Solar Wind Ion Composition Spectrometer (SWICs) experiment on Ulysses. The ratio O(+7)/O(+6) (as a relative measure of ionization temperature) is shown to be useful in identifying possible coronal mass ejection (CME) events. We report measurements of silicon/oxygen abundance ratios and silicon and oxygen charge state distributions in the solar wind during a CME event and compare these compositions to a 'normal' solar wind time period.

Galvin, A. B.↗
NASA NTRS1993

Sulfur abundances in the solar wind measured by SWICS on Ulysses

One of the nine experiments on Ulysses (launched October, 1990), the Solar Wind Ion Composition Spectrometer, utilizes an energy per charge deflection system along with time of flight technology to uniquely determine the mass and mass per charge of solar wind particles. Thus the composition of various solar wind types can be analyzed. Using the SWICS data accumulated during the in-ecliptic phase of the mission, we have determined the sulfur abundance, relative to silicon, in two different types of solar wind: transient and coronal hole associated flows. Sulfur is of extreme interest because it is one of the few elements that lies in the transitional region of the FIP-dependent relative abundance enrichment function, observed for solar energetic particles and some types of solar wind flows.

Shafer, C. M.↗
NASA NTRS1994

Ulysses charged particle measurements between 1 and 5 AU from the Sun

Proton fluxes obtained by two instruments carried on the European Space Agency (ESA)/NASA Ulysses spacecraft are reported for the period from launch in October 1990 till Jupiter encounter in February 1992. Proton energy ranges are 24-59, 71-99, 130-320, 320-2100 and greater than 2100 MeV. The Sun was very active during this period, the events of March 1991 being some of the largest of the solar cycle. The relationship between events on the Sun and the observed proton flux is discussed.

Page, D. E.↗
NASA NTRS1995

Ulysses orbit determination at high declinations

The trajectory of the Ulysses spacecraft caused its geocentric declination to exceed 60 deg South for over two months during the Fall of 1994, permitting continuous tracking from a single site. During this time, spacecraft operations constraints allowed only Doppler tracking data to be collected, and imposed a high radial acceleration uncertainty on the orbit determination process. The unusual aspects of this situation have motivated a re-examination of the Hamilton-Melbourne results, which have been used before to estimate the information content of Doppler tracking for trajectories closer to the ecliptic. The addition of an acceleration term to this equation is found to significantly increase the declination uncertainty for symmetric passes. In addition, a simple means is described to transform the symmetric results when the tracking pass is non-symmetric. The analytical results are then compared against numerical studies of this tracking geometry and found to be in good agreement for the angular uncertainties. The results of this analysis are applicable to the Near Earth Asteroid Rendezvous (NEAR) mission and to any other missions with high declination trajectories, as well as to missions using short tracking passes and/or one-way Doppler data.

Mcelrath, Timothy P.↗
NASA NTRS1994

X-ray bright points and high-speed wind streams: A preliminary analysis from Yohkoh and Ulysses data

The following aspect of the solar wind mass flux, and of its variation, is examined: whether coronal plumes might be responsible for the long-term variability of the mass flux in high-speed streams emanating from coronal holes. The assumption that plumes are rooted in coronal bright points (BP's) is made. The behavior of X-ray BP's, imaged by the Yohkoh soft X-ray telescope (SXT), during a seven month period when Ulysses experiments observed a series of recurrent high-speed streams, is analyzed. If plumes/BP's are sources of the wind mass flux, changes in the coronal hole BP density to mimic changes of the mass flux in high-speed streams are expected. SOHO will have the capability of measuring the solar wind speed/density at small heliocentric distances while simultaneously observing coronal BP's and coronal plumes.

Poletto, Giannina↗
NASA NTRS1994

Null fields in the outer Jovian magnetosphere: Ulysses observations

This paper reports on a magnetic field phenomenon, hereafter referred to as null fields, which were discovered during the inbound pass of the recent flyby of Jupiter by the Ulysses spacecraft. These null fields which were observed in the outer dayside magnetosphere are characterised by brief but sharp decreases of the field magnitude to values less than 1 nT. The nulls are distinguished from the current sheet signatures characteristic of the middle magnetosphere by the fact that the field does not reverse across the event. A field configuration is suggested that accounts for the observed features of the events.

Haynes, P. L.↗
NASA NTRS1994

Ulysses near-ecliptic observations of differential flow between protons and alphas in the solar wind

The evolution of differential streaming between protons and alpha particles in the solar wind was observed with the solar wind plasma experiment on the Ulysses spacecraft over the solar range of 1.15 to 5.40 AU between November 18, 1990, and May 5, 1992. The correlation of the difference in ion speeds, Delta V = the absolute value of V(sub alpha) - the absolute value of V(sub p), with the proton speed V(sub p) observed by other spacecraft at solar distances less than or equal to 1 AU disappeared at approximately 2 AU. At solar distances greater than or equal to 2.85 AU, the largest values of both V(sub alpha p) = the absolute value of V(sub alpha p) = the absolute value of V(sub alpha) - V(sub p) and the absolute value of Delta V were found in the interaction regions on the leading edges of high-speed streams. The differential streaming was typically enhanced just downstream of strong forward and reverse shocks, and large negative values of Delta V were frequently encountered in the interaction regions. A correlation between V(sub alpha p) and the ratio tau(sub zero)/tau(sub e) of Coulomb collision time to expansion time was observed at all distances, but it is suggested that at the larger values of tau(sub zero)/tau(sub e) observed correlation may arise from enhanced production of differential streaming by processes that also increase the entropy of the solar wind protons.

Neugebauer, M.↗
NASA NTRS1994

Particle acceleration by an interplanetary shock-pair seen at Ulysses at 3.15 AU

Observations from the HI-SCALE instrument on Ulysses of the ions and electrons associated with an interplanetary shock-pair at about 3.15 AU are presented. An empirical model is used to derive the evolution of the particle distribution in the solar wind frame. The forward shock is shown to be the primary source of ion acceleration, while the weaker and younger reverse shock is found to trap particles in its vicinity. There is also evidence of electron acceleration at the forward shock. We find evidence of multiple shock encounters for both ions and electrons.

Tappin, S. J.↗
NASA NTRS1995

Variation of fractional electron density fluctuations inside 40 R(sub 0) observed by Ulysses ranging measurements

The first measurements of fractional electron density fluctuations delta-n(sub e)/n(sub e), where delta-n(sub e) is rms electron density fluctuation and n(sub e) is the mean electron density, have been carried out inside 40 R(sub 0) using 1991 Ulysses dual-frequency S- and X-band (13 and 3.6 cm) ranging (time delay) measurements. In the frequency band of approximately 6 x 10(exp -5) - 8 x 10(exp -4) Hz (periods of 20 min to 5 hr), delta-n(sub e)/n(sub e) varies from a high near 20% in the slow wind close to the neutral line to a low of 1% in the fast wind far from the neutral line. For spatial wavenumber K approximately = 1.4 x 10(exp -6)/km (period of 5 hr at 250 km/s), delta-n(sub e)/n(sub e) is essentially independent of heliocentric distance over 0.03-1.0 AU in the slow wind; it is a factor of 30 lower in the fast wind than in the slow wind inside 0.1 AU, but exhibits dramatic growth with heliocentric distance inside 0.3 AU. This latter result reinforces current views of the evolution of MHD turbulence and the association of Alfven waves with high speed streams based on in situ fields and particles measurements beyond 0.3 AU. That regions of enhanced density fluctuations near or above the neutral line coincide with regions of enhanced density confirms previous conclusions that they are the interplanetary manifestation of the heliospheric current sheet and extensions of coronal streamers. While the regions of enhanced density fluctuations lie within those of enhanced density, they have boundaries that are distinctly more abrupt, suggesting the separation of plasma of different nature and origin.

Woo, Richard↗
NASA NTRS1994

The speeds of coronal mass ejections in the solar wind at mid heliographic latitudes: Ulysses

Six CMEs (coronal mass ejections) have been detected in the Ulysses plasma observations poleward of S31 deg. The most striking aspect of these mid-latitude CMEs was their high speeds; the overall average speed of these CMEs was approximately 740 km/s, which was comparable to that of the rest of the solar wind at these latitudes. This average CME speed is much higher than average CME speeds observed in the solar wind in the ecliptic or in the corona close to the Sun. The evidence indicates that the CMEs were not pushed up to high speeds in interplanetary space by interaction with trailing high-speed plasma. Rather, they simply seem to have received the same basic acceleration as the rest of the solar wind at these mid-latitudes. Our results suggest that the basic acceleration process for many CMEs at all latitudes is essentially the same as for the normal solar wind. Frequently most of this acceleration must occur well beyond 6 solar radii from Sun center.

Gosling, J. T.↗
NASA NTRS1993

Jovian electron propagation in three dimensions of the heliosphere: The Ulysses investigations

We report investigations of Jovian relativistic electrons in the interplanetary medium that provide new insights into both the physical processes by which the Jovian magnetosphere releases its trapped, relativistic electrons into the interplanetary medium, and the modes of their interplanetary propagation. These studies were dependent on the unique postencounter trajectory for Ulysses. The spacecraft remained close to the radial distance of Jupiter (approximately 5.2 AU) and moved southward on the duskside by only approximately 12 deg in heliographic latitude and less than 8 deg in the heliographic azimuth relative to Jupiter for the period of approximately 100 deg days of this study. During this period the nominal Parker spiral interplanetary magnetic field with its alternating polarities sector structure established direct magnetic field line connections frequently between Jupiter and the spacecraft. These unique conditions made it possible to investigate in detail, for approximately four solar rotations, both the Jovian electron burst phenomenon and the continuous, diffusive interplanetary propagation of Jovian electrons.

Simpson, J. A.↗
NASA NTRS1993

ULF waves in the Io torus: Ulysses observations

Throughout the Io torus, Ulysses has observed intense ultralow frequency (ULF) wave activity in both electric and magnetic components. Such ULF waves have been previously suggested as the source of ion precipitation leading to Jovian aurorae. The peaks of the wave spectra are closely related to the ion cyclotron frequencies, which is evidence of the waves being ion cyclotron waves (ICWs). Analysis of the dispersion relation using a multicomponent density model shows that at high latitudes (approximately 30 deg), peak frequencies of the waves fall into L mode branches of guided or unguided ICWs. Near the equator, in addition to the ICWs below f(sub cO(2+)), there are strong signals at approximately 10 Hz which require an unexpectedly large energetic ion temperature anistropy to be explained by the excitation of either convective or nonconvective ion cyclotron instabilities. Their generation mechanism remains open for the future study. Evaluation of the Poynting vector and the dispersion relation analysis suggest that the waves near the equator had a small wave angle relative to the magnetic field, while those observed at high latitudes were more oblique. The polarization of the waves below f(sub cH(+)) is more random than that of the whistler mode waves, but left-hand-polarized components of the waves can still be seen. The intensity of the ICWs both near the equator and at high latitudes are strong enough to meet the requirement for producing strong pitch angle scattering of energetic ions.

Lin, Naiguo↗
NASA NTRS1993

Ulysses plasma observations in the Jovian magnetosheath

The solar wind plasma experiment aboard the Ulysses spacecraft, including separate ion and electron instruments, measured the plasma properties of the Jovian magnetosheath during the February 1992 encounter with Jupiter. Seven separate magnetosheath intervals were observed, as well as four bow shock crossings and numerous encounters with the magnetopause and its boundary layer. We present an overview of ion and electron bulk parameters and a sampling of distribution shapes for the magnetosheath and adjacent plasma regions. Plasma flows are generally appropriate for slowing and deflection of the solar wind flow about a relatively stationary obstacle, with the notable exception of the first inbound sheath transit, when an expanding magnetosphere resulted in sunward flow just above the magnetopause. The existence of a planetary depletion layer is suggested by trends in plasma density for some magnetopause encounters. The magnetopause boundary layer is characterized by a combination of sheathlike and magnetospheric distributions of both ions and electrons. The ion population in the sheath is observed to include a significant population of suprathermal protons. Electron distributions have a distinctive shape previously observed in the terrestrial magnetosheath, with fluxes parallel to the magnetic field dominating at thermal energies and perpendicular fluxes dominating at higher energies. Trends in electron temperature near the bow shock indicate that shock motion plays an important role in heating the electrons. In general, the plasma characteristics of the Jovian magnetosheath are quite similar to those in its terrestrial counterpart, but the compressible nature of the Jovian magnetosphere accentuates the importance of boundary motions.

Phillips, J. L.↗
NASA NTRS1993

A survey of low frequency waves at Jupiter: The Ulysses encounter

We report the results of a survey of low-frequency (LF) plasma waves detected during the Ulysses Jupiter flyby. In the Jovian foreshock, two predominant wave periods are detected: 10(exp 2)-s and 5-s, as measured in the spacecraft frame. The 10(exp 2)-s waves are highly nonlinear propagate at large angles to vector-B(sub 0) (typically 50 deg), are steepened, and sometimes have attached whistler packets. For the interval analyzed the 10(exp 2)-s waves had mixed right-and left-hand polarizations. We argue that these are all consistent with being right-hand magnetosonic waves in the solar wind frame. The 10(exp 2)-s waves with attached whistler are similar to cometary waves. The trailing portions are linearly polaraized and the whistler portions circularly polarized with amplitudes decreasing linearly with time. The emissions are generated by approximately 2-keV protons flowing from the Jovian bow shock/magnetosheath into the upstream region. The instability is the ion beam instability. Higher Z ions were considered as a source of the waves but have been ruled out because of the low sunward velocities needed for their resonance. The 5-s waves have delta vector-B/B(sub 0 approximately = 0.5, are compressive and are left-hand polarized in the spacecraft frame. Local generation by three different resonant interactions were considered and have been ruled out. One possibility is that these waves are whistler mode by-products of the steepened lower-frequency magnetosonic waves. Mirror mode structures were detected throughout the outbound magnetosheath passes. For these structures, the theta(sub kB) values were consistently in the range of 80 deg to 90 deg, exceptionally high values.

Tsurutani, Bruce T.↗
NASA NTRS1993

Upper limits to Jovian hard X radiation from the Ulysses gamma ray burst experiment

We describe the first in situ search for Jovian X radiation with a dedicated X ray instrument. Upper limits to Jupiter's X ray power in the 27 - 48 keV range are presented using data taken by the gamma ray burst experiment on the experiment on the inbound Ulysses trajectory, at distances between 163 and 110 R(sub J). The data were analyzed using three methods for detection of (1) a steady flux, (2) a flux linked to System III rotation, and (3) a sporadic flux. The 3 sigma upper limits lie between 1.1 x 10(exp 8) and 5.6 x 10(exp 8) W. The results are consistent with the idea that the bulk of the Jovian UV auroral emissions are due to energetic electrons, while the previously observed low-energy X radiation is due to ion precipitation.

Hurley, K.↗
NASA NTRS1993

Latitudinal variation of solar wind corotating stream interaction regions: Ulysses

Ulysses' initial transit tot high heliographic latitudes at a heliocentric distance of approximately 5 AU has revealed systematic effects in the latitudinal evolution of corotating interaction regions (CIRs). At a latitude corresponding roughly to, but slightly less than, the inferred tilt of the coronal streamer belt and embedded heliospheric current sheet, the strong forward shocks commonly associated with CIRs at lower latitudes disappeared almost entirely; however, the reverse shocks associated with these CIRs persisted to latitudes approximately 10 deg above the streamer belt. Systematic meridional flow deflections observed in association with the forward and reverse waves bounding the CIRs demonstrate that the above effect is the result of the fact that the forward waves propagate to lower latitudes and the reverse waves to higher latitudes with increasing heliocentric distance. These observational results are in excellent agreement with the predictions of a three-dimensional model of corotating solar wind flows that originate in a tilted dipole geometry back at the Sun.

Gosling, J. T.↗
NASA NTRS1993

Ulysses observations of auroral hiss at high Jovian latitudes

During the Ulysses flyby of Jupiter, a whistler-mode emission was periodically detected by the unified Radio and Plasma wave (URAP) experiment during intervals when the spacecraft extended to high magnetic latitudes. The signal was detected between the local electron plasma frequency and lower hybrid resonance and appears as a funnel-shaped structure on frequency-versus-time spectrograms; these characteristics are very reminiscent of whistler-mode auroral hiss observed at high latitudes at Earth. Ray tracing of the emission occurrences suggests the emission source is on magnetic field lines extending out to at least 65 R(sub J). This location associates the emission with the boundary between open and closed field lines -- not the Io torus. The emission radiates about 10(exp 7) W of power. Consequently, the auroral input power derived from the solar wind to drive the emission is believed to be 10(exp 10-12) W (or about 1% of the energy associated with Io torus electrical processes).

Farrell, W. M.↗