C. G. Maclennan, L. J. Lanzerotti, and R. E. Gold,
Low Energy (0.5-8 MeV/nuc.) Anomalous Cosmic Ray Ions at
High Heliolatitudes and in the Ecliptic Plane, Spring
AGU Meeting, May 1999, Abstract SH32B-04.
The HISCALE instrument on the Ulysses
spacecraft measured low energy (~0.5-8 MeV/nucl)
Anomalous Cosmic Ray (ACR) ions at high
heliolatitudes during the years 1993-1997, as
well as in the ecliptic plane at 5 AU in
1997-1998. The fluxes of ACR nitrogen, oxygen,
and neon measured at northern heliolatitudes
were a factor of about 2 larger than those
measured at southern high heliolatitudes.
Comparison of the ACR fluxes in the ecliptic at
5 AU in 1997-1998 with measurements made with a
similar instrument (EPAM) on the ACE spacecraft
at 1 AU shows that there is little evidence for
0.5-1.0 MeV/nucl ACR oxygen at 1 AU. At 5 AU in
the ecliptic in 1997 and early 1998, the ACR O
fluxes are at approximately the same level as
those measured at high northern heliolatitudes.
However, in July 1998, following an interval of
enhanced solar activity, the 5 AU in-ecliptic
ACR O fluxes disappear. Thus, in 1997-1998 the
in-ecliptic radial gradient of low energy ACR O
between 1 and 5 AU is quite large, but after
about mid-1998 this gradient is no longer
meaningful, as low energy ACR O fluxes can no
longer be measured.
C. G. Maclennan, L. J. Lanzerotti, R. B. Decker, R.
E. Gold, S. E. Hawkins, and D. Haggerty, Charged
Particle Composition in the Inner Heliosphere During the
Rise to Maximum of Solar Cycle 23, Fall AGU Meeting,
December 1999, Abstract SH42A-13.
The beginning and rise to maximum of solar
cycle 23 has the Ulysses spacecraft fortuitously
placed at ~5 AU near the ecliptic plane and on a
trajectory toward the southern heliosphere pole.
The twin instruments, HISCALE on Ulysses and
EPAM on the ACE spacecraft (at 1 AU), provide an
opportunity at this time in the solar cycle to
investigate the spatial distribution of charged,
solar-produced particles in the near-ecliptic
heliosphere inside 5 AU. We report here
examinations and comparisons of the composition
(Z > 2 ions) of heliosphere particles with
energies ~0.5 - ~10 MeV/nucl during the years
1998 to present as measured at these two
locations. Two of the larger solar-energetic
particle events that were observed during this
interval occurred on about day 60 and day 180,
1999. Both of these events at Ulysses had
time-intensity profiles of "classical'' particle
events accompanied by traveling interplanetary
shocks. Relatively high intensities of Z > 5 and
Z > 10 ions were measured in both events. In
addition to comparing the HISCALE and the EPAM
heavy ion composition measurements, we will
discuss the influence of shock accelerations on
the heliosphere composition as the
interplanetary shocks travel from near earth to
5 AU. These results will be compared with
previous HISCALE studies that concluded that the
most significant acceleration by CIR events
occurred at 3 AU and at heliolatitudes of ~30
degrees.
D. J. Thomson, L. J. Lanzerotti, and C. G. Maclennan,
Linear Transport of Interplanetary Electrons Between ACE
and Ulysses in the Heliosphere, Spring AGU Meeting, May
1999, Abstract SH42A-05.
During
late 1997 and early 1998 the ACE and Ulysses
spacecraft were in approximate magnetic or
radial alignment in the heliosphere. ACE was
upstream from Earth in the ecliptic plane at 0.9
AU, and Ulysses was within 12 degrees of the
ecliptic at 5.4 AU. Increasing solar activity
and proximity to the heliospheric current sheet
provided sufficient particle fluxes to
investigate, statistically, the relationships
between measurements made at these two separated
sites. Time-series analysis of the measured low
energy electron fluxes recorded by the similar
instruments EPAM and HISCALE, on ACE and
Ulysses, respectively, during this interval show
that the power spectra estimated from data at
the two spacecraft are quite similar. These
spectra show strong modal structure, with many
of the discrete lines reported by the authors inNature,
376, 139-144 (1995) appearing at high
significance levels in both spacecraft. (The
modal lines in theNaturearticle
were obtained when Ulysses was at
mid-heliolatitudes in the southern heliosphere.)
In addition to the similar features seen in the
spectra, the time series are found to be quite
coherent. For example, using similar energy
electron channels on both spacecraft, half of
the coherence estimates in the frequency range 0
- 140 μHz are found to be above the 80%
significance level. Much theoretical work on the
interplanetary medium is based on the hypothesis
that nonlinear hydrodynamics generate
turbulence, with the implied consequence that
propagation of discrete frequency modes in the
heliosphere is unlikely. We assume that the
electron data is a sample of a nonstationary
time series, so that structures at different
frequencies would be correlated. Quadratic
nonlinearities, such as could be expected from
terms of the formu(nabla)u,
are characterized by cross-terms that create sum
and difference frequencies. Testing for the
generation of such cross-terms between ACE and
Ulysses give statistics compatible with linear
propagation between the two spacecraft. Using
this finding, an estimate of the linear transfer
function between the two spacecraft shows that
the bulk of the `flow' occurs with time delays
between about 50 and 200 hours.
D. J. Thomson, L. J.
Lanzerotti, and C. G. Maclennan, Time Series Analysis of
Interplanetary Magnetic Field Data and Implications for
Discrete Oscillatory Modes in the Inner Heliosphere,
Fall AGU Meeting, December 1999, Abstract SH21C-10.
We have previously reported that multitaper
time series analysis of charged particle data
from Ulysses and several other interplanetary
spacecraft in the heliosphere beyond ~1 AU
exhibit evidence for discrete, high Q, modes
that have been attributed to solar acoustic and
gravity mode oscillations (Nature, 1995). There
have been challenges to these conclusions, often
on the basis that the interplanetary medium can
be characterized as random and chaotic. We
report in this paper a statistical study of
interplanetary magnetic field (IMF) data taken
by the Ulysses spacecraft at several heliosphere
locations during its first orbit of the sun. We
find that (1) the spectra of the IMF data
contain many peaks that are too large to be
random fluctuations; (2) the fluctuations in the
spectra are unlike those expected from random
data; (3) filtering of the IMF data at the
frequencies given in the Nature paper yield
phases that are linear in time over more than a
year, in the ecliptic plane and post Jupiter;
(4) histograms of differences between
frequencies that were estimated from IMF data
over the south solar pole (Dennison and Walden,
1999) and those from the Nature paper (acquired
predominantly near the ecliptic plane) have a
null near zero; that is, there are fewer close
matches than would be expected if the data were
completely random, thus implying a systematic
difference that is probably a result of real
physical effects; (5) Echelle plots made from
high resolution IMF data in charged particle
propagation "channels" (Buttighofer, 1998) show
~135 μHz peak spacing, characteristic of solar
p-modes (although the time duration of the
channels is insufficient to allow identification
of individual modes).
M. E. Burton, E.
J. Smith, D. J. McComas, and K. A. Anderson, Ulysses
Observations of a Pair of Slow Mode Shocks Inside a
Coronal Mass Ejection, Spring AGU Meeting, May 1998,1998
Spring Meeting Supplement to EOS, S287, 1998, Abstract
SH51E-05.
From February 3-5, 1995,
as Ulysses was approaching the ecliptic at 24° S
latitude, it was intercepted by the first CME
that had been seen in many months. The CME was
not of the "over-expansion" type seen previously
at high latitudes and was accompanied by
energetic ions and electrons. The magnetic field
and plasma measurements revealed a signature
within the CME similar to that first seen in the
Earth's distant magnetotail by ISEE-3. The
latter signature has been identified as a pair
of slow mode shocks bounding a region (plasma
sheet) containing reconnected field lines.
Analysis of the Ulysses data has confirmed that
a pair of slow mode shocks are present at the
boundaries of this structure. In addition, a
current sheet, across which the field reverses
direction, has been found to lie between the
shocks. The existence of this complex structure
suggests magnetic reconnection within a CME at
an x-type neutral point, evidence of which has
proved elusive in the past.
R. E. Gold, L. J.
Lanzerotti, C. G. Maclennan, and S. E. Hawkins III,
Measurements of the November 1997 Solar Particle Event
at 1 and 5 AU, Spring AGU Meeting, May 1998,1998
Spring Meeting Supplement to EOS, S256, 1998, Abstract
SH21D-09.
The
question of how solar energetic particle events
populate the heliosphere can be studied by
examining the temporal and spatial distributions
of the ion species at multiple locations. The
EPAM instrument on ACE at 1 AU and the HISCALE
instrument on Ulysses (presently in the ecliptic
at ~ 5 AU) are identical experiments that
measure low energy electron and ion fluxes in
the heliosphere. Comparisons of the time
profiles of electrons and ions in this large
event at the two heliosphere locations will be
given. It is found that for particles with
energies 0.5 - 1.0 MeV/nucl, near the peak of
the November 1997 solar particle event at each
location when the two spacecraft were separated
in heliolongitude by ~ 90 °, JULS/JACE(p)
~ JULS/JACE(He) ~ 10-3; JULS/JACE(CNO)
~ 1.5 x 10-3. At both locations it is found that
J(CNO)/J(Fe group) ~ 1. Additional details of
the measurements made during this large solar
event will be presented.
C. G.
Maclennan and L. J. Lanzerotti, Low Energy Anomalous Ion
Components at Northern Heliolatitudes, Spring AGU
Meeting, May 1998, 1998 Spring Meeting Supplement to
EOS, S281, 1998, Abstract SH42C-11.
The
traversal of the Ulysses spacecraft through the
northern heliolatitudes, from a distance of ~
1.35 AU near the ecliptic to the return to the
ecliptic at ~ 5.4 AU, was largely devoid of
solar particle events and co-rotating
interaction regions. Thus, the low energy (~
0.5-5 MeV/nucl) anomalous components of the
heliospheric particle fluxes could be more
easily separated from other heliosphere
processes than during the southern heliolatitude
passage of the mission. Using measurements from
the Wart telescope in the HISCALE instrument on
Ulysses we find that the anomalous oxygen fluxes
have essentially a flat spectrum over this
energy range and are ~ 3-4 x 10-8/(cm2s
ster keV nucl-1). The spectra for the N and Ne
fluxes are also flat and, in this energy range,
J(N)/J(O) ~ 0.2; J(Ne)/J(O) ~ 0.1. The fluxes of
anomalous O in the northern heliolatitudes are a
factor of ~ 2 larger than those measured in the
southern heliolatitudes. Finally, in both
heliohemispheres, the carbon spectra in this
energy range have an energy/nucleon (E)
dependence of ~E-2.
C. G. Maclennan, L. J.
Lanzerotti, R. E. Gold, and T. P. Armstrong, Low Energy
Particles Near the Ecliptic at ~5 AU at the Onset of
Solar Activity Cycle 23, Fall AGU Meeting, Dec. 1998,
Abstract SH41B-18.
The near-ecliptic, ~5 AU, location of the
Ulysses spacecraft at the beginning of the 23rd
solar cycle provides an opportunity to observe
the beginnings of the effects of the cycle in
the distant heliosphere and to compare these
with observations made near Earth. We present
here low energy (electrons and ions > 50 keV)
particle data from the Ulysses HISCALE and the
ACE EPAM instruments during the interval ranging
from late 1997 to the present. We compare
especially the ion composition at these two
locations in the heliosphere for several solar
particle events during this time interval. The
onset of solar activity also contributes to a
decrease in the low energy anomalous cosmic ray
(ACR) ions in the heliosphere. We have
previously shown that the ACR oxygen fluxes were
measured by HISCALE to be about a factor of two
larger in the northern heliosphere than in the
southern. Also presented here are the changes
that are being measured in the ACR fluxes at ~5
AU as solar activity begins to increase.
E. C. Roelof, R.
E. Gold, D. K. Haggerty, S. E. Hawkins III, and G. M.
Simnett, Conditions for Energetic Particle Propagation
in the Inner Heliosphere During the November 1997 Solar
Events: ACE/EPAM and Ulysses/HISCALE Observations,
Spring AGU Meeting, May 1998,1998 Spring
Meeting Supplement to EOS, S256, 1998, Abstract
SH21D-10.
The EPAM energetic
ion/electron experiment on ACE [Krimigis et al.,
this conference] is essentially identical to the
HISCALE instrument on Ulysses. As ACE was
launched, Ulysses was near its aphelion and
moving southward towards its heliographic
equator crossing in mid-December 1997. The rise
in activity of Solar Cycle 23 produced a major
series of solar particle events, beginning with
a small electron event on 3 November 1997 (day
307) at ACE and lasting throughout the rest of
the month at both spacecraft [Gold et al., this
con-ference]. In this paper we examine the state
of the equatorial heliosphere during several
solar rotations prior to the November event.
There were 26-day recurrent energetic ion events
identifiable at Ulysses, in a series leading up
to the November solar events. They peaked on
days 216, 244, 271, and 296. These small ion
events at Ulysses did not have unambiguous
counterparts at ACE, even though ACE and Ulysses
were nearly on the same spiral field line in
mid-October for a solar wind velocity of 450
km/s. Also, they were not the only ion events
observed near 5 AU. For example, there was a
CME-associated energetic particle event on days
242-243 (just preceding the recurrent event
beginning on day 244) whose time profile is
similar to the CME event reported by Armstrong
et al. [Geophys. Res. Lett., 21, 1747, 1994].
Nonetheless, the existence of a series of
recurrent ion events at Ulysses implies a
somewhat stable IMF in the inner heliosphere
just prior to the November solar events. We
therefore conclude that those energetic
particles were injected into a relatively
ordered global magnetic field with
correspondingly uncomplicated propagation
conditions. Consequently, the timing of the
November 1997 events, right at the rise of solar
activity, offers the possibility of a much more
straight-forward interpretation of their
evolution than would be the case at solar
maximum.
E. T. Sarris, G.
Kasotakis, L. J. Lanzerotti, and S. M. Krimigis,
ULYSSES/HISCALE Observations of High Beta Conditions in
the Interplanetary Medium, Spring AGU Meeting, May 1998,1998
Spring Meeting Supplement to EOS, S292, 1998, Abstract
SH52B-11.
We present detailed
observations of energetic (50 keV to 5 MeV) ion
intensities measured by the Ulysses/HI-SCALE
instrument during certain distinct periods when
the energy density contained in the suprathermal
tail of the interplanetary particle distribution
is comparable to, and occasionally exceeds, that
of the magnetic field, thus creating conditions
of an unusual high-beta plasma. These high-beta
events appear to be associated with regions of
intense shock acceleration or the presence of
magnetic field depressions (magnetic holes). The
existence of high-beta plasma regimes produced
by suprathermal particles in the interplanetary
medium have profound implications for the
propagation of these particles throughout the
heliosphere. In such regions, the usual
theoretical assumptions of particle confinement
and scattering by the local interplanetary
magnetic field are violated. For example, the
particles can freely `traverse' the local
fields.
D. J. Thomson, L. J. Lanzerotti, C. G. Maclennan, H.
Kunow, B. Heber, and R. E. Gold, Long-Period (>1 Day)
Modes in Interplanetary Particle Fluxes and Relations to
Solar Processes, Fall AGU Meeting, Dec. 1998, Abstract
SH41B-17.
Time series studies of interplanetary
particle fluxes measured on the Ulysses
spacecraft in and out of the ecliptic plane show
numerous long-period (periods > 1 day) discrete
modes, providing evidence that the
interplanetary medium is not a completely
chaotic system. The frequencies determined to be
most significant by sensitive statistical tests
do not all correspond to harmonics of the solar
rotation (those most evident in interplanetary
particle and plasma data as quasi-26 day
enhancements produced by co-rotating interaction
regions). We present analysis of low energy (E >
50 keV) electron and ion, and high energy (E >
100 MeV) proton, data obtained by the Ulysses
HISCALE and KET instruments. A period of about
2.2 days is especially prominent when a highly
sensitive test of coherence and phase of the
time series of these particles (with vastly
different rigidities) is performed. The phase
difference between the variations of the low
energy and high energy particle fluxes at this
period is found to be ~90 deg. These results
provide independent evidence of solar phenomena
(in addition to, for example, the motions of
coronal hole boundaries and interplanetary CIRs)
modulating cosmic rays in the heliosphere. We
have previously suggested that periodicities
such as this could be evidence of fundamental
solar oscillations. We also present evidence of
the presence of similar periodicities in time
series of other solar, and solar-influenced,
data.
K. A. Anderson,
R. P. Lin, J. T. Gosling, E. J. Smith, T. P. Armstrong,
and E. C. Roelof, An Unusual, CME-Related Energetic
Particle Event, Fall AGU Meeting, December 1997,1997
Fall Meeting Supplement to EOS, F540, 1997, Abstract
SH22A-03.
On 4 February 1995 an
unusual energetic particle event occurred near
the center of a CME structure. At this time the
Ulysses spacecraft was located about 1.4 AU from
the Sun. The energetic particles are contained
in a complex plasma and magnetic field region
that required about 13 hours to sweep past the
spacecraft. Many changes in the energetic
particle intensities are related to features of
the CME such as the helium to hydrogen ratio,
the solar wind plasma density, and magnetic
field variations. We believe that the energetic
electrons are not CIR-accelerated and it is
unlikely they have been accelerated by shock
waves in the interplanetary medium. There is
some evidence that both the electron and ion
components were accelerated near the Sun, but
associated solar activity (flares, X-ray bursts)
has not been found. The electrons exhibit a loss
cone implying a mirror field of about 25 nT.
Such a strong field means that the electrons,
after passing the spacecraft at 1.4 AU distance
from the Sun, must have moved toward the Sun to
approximately heliocentric distance of 0.7 AU.
The ions have not mirrored. They move at a speed
of ~ 1/25 that of the electrons and evidently
have not had sufficient time to reach the mirror
field. Recently Smith et al. (see preceding
abstract) have found what they believe to be a
pair of slow mode shocks and a current sheet
during this particle event. The times of the
shocks correspond to changes in the fast
electron fluxes. In particular the electron flux
drops markedly at the time of the outbound
shock.
A. Buttighoffer,
R. P. Lin, K. A. Anderson, and M. Pick, Stereoscopic
Observations of Solar Particle Events Observed by
Ulysses and WIND, Spring AGU Meeting, May 1997,1997
Spring Meeting Supplement to EOS, S260, 1997, Abstract
SH51C-01.
The mechanisms involved
in coronal energetic particle injection to the
interplanetary medium (IPM) are not fully
understood. Many questions remain about how
particles are accelerated or what is the role of
coronal mass ejection (CME) often observed
during such solar events. In this paper, we
present joint coronal and stereoscopic particle
observations made during solar energetic
particle events from 1995 to 1997. The
stereoscopic particle observations are from the
HISCALE instrument (30-300 keV electrons and 50
keV - 5 MeV ions) on the Ulysses spacecraft and
the 3D Plasma and Energetic Particle instrument
(~10 eV - ~1 MeV electrons and ~10 eV - 6 MeV
ions) on the WIND spacecraft. The relative
position of Ulysses and WIND spans an interval
of some 80 deg. in latitude and ±180 deg. in
longitude. The joint coronal observations used
here were made mainly in X-rays and white light
by the YOHKOH and SOHO satellites and in radio
by the Nancay Radio Heliograph (NRH). The
coronal observations at various wavelengths are
used to study solar activity at different
altitudes in the corona during flares. The
characteristics of the particle events
(intensity, energy, composition, pitch angle
evolution, etc.) depend on both the
characteristics of their injection in the corona
and the particle propagation to the observer.
The evolution of these characteristics with
longitude and/or latitude to the injection site
allow us to separate more easily propagation
from injection effects.
M. I. Desai, R.
G. Marsden, T. R. Sanderson, G. M. Simnett, and R. J.
Forsyth, Energy Spectra of 50 keV to 20 MeV Protons
Accelerated at Corotating Interaction Regions in the
Three-Dimensional Heliosphere, Fall AGU Meeting,
December 1997,1997 Fall Meeting Supplement
to EOS, F550, 1997, Abstract SH41B-03.
We present a detailed
analysis of the differential energy spectra of
50 keV to 20 MeV protons accelerated at or near
the forward and reverse shocks of corotating
interaction regions (CIRs) detected by the
Ulysses spacecraft throughout the
three-dimensional heliosphere. The energy
spectra are derived from simultaneous
measurements obtained by two different particle
instruments (namely, HISCALE and COSPIN/LET) in
11 discrete energy channels. In general, we find
that the energy spectra at the CIR shocks are
well represented by the Fermi model [Fisk and
Lee, 1980] which includes both a power-law and
an exponential dependence on the energy of the
particle. We examine in detail the relationship
between the spectral fit parameters and the
plasma and magnetic field data and compare our
results with theoretical predictions of the
Fermi model. Specifically, we highlight the
significant differences in these relationships
for the forward and reverse shocks and discuss
implications for the acceleration mechanisms
that could be responsible for producing the
observed differences.
R. E. Gold, D. A.
Lohr, D. K. Haggerty, S. M. Krimigis, T. P. Armstrong,
and L. J. Lanzerotti, First Observations from the
Electron, Proton, and Alpha Monitor (EPAM) on the ACE
Spacecraft, Fall AGU Meeting, December 1997,1997
Fall Meeting Supplement to EOS, F562, 1997, Abstract
SH52C-06.
The EPAM instrument on
the Advanced Composition Explorer (ACE) measures
the overall state of energetic particles between
50 keV and 5 MeV/nuc. With its full unit sphere
coverage, atomic composition coverage from H to
Fe, and dynamic range from low to very high flux
levels, EPAM provides a monitor of the
near-earth interplanetary low energy particle
populations. EPAM is also one of four
instruments in the Real Time Solar Wind (RTSW)
data stream that will provide 24 hour coverage
of space weather phenomena of importance to
telecommunications, electrical power
transmission, and other technologies at Earth.
EPAM was constructed from the flight spare of
the HISCALE instrument on Ulysses; therefore, it
is an excellent basis for comparisons of
energetic particle populations in other regions
of the heliosphere. This initial report of
measurements from EPAM provides comparisons of
low energy electrons (E > 50 keV) and ions (E >
50 keV, including composition data (E > 0.5
MeV/nuc), in the ecliptic as ACE approaches L1
with measurements presently being acquired by
HISCALE at about 5 A.U. and 10 deg. heliographic
latitude as Ulysses completes its first solar
polar orbit.
D. K. Haggerty
and T. P. Armstrong, HI-SCALE Observations of Jovian
Interplanetary Events, Fall AGU Meeting, December 1997,1997
Fall Meeting Supplement to EOS, F625, 1997, Abstract
SM52C-08.
The
HISCALE experiment on board the Ulysses
spacecraft measured upstream ion and electron
events during the Jovian flyby in February 1992.
From 1700 RJupstream of Jupiter to
3750 RJsouth of the ecliptic,
HISCALE measured 193 distinct 61-77 keV
interplanetary ion events of probable Jovian
origin. Event averaged characteristics such as
intensities, anisotropies, power law spectral
exponents, averaged event durations, and
magnetic field components were obtained. All ion
observations above 2.92 particles/cm2• str •sec• keV,
within 1000 RJ, were found to be of probable
Jovian origin. Evidence for field aligned,
velocity dispersive, ion events was observed.
Observations of rotations in ion pitch angle
distributions during the event onsets and decays
give a clear signature that a spatial structure
was convected past the spacecraft.
S. E. Hawkins III, A. F.
Cheng, and L. J. Lanzerotti, Global Flows of Hot Plasma
in Jupiter's Magnetosphere, Fall AGU Meeting, December
1997, Abstract P51A-11.
We present a picture of the dominant flow
patterns of hot plasma in the Jovian
magnetosphere using data acquired by the HISCALE
instrument on the Ulysses spacecraft, and
compare with results from Galileo. Because of
the unique trajectory of Ulysses, we observed
flows of energetic particles in the duskside,
high latitude region of the magnetosphere. The
HISCALE instrument, with its nearly full
3-dimensional coverage of the angular
distributions, high time resolution, broad
energy range (~50 - 3000 keV/nuc), and
composition measurements, is ideally suited to
resolve the issues of plasma flow in the Jovian
magnetosphere. Ulysses inbound, in the late
morning sector, observed a persistent radial
outflow (or sunward flow). The azimuthal
component of velocity was generally higher in
the plasma current sheet than at higher magnetic
latitudes. During the outbound pass, Ulysses
entered the previously unexplored dusk region.
The inferred azimuthal flow velocity suggests,
surprisingly, sunward flows--opposite to
planetary rotation. Our analysis finds gradient
anisotropies present throughout the Jovian
magnetosphere but dominated by convected flows.
We suggest that flows of hot plasma are
dominated by subcorotation at low latitudes but
by sunward flow at high latitudes.
L. J. Lanzerotti,
D. J. Thomson, C. G. Maclennan, H. Kunow, and B. Heber,
Long-Period (5 day) Modes in Interplanetary Particle
Fluxes and Relations to Cosmic Ray Modulation, Fall AGU
Meeting, December 1997,1997 Fall Meeting
Supplement to EOS, F550, 1997, Abstract SH41B-04.
Time series analysis
studies of interplanetary particle fluxes
obtained in and out of the ecliptic plane show
numerous long-period - periods ranging from five
days to more than a solar rotation - discrete
modes, providing evidence that the
interplanetary medium is not a completely
chaotic system, and may be driven at these
frequencies by solar processes. The frequencies
determined to be most significant by sensitive
statistical tests do not all correspond to
harmonics of the solar rotation that is most
evident in the appearance of quasi-26 day
variations in co-rotating interaction regions.
This paper presents the results of analysis of
low energy (E > 50 keV) electron and ion, and
high energy (E > 100 MeV) proton, data obtained
on the Ulysses spacecraft at high southern solar
latitudes from the HISCALE and KET instruments.
High energy proton data obtained near Earth on
IMP8 as well as ground-based neutron data are
examined, and show similar frequencies as at
Ulysses. The analyses also show important
changes in the amplitude and phase of some of
the longer period modes during intervals of
change in the amount of modulation of > 100 MeV
cosmic rays as measured on Ulysses and IMP8.
These near-simultaneous occurrences provide
independent evidence of solar phenomena (in
addition to, for example, motions of coronal
hole boundaries) in the modulation of cosmic
rays.
E. C. Roelof, R.
B. Decker, R. E. Gold, G. M. Simnett, L. J. Lanzerotti,
C. G. Maclennan, and T. P. Armstrong, Reappearance of
Recurrent Low Energy Particle Events in the Northern
Heliosphere: Ulysses, Voyager 1/2, and IMP8, Spring AGU
Meeting, May 1997,1997 Spring Meeting
Supplement to EOS, S259, 1997, Abstract SH51B-05.
Quasi-recurrent 26-day increases of 40 - 65 keV
electrons have measured in the high latitude
northern hemisphere of the heliosphere during 11
solar rotations, from October 1995 through July
1996, by the HISCALE energetic particle
detectors on Ulysses. They do not appear on all
rotations, but when they do, they are associated
with increases in 0.5 - 1.0 MeV protons
(preceding them 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 mid- to high- latitude
southern hemisphere from mid-1993 to the
beginning of 1995 [Roelof et al.,Astron.
Astrophys.316, 481, 1996].
Correlated energetic particles measurements from
IMP8 at Earth and Voyager 1/2 at 42 - 62 AU
establish that recurrent events during this
period were indeed 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 [J.
Geophys. Res.101, 15547, 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 (CIRs) at lower latitudes
>10 AU beyond the spacecraft where the low
energy particles are accelerated and the
galactic cosmic rays are modulated. The observed
evolutions of the northern polar coronal
structure, as revealed in FeXIV (5303Å) synoptic
maps and confirmed by SOHO/EIT FeXII (195Å)
extreme ultraviolet images, is indeed that which
is required, according to the model, to explain
the evolution of the low energy particle
recurrences as observed by Ulysses/HISCALE in
the northern heliosphere.
E. C. Roelof, M.
I. Desai, and G. M. Simnett, Jovian Electrons as Probes
of Low-Rigidity Propagation in the Heliosphere
(invited), Fall AGU Meeting, December 1997,1997
Fall Meeting Supplement to EOS, F551, 1997, Abstract
SH41C-05.
The
Ulysses HISCALE instrument measured pitch-angle
distributions of 40-178 keV electrons of Jovian
origin within 0.4 AU pre-encounter (8 events)
and 1.5 AU post-encounter (46 AU). These
near-relativistic particles have rigidities
0.21-0.46 MV, an order of magnitude smaller than
that of a 1 keV pickup He+ ion in the solar wind
frame. According to scattering theory (Roelof,
1969), their unidirectional differential
intensities j(μ) obey the relationship
Tdj/dt+Aj'-j''=0 where j is evaluated at 90 deg
pitch angle (μ=0), j' and j" are first and
second derivatives with respect to μ,
respectively, T is the pitch-angle scattering
time at μ=0, and A=vT/2L, v being the particle
velocity and L=-dlnB/dx is the parallel scale
length of the local magnetic field. In a
particular event, we can measure j'(0) and
j''(0), but not dj(0)/dt. However, using many
events, we have applied a novel approach to
obtaining statistical distributions for the two
unknownsε=Tdlnj/dt
and A. Usuallyε<0
and A>0 (although not always), consistent with
the intensities slowly decaying and the local
field decreasing (outward). We derive values of
order unity for both. For A near unity, the
path-length travelled by near-mirroring
electrons is about 2L, and the scale for a
Parker field at 5 AU is L=25 AU. Even if the
local scale is about 1 AU, the scattering is
still very weak at 90 deg. We therefore conclude
that at 5 AU the "mean-free-path", although an
ill-defined concept, is more likely controlled
by "meso-scale" (~1 AU) variations in the
magnitude of B rather than by small-angle
scattering for pitch angles near 90 deg.
