Fundamental Technologies

Ulysses HISCALE Pages

Additional Ulysses HISCALE Publications and Presentations

Simnett, G. M., E. C. Roelof, and S. J. Tappin, Electron Anisotropies During the Period Ulysses Spent Out of the Ecliptic Plane (1993-1997), in Correlated Phenomena at the Sun, in the Heliosphere, and in Geospace, Proc. 31st ESLAB Symposium, ESA Spec. Publ. SP-415, 69-74, 1997.

Abstract (draft). The HISCALE instrument on Ulysses has been able to study the anisotropy of the electron intensity in the energy region ~40 keV to ~300 keV; this energy is well away from the regime where solar wind convection effects could be important. We find the largest anisotropies during the south and north polar passes, where they occasionally exceed a factor of three in the 2-day averages at the lowest energy. These are most pronounced in the lowest energy channels in foreward and backward facing HISCALE telescopes (WART-B and LEFS 150) during the high latitude polar passes in 1994 and 1995. There is a marked asymmetry beween the south and north polar passes. In the south, the period of high anisotropy in the LEFS 150 detector lasted only around 4 months, whereas in the north the electron intensity did not return to isotropy (3%) until early 1997, which is a period of ~20 months. We have correlated the anisotropy with the direction of the interplanetary magnetic field, and we find that over the poles electrons at small pitch angles are depleted. This is unlikely to be a loss-cone effect, as the solid angle for loss into the corona is very small. However, it could be the result of adiabatic energy loss. Implications of these results for the acceleration and transport of electrons throughout the heliosphere, and the ingress of galactic cosmic ray electrons, are discussed.

Lanzerotti, L. J., R. E. Gold, K. A. Anderson, T. P. Armstrong, S. E. Hawkins, S. M. Krimigis, R. P. Lin, C. G. Maclennan, M. Pick, E. C. Roelof, E. T. Sarris, and D. J. Thomson, Low Energy Interplanetary Charged Particles: Solar South Pole to Solar North Pole, Il Nuovo Cimento, 19C, 927, 1996.

Abstract (draft). Low energy (~>50 keV) charged particles measured by the HISCALE instrument on the Ulysses spacecraft provided unique information on the particle composition and intensity in both polar regions of the Sun. Further, the rapid 160 deg. South-to-North solar transit of Ulysses in early 1995 yielded new information on heliospheric structure. This paper reviews several of the key HISCALE results, including the latitude dependence of particle acceleration by corotating interaction regions, particle propagation from equatorial regions of the Sun to high heliolatitudes, and the appearance of numerous periodic components in the power specra of the particle variations, the frequencies of which are consistent with those estimated (but not as yet confirmed) for gravity-mode oscillations of the Sun.

M. Boufaida, Gradients of 0.3 to 5 MeV Protons in the 1-5 AU In-Ecliptic Plane: Propagation, Modulation and Acceleration, Ph.D. dissertation, Univ. of Kansas, 1995.

Abstract. Low energy charged particles with energies ranging from 0.3 to 2 MeV are nearly always present in the environment of the Earth. Specific solar flare events and interplanetary shock waves are identified as producing or enhancing these fluxes. However, interplanetary particles are observed even in the absence of solar flares. The explanation of the presence of these proton fluxes in the interplanetary medium and accounting for their variations is a major problem in space physics.
   Observations of interplanetary proton fluxes have been made continuously at 1 AU with IMP 8 from 1973 to the present and in the 1-5 AU range by Voyager 1 and 2 (1977-78) and Ulysses (1990-91). Daily-averaged proton fluxes of IMP 8, Voyager 1 and 2, and Ulysses have been carefully interpolated to matching energy passbands so that fluxes in the same passbands at two radial distances could be compared. These daily-averaged fluxes were then compared as ratios, autocorrelation, cross correlation as functions of time delay. The radial gradient, the energy spectra and the distribution of these proton fluxes were also examined.
   The results showed that protons in the 0.3 to 5 MeV energy range using the Voyager 1/IMP 8, Voyager 2/IMP 8, and Ulysses/IMP 8 paired observations in the 1 to 5 AU in-ecliptic region tend to "decorrelate" within increasing radial separation and become uncorrelated by about 4 or 5 AU. Higher energy fluxes decorrelate less rapidly, and lower energy proton fluxes have smaller radial gradients than higher energy. The radial gradient of 0.3 to 0.5 MeV proton fluxes is dominantly positive for 1-5 AU, whereas the radial gradient of 2 to 4 MeV proton fluxes is negative. We conclude that 0.3 to 0.5 MeV protons are much more subject to interplanetary acceleration than 2 to 5 MeV protons. The results also showed that radial gradients are robust and persist even if all heliolongitude coherence is purposely removed by shuffling the time order.
   Our interpretation of this is that modulation of particle fluxes and spectra are dominated by interplanetary acceleration. Interplanetary shocks are the most likely agents to produce this acceleration. We suspect that "SDA" (Shock Drift Acceleration) is more effective here than diffusive shock acceleration because of the IMF (Interplanetary Magnetic Field) geometry producing the high shock normal angle for which "SDA" is most efficient. This interplanetary process or "SDA" maintains and redistributes the intensities of 0.3 to 1 MeV protons, whereas most of the intensities of higher energy protons (>1 MeV) are unaffected by this mechanism and originate within 1 AU (as would be due to solar flares).

M. Pick, A. Mangeney, S. Hoang, P. Chaizy, K. A. Anderson, R. P. Lin, E. T. Sarris, and R. Forsyth, Ulysses Observations of a Pure Electron Event and Its Associated Type III Radio Emission on December 15, 1990, COSPAR Meeting, Washington D.C., Aug., 1992. (Ed. note: We have information that this was published in Adv. Space Res., 13/9, and also in Fundamental Problems in Solar Activity (edited by M. Pick and M. E. Machado, published by Elsevier, and now out of print.)

Abstract (draft). We describe an electron event associated with a type III burst observed by Ulysses. This event was observed when the spacecraft crossed the region of strong compression between a fast and a slow solar wind stream, characterized by a relatively high density and a complex behavior of the plasma density, magnetic field and energetic electron anisotropy. There is a clear influence of the local plasma frequency on the time profiles of the type III burst, even at frequencies significantly higher than the average local plasma frequency, which can be interpreted as due to the reflection of the electromagnetic radiation by randomly distributed regions of high density.

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Last modified March 27, 2006
T. Hunt-Ward