Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “heliosphere 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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

The Ulysses mission in the high latitude heliosphere

Ulysses, a joint ESA/NASA mission launched in October 1990, will be the first to explore the high latitude heliosphere. Launch will be from the Shuttle and a Jupiter gravity assist will be used to send the spacecraft first over the southern solar pole approximately three and one half years after launch and then over the northern solar pole one year later. Instruments will be carried to study the solar wind, the heliospheric magnetic field, energetic solar particles, galactic cosmic rays, solar X-rays, cosmic gamma rays, cosmic dust and interstellar neutral helium. The radio signals used to track and transmit spacecraft data will be used also to sound the corona and to search for gravitational waves.

Page, D. E.↗
NASA NTRS1995

Energetic particles and coronal mass ejections in the high latitude heliosphere: Ulysses-LET observations

The COSPIN Low Energy Telescope (LET) onboard the Ulysses spacecraft measures protons, alphas and heavier ions at energies of approximately 1 to 50 MeV/n. Ulysses measurements offer favorable opportunities to study the effects of solar activity in the out-of-ecliptic regions of the heliosphere. Using LET data, we have investigated the properties of transient energetic ions at high heliographic latitudes when Ulysses was permanently immersed in high speed solar wind and magnetically connected to the Sun on open magnetic field lines. Recurrent increases in the fluxes of energetic ions at high heliographic latitudes at frequencies related to the solar rotation period were found to occur in association with co-rotating interaction regions (CIRs). Here we investigate fluxes of energetic particles that showed no relationship to ClRs. From the investigation of plasma and magnetic held data it is found that all of the transient high latitude particle events were associated with the passage of a coronal mass ejection (CME) over Ulysses. Enhancements in particle fluxes several days prior to the arrival of a CME, but with a significant time delay with respect to the estimated CME-onset at the Sun, were most probably associated with interplanetary shocks driven by fast CMEs. These particle events exhibit unusually high rho/alpha-ratios and are not observed for CMEs not driving a shock. However, not all CMEs that passed Ulysses were associated with a particle event. We find evidence that at high solar latitudes, solar flare particles cannot reach Ulysses on open magnetic field lines, but can reach the spacecraft if particles are injected into magnetic flux-ropes (CMEs) at the Sun. These findings are supported by soft X-ray observations from the Japanese Yohkoh-satellite.

Bothmer, V.↗
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

Disappearance of the heliospheric sector structure at Ulysses

In May, 1993, the heliospheric current sheet (HCS) ceased to be seen by the Ulysses spacecraft at a heliocentric latitude of approximately 30 deg S and distance of 4.7 AU. The disappearance of the HCS coincided with the solar wind speed remaining greater than 560 km/s and with the disappearance of one of four interaction regions previously seen on each solar rotation. The heliographic latitude of the disappearance of the HCS at Ulysses was 11 deg equatorward of the latitude of the magnetic neutral sheet computed at the source surface at 2.5 solar radii, and it occurred a half year earlier than predicted on the basis of the persistance of the time profile of the neutral sheet tilt from one solar cycle to the next.

Smith, E. J.↗
NASA NTRS1989

Ulysses - The first high-latitude heliospheric mission

The Ulysses mission will, for the first time, explore the heliosphere within a few astronomical units of the sun over the full range of heliographic latitudes, thereby providing the first characterization of the uncharted third dimension. Highly sophisticated scientific instrumentation carried on board the spacecraft is designed to measure the properties of the solar wind, the sun/wind interface, the heliospheric magnetic field, solar radio bursts and plasma waves, solar X-rays, solar and galactic cosmic rays, and interplanetary/interstellar neutral gas and dust. This collaborative ESA/NASA mission, scheduled for launch in October 1990, will use a Jupiter gravity-assist to achieve a trajectory extending to high solar latitudes /1,2/.

Wenzel, K.-P.↗
NASA NTRS1995

The radial component of the heliospheric magnetic field: Ulysses observations

The radial field component, B(sub R), has been monitored continuously since the Ulysses spacecraft left the ecliptic plane in February 1992 travelling toward the southern pole of the Sun. In order to separate spatial from temporal changes, the Ulysses measurements from 0 to 80 heliographic latitude were compared with in-ecliptic measurements of B(sub R) being made simultaneously by IMP-8. The data revealed essentially the same field strengths and time variations at both locations. The conclusion was drawn that there was no significant latitude gradient in B(sub R) and that the stronger polar cap coronal magnetic fields were being transported equatorward to yield a uniform field in the solar wind. The results contrasted with the predictions of the various source surface models which ignore magnetic stresses within 2.5 solar radii. Since the maximum south latitude was attained in September, 1994, Ulysses has traveled northward toward an ecliptic crossing in March 1995 and onward into the north solar hemisphere. The recent results will be presented and compared with those obtained in the southern hemisphere.

Smith, E. J.↗
NASA NTRS1993

Disappearance of the Heliospheric Sector Structure at ULYSSES

In may, 1993, the heliopheric current sheet (HCS) ceased to be seen by the Ulysses spacecraft at a heliocentric latitude of ~30degrees S and distance of 4.7 AU. The disapearance of the HCS coincided with the solar wind speed remaining >560km/s and with the disappearance of one of four interaction regions previously seen on each solar rotation.

Heliosphere↗
NASA NTRS2002

Low-Latitude Solar Wind During the Fall 1998 SOHO-Ulysses Quadrature

Solar and Heliospheric Observatory (SOH0)-Ulysses quadratures occur when the SOHO-Sun-Ulysses-included angle is 90 deg. These offer the opportunity to directly compare properties of plasma parcels, observed by SOHO [Dorningo et al.] in the low corona, with properties of the same parcels measured, in due time, in situ, by Ulysses [ Wenzel et al]. We refer the reader to Suess et al. for an extended discussion of SOHO-Ulysses quadrature geometry. Here it suffices to recall that there are two quadratures per year, as SOHO makes its one-year revolution around the Sun. This, because SOHO is at the L1 Lagrangian point, in essentially the same place as the Earth, while Ulysses is in a near-polar -5-year solar orbit with a perihelion of 1.34 AU and aphelion of 5.4 AU.

Poletto, G.↗
NASA NTRS1994

Ulysses Observations of Latitude Gradients in the Heliospheric Magnetic Field

Several parameters measured by Ulysses as it traveled southward to heliographic latitudes of -50° are presented and analyzed. Three topics of scientific importance are investigated: (1) latitude gradient; (2) extent of agreement between observed and Parker spiral angles near -50°; (3) field variances and their interpretation.

Ulysses↗
NASA NTRS2016

Validation for Global Solar Wind Prediction Using Ulysses Comparison: Multiple Coronal and Heliospheric Models Installed at the Community Coordinated Modeling Center

The prediction of the background global solar wind is a necessary part of space weather forecasting. Several coronal and heliospheric models have been installed and/or recently upgraded at the Community Coordinated Modeling Center (CCMC), including the Wang-Sheely-Arge (WSA)-Enlil model, MHD-Around-a-Sphere (MAS)-Enlil model, Space Weather Modeling Framework (SWMF), and Heliospheric tomography using interplanetary scintillation data. Ulysses recorded the last fast latitudinal scan from southern to northern poles in 2007. By comparing the modeling results with Ulysses observations over seven Carrington rotations, we have extended our third-party validation from the previous near-Earth solar wind to middle to high latitudes, in the same late declining phase of solar cycle 23. Besides visual comparison, wehave quantitatively assessed the models capabilities in reproducing the time series, statistics, and latitudinal variations of solar wind parameters for a specific range of model parameter settings, inputs, and grid configurations available at CCMC. The WSA-Enlil model results vary with three different magnetogram inputs.The MAS-Enlil model captures the solar wind parameters well, despite its underestimation of the speed at middle to high latitudes. The new version of SWMF misses many solar wind variations probably because it uses lower grid resolution than other models. The interplanetary scintillation-tomography cannot capture the latitudinal variations of solar wind well yet. Because the model performance varies with parameter settings which are optimized for different epochs or flow states, the performance metric study provided here can serve as a template that researchers can use to validate the models for the time periods and conditions of interest to them.

Jian, L. K.↗
NASA NTRS1992

Low-energy solar electrons and ions observed at Ulysses February-April, 1991 - The inner heliosphere as a particle reservoir

Ulysses observations at 2.5 AU of 38-315 keV electrons and 61-4752 keV ions during February-April 1991 suggest in several ways that, during periods of sustained high solar activity, the inner heliosphere serves as a 'reservoir' for low-energy solar particles. Particle increases were not associated one-to-one with large X-ray flares because of their poor magnetic connection, yet intensities in March-April remained well above their February levels. The rise phase of the particle event associated with the great flare of 2245UT March 22 lasted most of two days, while throughout the one-week decay phase, the lowest-energy ion fluxes were nearly equal at Ulysses and earth (IMP-8).

Roelof, E. C.↗
NASA NTRS1995

The underlying magnetic field direction in Ulysses observations of the southern polar heliosphere

Between May 1993 and January 1995, the Ulysses spacecraft has probed the southern polar heliosphere at latitudes greater than 30 deg S, reaching a maximum latitude of 80.2 deg S in September 1994. Using hourly averages of the data obtained by the magnetometer experiment on Ulysses we have studied the underlying direction of the magnetic field threading this region of the heliosphere, away from the influence of the magnetic sector structure which complicates similar analyses in the ecliptic plane. We have constructed histograms of the measured magnetic field direction using the simple Parker spiral model field direction as a reference. We find that throughout this region the meridional angle between the field vector and the Parker model direction has a distribution which is symmetric and has a most probable value consistent with the model. At latitudes below about 60 deg S the azimuthal angle distribution also has a most probable value consistent with the model but this distribution is highly asymmetric with a greater number of observations of field lines less tightly wound than the expected spiral direction. At latitudes greater than 60 deg S the most probable value of the azimuthal angle is found to have become nearly 30 more tightly wound than the expected direction, but due to the asymmetric distribution still with a greater number of observations less tightly wound than expected. We consider possible causes of both the asymmetry in the distributions and the shift in the most probable value at the highest latitudes, one of which may be the presence of large amplitude, long period Alfven waves in the magnetic field originating from the Sun's southern polar coronal hole.

Forsyth, R. J.↗