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The rate of occurrence of interplanetary discontinuities (ROID) is examined using Ulysses magnetic field and plasma data from 1 to 5 AU radial distance from the Sun and at high heliospheric latitudes. It is found that there are two regions in interplanetary space where the ROID is high: in stream-stream interaction regions and in Alfven wave trains.
The rate of occurrence of interplanetary discontinuities (ROID) is examined using Ulysses magnetic field and plasma data from 1 to 5 AU radial distance from the Sun and at high heliographic latitudes. We find two regions where the ROID is high: in stream-stream interaction regions and in Alfven wave trains. This latter feature is particularly obvious at high latitudes when Ulysses enters a high speed stream associated with a polar coronal hole. These streams are characterized by the presence of continuous, large-amplitude (Delta (vector 13)/absolute value of B is about 1-2 Alfven waves and an extraordinarily high ROID value (approximately 150 discontinuities/day). In a number of intervals examined, it is found that (rotational) discontinuities are an integral part of the Alfven waves. The nonlinear Alfven waves are spherically polarized, i.e., the tip of the perturbation vector resides on the surface of a sphere (a consequence of constant absolute value of B). The slowly rotating part of the wave rotates approximately 270 deg in phase. There is a slight arc in the B(sub 1) - B(sub 2) hodogram, suggesting an almost linear polarization. The phase rotation associated with the discontinuity is about 90 deg, lies in the same plane as the slowly rotaing part of the Alfven wave, and therefore completes the 360 deg phase rotation. The best description of the overall Alfven wave plus discontinuity is a spherical, arc-polarized, phase-steepened wave.
Ulysses observations provide a unique opportunity to study diverse problems related to Alfven and magnetosonic waves. The large amplitude of the Alfven waves influences the distribution functions of the spiral angle, the azimuthal field component and, possibly, the radial component such that their averages are not equal to their most probable values.
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The Ulysses mission explored for the first time our heliosphere at all latitudes up to +/-80 and therefore has been an ideal mission to study potential gradients in heliolatitude(and radial distance) of discontinuity occurrence rates and types.
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The Ulysses mission explored for the first time our heliosphere at all latitudes up to +/-80 and therefore has been an ideal mission to study potential gradients in heliolatitude of discontinuity occurrence rates and types.
This paper presents results from the first statistical study of interplanetary directional discontinuities at high heliographic latitudes. Ulysses data showed that the rate of occurrence of interplanetary discontinuities (ROIDs) increased dramatically from the ecliptic plane to high (-80 degrees) heliographic latitudes. The high speed streams included Alfven waves.
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One of the characteristic features of the polar heliosphere discovered by Ulysses is the continuous.
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Properties of the large amplitude Alfven waves which are a dominant feature of the high latitude solar wind have been studied during the pole-to-pole passage of Ulysses.
The Ulysses mission goes to the polar regions of the heliosphere and therefore is an ideal mission to study Alfven waves and discontinuities.
We review observations of nonlinear plasma waves detected by interplanetary spacecraft. For this paper we will focus primarily on the phase-steepened properties of such waves. Plasma waves at comet Giacobini-Zinner measured by the International Cometary Explorer (ICE), at comets Halley and Grigg-Skjellerup measured by Giotto, and interplanetary Alfven waves measured by Ulysses, will be discussed and intercompared.
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Ulysses magnetic and plasma data obtained in the fast polar solar wind are used to study the nature of fluctuations in the frequency range between the turbulent inertial range and the lower-frequency range dominated by quasi-static structures originating at the Sun. For daily variations of hourly averages of the magnetic field components the anisotropy of the fluctuations is less than in the higher-frequency range, and the minimum varianced direction loses its alignment with the magnetic field in favor of a more radial direction as the solar distance increases.
The properties of Alfven waves detected in both high-speed and slow-speed streams as detected by Ulysses will be reviewed.