Search Publications
Ulysses electron distributions fitted with Kappa functions
Maksimovic, Milan; Riley, Pete; Pierrard, Viviane
We fit Kappa functions to 16,000 velocity distribution functions measured in the solar wind by the electron plasma instrument on board Ulysses. Statistically, the electron distributions are observed to have important high velocity tails in the fast solar wind but are closer to a Maxwellian in the slow wind. We also discuss how this result could su…
An Empirical Study of the Electron Temperature and Heavy Ion Velocities in the South Polar Coronal Hole
Gloeckler, George; Geiss, Johannes; Fisk, Lennard A. +2 more
The solar wind ions flowing outward through the solar corona generally have their ionic fractions `freeze-in' within 5 solar radii. The altitude where the freeze-in occurs depends on the competition between two time scales: the time over which the wind flows through a density scale height, and the time over which the ions achieve ionization equili…
Anomalously small magnetic field in the local interstellar cloud
Gloeckler, George; Geiss, Johannes; Fisk, L. A.
The solar wind carves out a cavity, known as the heliosphere, in the warm local interstellar cloud, which is itself embedded in a larger hot cloud. It is generally assumed that there is an overall pressure balance between these three regions. Thermal pressure and magnetic field pressure in the local interstellar cloud should therefore balance the …
Solar wind stream interfaces in corotating interaction regions: SWICS/Ulysses results
Wimmer-Schweingruber, Robert F.; von Steiger, Rudolf; Paerli, Raoul
Motivated by the well-known differences in charge state and even elemental composition of the slow solar wind as compared to high-speed streams, we have analyzed observations made by the Solar Wind Ion Composition Spectrometer (SWICS)/Ulysses mass spectrometer of the series of corotating interaction regions (CIRs) encountered by Ulysses in 1992/19…
Structure function measurements of the intermittent MHD turbulent cascade
Balogh, A.; Horbury, T. S.
The intertmittent nature of turbulence within solar wind plasma has been demonstrated by several studies of spacecraft data. Using magnetic field data taken in high speed flows at high heliographic latitudes by the Ulysses probe, the character of fluctuations within the inertia] range is discussed. Structure functions are used extensively. A simpl…
Solar Wind Stream Interactions and the Wind Speed-Expansion Factor Relationship.
Goldstein, B. E.; Phillips, J. L.; Sheeley, N. R., Jr. +1 more
Previous studies have shown that the solar wind speed observed near Earth is inversely correlated with the divergence rate of magnetic flux tubes near the Sun. We test the global validity of this relationship by employing Ulysses wind speed measurements during 1990-1997 as well as inecliptic data for 1976-1997. When the correspondence between wind…
A two-dimensional simulation of the radial and latitudinal evolution of a solar wind disturbance driven by a fast, high-pressure coronal mass ejection
Riley, Pete; Gosling, J. T.; Pizzo, V. J.
Using a hydrodynamic simulation, we have studied the two-dimensional (symmetry in the azimuthal direction) evolution of a fast, high-pressure coronal mass ejection (CME) ejected into a solar wind with latitudinal variations similar to those observed by Ulysses. Specifically, the latitudinal structure of the ambient solar wind in the meridional pla…
Acceleration of Solar Wind Ions by Nearby Interplanetary Shocks: Comparison of Monte Carlo Simulations with Ulysses Observations
Baring, Matthew G.; Forsyth, Robert J.; W. Ogilvie +1 more
Various theoretical techniques have been devised to determine distribution functions of particles accelerated by the first-order Fermi mechanism at collisionless astrophysical shocks. The most stringent test of these models as descriptors of the phenomenon of diffusive acceleration is a comparison of the theoretical predictions with observational …
SWICS/Ulysses observations: The three-dimensional structure of the heliosphere in the declining/minimum phase of the solar cycle
Livi, S.; Woch, J.; Geiss, J. +5 more
The ESA/NASA spacecraft Ulysses provides the first in-situ observation of the solar wind at high solar latitudes. Data obtained with the Solar Wind Ion Composition Spectrometer (SWICS) during the first orbit of Ulysses around the Sun can be used to obtain a global view of the solar wind pattern within the heliosphere during the declining/minimum p…
Direct observational evidence for a heliospheric magnetic field with large excursions in latitude
Schwadron, N. A.; Zurbuchen, T. H.; Fisk, L. A.
Fisk has pointed out that the heliospheric magnetic field in fast solar wind, that is, at the higher heliographic latitudes, may undergo large excursions in heliographic latitudes, and thus that the field will deviate from the expected Archimedes spiral pattern. These excursions result from the interplay between the nonradial expansion of the sola…