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Ulysses HISCALE Pages

Ulysses HISCALE Publications in Astronomy and Astrophysics

Note: Astronomy and Astrophysics abstracts and articles published before 2001 are not available on the journal website at this time. Submission drafts are presented below.

Buttighoffer, A., Solar Electron Beams Associated with Radio Type III Bursts: Propagation Channels Observed by Ulysses Between 1 and 4 AU, Astron. Astrophys., 335, 295, 1998.

Abstract (draft). Solar and interplanetary type III (TIII) radio bursts are produced by solar electron beams of flare origin streaming away in the interplanetary medum. The radio emission process imples the excitation of Langmuir waves by the electron beam which are converted by non-linear processes into transverse electromagnetic waves. The study of the beam properties reveals information about their propagation regime in the interplanetary medium. The local plasma conditions observed in the vicinity of the radio emission zone are important in understanding the Langmuir wave excitation process and their conversion into electromagnetic radiation as well as the propagation of the electron beams. Interplanetary TIII have therefore long been studied for either of these aspects, but only for a few isolated cases could the three aspects of such events be studied together. This paper presents for the first time a complete study of the three aspects of nine interplanetary TIII events observed by the radio, particle, and plasma experiments aboard the Ulysses spacecraft between 1.3 and 4.3 AU. The main result of this study is to establish that the interplanetary medium contains well beyond 1 AU "propagation channels" previously identified around 1 AU. These plasma structures are rooted in the solar corona and seem to channel the propagation of solar electron beams. They have been identified in each of the nine events studied here; Langmuir waves and almost scatter-free propagation of the solar electrons were observed while the spacecraft was crossing these formations. Plasma properties of the "propagation channels" have been studied; their main characteristic is a very low level of magnetic field fluctuation. This property may be at the origin of a stabilization process of the plasma inside the channels explaining why they are maintained at such large distances, as well as a key element in understanding the particle propagation regime and Langmuir waves excitation observed inside. The implications of the medium distance (1-5 AU) heliosphere are also discussed.

Sayle, K. A., and G. M. Simnett, High Latitude Ulysses Observations of CIR Accelerated Ions and Electrons, Astron. Astrophys., 331, 401, 1998.

Abstract (draft). From the comparison of the intensity maxima of ~1 MeV/nuc ions with those of the 40-65 keV electrons and higher energy ions (~2-4 and 4-8 MeV/nuc) during Ulysses' ascent to the solar south pole, 1992-1994, evidence has been found for the ~1 MeV/nuc ions observed at high latitude by the Ulysses spacecraft to have originated at mid-latitudes and greater radial distances. The key observations presented in this paper are: 1) The ~1 MeV/nuc ion intensity maxima were observed to decay exponentially with latitude, above the streamer belt, whereas the electron intensity maxima and higher energy (~4-8 MeV/nuc) ion intensity maxima varied about a constant level; 2) When the ratios were taken of the ion intensity maxima to the electron intensity maxima for each of the CIR events, above the streamer belt, the ratios decayed exponentially with latitude; and 3) Upon the spacecraft's departure from the streamer belt, the electron maxima were observed to be delayed by ~1-4 days, with respect to the ~1 MeV/nuc ion maxima. Within the streamer belt they had been typically simultaneous. Evidence was also found for a delay in the higher energy (~> MeV/nuc) ions with respect to the lower energy ~1 MeV/nuc ions. From the exponential decay of the ion/electron ratios above the streamer belt, we concluded that the ~1 MeV/nuc ions originated from the CIR reverse shock at lower latitudes and greater radial distances, along with the electrons.

The observed delays in the electrons and higher energy ions were a consequence of the particles traveling from the distant reverse shock. Hence it appears that the ions were accelerated at the reverse shock at lower latitudes, and not at the local poleward propagating reverse shocks as had been previously suggested.

Biesecker, D. A., A Search for 3He Enhancements in SEP and CIR-Associated Events with ULYSSES/HI-SCALE, Astron. Astrophys., 316, 487, 1996.

Abstract (draft). We identify 17 solar energetic particle (SEP) events with enhanced abundances of 3He relative to 4He detected by the Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energies (HISCALE) on the Ulysses spacecraft. These events were all detected while Ulysses was within 5 of the ecliptic plane, but at distances from the sun of 1-5 AU. We compare these results to those obtained with the ONR-604 instrument on the Combined Release and Radiation Effects Satellite (CRRES) mission (Chen et al., Astrophys J., 1995). Chen et al. found 13 events with enhancements of 3He above normal solar abundances at energies >50 MeV/nucleon. The HISCALE instrument measures He ions with energies between 0.3 and 3.1 MeV/nucleon. We identify flux increases in the HISCALE data which correspond to 6 of the CRRES events, but we find an enhancement in 3He in only one of these events. We believe this single coincident detection to be a chance occurrence. We use these results, together with the multitude of previous results at different energies, to discuss the overall picture of 3He-rich events as a function of energy. We also analyze the data for 3He enhancements in high latitude co-rotating interaction (CIR)-associated events observed while the spacecraft was in the southern solar hemisphere above the streamer belt. We find, within the sensitivity of the HISCALE instrument, that there is no 3He enhancement in these CIR-associated events. We then briefly discuss how this relates to particle acceleration mechanisms in solar flares.

Lanzerotti, L. J., C. G. Maclennan, T. P. Armstrong, E. C. Roelof, R. E. Gold, and R. B. Decker, Low Energy Charged Particles in the High Latitude Heliosphere, Astron. Astrophys., 316, 457, 1996.

Abstract (draft). Low energy ion and electron measurements made over the south and north polar regions of the sun by the HISCALE instrument on the Ulysses spacecraft during its solar minimum polar passages are summarized. The polar flux levels were considerably reduced in comparison to fluxes in the vicinity of the heliospheric current sheet. Flux variations with a period of ~26 days were seen to nearly 80 S but were not observed over the northern pole. Solar particle events originating from near-equatorial activity were seen at high southern latitudes, but not at high northern latitudes. Comparisons with in-ecliptic measurements made during the same time interval on the IMP 8 spacecraft suggest that the polar differences are largely spatial and not temporal. The flux of low energy (~0.8-5.0 MeV/nuc) anomalous oxygen was measured to be ~50% higher over the northern polar region than in the south. The flux of solar wind iron, measurable because of its convection into the instrument by the high speed polar solar wind, is estimated to be about a factor of two larger over the south pole than over the north.

Roelof, E. C., G. M. Simnett, and S. J. Tappin, The Regular Structure of Shock-Accelerated ~40-100 keV Electrons in the High Latitude Heliosphere, Astron. Astrophys., 316, 481, 1996.

Abstract (draft). The passage of Ulysses through the high latitude heliosphere has given us a new insight into the interplanetary dynamical processes which are occurring, at any rate near solar minimum, in the heliosphere above the streamer belt. We report here observations of ~40-100 keV electrons and ~0.5 MeV protons detected by HISCALE from 1992-96. Apart from a few increases associated with solar energetic particle events and coronal mass ejections, the dominant events were recurrent and associated with a long-lived corotating interaction region (CIR). Furthermore, we show that for the majority of the high latitude events, the acceleration region is at radial distances many AU beyond the spacecraft. Beginning with the hypothesis that the acceleration is taking place at the reverse shock of a regular but expanding CIR, we show that the appearance of the electron increases at Ulysses is ordered by the right ascension and radial distance of Ulysses in the frame of reference corotating with the sun. The timing of the maximum of the electron recurrences is predicted sufficiently accurately with this model so that the accelerated electrons can be used as a clock during the high latitude phase of the mission. Although the recurrent events are not as strong in the northern hemisphere as in the south, those seen up to the middle of March 1996 are consistent with the model when known changes in the coronal structure are taken into account.

Manganey, A., M. Pick, S. Hoang, P. Chaizy, K. Anderson, L. J. Lanzerotti, R. P. Lin, E. T. Sarris, R. Forsyth, J. L. Phillips, and S. Enome, Observations by Ulysses of a Pure Electron Event and Its Associated Type III Radio Emission of 15 December 1990, Astron. Astrophys., 283, 982, 1994.

Tappin, S. J., E. C. Roelof, and L. J. Lanzerotti, Particle Acceleration by an Interplanetary Shock-pair Seen at Ulysses at 3.15 AU, Astron. Astrophys., 292, 311, 1994.

Lanzerotti, L. J., R. E. Gold, K. A. Anderson, T. P. Armstrong, R. P. Lin, S. M. Krimigis, M. Pick, E. C. Roelof, E. T. Sarris, G. M. Simnett, and W. E. Frain, Heliosphere Instrument for Spectral, Composition and Anisotropy at Low Energies, Astron. Astrophys. Suppl., 92, 349, 1992. For a scanned version of the entire paper (used with permission), click here.

Abstract (draft). The Heliosphere Instrument for Spectra, Composition, and Anisotropy at Low Energies (HISCALE) is designed to make measurements of interplanetary ions and electrons through the entire Ulysses mission. The ions (Ei>~50 keV) and electrons (Ee>~30 keV) are identified uniquely and detected by five separate solid-state detector telescopes that are oriented to give nearly complete pitch-angle coverage (i.e., coverage of essentially 4p ster) from the spinning spacecraft. Ion elemental abundances are determined by a ΔE vs. E telescope using a thin (5 μm) front solid state detector element in a three-element telescope. Experiment operation is controlled by a microprocessor-based data system. Inflight calibration is provided by radioactive sources mounted on telescope covers which can be closed for calibration purposes and for radiation protection during the course of the mission. Ion and electron spectral information is determined using both broad-energy-range rate channels and a 32-channel pulse height analyzer (channels spaced logarithmically) for more detailed spectra. The instrument weights 5.775 kg and uses 4.0 W of power. Some initial in-ecliptic measurements are presented which demonstrate the features of the instrument.  

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Last modified February 3, 2006
T. Hunt-Ward