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In this paper we analyze a solar particle event that was measured at two
locations in the heliosphere. Ulysses was at 40°north heliolatitude
and 130°west in heliolongitude from Earth while WIND was near Earth
at 1 AU in the ecliptic plane. To establish the origin of the particle
events, solar coronal activity is investigated. Direct observational
e...
Contexts in source publication
Context 1
... solar type III bursts observed here have been followed from 1 MHz down to some tens of kHz thanks to this instrument. Table 1 for details. The projections of the corre- sponding spirals onto the ecliptic are represented at the bottom of the figure. ...
Context 2
... respective positions of Ulysses, WIND and Earth are rep- resented in Fig. 2 with the theoretical Parker spirals connecting them to the Sun. Calculations were made with a solar wind speed of 750 km/s for Ulysses (as measured by the solar wind instru- ment on the spacecraft) and 310 km/s for WIND/Earth (from IMP8 measurements printed in Solar Geophysical Data) and are summarized in Table 1. Ulysses is located at a longitude of about 130 • away from the Earth/Sun line and at 40 • north of the ecliptic plane. ...
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Citations
... This value was comparable to the H/He ratios observed during the first CIR events in 1992 (not shown here) when Ulysses was closer to the ecliptic plane (Simnett et al., 1994). The only easily-identified SEP events during the fast latitude scan were observed on day 82 of 1995 and in late April 1995 (Buttighoffer et al., 1996), when the H/He ratio reached values around ∼20. ...
We study the variability
of the heliospheric energetic proton-to-helium abundance ratios during
different phases of the solar cycle. We use energetic particle, solar wind, and
magnetic field data from the Ulysses, ACE and IMP-8 spacecraft to compare the
H/He intensity ratio at high heliographic latitudes and in the ecliptic plane.
During the first out-of-ecliptic excursion of Ulysses (1992–1996), the
HI-SCALE instrument measured corotating energetic particle intensity
enhancements characterized by low values (< 10) of the 0.5–1.0 MeV
nucleon-1 H/He intensity ratio. During the second out-of-ecliptic
excursion of Ulysses (1999–2002), the more frequent occurrence of solar
energetic particle events resulted in almost continuously high (< 20)
values of the H/He ratio, even at the highest heliolatitudes reached by
Ulysses. Comparison with in-ecliptic measurements from an identical instrument
on the ACE spacecraft showed similar H/He values at ACE and Ulysses, suggesting
a remarkable uniformity of energetic particle intensities in the solar maximum
heliosphere at high heliolatitudes and in the ecliptic plane. In-ecliptic
observations of the H/He intensity ratio from the IMP-8 spacecraft show
variations between solar maximum and solar minimum similar to those observed by
Ulysses at high heliographic latitudes. We suggest that the variation of the
H/He intensity ratio throughout the solar cycle is due to the different level
of transient solar activity, as well as the different structure and duration
that corotating solar wind structures have under solar maximum and solar
minimum conditions. During solar minimum, the interactions between the two
different types of solar wind streams (slow vs. fast) are strong and
long-lasting, allowing for a continuous and efficient acceleration of
interstellar pickup He +. During solar maximum, transient events of solar
origin (characterized by high values of the H/He ratio) are able to globally
fill the heliosphere. In addition, during solar maximum, the lack of strong
recurrent high-speed solar wind streams, together with the dynamic character of
the Sun, lead to weak and short-lived solar wind stream interactions. This
results in a less efficient acceleration of pickup He +, and thus a higher
value of the H/He intensity ratio.Key words. Interplanetary physics
(energetic particles, interplanetary shocks; solar wind plasma)
The Oporto radiospectrograph and the Nançay radioheliograph recorded a radio event on November 6, 1997, closely related in time with a flare on National Oceanic and Atmospheric Administration (NOAA) active region 8100. At the beginning of the event the radio sources are located on a rather small volume in the vicinity of the flare site. In a timescale of only a few minutes the radio emission sites spread over a large volume in the corona, covering a range of 100° in heliolatitude. During the period of the radio event the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) observed an extremely fast coronal mass ejection (CME), with a velocity around 2000 km s-1. This CME presents the particularity of having a fast lateral expansion, giving it a shape reminiscent of a "coat hanger." There is a very good association between the latitudinal extent and time development of the CME seen by LASCO and the radio sources recorded by the radio instruments.
As observed from the ecliptic plane and at a distance of 1 AU from the Sun, the energetic particle population of the heliosphere drastically changes from solar maximum to solar minimum. The energetic particle populations in the inner heliosphere include:
(1)
Galactic cosmic rays (GCRs) originated in the interstellar medium and able to penetrate into the heliosphere.
(2)
Anomalous cosmic rays (ACRs) that originate as interstellar neutral atoms traveling into the heliosphere, ionized by solar UV and carried out as pickup ions in the solar wind to be finally accelerated to energies as high as ∼100 MeV/nucleon presumably close to the solar wind termination shock or in the heliosheath.
(3)
Solar energetic particles (SEPs) that originate near the Sun in association with solar flares and/or large coronal mass ejections (CMEs). As CMEs expand outward from the Sun, they may be able to drive interplanetary shock waves that can reaccelerate SEPs to form large gradual SEP events. Occasionally, SEP events are observed at very high energies reaching ∼GeV for protons and ∼100 MeV for electrons.
(4)
Energetic particles accelerated by other shocks and disturbances in the solar wind such as shocks formed in the solar wind stream interaction regions (SIs) or corotating interaction regions (CIRs).
(5)
Energetic particles accelerated in planetary magnetospheres, such as Jovian electrons observed in the inner heliosphere at energies from a few hundred keV to less than about 30 MeV.
The Oporto radiospectrograph and the Nançay radioheliograph recorded a radio event on November 6, 1997, closely related in time with a flare on National Oceanic and Atmospheric Administration (NOAA) active region 8100. At the beginning of the event the radio sources are located on a rather small volume in the vicinity of the flare site. In a timescale of only a few minutes the radio emission sites spread over a large volume in the corona, covering a range of 100° in heliolatitude. During the period of the radio event the Large Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric Observatory (SOHO) observed an extremely fast coronal mass ejection (CME), with a velocity around 2000 kms-1. This CME presents the particularity of having a fast lateral expansion, giving it a shape reminiscent of a ``coat hanger.'' There is a very good association between the latitudinal extent and time development of the CME seen by LASCO and the radio sources recorded by the radio instruments.
We combine data from several instruments on the Wind spacecraft with ground-based observations of the position of the heliospheric current sheet for the first 2.5 years of the mission, which covers the period from the end of solar cycle 22, through solar minimum, and into the start of cycle 23. We use data from the three-dimensional (3-D) plasma instrument (3DP), magnetometer (MFI), and Solar Wind Experiment (SWE). We examine the energetic ion and electron increases associated with corotating interaction regions (CIR) and relate them to the position and shape of the current sheet. The characteristics of the energetic particle increases associated with the observed CIRs change several times during the mission. We identify these periods and find that we can relate these particle signatures of the CIRs to the plasma conditions which themselves depend upon the changing tilt and warp of the current sheet. We examine the additional increases associated with magnetic clouds and impulsive solar flares that were observed at irregular intervals during the mission. We show how the Sun's magnetic field influences the interplanetary medium at 1 AU, as variations in the shape and inclination of the source surface current sheet propagate out to 1 AU. We identify the three major sources of these variations, (1) the long-term, slowly varying tilt of the current sheet with a timescale of the solar cycle, (2) the medium-term small but significant annual movement of the position of the Earth relative to the current sheet due to the inclination of the plane of the ecliptic with respect to the heliographic equator, and (3) the short-term warps and bulges which come and go due to the appearance of active regions, lasting only a few solar rotations.
In the high-latitude northern hemisphere of the heliosphere, the Heliosphere Instru- ment for Spectra Composition and Anisotropy at Low Energies (HI-SCALE) energetic particle detectors on Ulysses have measured quasi-recurrent ~26-day increases of 40-65 keV electrons during 11 solar rotations from October 1995 through July 1996. They do not appear on all rotations, but when they do, they are associated with increases in 0.5-1.0 MeV protons (preceding the electron increases by several days) and sometimes with decreases in galactic cosmic rays. The northern recurrences form two series shifted half a solar rotation with respect to each other, unlike the very regular and more intense series of 21 recurrences observed by the same instrument throughout the middle-to-high-latitude southern hemisphere from mid-1993 to the beginning of 1995. Correlated energetic particle measurements from IMP 8 at Earth and Voyagers 1 and 2 at 42-62 AU establish that recurrent events during this period were intrinsically stronger in the southern heliosphere than in the north. The variability of the northern recurrences is attributed, using a generalization of the model of Fisk (1996), to temporal changes during 1966 in the near-Sun polar magnetic field configuration. These changes would affect the connection of Ulysses via magnetic field lines to the corotating interaction regions at lower latitudes >10 AU beyond the spacecraft, where the low-energy particles are accelerated and the galactic cosmic rays are modulated. The observed evolution of the northern polar coronal structure, as revealed in FeXIV (5303) synoptic maps and confirmed by FeXII (195) images from the Extreme Ultra-Violet Imaging Telescope on the SOHO spacecraft, is just that which is required, according to the model, to explain the evolution of the low-energy particle recurrences as observed by Ulysses/HI-SCALE in the northern heliosphere.
A comparative study of two events accompanied by both a flare and a CME has been performed. The data analysis has been made by comparing the observations of the LASCO/SOHO coronagraphs with those of the Nancay radioheliograph. The observations show a clear connection between coronal green and red line transient activity, burst radio emission and the CME development which is due to successive loop interactions. Signatures of these interactions are given by the radio emission. One can identify successive sequences in the evolution of the coronal restructuring leading to the full development of the CME. Identification and timing of these sequences result from the radio emission analysis. For flare-CME events, the evolution takes place in the low corona and is extremely fast of the order, on a few minutes.
The current fleet of both heliospheric and magnetospheric spacecraft provides a unique opportunity of studying spatio-temporal plasma phenomena. Among the numerous topics that can be addressed by such a fleet, figures the 3D study of energetic (greater than 20 keV) solar electron) solar electron events. WIND and GEOTAIL are particulary interesting for such analysis: more than two years of data; up to 3/4 continuous days spent by GEOTAIL in the solar wind; and comparable experiments. During solar electron events, rapid electron flux changes can be associated with these structures. Sometimes they are seen at both spacecraft with a time difference corresponding to the convection time, but sometimes they are observed at one spacecraft but not at the other. Several preliminary conclusions can be drawn from such events: (1) there is direct evidence that, within distances lower than 1.5 x 10(exp 6) km at 1 A (approximately 7000 km at the sun), there are significant spatial variations of (a) the magnetic field line connections to the source region and probably of (b) the particle propagation features; (2) magnetic field lines inside and outside particle propagation structures can keep distinct access to the source region for more than one hour; (3) flux waves, of probable local origin, were observed; and (4) within one hour, spatial flux discrepancies, separated by magnetic structures, may remain or disappear.
The development of a coronal mass ejection on 9 July 1996 has been analyzed by comparing the observations of the LASCO/SOHO coronagraphs with those of the Nancay radioheliograph. The spatial and temporal evolution of the associated radioburst is complex and involves a long-duration continuum. The analysis of the time sequence of the radio continuum reveals the existence of distinct phases associated with distinct reconnection processes and magnetic restructuring of the corona. Electrons are accelerated in association with these reconnection processes. An excellent spatial association is found between the position and extension of the radio source and the CME seen by LASCO. Furthermore, it is shown that the topology and evolution of the source of the radio continuum involve successive interactions between two systems of loops. These successive interactions lead to magnetic reconnection, then to a large scale coronal restructuring. Thus electrons of coronal origin may have access to the interplanetary medium in a large range of heliographic latitudes as revealed by the Ulysses observations.
