Author name code: reames
ADS astronomy entries on 2022-09-14
author:Reames, Donald V.
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Title: Solar Energetic Particles: Spatial Extent and Implications
of the H and He Abundances
Authors: Reames, Donald V.
Bibcode: 2022SSRv..218...48R
Altcode: 2022arXiv220506883R
One of the earliest indicators of the importance of shock acceleration
of solar energetic particles (SEPs) was the broad spatial extent
of the "gradual" SEP events produced as the shock waves, driven by
wide, fast coronal mass ejections (CMEs), expand across the Sun with
cross-field transport mediated by the shocks. Contrasting "impulsive"
SEP events, with characteristic enhancements of 3He and
of heavy elements, are now associated with magnetic reconnection
on open field lines in solar jets. However, large shock waves can
also traverse pools of residual impulsive suprathermal ions and jets
can produce fast CMEs that drive shock waves; in both cases shocks
reaccelerate ions with the "impulsive" abundance signatures as well as
coronal plasma. These more-complex events produce "excess protons" that
identify this process, and recently, differences in the distribution
of 4He abundances have also been found to depend upon
the combination of seed population and acceleration mode. Extreme
differences in the 4He abundances may reflect underlying
differences in the abundances of the coronal regions being sampled by
solar jets and, surprisingly, SEP events where shock waves sample two
seed-particle populations seem to have about twice the 4He/O
ratio of those with a single source.
Title: A Perspective on Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2022FrASS...9.0864R
Altcode: 2022arXiv220315886R
The author has been fortunate to observe and participate in the rise of
the field of solar energetic particles (SEPs), from the early abundance
studies, to the contemporary paradigm of shock acceleration in large
SEP events, and element abundance enhancements that are power laws
in mass-to-charge ratios from H to Pb. Through painful evolution the
"birdcage" model and the "solar-flare myth" came and went, leaving us
with shock waves and solar jets that can interact as sources of SEPs.
Title: Energy Spectra vs. Element Abundances in Solar Energetic
Particles and the Roles of Magnetic Reconnection and Shock
Acceleration
Authors: Reames, Donald V.
Bibcode: 2022SoPh..297...32R
Altcode: 2021arXiv211201568R
We reexamine the relationship between energy spectral indices and
element abundance enhancements in solar energetic particle (SEP) events
at energies of a few MeV amu−1. We find a correlated
behavior only in the largest gradual SEP4 events when all ions are
accelerated from the ambient coronal plasma by shock waves driven by
fast, wide coronal mass ejections (CMEs). This correlated abundance
behavior can track complex time variations in the spectral indices
during an event. In other (SEP3) events, CME-driven shock waves,
days apart, sample seed particles from a single pool of suprathermal
impulsive ions contributed earlier. Of the smaller, Fe-rich,
impulsive SEP events, previously related to magnetic reconnection in
solar jets, over half are subsequently reaccelerated by CME-driven
shock waves (SEP2), causing typical ion intensities to have a 64%
correlation with shock speeds. In these SEP2 events, the onset of
shock acceleration is signaled by a new component in the abundances,
large proton excesses. The remaining SEP1 events lack evidence of
shock acceleration. However, for all these events (SEP1-SEP3) with
abundances determined by magnetic reconnection, energy spectra and
abundances are decoupled.
Title: Fifty Years of 3 He-rich Events
Authors: Reames, Donald V.
Bibcode: 2021FrASS...8..164R
Altcode: 2021arXiv211006251R
The early 1970s saw a new and surprising feature in the composition
of solar energetic particles (SEPs), resonant enhancements up to
10,000-fold in the ratio 3He/4He that could even make 3He dominant
over H in rare events. It was soon learned that these events also
had enhancements in the abundances of heavier elements, such as a
factor of ~10 enhancements in Fe/O, which was later seen to be part
of a smooth increase in enhancements vs. mass-to-charge ratio A/Q
from H to Pb rising by a factor of ~1000. These events were also
associated with streaming 10 - 100 keV electrons that produce type
III radio bursts. In recent years we have found these "impulsive"
SEP events to be accelerated in islands of magnetic reconnection
from plasma temperatures of 2 - 3 MK on open field lines in solar
jets. Similar reconnection on closed loops traps the energy of the
particles to produce hot (>10 MK), bright flares. Sometimes impulsive
SEP intensities are boosted by shock waves when the jets launch fast
coronal mass ejections. No single theory yet explains both the sharp
resonance in 3He and the smooth increase up to heavier elements; two
processes seem to occur. Sometimes the efficient acceleration even
exhausts the rare 3He in the source region, limiting its fluence.
Title: Sixty Years of Element Abundance Measurements in Solar
Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2021SSRv..217...72R
Altcode: 2021arXiv210714313R
Sixty years ago the first observation was published showing solar
energetic particles (SEPs) with a sampling of chemical elements with
atomic numbers 6 ≤Z ≤18 above 40 MeV amu−1. Thus
began study of the direct products of dynamic physics in the solar
corona. As we have progressed from 4-min sounding-rocket samples
to continuous satellite coverage of SEP events, we have extended
the observations to the unusual distribution of element abundances
throughout the periodic table. Small "impulsive" SEP events from
islands of magnetic reconnection on open magnetic-field lines in solar
jets generate huge enhancements in abundances of 3He and
of the heaviest elements, enhancements increasing as a power of the
ion mass-to-charge ratio as (A /Q )3.6, on average. Solar
flares involve the same physics but there the SEPs are trapped on
closed loops, expending their energy as heat and light. The larger,
energetic "gradual" SEP events are accelerated at shock waves driven
by fast, wide coronal mass ejections (CMEs). However, these shocks can
also reaccelerate ions from pools of residual suprathermal impulsive
ions, and CMEs from jets can also drive fast shocks, complicating the
picture. The underlying element abundances in SEP events represent
the solar corona, which differs from corresponding abundances in the
photosphere as a function of the first ionization potential (FIP) of
the elements, distinguishing low-FIP (<10 eV) ions from high-FIP
neutral atoms as they expand through the chromosphere. Differences in
FIP patterns of SEPs and the solar wind may distinguish closed- and
open-field regions of formation at the base of the corona. Dependence
of SEP acceleration upon A /Q allows best-fit estimation of ion Q
-values and hence of the source plasma temperature of ∼1 - 3 MK,
derived from abundances, which correlates with recent measures of
temperatures using extreme ultraviolet emission from jets. Thus, element
abundances in SEPs have become a powerful tool to study the underlying
solar corona and to probe physical processes of broad astrophysical
significance, from the "FIP effect" to magnetic reconnection and shock
acceleration. New questions arise, however, about the theoretical
basis of correlations of energy-spectral indices with power-laws of
abundances, about the coexistence of separate resonant and non-resonant
mechanisms for enhancements of 3He and of heavy elements,
about occasional events with unusual suppression of He and about the
overall paucity of C in FIP comparisons.
Title: The Evolution of Research on Abundances of Solar Energetic
Particles
Authors: Reames, Donald
Bibcode: 2021Univ....7..292R
Altcode:
No abstract at ADS
Title: Sulfur data from the Wind spacecraft for January 2014
Authors: Brooks, David; Yardley, Stephanie; Reames, Donald
Bibcode: 2021zndo...4596004B
Altcode:
No abstract at ADS
Title: Solar Energetic Particles. A Modern Primer on Understanding
Sources, Acceleration and Propagation
Authors: Reames, Donald V.
Bibcode: 2021LNP...978.....R
Altcode: 2020arXiv201008517R
In a field overflowing with beautiful images of the Sun, solar energetic
particle (SEP) events are a hidden asset, perhaps a secret weapon,
that can sample the solar corona and carry away unique imprints of its
most bizarre and violent physics. Only recently have we found that the
abundances of the elements in SEPs carry a wealth of data, not only on
their own acceleration and history, but on plasma temperatures at their
source, and on aspects of the genesis of the corona itself. SEPs are the
tangible product of differing energetic outbursts at the Sun. They come
in extremes. Little "impulsive" SEP events from magnetic reconnection
in solar jets (also in flares), have most unusual 1000-fold resonant
enhancements of 3He and of heavy elements like Au or Pb, while large
"gradual" SEP events accelerated at shock waves driven by coronal mass
ejections (CMEs), sample the composition of the corona itself, but
also accelerate GeV protons that threaten Mars-bound astronauts with
hazardous radiation. Direct SEP measurements plus solar images provide
complimentary, "multi-messenger" data on high-energy physics at the Sun.
Title: On the Correlation between Energy Spectra and Element
Abundances in Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2021SoPh..296...24R
Altcode: 2020arXiv200806985R
In solar energetic particle (SEP) events, the physical processes
of both shock acceleration and scattering during transport can
cause energy-spectral indices to be correlated with enhancement or
suppression of element abundances versus mass-to-charge ratios A /Q
. We observe correlations for those "gradual" SEP events where shock
waves accelerate ions from the ambient coronal plasma, but there are
no such correlations for "impulsive" SEP events produced by magnetic
reconnection in solar jets, where abundance enhancement in different
events vary from (A/Q ) +2 to (A/Q ) +8, nor
are there correlations when shock waves reaccelerate these residual
impulsive ions. In the latter events the abundances are determined
separately, prior to the accelerated spectra. Events with correlated
spectra and abundances show a wide variety of interesting behavior
that has not been described previously. Small and moderate gradual SEP
events, with relative abundances typically depending approximately upon
(A/Q ) −1 and the spectra upon energy E−2.5,
vary little with time. Large SEP events show huge temporal variations
skirting the correlation line; in one case O spectra vary with time
from E−1 to E−5 while abundances vary from
(A/Q ) +1 to (A/Q ) −2 during the event. In very
large events, streaming-limited transport through proton-generated
resonant Alfvén waves flattens the spectra and enhances heavy
ion abundances prior to local shock passage, then steepens the
spectra and reduces enhancements afterward, recapturing the typical
correlation. Systematic correlation of spectra and element abundances
provide a new perspective on the "injection problem" of ion selection
by shocks and on the physics of SEP acceleration and transport.
Title: Distinguishing the Rigidity Dependences of Acceleration and
Transport in Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2020SoPh..295..113R
Altcode: 2020arXiv200611338R
In solar energetic particle (SEP) events, the power-law dependence
of element abundance enhancements on their mass-to-charge ratios
[A /Q ] provides a new tool that measures the combined rigidity
dependences from both acceleration and transport. Distinguishing
between these two processes can be challenging. However, the effects
of acceleration dominate when SEP events are small or when the ions
propagate scatter-free, and transport can dominate the temporal time
evolution of large events with streaming-limited intensities. Magnetic
reconnection in solar jets produces positive powers of A /Q from +2 to
+7 and shock acceleration produces mostly negative powers from −2
to +1 in small and moderate SEP events where transport effects are
minimal. This variation in the rigidity dependence of shock acceleration
may reflect the non-planar structure, complexity, and temporal time
variation of coronal shocks themselves. Wave amplification by streaming
protons in the largest SEP events suppresses the escape of ions with low
A /Q , creating observed powers of A /Q from +1 to +3 upstream of the
accelerating shock, decreasing to small negative powers downstream. For
shock acceleration, the powers of A /Q are correlated with the energy
spectral indices of He, O, and Fe, yet unexplained departures exist.
Title: Virtues of Including Hydrogen in the Patterns of Element
Abundances in Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2020arXiv200412229R
Altcode:
We revisit a multi-spacecraft study of the element abundances of
solar energetic particles (SEPs) in the 23 January 2012 event, where
the power-law pattern of enhancements versus the mass-to-charge ratio
A/Q for the elements C through Fe was partly disrupted by a break near
Mg, which turned out to be an unfortunate distraction. In the current
article we find that extending that least-squares fits for C - Fe down
to H at A/Q = 1 lends much more credence to the power laws, even though
H itself was not included in the fits. We also investigate the extent
of an adiabatically invariant "reservoir" of magnetically-trapped
particles behind the shock wave in this event.
Title: Four Distinct Pathways to the Element Abundances in Solar
Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2020SSRv..216...20R
Altcode: 2019arXiv191206691R
Based upon recent evidence from abundance patterns of chemical elements
in solar energetic particles (SEPs), and, ironically, the belated
inclusion of H and He, we can distinguish four basic SEP populations:
(1) SEP1—pure "impulsive" SEPs are produced by magnetic reconnection
in solar jets showing steep power-law enhancements of 1 ≤Z ≤56
ions versus charge-to-mass ratio A /Q from a ≈3 MK plasma. (2)
SEP2—ambient ions, mostly protons, plus SEP1 ions reaccelerated
by the shock wave driven by the narrow coronal mass ejection (CME)
from the same jet. (3) SEP3—a "gradual" SEP event is produced when
a moderately fast, wide CME-driven shock wave barely accelerates
ambient protons while preferentially accelerating accumulated remnant
SEP1 ions from an active region fed by multiple jets. (4) SEP4—a
gradual SEP event is produced when a very fast, wide CME-driven shock
wave is completely dominated by ambient coronal seed population of
0.8-1.8 MK plasma usually producing a full power law vs. A /Q for 1
≤Z ≤56 ions. We begin with element abundances in the photosphere
that are fractionated during transport up to the corona based upon
their first ionization potential (FIP); this important "FIP effect"
for SEPs provides our reference abundances and is different for SEPs
from that for the solar wind. We then show evidence for each of the
processes of acceleration, reacceleration, and transport that conspire
to produce the four abundances patterns we distinguish.
Title: Element Abundances of Solar Energetic Particles and the
Photosphere, the Corona, and the Solar Wind
Authors: Reames
Bibcode: 2019Atoms...7..104R
Altcode: 2019arXiv191001209R
From a turbulent history, the study of abundances of elements in solar
energetic particles (SEPs) has grown into an extensive field that
probes the solar corona and the physical processes of SEP acceleration
and transport. Underlying SEPs are the abundances of the solar corona,
which differ from photospheric abundances as a function of the first
ionization potentials (FIPs) of the elements. The FIP-dependence of
SEPs also differs from that of the solar wind; each has a different
magnetic environment where low-FIP ions and high-FIP neutral atoms
rise toward the corona. Two major sources generate SEPs: The small
"impulsive" SEP events are associated with magnetic reconnection
in solar jets that produce 1000-fold enhancements from H to Pb as a
function of mass-to-charge ratio A/Q, and also 1000-fold enhancements
in 3He/4He produced by resonant wave-particle interactions. In
large "gradual" events, SEPs are accelerated at shock waves driven
out from the Sun by wide, fast coronal mass ejections (CMEs). A/Q
dependence of ion transport allows us to estimate Q and hence the
source plasma temperature T. Weaker shock waves favor reacceleration
of suprathermal ions accumulated from earlier impulsive SEP events,
along with protons from the ambient plasma. In strong shocks the ambient
plasma dominates. Ions from impulsive sources have T ~ 3 MK; those from
ambient coronal plasma have T = 1 - 2 MK. These FIP- and A/Q-dependences
explore complex new interactions in the corona and in SEP sources.
Title: Excess H, Suppressed He, and the Abundances of Elements in
Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2019SoPh..294..141R
Altcode: 2019arXiv190802321R
Recent studies of the abundances of H and He relative to those
of heavier ions in solar energetic particle (SEP) events suggest
new features in the underlying physics. Impulsive SEP events,
defined by uniquely large enhancements of Fe/O, emerge from magnetic
reconnection in solar jets. In small, "pure," shock-free, impulsive SEP
events, protons with mass-to-charge ratio A /Q =1 fit the power-law
dependence of element abundance enhancements versusA /Q extrapolated
from the heavier elements 6 ≤Z ≤56 . Sometimes these events have
order-of-magnitude suppressions of He, even though H fits with heavier
elements, perhaps because of the slower ionization of He during a
rapid rise of plasma from the chromosphere. In larger impulsive SEP
events, He fits, but there are large proton excesses relative to the
power-law fit of Z >2 ions, probably because associated coronal
mass ejections (CMEs) drive shock waves fast enough to reaccelerate
the impulsive SEPs but also to sample protons from the ambient solar
plasma. In contrast, gradual SEP events are accelerated by wide, fast
CME-driven shock waves, but those with smaller, weaker shocks, perhaps
quasi-perpendicular, favor impulsive suprathermal residue left by many
previous jets, again supplemented with excess protons from ambient
coronal plasma. In the larger, more common gradual SEP events, faster,
stronger shock waves sample the ambient coronal plasma more deeply,
overwhelming any impulsive-ion component, so that proton abundances
again fit the same power-law distribution as all other elements. Thus,
studies of the power-law behavior in A /Q of SEP element abundances give
compelling new information on the varying physics of SEP acceleration
and properties of the underlying corona.
Title: Hydrogen and the Abundances of Elements in Gradual Solar
Energetic-Particle Events
Authors: Reames, Donald V.
Bibcode: 2019SoPh..294...69R
Altcode: 2019arXiv190203208R
Despite its dominance, hydrogen has been largely ignored in studies
of the abundance patterns of the chemical elements in gradual solar
energetic particle (SEP) events; those neglected abundances show
a surprising new pattern of behavior. Abundance enhancements of
elements with 2 ≤Z ≤56 , relative to coronal abundances, show a
power-law dependence versus their average mass-to-charge ratio A /Q
, which varies from event to event and with time during events. The
ion charge states Q depend upon the source plasma temperature T . For
most gradual SEP events, shock waves have accelerated ambient coronal
material with T <2 MK with decreasing power laws in A /Q . In this
case, the proton abundances agree rather well with the power-law fits
extrapolated from elements with Z ≥6 at A /Q >2 down to hydrogen
at A /Q =1 . Thus the abundances of the elements with Z ≥6 fairly
accurately predict the observed abundance of H, at a similar velocity,
in most SEP events. However, for those gradual SEP events where ion
enhancements follow positive powers of A /Q , especially those with T
>2 MK where shock waves have reaccelerated residual suprathermal
ions from previous impulsive SEP events, proton abundances commonly
exceed the extrapolated expectation, usually by a factor of order
ten. This is a new and unexpected pattern of behavior that is unique
to the abundances of protons and may be related to the need for more
streaming protons to produce sufficient waves for scattering and
acceleration of more heavy ions at the shock.
Title: Hydrogen and the Abundances of Elements in Impulsive Solar
Energetic-Particle Events
Authors: Reames, Donald V.
Bibcode: 2019SoPh..294...37R
Altcode: 2019arXiv190104369R
Hydrogen has been almost completely ignored in studies of the abundance
patterns of the chemical elements in solar energetic particles
(SEPs). We seek to find impulsive events where H fits these abundance
patterns and document the events that do not, suggesting possible
reasons for the disparity. For 24% of the smaller impulsive SEP events,
the relative abundance of H fits within one standard deviation of the
power-law fit of the abundances of elements 6 ≤Z ≤56 , relative
to coronal abundances. In impulsive events with high intensities, H
can be 10 to 100 times its expected value. In a few of these larger
events, increased scattering at high wavenumber may preferentially
detain H, perhaps with self-amplified waves; in some events pre-event
proton background may contribute. In most large impulsive SEP events,
however, associated shock waves must play a much greater role than
previously thought; fast (>500 kms−1) coronal mass
ejections contribute to 62% of impulsive events. Shocks may sample
protons from the ambient coronal plasma or residual background as well
as reaccelerating heavier impulsive SEP ions injected from the region
of magnetic reconnection in solar jets. Excess H may be a signature
of shock acceleration.
Title: Helium Suppression in Impulsive Solar Energetic-Particle Events
Authors: Reames, Donald V.
Bibcode: 2019SoPh..294...32R
Altcode: 2018arXiv181201635R
We have studied the element abundances and energy spectra of the small
"He-poor" impulsive solar energetic-particle (SEP) events, comparing
them with other impulsive SEP events with more-normal abundances of
He. He-poor events can have abundances as low as He/O ≈ 2, while
both impulsive and gradual SEP events usually have source abundances of
30 ≤He/O≤100 with mean values of ≈ 50 - 60. He/C ratios are not
only low, but often decrease with energy in He-poor events. Abundance
enhancement patterns of other elements with atomic numbers 6 ≤Z
≤56 , and likely values of their mass-to-charge ratios A /Q , are
generally unaltered in He-poor events, as are the probable source-plasma
temperatures of 2.5 - 3.2 MK for all impulsive SEP events. One He-poor
event is also an example of a rarer C-poor event with C/O=0.08 ±0.04 ,
suppressed by a factor over five from the mean. We discuss suggestions
of a possible A /Q threshold during acceleration and of the sluggish
ionization of He entering the corona, because of its uniquely high
first ionization potential (FIP), but the suppression of He and the
decline of He/C with energy is difficult to explain if both He and C
are fully ionized with A /Q =2 as expected at 2.5 - 3.2 MK. Although
less dramatic, a possible excess enhancement of Ne in some impulsive
SEP events is also considered. Possible causes of the large ≈
30% spectral and abundance variations in impulsive events are also
discussed. However, the physics of the He-poor events remains a mystery.
Title: Corotating Shock Waves and the Solar-wind Source of Energetic
Ion Abundances: Power Laws in A /Q
Authors: Reames, Donald V.
Bibcode: 2018SoPh..293..144R
Altcode: 2018arXiv180806132R
We find that element abundances in energetic ions accelerated by
shock waves formed at corotating interaction regions (CIRs) mirror
the abundances of the solar wind modified by a decreasing power-law
dependence on the mass-to-charge ratio A /Q of the ions. This behavior
is similar in character to the well-known power-law dependence on A /Q
of abundances in large gradual solar energetic particles (SEP). The
CIR ions reflect the pattern of A /Q , with Q values of the source
plasma temperature or freezing-in temperature of 1.0 - 1.2 MK typical
of the fast solar wind in this case. Thus the relative ion abundances
in CIRs are of the form (A/Q ) a, where a is nearly always
negative and evidently decreases with distance from the shocks, which
usually begin beyond 1 AU. For one unusual historic CIR event where
a ≈0 , the reverse shock wave of the CIR seems to occur at 1 AU,
and these abundances of the energetic ions become a direct proxy for
the abundances of the fast solar wind.
Title: Solar particle event storm shelter requirements for missions
beyond low Earth orbit
Authors: Townsend, L. W.; Adams, J. H.; Blattnig, S. R.; Clowdsley,
M. S.; Fry, D. J.; Jun, I.; McLeod, C. D.; Minow, J. I.; Moore,
D. F.; Norbury, J. W.; Norman, R. B.; Reames, D. V.; Schwadron,
N. A.; Semones, E. J.; Singleterry, R. C.; Slaba, T. C.; Werneth,
C. M.; Xapsos, M. A.
Bibcode: 2018LSSR...17...32T
Altcode:
No abstract at ADS
Title: Abundances, Ionization States, Temperatures, and FIP in Solar
Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2018SSRv..214...61R
Altcode: 2017arXiv170900741R
The relative abundances of chemical elements and isotopes have been
our most effective tool in identifying and understanding the physical
processes that control populations of energetic particles. The
early surprise in solar energetic particles (SEPs) was 1000-fold
enhancements in {}3He/{}4He from resonant
wave-particle interactions in the small "impulsive" SEP events that
emit electron beams that produce type III radio bursts. Further
studies found enhancements in Fe/O, then extreme enhancements in
element abundances that increase with mass-to-charge ratio A/Q,
rising by a factor of 1000 from He to Au or Pb arising in magnetic
reconnection regions on open field lines in solar jets. In contrast,
in the largest SEP events, the "gradual" events, acceleration occurs
at shock waves driven out from the Sun by fast, wide coronal mass
ejections (CMEs). Averaging many events provides a measure of solar
coronal abundances, but A/Q-dependent scattering during transport
causes variations with time; thus if Fe scatters less than O, Fe/O is
enhanced early and depleted later. To complicate matters, shock waves
often reaccelerate impulsive suprathermal ions left over or trapped
above active regions that have spawned many impulsive events. Direct
measurements of ionization states Q show coronal temperatures of 1-2
MK for most gradual events, but impulsive events often show stripping
by matter traversal after acceleration. Direct measurements of Q are
difficult and often unavailable. Since both impulsive and gradual SEP
events have abundance enhancements that vary as powers of A/Q, we can
use abundances to deduce the probable Q-values and the source plasma
temperatures during acceleration, ≈3 MK for impulsive SEPs. This
new technique also allows multiple spacecraft to measure temperature
variations across the face of a shock wave, measurements otherwise
unavailable and provides a new understanding of abundance variations
in the element He. Comparing coronal abundances from SEPs and from
the slow solar wind as a function of the first ionization potential
(FIP) of the elements, remaining differences are for the elements C,
P, and S. The theory of the fractionation of ions by Alfvén waves
shows that C, P, and S are suppressed because of wave resonances
during chromospheric transport on closed magnetic loops but not on open
magnetic fields that supply the solar wind. Shock waves can accelerate
ions from closed coronal loops that easily escape as SEPs, while the
solar wind must emerge on open fields.
Title: The "FIP Effect" and the Origins of Solar Energetic Particles
and of the Solar Wind
Authors: Reames, Donald V.
Bibcode: 2018SoPh..293...47R
Altcode: 2018arXiv180105840R
We find that the element abundances in solar energetic particles (SEPs)
and in the slow solar wind (SSW), relative to those in the photosphere,
show different patterns as a function of the first ionization potential
(FIP) of the elements. Generally, the SEP and SSW abundances reflect
abundance samples of the solar corona, where low-FIP elements, ionized
in the chromosphere, are more efficiently conveyed upward to the corona
than high-FIP elements that are initially neutral atoms. Abundances of
the elements, especially C, P, and S, show a crossover from low to high
FIP at ≈10 eV in the SEPs but ≈14 eV for the solar wind. Naively,
this seems to suggest cooler plasma from sunspots beneath active
regions. More likely, if the ponderomotive force of Alfvén waves
preferentially conveys low-FIP ions into the corona, the source plasma
that eventually will be shock-accelerated as SEPs originates in magnetic
structures where Alfvén waves resonate with the loop length on closed
magnetic field lines. This concentrates FIP fractionation near the top
of the chromosphere. Meanwhile, the source of the SSW may lie near the
base of diverging open-field lines surrounding, but outside of, active
regions, where such resonance does not exist, allowing fractionation
throughout the chromosphere. We also find that energetic particles
accelerated from the solar wind itself by shock waves at corotating
interaction regions, generally beyond 1 AU, confirm the FIP pattern
of the solar wind.
Title: The Abundance of Helium in the Source Plasma of Solar
Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2017SoPh..292..156R
Altcode: 2017arXiv170805034R
Studies of patterns of abundance enhancements of elements, relative
to solar coronal abundances, in large solar energetic-particle (SEP)
events, and of their power-law dependence on the mass-to-charge
ratio, A /Q , of the ions, have been used to determine the effective
source-plasma temperature, T , that defines the Q -values of the
ions. We find that a single assumed value for the coronal reference He/O
ratio in all SEP events is often inconsistent with the transport-induced
power-law trend of the other elements. In fact, the coronal He/O varies
rather widely from one SEP event to another. In the large Fe-rich SEP
events with T ≈3 MK, where shock waves, driven out by coronal mass
ejections (CMEs), have reaccelerated residual ions from impulsive
suprathermal events that occur earlier in solar active regions,
He/O≈90 , a ratio similar to that in the slow solar wind, which may
also originate from active regions. Ions in the large SEP events with
T <2 MK may be accelerated outside active regions, and have values
of 40 ≤He/O≤60 . Mechanisms that determine coronal abundances,
including variations of He/O, are likely to occur near the base of the
corona (at ≈1.1 RS) and thus to affect both SEPs (at 2 -
3 RS) and the solar wind. Other than He, reference coronal
abundances for heavier elements show little temperature dependence or
systematic difference between SEP events; He, the element with the
highest first-ionization potential, is unique. The CME-driven shock
waves probe the same regions of space, at ≈2 RS near
active regions, which are also likely sources of the slow solar wind,
providing complementary information on conditions in those regions.
Title: Spatial Distribution of Element Abundances and Ionization
States in Solar Energetic-Particle Events
Authors: Reames, Donald V.
Bibcode: 2017SoPh..292..113R
Altcode: 2017arXiv170507471R
We have studied the spatial and temporal distribution of abundances of
chemical elements in large "gradual" solar energetic-particle (SEP)
events, and especially the source plasma temperatures, derived from
those abundances, using measurements from the Wind and Solar TErrestrial
RElations Observatory (STEREO) spacecraft, widely separated in solar
longitude. A power-law relationship between abundance enhancements and
mass-to-charge ratios [A /Q ] of the ions can be used to determine
Q -values and source plasma temperatures at remote spacecraft with
instruments that were not designed for charge-state measurements. We
search for possible source variations along the accelerating shock wave,
finding one clear case where the accelerating shock wave appears to
dispatch ions from 3.2 ±0.8 MK plasma toward one spacecraft and those
from 1.6 ±0.2 MK plasma toward another, 116∘ away. The
difference persists for three days and then fades away. Three other
SEP events show less-extreme variation in source temperatures at
different spacecraft, in one case observed over 222∘ in
longitude. This initial study shows how the power-law relation between
abundance enhancements and ion A /Q -values provides a new technique to
determine Q and plasma temperatures in the seed population of SEP ions
over a broad region of space using remote spacecraft with instruments
that were not originally designed for measurements of ionization states.
Title: Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2017LNP...932.....R
Altcode:
No abstract at ADS
Title: Element Abundances and Source Plasma Temperatures of Solar
Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2016JPhCS.767a2023R
Altcode: 2016arXiv161200030R
Thirty years ago Breneman and Stone [1] observed that the enhancement
or suppression of element abundances in large solar energetic-particle
(SEP) events varies as a power of the mass-to-charge ratio, A/Q, of
the elements. Since Q during acceleration or transport may depend upon
the source plasma temperature T, the pattern of element enhancements
can provide a best-fit measure of T. The small SEP events we call
3He-rich or “impulsive” show average enhancements,
relative to coronal abundances, rising as the 3.6 power of A/Q to a
factor of ∼1000 for (76<Z<82)/O and temperature in the range
2-4 MK. This acceleration is believed to occur in islands of magnetic
reconnection on open field lines in solar flares and jets. It has
been recently found that the large shock-accelerated “gradual”
SEP events have a broad range of source plasma temperatures; 69%
have coronal temperatures of T <1.6 MK, while 24% have T ∼ 3 MK,
the latter suggesting a seed population containing residual impulsive
suprathermal ions. Most of the large event-to-event abundance variations
and their time variation are largely explained by variations in T
magnified by A/Q-dependent fractionation during transport. However,
the non-thermal variance of impulsive SEP events (∼30%) exceeds that
of the ∼3 MK gradual events (∼10%) so that several small impulsive
events must be averaged together with the ambient plasma to form the
seed population for shock acceleration in these events.
Title: The Origin of Element Abundance Variations in Solar Energetic
Particles
Authors: Reames, Donald V.
Bibcode: 2016SoPh..291.2099R
Altcode: 2016SoPh..tmp..110R; 2016arXiv160306233R
Abundance enhancements, during acceleration and transport in both
gradual and impulsive solar energetic particle (SEP) events, vary
approximately as power laws in the mass-to-charge ratio [A /Q ] of the
ions. Since the Q -values depend upon the electron temperature of the
source plasma, this has allowed a determination of this temperature
from the pattern of element-abundance enhancements and a verification
of the expected inverse-time dependence of the power of A /Q for
diffusive transport of ions from the SEP events, with scattering mean
free paths found to be between 0.2 and 1 AU. SEP events derived from
plasma of different temperatures map into different regions in typical
cross-plots of abundances, spreading the distributions. In comparisons
of SEP events with temperatures above 2 MK, impulsive events show
much broader non-thermal variation of abundances than do gradual
events. The extensive shock waves accelerating ions in gradual events
may average over much of an active region where numerous but smaller
magnetic reconnections, "nanojets", produce suprathermal seed ions,
thus averaging over varying abundances, while an impulsive SEP event
only samples one local region of abundance variations. Evidence for a
reference He/O-abundance ratio of 91, rather than 57, is also found for
the hotter plasma. However, while this is similar to the solar-wind
abundance of He/O, the solar-wind abundances otherwise provide an
unacceptably poor reference for the SEP-abundance enhancements,
generating extremely large errors.
Title: Temperature of the Source Plasma in Gradual Solar Energetic
Particle Events
Authors: Reames, Donald V.
Bibcode: 2016SoPh..291..911R
Altcode: 2015arXiv150908948R; 2016SoPh..tmp...25R
Scattering during interplanetary transport of particles during
large, "gradual" solar energetic-particle (SEP) events can cause
element abundance enhancements or suppressions that depend upon the
mass-to-charge ratio [A /Q ] of the ions as an increasing function
early in events and a decreasing function of the residual scattered ions
later. Since the Q -values for the ions depend upon the source plasma
temperature [T ], best fits of the power-law dependence of enhancements
vs.A /Q can determine T . These fits provide a fundamentally new
method to determine the most probable value of T for these events in
the energy region 3 -10 MeVamu−1. Complicated variations
in the grouping of element enhancements or suppressions match similar
variations in A /Q at the best-fit temperature. We find that fits to
the times of increasing and decreasing powers give similar values of
T , in the range of 0.8 - 1.6 MK for 69 % of events, consistent with
the acceleration of ambient coronal plasma by shock waves driven out
from the Sun by coronal mass ejections (CMEs). However, 24 % of the SEP
events studied showed plasma of 2.5 - 3.2 MK, typical of that previously
determined for the smaller impulsive SEP events; these particles may
be reaccelerated preferentially by quasi-perpendicular shock waves
that require a high injection threshold that the impulsive-event ions
exceed or simply by high intensities of impulsive suprathermal ions at
the shock. The source-temperature distribution of ten higher-energy
ground-level events (GLEs) in the sample is similar to that of the
other gradual events, at least for SEPs in the energy-range of 3 -10
MeVamu−1. Some events show evidence that a portion of
the ions may have been further stripped of electrons before the shock
acceleration; such events are smaller and tend to cluster late in the
solar cycle.
Title: Dropout of Directional Electron Intensities in Large Solar
Energetic Particle Events
Authors: Tan, Lun C.; Reames, Donald V.
Bibcode: 2016ApJ...816...93T
Altcode:
In the “gradual” solar energetic particle (SEP) event during solar
cycle 23 we have observed the dispersionless modulation (“dropout”)
in directional intensities of nonrelativistic electrons. The average
duration of dropout periods is ∼0.8 hr, which is consistent with the
correlation scale of solar wind turbulence. During the dropout period
electrons could display scatter-free transport in an intermittent
way. Also, we have observed a decrease in the anisotropic index of
incident electrons with increasing electron energy (Ee),
while the index of scattered/reflected electrons is nearly independent
of Ee. We hence perform an observational examination
of the correlation between the anisotropic index of low-energy
scattered/reflected electrons and the signature of the locally measured
solar wind turbulence in the dissipation range, which is responsible
for resonant scattering of nonrelativistic electrons. Since during
the dropout period the slab turbulence fraction is dominant (0.8 ±
0.1), we pay close attention to the effect of slab fraction on the
correlation examined. Our observation is consistent with the simulation
result that in the dominance of the slab turbulence component there
should exist a dispatched structure of magnetic flux tubes, along
which electrons could be transported in a scatter-free manner. Since
a similar phenomenon is exhibited in the “impulsive” SEP event,
electron dropout should be a transport effect. Therefore, being
different from most ion dropout events, which are due to a compact
flare source, the dropout of directional electron intensities should
be caused by the change of turbulence status in the solar wind.
Title: What Are the Sources of Solar Energetic Particles? Element
Abundances and Source Plasma Temperatures
Authors: Reames, Donald V.
Bibcode: 2015SSRv..194..303R
Altcode: 2015SSRv..tmp..103R; 2015arXiv151003449R
We have spent 50 years in heated discussion over which populations
of solar energetic particles (SEPs) are accelerated at flares and
which by shock waves driven out from the Sun by coronal mass ejections
(CMEs). The association of the large "gradual" SEP events with shock
acceleration is supported by the extensive spatial distribution of
SEPs and by the delayed acceleration of the particles. Recent STEREO
observations have begun to show that the particle onset times correspond
to the observed time of arrival of the shock on the observer's magnetic
flux tube and that the SEP intensities are related to the local
shock speed. The relative abundances of the elements in these gradual
events are a measure of those in the ambient solar corona, differing
from those in the photosphere by a widely-observed function of the
first ionization potential (FIP) of the elements. SEP events we call
"impulsive", the traditional "3He-rich" events with enhanced
heavy-element abundances, are associated with type III radio bursts,
flares, and narrow CMEs; they selectively populate flux tubes that
thread a localized source, and they are fit to new particle-in-cell
models of magnetic reconnection on open field lines as found in solar
jets. These models help explain the strong enhancements seen in heavy
elements as a power (of 2-8) in the mass-to-charge ratio A/Q throughout
the periodic table from He to Pb. A study of the temperature dependence
of A/Q shows that the source plasma in impulsive SEP events must lie in
the range of 2-4 MK to explain the pattern of abundances. This is much
lower than the temperatures of >10 MK seen on closed loops in solar
flares. Recent studies of A/Q-dependent enhancements or suppressions
from scattering during transport show source plasma temperatures in
gradual SEP events to be 0.8-1.6 MK in 69 % of the events, i.e. coronal
plasma; 24 % of the events show reaccelerated impulsive-event material.
Title: Coronal Sources of Impulsive Fe-Rich Solar Energetic Particle
Events
Authors: Kahler, S.; Reames, D.; Cliver, E.
Bibcode: 2015ICRC...34...49K
Altcode: 2015arXiv150909260K; 2015PoS...236...49K
We review recent work on 111 Fe-rich impulsive solar energetic
($\sim$ 3 MeV/nuc) particle (SEP) events observed from 1994 to
2013. Strong elemental abundance enhancements scale with A/Q, the
ion mass-to-charge ratio, as (A/Q)$^{\alpha}$, where 2 $< \alpha
<$ 8 for different events. Most Fe-rich events are associated with
both flares and coronal mass ejections (CMEs), and those with larger
$\alpha$ are associated with smaller flares, slower and narrower CMEs,
and lower SEP event fluences. The narrow equilibrium temperature
range required to fit the observed A/Q enhancements is 2.5--3.2 MK,
far below the characteristic flare temperatures of $>$ 10 MK. Only
a small number of SEP events slightly outside this temperature range
were found in an expanded search of impulsive Fe-rich events. Event
characteristics are similar for events isolated in time and those
occurring in clusters. The current challenge is to determine the
solar sources of the Fe-rich events. Ambient coronal regions in the
2.5--3.2 MK range are broadly distributed both in and outside active
regions. We explore the possibility of acceleration from thermal plasmas
at reconnecting current sheets in the context of observed standard and
blowout jets. Recent current sheet reconnection modelling provides a
basis for the A/Q enhancements.
Title: Where are the Sources of Solar Energetic Particles?
Authors: Reames, Donald V.
Bibcode: 2015shin.confE..64R
Altcode:
We have spent 50 years arguing over which populations of solar
energetic particles (SEPs) are accelerated at flares and which
by shock waves driven out from the Sun by coronal mass ejections
(CMEs). The association of the large 'gradual' SEP events with shock
acceleration is supported by the extensive spatial distribution of
the particles. Recent STEREO observations have begun to show that the
particle onset times corresponds to the observed time of arrival of
the shock at the observer's magnetic flux tube and the SEP intensities
are related to the local shock speed. The relative abundances of the
elements in these gradual events are a measure of those in the ambient
solar corona, differing from those in the photosphere by a well-studied
function of the first ionization potential (FIP). SEP events we call
'impulsive', the traditional '3He-rich events,' are associated type III
radio bursts, flares, and narrow CMEs, they selectively populate flux
tubes that thread the localized source, and they are better fit to new
particle-in-cell models of magnetic reconnection on open field lines
as seen in jets. These models help explain the strong enhancements
seen in heavy elements as a power (of 2 - 8) in the mass-to-charge
ratio A/Q throughout the periodic table from He to Pb. A study of the
temperature dependence of A/Q shows that the source plasma in impulsive
SEP events must lie in the range of 2-4 MK to explain the pattern of
abundances. This is much lower than the temperatures of >10 MK seen
on closed loops in flares.
Title: Temperature of the Source Plasma for Impulsive Solar Energetic
Particles
Authors: Reames, Donald V.; Cliver, Edward W.; Kahler, Stephen W.
Bibcode: 2015SoPh..290.1761R
Altcode: 2015SoPh..tmp...81R; 2015arXiv150502741R
The steep power-law dependence of element abundance enhancements
on the mass-to-charge ratios [A /Q ] of the ions in impulsive solar
energetic-particle (SEP) events causes these enhancements to reflect
the temperature-dependent pattern of Q of the ions in the source
plasma. We searched for SEP events from coronal plasma that is hotter
or cooler than the limited region of 2.5 - 3.2 MK previously found to
dominate 111 impulsive SEP events. Fifteen new events were found, four
(three) originating in 2-MK (4-MK) plasma, but none from outside this
temperature range. Although the impulsive SEP events are strongly
associated with flares, this result indicates that these ions are
not accelerated from flare-heated plasma, which can often exceed
10 MK. Evidently the ions of 2 -20 MeVamu−1 that we
observe in space are accelerated from active-region plasma on open
magnetic-field lines near the flare, but not from the closed loops of
the flare. The power-law dependence of the abundance enhancements on
A /Q of the ions is expected from theoretical models of acceleration
from regions of magnetic reconnection.
Title: Element abundances in solar energetic particles: two physical
processes, two abundance patterns
Authors: Reames, Donald V.
Bibcode: 2015arXiv150100610R
Altcode:
Abundances of elements comprising solar energetic particles (SEPs) come
with two very different patterns. Historically called "impulsive" and
"gradual" events, they have been studied for 40 years, 20 years by the
Wind spacecraft. Gradual SEP events measure coronal abundances. They
are produced when shock waves, driven by coronal mass ejections (CMEs),
accelerate the ambient coronal plasma; we discuss the average abundances
of 21 elements that differ from corresponding solar photospheric
abundances by a well-known dependence on the first ionization
potential (FIP) of the element. The smaller impulsive ("3He-rich")
SEP events are associated with magnetic reconnection involving open
field lines from solar flares or jets that also eject plasma to produce
accompanying CMEs. These events produce striking heavy-element abundance
enhancements, relative to coronal abundances, by an average factor of
3 at Ne, 9 at Fe, and 900 for elements with 76<Z<82. This is a
strong, power-law dependence on A/Q with a ~3.6 power when Q values
are determined at coronal temperatures near 3 MK. Small individual SEP
events with the steepest enhancements (~6th power of A/Q), from ~2.5 MK
plasma, are associated with B- and C-class X-ray flares, and with narrow
(<100 deg) CMEs. Enhancements in 3He/4He can be as large as those
in heavy elements but are uncorrelated with them. However, events with
3He/4He > 0.1 are even more strongly associated with narrow, slow
CMEs, cooler coronal plasma, and smaller X-ray flares. The impulsive
SEP events do not come from hot flare plasma; they are accelerated
early and/or on adjacent open field lines.
Title: Variations in Abundance Enhancements in Impulsive Solar
Energetic-Particle Events and Related CMEs and Flares
Authors: Reames, Donald V.; Cliver, Edward W.; Kahler, Stephen W.
Bibcode: 2014SoPh..289.4675R
Altcode: 2014arXiv1407.7838R; 2014SoPh..tmp..121R
We study event-to-event variations in the abundance enhancements of the
elements He through Pb for Fe-rich impulsive solar energetic-particle
(SEP) events, and their relationship with properties of associated
coronal mass ejections (CMEs) and solar flares. Using a least-squares
procedure we fit the power-law enhancement of element abundances as
a function of their mass-to-charge ratio A/Q to determine both the
power and the coronal temperature (which determines Q) in each of
111 impulsive SEP events identified previously. Individual SEP events
with the steepest element enhancements, e.g. ∼ (A/Q)6,
tend to be smaller, lower-fluence events with steeper energy spectra
that are associated with B- and C-class X-ray flares, with cooler (∼
2.5 MK) coronal plasma, and with narrow (< 100∘),
slower (< 700 km s−1) CMEs. On the other hand,
higher-fluence SEP events have flatter energy spectra, less-dramatic
heavy-element enhancements, e.g. ∼ (A/Q)3, and come from
somewhat hotter coronal plasma (∼ 3.2 MK) associated with C-, M-,
and even X-class X-ray flares and with wider CMEs. Enhancements in
3He/4He are uncorrelated with those in heavy
elements. However, events with 3He/4He≥0.1
are even more strongly associated with narrow, slow CMEs, with
cooler coronal plasma, and with B- and C-class X-ray flares than
are other Fe-rich impulsive SEP events with smaller enhancements of
3He.
Title: Abundance Enhancements in Impulsive Solar Energetic-Particle
Events with Associated Coronal Mass Ejections
Authors: Reames, Donald V.; Cliver, Edward W.; Kahler, Stephen W.
Bibcode: 2014SoPh..289.3817R
Altcode: 2014SoPh..tmp...86R; 2014arXiv1404.3322R
We study the abundances of the elements He through Pb in Fe-rich
impulsive solar energetic-particle (SEP) events with measurable
abundances of ions with atomic number Z>2 observed on the Wind
spacecraft, and their relationship with coronal mass ejections
(CMEs) observed by the Large Angle and Spectrometric Coronagraph
(LASCO) onboard the Solar and Heliospheric Observatory (SOHO). On an
average the element abundances in these events are similar to coronal
abundances at low Z but, for heavier elements, enhancements rise as
a power law in the mass-to-charge ratio A/Q of the ions (at coronal
temperatures of 2.5 - 3 MK) to a factor of 3 at Ne, 9 at Fe, and 900
for 76≤Z≤82. Energy dependences of abundances are minimal in the 2
- 15 MeV amu−1 range. The 111 of these Fe-rich impulsive
SEP events we found, between November 1994 and August 2013 using the
Wind spacecraft, have a 69 % association rate with CMEs. The CMEs are
narrow with a median width of 75∘, are characteristically
from western longitudes on the Sun, and have a median speed of ≈
600 km s−1. Nearly all SEP onsets occur within 1.5 -
5 h of the CME onset. The faster (> 700 km s−1),
wider CMEs in our sample are related to SEPs with coronal abundances
indicating hot coronal plasma with fully ionized He, C, N and O and
moderate enhancements of heavier elements, relative to He, but slower
(< 700 km s−1), narrower CMEs emerge from cooler
plasma where higher SEP mass-to-charge ratios, A/Q, yield much greater
abundance enhancements, even for C/He and O/He. Apparently, the open
magnetic-reconnection region where the impulsive SEPs are accelerated
also provides the energy to drive out CME plasma, accounting for a
strong, probably universal, impulsive SEP-CME association.
Title: Correlation of Electron Path Lengths Observed in the Highly
Wound Outer Region of Magnetic Clouds with the Slab Fraction of
Magnetic Turbulence in the Dissipation Range
Authors: Tan, Lun C.; Reames, Donald V.; Ng, Chee K.; Shao, Xi;
Wang, Linghua
Bibcode: 2014ApJ...786..122T
Altcode:
Three magnetic cloud events, in which solar impulsive electron
events occurred in their outer region, are employed to investigate
the difference of path lengths L 0eIII traveled by
non-relativistic electrons from their release site near the Sun to
the observer at 1 AU, where L 0eIII = v l ×
(t l - t III), v l and t l
being the velocity and arrival time of electrons in the lowest energy
channel (~27 keV) of the Wind/3DP/SST sensor, respectively, and t
III being the onset time of type III radio bursts. The
deduced L 0eIII value ranges from 1.3 to 3.3 AU. Since
a negligible interplanetary scattering level can be seen in both L
0eIII > 3 AU and ~1.2 AU events, the difference in L
0eIII could be linked to the turbulence geometry (slab or
two-dimensional) in the solar wind. By using the Wind/MFI magnetic field
data with a time resolution of 92 ms, we examine the turbulence geometry
in the dissipation range. In our examination, ~6 minutes of sampled
subintervals are used in order to improve time resolution. We have
found that, in the transverse turbulence, the observed slab fraction is
increased with an increasing L 0eIII value, reaching ~100%
in the L 0eIII > 3 AU event. Our observation implies
that when only the slab spectral component exists, magnetic flux tubes
(magnetic surfaces) are closed and regular for a very long distance
along the transport route of particles.
Title: Element Abundances in Solar Energetic Particles and the
Solar Corona
Authors: Reames, Donald V.
Bibcode: 2014SoPh..289..977R
Altcode: 2013arXiv1306.2246R
This is a study of abundances of the elements He, C, N, O, Ne, Mg,
Si, S, Ar, Ca, and Fe in solar energetic particles (SEPs) in the 2
- 15 MeV amu−1 region measured on the Wind spacecraft
during 54 large SEP events occurring between November 1994 and June
2012. The origin of most of the temporal and spatial variations
in abundances of the heavier elements lies in rigidity-dependent
scattering during transport of the particles away from the site of
acceleration at shock waves driven out from the Sun by coronal mass
ejections (CMEs). Variation in the abundance of Fe is correlated with
the Fe spectral index, as expected from scattering theory but not
previously noted. Clustering of Fe abundances during the "reservoir"
period, late in SEP events, is also newly reported. Transport-induced
enhancements in one region are balanced by depletions in another, thus,
averaging over these variations produces SEP abundances that are energy
independent, confirms previous SEP abundances in this energy region,
and provides a credible measure of element abundances in the solar
corona. These SEP-determined coronal abundances differ from those in
the solar photosphere by a well-known function that depends upon the
first ionization potential (FIP) or ionization time of the element.
Title: Spatial Distribution of Solar Energetic Particles in the
Inner Heliosphere
Authors: Reames, Donald V.; Ng, Chee K.; Tylka, Allan J.
Bibcode: 2013SoPh..285..233R
Altcode: 2012SoPh..tmp..126R
We study the spatial distribution of solar energetic particles (SEPs)
throughout the inner heliosphere during six large SEP events from the
period 1977 through 1979, as deduced from observations on the Helios 1
and 2, IMP 7 and 8, ISEE 3, and Voyager 1 and 2 spacecraft. Evidence of
intensity maxima associated with the expanding shock wave is commonly
seen along its central and western flanks, although the region of peak
acceleration or "nose" of the shock is sometimes highly localized
in longitude. In one event (1 January 1978) a sharp peak in 20 -
30 MeV proton intensities is seen more strongly by Voyager at ∼ 2
AU than it is by spacecraft at nearby longitudes at ∼ 1 AU. Large
spatial regions, or "reservoirs," often exist behind the shocks with
spatially uniform SEP intensities and invariant spectra that decrease
adiabatically with time as their containment volume expands. Reservoirs
are seen to sweep past 0.3 AU and can extend out many AU. Boundaries
of the reservoirs can vary with time and with particle velocity,
rather than rigidity. In one case, a second shock wave from the Sun
reaccelerates protons that retain the same hard spectrum as protons
in the reservoir from the preceding SEP event. Thus reservoirs can
provide not only seed particles but also a "seed spectrum" with a
spectral shape that is unchanged by a weaker second shock.
Title: The Two Sources of Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2013SSRv..175...53R
Altcode: 2013arXiv1306.3608R; 2013SSRv..tmp....6R
Evidence for two different physical mechanisms for acceleration of solar
energetic particles (SEPs) arose 50 years ago with radio observations
of type III bursts, produced by outward streaming electrons, and
type II bursts from coronal and interplanetary shock waves. Since
that time we have found that the former are related to "impulsive"
SEP events from impulsive flares or jets. Here, resonant stochastic
acceleration, related to magnetic reconnection involving open field
lines, produces not only electrons but 1000-fold enhancements of
3He/4He and of ( Z>50)/O. Alternatively, in
"gradual" SEP events, shock waves, driven out from the Sun by coronal
mass ejections (CMEs), more democratically sample ion abundances that
are even used to measure the coronal abundances of the elements. Gradual
events produce by far the highest SEP intensities near Earth. Sometimes
residual impulsive suprathermal ions contribute to the seed population
for shock acceleration, complicating the abundance picture, but this
process has now been modeled theoretically. Initially, impulsive events
define a point source on the Sun, selectively filling few magnetic
flux tubes, while gradual events show extensive acceleration that can
fill half of the inner heliosphere, beginning when the shock reaches
∼2 solar radii. Shock acceleration occurs as ions are scattered
back and forth across the shock by resonant Alfvén waves amplified
by the accelerated protons themselves as they stream away. These
waves also can produce a streaming-limited maximum SEP intensity and
plateau region upstream of the shock. Behind the shock lies the large
expanse of the "reservoir", a spatially extensive trapped volume of
uniform SEP intensities with invariant energy-spectral shapes where
overall intensities decrease with time as the enclosing "magnetic
bottle" expands adiabatically. These reservoirs now explain the slow
intensity decrease that defines gradual events and was once erroneously
attributed solely to slow outward diffusion of the particles. At
times the reservoir from one event can contribute its abundances and
even its spectra as a seed population for acceleration by a second
CME-driven shock wave. Confinement of particles to magnetic flux tubes
that thread their source early in events is balanced at late times by
slow velocity-dependent migration through a tangled network produced
by field-line random walk that is probed by SEPs from both impulsive
and gradual events and even by anomalous cosmic rays from the outer
heliosphere. As a practical consequence, high-energy protons from
gradual SEP events can be a significant radiation hazard to astronauts
and equipment in space and to the passengers of high-altitude aircraft
flying polar routes.
Title: Comparison between Path Lengths Traveled by Solar Electrons
and Ions in Ground-Level Enhancement Events
Authors: Tan, Lun C.; Malandraki, Olga E.; Reames, Donald V.; Ng,
Chee K.; Wang, Linghua; Patsou, Ioanna; Papaioannou, Athanasios
Bibcode: 2013ApJ...768...68T
Altcode:
We have examined the Wind/3DP/SST electron and Wind/EPACT/LEMT
ion data to investigate the path length difference between solar
electrons and ions in the ground-level enhancement (GLE) events in
solar cycle 23. Assuming that the onset time of metric type II or
decameter-hectometric (DH) type III radio bursts is the solar release
time of non-relativistic electrons, we have found that within an
error range of ±10% the deduced path length of low-energy (~27 keV)
electrons from their release site near the Sun to the 1 AU observer is
consistent with the ion path length deduced by Reames from the onset
time analysis. In addition, the solar longitude distribution and IMF
topology of the GLE events examined are in favor of the coronal mass
ejection-driven shock acceleration origin of observed non-relativistic
electrons. We have also found an increase of electron path lengths with
increasing electron energies. The increasing rate of path lengths is
correlated with the pitch angle distribution (PAD) of peak electron
intensities locally measured, with a higher rate corresponding to a
broader PAD. The correlation indicates that the path length enhancement
is due to the interplanetary scattering experienced by first arriving
electrons. The observed path length consistency implies that the maximum
stable time of magnetic flux tubes, along which particles transport,
could reach 4.8 hr.
Title: Modeling Multi-Spacecraft Observation to Understand SEP Origin,
Acceleration, and Transport and to Infer their Radial, Latitudinal
and Longitudinal Variations
Authors: Ng, C. K.; Reames, D. V.; Rouillard, A. P.; Tan, L. C.;
Tylka, A. J.; von Rosenvinge, T. T.
Bibcode: 2012AGUFMSH23B..01N
Altcode:
We present interesting examples of our study of the spatial
distribution of SEPs inferred from observations on the Helios 1 and
2, IMP7 and 8, ISEE3, and Voyager 1 and 2 spacecraft in the time
interval 1977-1979. The study is on the concurrent observation of
protons in three energy bins from a few MeV to >100 MeV and ~
6 MeV electrons, spanning heliocentric distances from 0.3 AU to
several AU and a wide longitude range. We take advantage of the unique
spacecraft configuration in each case to infer the implications of the
multi-point observations on the origin, acceleration, and transport of
SEPs, in particular as regards "reservoir" formation, perpendicular
transport, and relation to CME-driven shocks. For the recent 2011
March 21 event, we present model fits to the SEP intensity time
profiles and energy spectra observed by STEREO-A and many spacecraft
at Earth's L1 Lagrangian point. We also present the evolution of
the SEP intensity radial profiles on field lines leading to STEREO
and L1 as predicted by the focused transport model, which includes
self-consistent SEP-amplified Alfvén waves. The radial dependence
of the maximum intensity and fluence at various SEP energies from the
same fitted model at STEREO A and L1 will be presented. This work is
supported in part by NASA grants NNX09AU98G, NNG11PV53P, NNX08AQ02G,
and NNH09AK79I. Work at GSFC is funded by NASA.
Title: Particle Energy Spectra at Traveling Interplanetary Shock Waves
Authors: Reames, Donald V.
Bibcode: 2012ApJ...757...93R
Altcode:
We have searched for evidence of significant shock acceleration of
He ions of ~1-10 MeV amu-1 in situ at 258 interplanetary
traveling shock waves observed by the Wind spacecraft. We find that the
probability of observing significant acceleration, and the particle
intensity observed, depends strongly upon the shock speed and less
strongly upon the shock compression ratio. For most of the 39 fast
shocks with significant acceleration, the observed spectral index
agrees with either that calculated from the shock compression ratio or
with the spectral index of the upstream background, when the latter
spectrum is harder, as expected from diffusive shock theory. In many
events the spectra are observed to roll downward at higher energies,
as expected from Ellison-Ramaty and from Lee shock-acceleration
theories. The dearth of acceleration at ~85% of the shocks is explained
by (1) a low shock speed, (2) a low shock compression ratio, and (3)
a low value of the shock-normal angle with the magnetic field, which
may cause the energy spectra that roll downward at energies below our
observational threshold. Quasi-parallel shock waves are rarely able to
produce measurable acceleration at 1 AU. The dependence of intensity on
shock speed, seen here at local shocks, mirrors the dependence found
previously for the peak intensities in large solar energetic-particle
events upon speeds of the associated coronal mass ejections which
drive the shocks.
Title: Composition of the Solar Corona, Solar Wind, and Solar
Energetic Particles
Authors: Schmelz, J. T.; Reames, D. V.; von Steiger, R.; Basu, S.
Bibcode: 2012ApJ...755...33S
Altcode:
Along with temperature and density, the elemental abundance is a basic
parameter required by astronomers to understand and model any physical
system. The abundances of the solar corona are known to differ from
those of the solar photosphere via a mechanism related to the first
ionization potential of the element, but the normalization of these
values with respect to hydrogen is challenging. Here, we show that the
values used by solar physicists for over a decade and currently referred
to as the "coronal abundances" do not agree with the data themselves. As
a result, recent analysis and interpretation of solar data involving
coronal abundances may need to be revised. We use observations from
coronal spectroscopy, the solar wind, and solar energetic particles
as well as the latest abundances of the solar photosphere to establish
a new set of abundances that reflect our current understanding of the
coronal plasma.
Title: The Longitudinal Properties of a Solar Energetic Particle
Event Investigated Using Modern Solar Imaging
Authors: Rouillard, A. P.; Sheeley, N. R.; Tylka, A.; Vourlidas,
A.; Ng, C. K.; Rakowski, C.; Cohen, C. M. S.; Mewaldt, R. A.; Mason,
G. M.; Reames, D.; Savani, N. P.; StCyr, O. C.; Szabo, A.
Bibcode: 2012ApJ...752...44R
Altcode:
We use combined high-cadence, high-resolution, and multi-point imaging
by the Solar-Terrestrial Relations Observatory (STEREO) and the Solar
and Heliospheric Observatory to investigate the hour-long eruption of a
fast and wide coronal mass ejection (CME) on 2011 March 21 when the twin
STEREO spacecraft were located beyond the solar limbs. We analyze the
relation between the eruption of the CME, the evolution of an Extreme
Ultraviolet (EUV) wave, and the onset of a solar energetic particle
(SEP) event measured in situ by the STEREO and near-Earth orbiting
spacecraft. Combined ultraviolet and white-light images of the lower
corona reveal that in an initial CME lateral "expansion phase," the
EUV disturbance tracks the laterally expanding flanks of the CME,
both moving parallel to the solar surface with speeds of ~450 km
s-1. When the lateral expansion of the ejecta ceases, the
EUV disturbance carries on propagating parallel to the solar surface
but devolves rapidly into a less coherent structure. Multi-point
tracking of the CME leading edge and the effects of the launched
compression waves (e.g., pushed streamers) give anti-sunward speeds
that initially exceed 900 km s-1 at all measured position
angles. We combine our analysis of ultraviolet and white-light images
with a comprehensive study of the velocity dispersion of energetic
particles measured in situ by particle detectors located at STEREO-A
(STA) and first Lagrange point (L1), to demonstrate that the delayed
solar particle release times at STA and L1 are consistent with the
time required (30-40 minutes) for the CME to perturb the corona over a
wide range of longitudes. This study finds an association between the
longitudinal extent of the perturbed corona (in EUV and white light)
and the longitudinal extent of the SEP event in the heliosphere.
Title: Use of Incident and Reflected Solar Particle Beams to Trace
the Topology of Magnetic Clouds
Authors: Tan, Lun C.; Malandraki, Olga E.; Reames, Donald V.; Ng,
Chee K.; Wang, Linghua; Dorrian, Gareth
Bibcode: 2012ApJ...750..146T
Altcode:
Occasionally, large solar energetic particle (SEP) events occur
inside magnetic clouds (MCs). In this work, the onset time analysis,
the peak intensity analysis, and the decay phase analysis of SEPs are
used to investigate two large SEP events inside MCs: the 1998 May 2
and 2002 April 21 events. The onset time analysis of non-relativistic
electrons and ~MeV nucleon-1 heavy ions shows the stability
of the magnetic loop structure during a period of a few hours in the
events examined. The joint analysis of pitch-angle distributions and
peak intensities of electrons exhibits that, depending on the particle
pitch angle observed at 1 AU, in the April event the reflection point of
particles may be distributed along a wide spatial range, implying that
the magnetic loop is a magnetic bottle connected to the Sun with both
legs. In contrast, in the May event particle reflection occurs abruptly
at the magnetic mirror formed by a compressed field enhancement behind
the interplanetary shock, consistent with its open field line topology.
Title: The Two Sources of Solar Energetic Particles
Authors: Reames, Donald V.
Bibcode: 2012AAS...22011201R
Altcode:
The identification of two different physical mechanisms for acceleration
of solar energetic particles (SEPs) began nearly 50 years ago with the
radio observations of type III bursts produced by outward streaming
electrons and type II bursts from coronal (and interplanetary) shock
waves. Since that time we have found that the former are related
to “impulsive” SEP events from flares or jets where resonant
stochastic acceleration, probably related to magnetic reconnection,
can produce 1000-fold enhancements of 3He/4He
and of (Z>50)/O, for example, while the latter “gradual” SEP
events sample ion abundances democratically and are used to measure
the coronal abundances of the elements. Sometimes, unfortunately,
residual impulsive suprathermal ions can also contribute to the seed
population for shock acceleration, complicating the picture, but
this process can now be modeled theoretically. Initially, impulsive
events behave like a point source on the Sun, while multi-spacecraft
observations of gradual events show extensive acceleration that can span
half of the inner heliosphere, beginning when the shock reaches 2 solar
radii. Acceleration occurs as ions are scattered back and forth across
the shock by proton-generated resonant Alfven waves. These waves also
define a streaming-limited maximum intensity or plateau region prior to
arrival of the shock. Behind the shock lies an extensive “reservoir”
region of spatially uniform SEP intensity that decreases with time as
the “magnetic bottle” enclosing it expands.
Title: Solar energetic particles: Shock acceleration and transport
through self-amplified waves
Authors: Ng, Chee K.; Reames, Donald V.; Tylka, Allan J.
Bibcode: 2012AIPC.1436..212N
Altcode:
This article reviews our work on the powerful influence of
self-amplified Alfvén waves on the interplanetary (IP) transport
and shock acceleration of solar energetic particles (SEPs). In large
gradual events, a huge number of shock-accelerated protons stream
through the IPmediumand amplify ambient Alfvén waves by orders of
magnitude. Nonlinear models that take account of selfamplified waves
semi-quantitatively explain many intriguing SEP observations at 1
AU: (a) upper limits to early SEP intensities, (b) flat intensity
energy spectra up to ~ 30 MeV/amu before shock arrival, and (c)
complex temporal, energy, and event-to-event variations of elemental
abundances. Streaming limit complicates estimation of the number and
energy of SEPs accelerated in a solar event but provides a safety
window for astronauts to seek shelter before a potential hazardous
intensity rise at shock passage. Self-amplified waves help bootstrap
shock acceleration and the high near-shock SEP intensity predicted at
<= 20rsolar. is relevant to inner heliospheric space missions.
Title: Comparative Modeling of 2011 March 21 SEP Event at STEREO-A
and Earth's L1
Authors: Ng, C. K.; Rouillard, A. P.; Reames, D. V.; Tylka, A. J.;
von Rosenvinge, T. T.
Bibcode: 2011AGUFMSH34A..03N
Altcode:
The 2011 March 21 solar energetic particle (SEP) event is strong at
STEREO-A and weak at Earth L1 Lagrangian point, with quite different
intensity time histories and energy spectra. Details of the SEP,
flare, CME and in situ plasma and field observations are presented by
Rouillard et al. at this conference. Here we report on our modeling
of the transport of multi-species SEPs coupled to Alfvén-wave
amplification by streaming energetic protons. The pre-shock proton
intensity observed by IMPACT at STEREO-A is averaged over 21 hours after
the fast rise. This "plateau" intensity spectrum flattens below 2 MeV
at a few 100 pfu, where 1 pfu = protons/(cm^2 s sr MeV). By contrast,
at 90 deg to the east, spacecraft at L1 observe a slow and small
intensity rise with power-law spectra while, 90 deg even further east,
STEREO-B observes no significant increase. Modeling SEP transport in
this event requires quite different energy- and time-dependent release
of accelerated SEPs at the traveling shock on the different field lines
leading to STEREO-A and L1. We infer that the shock accelerated a large
number of > 3 MeV protons on field lines leading to STEREO-A. The
numerous protons generate strong wave growth, which limits the proton
intensity and flattens the energy spectrum at < 2 MeV. In contrast,
on field lines leading to L1, the shock accelerated far fewer energetic
protons, which amplified few waves. With few self-amplified waves to
"trap" the SEPs near the shock, the proton intensity rises toward
low energy as a power law. This finding from observations at two
widely separated spacecraft in the same SEP event is consistent with
the conclusion of our comparative modeling of the weak 1998 May 2
and strong 2003 October 28 ground level events. Together, these four
event observations show a progression from weak shock acceleration and
power-law intensity spectrum at ~ 1 AU to strong shock acceleration
and a flattened energy spectrum. As shock acceleration to proton
intensity > 100 pfu increases its range from < 7 MeV to <
50 MeV going from the 2011 March 21 event at STEREO-A to the 2003 Oct
28 event at L1, the energy of spectral flattening rises from 2 MeV
to 20 MeV. We will also present fitting of the observed intensity and
spectra of minor ions. We thank Glenn Mason for his advice on ACE/ULEIS
observations. Work at GSFC is funded by NASA. Work of APR was partly
funded by NASA contracts NNX11AD40G-45527 and NNXIOAT06G. Work of
CKN, DVR, and AJT are supported in part by NASA grants NNX09AU98G,
NNX08AQ02G, and NNH09AK79I, respectively.
Title: What Causes Scatter-free Transport of Non-relativistic Solar
Electrons?
Authors: Tan, Lun C.; Reames, Donald V.; Ng, Chee K.; Shao, Xi;
Wang, Linghua
Bibcode: 2011ApJ...728..133T
Altcode:
We have examined the cause of the scatter-free transport of
non-relativistic solar electrons. Electron scatter-free transport
events are compared with the diffusive transport event. The emphasis
of our examination is on the energy dependence of electron angular
distributions and the steepening of interplanetary magnetic field
(IMF) power spectral densities (PSDs). Near and above the proton
gyrofrequency, the effects of both R-mode (whistler) and L-mode
(electromagnetic ion cyclotron, EMIC) waves need to be taken into
account separately. The PSD spectral steepening due to the EMIC
wave damping by solar-wind thermal ions becomes essential. In a
fast-rise-fast-decay impulsive electron event we have observed such
steepening, which significantly reduces PSD levels at frequencies
above the proton gyrofrequency. The spectral steepening thus produced
favors the occurrence of scatter-free transport of low-energy
electrons. Consequently, within the Wind/3D Plasma and Energetic
Particle Instrument/Silicon Semiconductor Telescope measured energy
range (~25-500 keV), there appears to be an electron energy window,
across which the scatter-free transport of lower energy electrons would
change to the diffusive transport of higher energy electrons. We have
observed such a change and found it is correlated with the occurrence
of broken power-law spectra of electrons. Thus the connection between
the transition from diffusive to scatter-free electron transport
and the concurrent transition from high to low IMF PSD levels with
corresponding breaks in the electron power-law energy spectrum and
PSD spectrum has been recognized.
Title: Exploring with Multiple Spacecraft the Scene of the Traveling
Strong Shock and its Driver
Authors: Berdichevsky, D. B.; Wu, C.; Reames, D. V.; MacDowall, R. J.;
Farrugia, C. J.
Bibcode: 2010AGUFMSH31D..07B
Altcode:
We explore the global morphology of the transient shock generated by
a fast solar ejection using multispacecraft observations, at wide
heliographic longitudes. We consider the gradual solar energetic
particle [SEP] events starting on 24 September 1977, 1 January and 23
September 1978, 26 March and 24 April 1979. To do this we use the solar
wind parameters at each spacecraft location at the time of passage of
the shock. In most cases data coverage at each shock passage enable us
to estimate the shock normal and its velocity relative to the upstream
solar wind. We remote sense the source of type II radio bursts, when
available. Here, for each case, at the nearest in-situ location to the
shocks nose, we present the findings; (1) the presence of unusual fast
and massive driver, within two hours or less of the shock passage and
the preliminary analysis of their unique plasma properties available,
(2) with regard to the driven shock, with the help of modeling the
inference of its morphological nature; (3) Further, the finding that
each one of these five shocks has a surface portion moving at least
more than 300 km/s faster than the upstream solar wind, enabling strong
shock conditions, as we know from the Earth's bow shock, which are
identified over distances from the Sun of 0.4 to 1.0 AU. Finally we
show that the shock with the most extended and fastest surface portion
(> 1600 km/s) is the one which produced the largest energetic proton
flux in each energy channel (< 60 MeV), at each location within an
extension of close to 180° in longitude. The shock with the smallest
increase in energetic particle intensities, which was limited to an
extension in longitude of less than 120°, had its fastest surface
portion moving at possibly less than 900 km/s.
Title: Streaming Limit: New Observations and Model Results
Authors: Ng, C. K.; Reames, D. V.; Tylka, A. J.
Bibcode: 2010AGUFMSH41C..06N
Altcode:
Solar energetic particle intensities at 1 AU often show an early
temporal plateau where the intensity is limited. This early intensity
limit may provide a valuable time window for astronauts to seek
shelter before large shock-associated intensity increase (if any). The
Ng and Reames (1994) time-dependent model of SEP transport through
self-amplified Alfvén waves predicts a maximum proton intensity of
~ 250 particles /(cm^2 s str MeV) at ~ 1 MeV, in agreement within a
factor of 2 with the observational survey by Reames and Ng (1998). In
fact, streaming-limited intensity is implicit in the steady-state
shock-acceleration solution of Bell (1978) and Lee (1983). Further
studies on the effect of self-amplified waves on SEP intensity spectra
have been made by Ng, Reames and Tylka (2003), Vanio (2003), and Lee
(2005). Intensities exceeding the Ng and Reames (1994) limit have been
reported (e.g., Lario et al. 2009). We present new observations of
multi-species SEP spectra at the temporal intensity plateau. We also
present new theoretical results on how the streaming limit depends on
ion species and energy, ambient wave intensity spectrum, Alfvén speed,
solar-wind speed, shock speed, and the presence of interplanetary shocks
and interaction regions. Among the new interesting observations is the
strong suppression of ion intensities near 1 MeV/amu in events that
have high 10-100 MeV proton intensity. New modeling results confirm
that this is due to these low-energy ions being strongly scattered at
small pitch angles by waves amplified by 10-100 MeV protons at large
pitch angles. As the high-energy protons travel upstream and scatter
from small to large pitch-angles, they simultaneously amplify waves en
route over a range of wavenumbers, including those that are resonant
with low-energy protons. Thus, wave amplification by streaming protons
and the pitch-angle dependence of the wave-particle resonance condition
are essential factors in understanding the limiting behavior. We thank
Glenn Mason for his advice on ACE/ULEIS observations. Work by CKN, DVR,
and AJT are supported in part by NASA grants NNX09AU98G, NNX08AQ02G,
and NNH09AK79I, respectively.
Title: Streaming-limited Intensities of Solar Energetic Particles
on the Intensity Plateau
Authors: Reames, Donald V.; Ng, Chee K.
Bibcode: 2010ApJ...723.1286R
Altcode:
We examine the energy spectra of H, He, O, and Fe ions on the temporal
intensity plateau region in large solar energetic-particle (SEP) events,
where intensities may be ''streaming limited.'' Upstream of shock waves
near the Sun, equilibrium may occur when outwardly streaming protons
amplify resonant Alfvén waves that then scatter subsequent protons
sufficiently to reduce the streaming. In the largest SEP events, the
so-called ground-level events (GLEs), we find proton energy spectra that
are peaked near ~10 MeV with the energy of similar peaks decreasing for
heavier ions and for smaller events. These spectra contrast sharply with
spectra near the time of shock passage which rise monotonically above
the plateau spectra with decreasing energy. We suggest that strong
suppression of upstream ion intensities near ~1 MeV amu-1
on the plateau occurs when those ions resonate with waves amplified
earlier by streaming protons of ~10 MeV and above. GLEs with much
lower intensities of 10-100 MeV protons on the plateau show spectra
of ions that rise monotonically toward low energies with no peaking
and no suppression of low-energy ions. Wave amplification by streaming
protons and the pitch-angle dependence of the resonance condition are
essential factors in our understanding of the limiting behavior.
Title: A Multi-spacecraft View of Solar-energetic-particle Onsets
in the 1977 November 22 Event
Authors: Reames, Donald V.; Lal, Nand
Bibcode: 2010ApJ...723..550R
Altcode:
We examine the onset timing of solar energetic particles in the large
ground-level event (GLE) of 1977 November 22 as observed from six
spacecraft at four distinct solar longitudes. In most cases, it was
possible to use velocity dispersion of the energetic protons to fix
the solar particle release (SPR) time and the path length traveled
by the initial particle burst from each solar longitude. We find
that the SPR times do depend upon solar longitude, being earliest for
spacecraft that are magnetically well connected to the source region,
and later for longitudes on the flanks of the outward-driven shock
wave. The earliest SPR time occurs well after peak photon emission
from the associated Hα flare. These observations are consistent with
conclusions derived from single-longitude observations of different
GLE events. They are consistent with shock acceleration over a broad
spatial region with heights rising, and/or shock speeds falling,
for longitudes on the flanks of the shock.
Title: Unusual time histories of galactic and anomalous cosmic rays
at 1 AU over the deep solar minimum of cycle 23/24
Authors: McDonald, Frank B.; Webber, William R.; Reames, Donald V.
Bibcode: 2010GeoRL..3718101M
Altcode:
The unusually quiet Sun of the cycle 23/24 solar minimum (that ended
in December, 2009) has resulted in lower values of the interplanetary
magnetic field and a slower approach of the tilt angle of the
heliospheric current sheet toward the solar equator than has been
observed for recent solar minima. As a result of these changes, the
time-histories of galactic and anomalous cosmic rays over this period
are very different from those of recent minima at the same phase of the
heliomagnetic cycle. Since ∼2005.6 there has been an on-going increase
in cosmic-ray intensity (except for one brief transient decrease)
that lasted for 4.4 years. The relative rigidity dependences of these
increases compared to previous cycles are complex and should provide
insight into the role of various solar and interplanetary phenomena
in the modulation process. The largest increase occurs in the nominal
“cross-over energy” region (where the modulation is essentially
the same for each minimum of the two past 22 year heliomagnetic cycles)
which extends from ∼200 MeV/n to >500 MeV/n.
Title: Remote Sensing of Magnetic-Cloud Topology
Authors: Reames, Donald V.
Bibcode: 2010SoPh..265..187R
Altcode: 2010SoPh..tmp...39R
We investigate the topology of magnetic clouds using energetic particles
from a variety of sources outside the clouds as probes to remotely
sense the interconnections of the magnetic field. We find that only a
small percentage of field lines in magnetic clouds are truly closed
directly to the Sun, so as to exclude particles from an external
source. Field lines that are open to the outer heliosphere must be
mixed with closed field lines on a fine spatial scale in the clouds
to explain the simultaneous observation of anomalous cosmic rays from
the outer heliosphere and of counter-streaming suprathermal electrons
from the corona. The results of this paper show that, given sufficient
time, particles accelerated at shock waves outside magnetic clouds
have access to the interior and to a wide region of solar longitude
in interplanetary space surrounding the clouds.
Title: The Deep Solar Minimum of Cycle 23/24: A New Look at the
Heliosphere and Solar Modulation
Authors: McDonald, F. B.; Webber, Bill; Reames, Donald; Stone, E. C.;
Cummings, A. C.; Heikkila, B. C.; Lal, N.
Bibcode: 2010cosp...38.1654M
Altcode: 2010cosp.meet.1654M
The Deep Solar Minimum of Cycle 23/24 (that apparently ended in
December, 2009) resulted in lower values of the interplanetary magnetic
field and a slower approach of the tilt angle of the heliospheric
current sheet to the lowest value observed in recent solar minima. As
a result of these unusual interplanetary conditions the time-histories
and intensities of galactic and anomalous cosmic rays over this period
are very different from those of previous solar minima at the same
phase of the heliomagnetic cycle -for example 200 MeV/n GCR He are 30
Title: Time Dependent Composition in Large Solar Energetic Particle
Events
Authors: Cohen, C. M.; Tylka, A. J.; Mason, G. M.; Mewaldt, R. A.;
Reames, D. V.
Bibcode: 2009AGUFMSH22A..01C
Altcode:
Temporal evolution in elemental abundance ratios in large solar
energetic particle (SEP) events has proven to be a powerful tool
in investigating interplanetary particle transport processes. In
particular, the Fe/O abundance measured at a common energy/nucleon (E/M)
typically decreases as a function of time in large SEP events. However,
it has been found that for some events originating in the western
solar hemisphere this time dependence lessens when the abundance
ratio is calculated using O measured at a higher E/M than Fe. Such
behavior may be the result of rigidity-dependent scattering processes
in the interplanetary medium. In this work, we examine the time
dependence of the Fe/O abundance in several large SEP events using
ratios calculated at many common and different E/M values between
0.3 and 80 MeV/nucleon. We will discuss the implications regarding
rigidity-dependent effects. In addition, we will present analysis of the
behavior of the He/H abundance where the charge states (and therefore,
the rigidities) of the elements are known.
Title: The Unusual Time History of Galactic an Anomalous Cosmic Rays
in the Heliosphere over the Deep Solar Minimum of Cycle 23/24
Authors: McDonald, F. B.; Webber, W. R.; Reames, D. V.; Stone, E. C.;
Cummings, A. C.; Heikkila, B. C.; Lal, N.
Bibcode: 2009AGUFM.U34A..07M
Altcode:
The continuing Quiet Sun of the cycle 23/24 solar minimum has resulted
in cosmic ray intensity time-histories at 1 AU that are very different
from those of the 1965 and 1987 solar minima at the same phase of
the 22 year heliomagnetic cycle. Instead of the sharp intensity peak
of these earlier cycles, the cosmic ray intensity displays a broad
plateau followed by an on-going increase that has now lasted for 1.4
years. Over the cycle 19 and 21 solar minima there was a suppression
of the cosmic ray intensity at rigidities below 0.5 GV while at neutron
monitor energies (72 GeV) the intensity was 3-5% higher than in qA>0
cycle. For cycle 23/24 in 2009.5 the 200 MeV/n He intensity is 25%
higher than its 1987 and the neutron monitor data from the North-West
University 4 Station Network is within 1.5% of those of 1987. However,
the intensity of 13.5 MeV/n ACR oxygen intensity is a factor of 2
below its 1987 level. These complex spectral differences are clearly
caused by the decrease in strength of the interplanetary field below
the level of previous minima and the relatively high inclination of
the heliospheric current sheet that persisted until ~ 2009.3 before
decreasing to lower values. In the heliosheath cosmic ray data from
Voyager 1 and 2 are showing significant increases that reflect the
changes that are occurring in the solar wind and magnetic fields in
the distant heliosphere. The relative behavior of 10 MeV GCR electrons
and 150-380 MeV/n He suggest these particles follow a different route
entering the heliosphere than the higher energy cosmic rays. At this
time the deep solar minimum is continuing so further changes in the
cosmic ray time histories can be expected.
Title: Solar Energetic-Particle Release Times in Historic Ground-Level
Events
Authors: Reames, Donald V.
Bibcode: 2009ApJ...706..844R
Altcode:
Ground-level events (GLEs) are large solar energetic-particle events
with sufficiently hard spectra for GeV protons to be detected by neutron
monitors at ground level. For each of 30 well-observed historic GLEs
from four solar cycles, extending back to 1973, I have plotted onset
times versus velocity-1 for particles observed on the IMP-7
and 8, ISEE-3, Wind, and GOES spacecraft and by neutron monitors. A
linear fit on such a plot for each GLE determines the initial solar
particle release (SPR) time, as the intercept, and the magnetic path
length traversed, as the slope, of the fitted line. Magnetic path
lengths and SPR times are well determined by the fits and cannot be
used as adjustable parameters to make particle and photon emission
times coincide. SPR times follow the onsets of shock-induced type
II radio bursts and the coronal height of the coronal mass ejection
(CME)-driven shock at SPR time can be determined for GLEs spanning an
interval of solar longitude of ~140 deg. For a given GLE, all particle
species and energies diverge from a single SPR point at a given coronal
height and footpoint longitude of the field line to the Earth. These
heights tend to increase with longitudinal distance away from the
source, a pattern expected for shock acceleration. Acceleration for
magnetically well-connected large GLEs begins at ~2 solar radii, in
contrast to non-GLEs that have been found to be strongly associated with
shocks above ~3 solar radii. The higher densities and magnetic field
strengths at lower altitudes may be responsible for the acceleration
of higher-energy particles in GLEs, while those GLEs that begin above
3R S may compensate by having higher shock speeds. These
results support the joint dependence of maximum particle energy on
magnetic field strength, injected particle density, and shock speed,
all predicted theoretically.
Title: Anomalous Cosmic Rays as Probes of Magnetic Clouds
Authors: Reames, D. V.; Kahler, S. W.; Tylka, A. J.
Bibcode: 2009ApJ...700L.196R
Altcode:
We report, for the first time, the observation near the Earth of
anomalous cosmic ray (ACR) particles throughout the interiors of
interplanetary magnetic clouds (MCs) at the same intensity as outside
the MCs. ACRs, accelerated in the outer heliosphere, have unique
elemental abundances making their identity unambiguous as they probe
these clouds from the outside. Thus, MCs, carried out from the Sun
by coronal mass ejections (CMEs), are seen to contain no structures
that are magnetically closed to the penetration of ions with energies
above a few MeV amu-1. As the MCs expand outward, they
must fill their increasing volume with ACRs dynamically, to the same
degree as neighboring "open" field lines. These observations cast
doubt on conventional ideas about the closed field topologies of
MCs and the cross-field transport of energetic particles. The ACR
observations conflict with some reports of significant exclusion
from MCs of solar energetic particles (SEPs) of comparable energy
and rigidity. A process that allows cross-field transport of ACRs may
also allow similar transport of SEPs late in events, causing the large
spatial extent and uniformity of SEPs in "invariant spectral regions"
extending far behind CME-driven shock waves.
Title: A Comparison of Elemental Abundance Ratios in Sep Events in
Fast and Slow Solar Wind Regions
Authors: Kahler, S. W.; Tylka, A. J.; Reames, D. V.
Bibcode: 2009ApJ...701..561K
Altcode:
The solar energetic (E > 1 MeV nucleon-1) particles
(SEPs) observed in gradual events at 1 AU are assumed to be accelerated
by coronal/interplanetary shocks from ambient thermal or suprathermal
seed particles. If so, then the elemental abundances of SEPs produced
in different solar wind (SW) stream types (transient, fast, and
slow) might be systematically distinguished from each other. We
look for these differences in SEP energy spectra and in elemental
abundance ratios (including Mg/Ne and Fe/C, which compare low/high
first ionization potential elements), in a large number of SEP time
intervals over the past solar cycle. The SW regions are characterized
by the three-component stream classification of Richardson et al. Our
survey shows no significant compositional or energy spectral differences
in the 5-10 MeV nucleon-1 range for SEP events of different
SW stream types. This result extends the earlier finding that SEP events
are observed frequently in fast SW streams, although their higher Alfven
and SW flow speeds should constrain SEP production by coronal mass
ejection-driven shocks in those regions. We discuss the implications
of our results for shock seed populations and cross-field propagation.
Title: Observational Evidence on the Presence of an Outer Reflecting
Boundary in Solar Energetic Particle Events
Authors: Tan, Lun C.; Reames, Donald V.; Ng, Chee K.; Saloniemi,
Oskari; Wang, Linghua
Bibcode: 2009ApJ...701.1753T
Altcode:
We have focused primarily on the 2001 September 24 solar energetic
particle (SEP) event to verify previous indications of the presence
of an outer reflecting boundary of SEPs. By using energetic electron
and ion data obtained from multi-spacecraft observations, we have
identified a collimated particle beam consisting of reflected particles
returning from an outer boundary. The peak of reflected particles
appears before the arrival of particles at 90° pitch angle. In
addition, an onset time analysis is carried out in order to determine
parameters characterizing the boundary. Our analysis suggests that the
presence of a counter-streaming particle beam with a deep depression
at ~90° pitch angle during the onset phase is evidence for a nearby
reflecting boundary. We have compared this property in the SEP events
of 2002 April 21 and August 24. A reflecting boundary that blocks a
flux tube is important in space weather forecasting since it can cause
the "reservoir" effect that may enhance the intensity and duration of
high-energy particles.
Title: The Solar Energetic Particle Event of 14 December 2006
Authors: von Rosenvinge, T. T.; Richardson, I. G.; Reames, D. V.;
Cohen, C. M. S.; Cummings, A. C.; Leske, R. A.; Mewaldt, R. A.; Stone,
E. C.; Wiedenbeck, M. E.
Bibcode: 2009SoPh..256..443V
Altcode:
The solar energetic particle event on 14 December 2006 was observed
by several near-Earth spacecraft including the Advanced Composition
Explorer (ACE), STEREO A and B, SOHO and Wind. An interesting feature
of this event is a series of unusual fluctuations in the particle
intensity that occurred during the first few hours. These fluctuations
were observed inside a magnetic cloud that originated in a solar
event on 13 December and show both similarities and variations at the
different spacecraft. Interestingly, the most striking difference is
between observations at the two closely-separated STEREO spacecraft. In
particular, large fluctuations in the proton intensity were seen by the
High Energy Telescope (HET) on STEREO A, and to a lesser extent at Wind
and ACE, but not by the STEREO B HET. We conclude that the differences
in intensity-time profiles were caused by anisotropies in the particle
distribution and the different viewing directions of the individual
particle telescopes. The intensity/anisotropy variations suggest that
flux tubes with different particle propagation conditions existed
within this magnetic cloud despite the absence of local magnetic field
signatures associated with these regions. The intensity fluctuations are
similar to those occasionally seen in impulsive particle events. There
were also spacecraft-to-spacecraft differences during the onset of
the particle event. An initial rapid onset of energetic (> 40
MeV) protons was observed by the STEREO A and B spacecraft outside
the magnetic cloud, but not by spacecraft such as SOHO that were
already inside the magnetic cloud at this time. The latter spacecraft
observed a slower, lower intensity increase. Evidently, energetic
proton propagation from the solar event to the vicinity of Earth was
inhibited within the magnetic cloud compared to outside.
Title: Solar Release Times of Energetic Particles in Ground-Level
Events
Authors: Reames, Donald V.
Bibcode: 2009ApJ...693..812R
Altcode:
We study the onset times of energetic particles of various species
and velocities, v, in large solar energetic particle events with
sufficiently hard spectra that are seen by neutron monitors at ground
level. Observations of He, O, and Fe from the Wind spacecraft provide
especially well-defined sequences of onset times, and data from
IMP-8, GOES, and neutron monitors contribute importantly at higher
energies. Plotting onset times versus v -1 yields a line
with the initial solar particle release (SPR) time as the intercept
and the magnetic path length as the slope. We find consistent results
for 13 of the 16 ground-level events that occurred from 1994 to 2007,
in solar cycle 23. Path lengths vary from 1.1 to 2.2 AU in the 13
events. In all of the events, SPR times occur after the onset of the
shock wave-induced type II radio emission. Events with well-defined SPR
times are found over a wide span of solar longitude, suggesting that
all ion species and energies are released together, even far from the
source longitude, with no evidence of energy- or rigidity-dependent
coronal transport. If the SPR time is converted to a radial distance
of the source shock wave from the Sun and plotted against longitude,
acceleration for well-connected events is found to begin at 2-4 solar
radii over a longitude span of ~ 100° and to rise to greater heights
only at longitudes more distant from the source, as would be expected
from shock-acceleration models.
Title: Exploring the global shock scenario at multiple points
between sun and earth: The solar transients launched on January 1
and September 23, 1978
Authors: Berdichevsky, D. B.; Reames, D. V.; Wu, C. -C.; Schwenn, R.;
Lepping, R. P.; MacDowall, R. J.; Farrugia, C. J.; Bougeret, J. -L.;
Ng, C.; Lazarus, A. J.
Bibcode: 2009AdSpR..43..113B
Altcode:
We revisit the transient interplanetary events of January 1 and
September 23, 1978. Using in-situ and remote sensing observations at
locations widely separated in longitudes and distances from the Sun,
we infer that in both cases the overall shock surface had a very fast
“nose” region with speeds >900 and >1500 km-1
in the January and September events, respectively, and much slower
flank speeds (∼600 km-1 or less), suggesting a shock
surface with a strong speed gradient with heliospheric longitude. The
shock-nose regions are thus likely efficient acceleration sites of MeV
ions, even at 1 AU from the Sun. Our 3D magnetohydrodynamics modeling
suggests that a 24° × 24° localized disturbance at 18 solar radii
injecting momentum 100 times the background solar wind input over 1
h can produce a disturbance in semi-quantitative agreement with the
observed shock arrival time, plasma density and velocity time series
in the January 1978 event.
Title: Role of Self-Amplified Waves in Coronal Shock Acceleration
Authors: Ng, C. K.; Reames, D. V.
Bibcode: 2008AGUFMSH23C..06N
Altcode:
Solar-energetic-proton (SEP) acceleration at a parallel shock is modeled
with self-consistent Alfvén-wave excitation and shock transmission. 18
- 50 keV seed protons at 0.001 plasma proton density are accelerated
in 10 minutes to a power-law intensity spectrum rolling over at ~
300 MeV by a 2500 km/s shock launched from 3.5 solar radii in typical
coronal condition with low ambient wave intensity. Scattering of large
pitch-angle high-energy SEPs by waves amplified by small pitch-angle
low-energy SEPs bootstraps the acceleration. The rapid acceleration
is inappreciably retarded by wavenumber shift of shock-transmitted
Alfvén waves or by the interaction of sunward streaming SEPs
with downstream waves. There is no significant second-order Fermi
acceleration. SEP acceleration beyond the 'knee' energy proceeds
from large to small pitch-angles, for gyroresonant wave-particle
interaction at k ~ B/(μ P). B is magnetic field, k wavenumber, P
rigidity and μ pitch-cosine. Classical mean-free-path is inapplicable
in this time-dependent process. Using the above μ-dependent resonant
condition to calculate wave-growth rates but the 'sharpened' condition
k ~ B/P to calculate μ-scattering rates underestimates scattering
by self-amplified waves, giving little acceleration (Berezhko et al
1998). Using k ~ B/P to calculate wave-growth and scattering rates
(Vainio & Laitinen 2007) is consistent but incorrectly requires the
SEPs to amplify unique waves from the weak ambient state. In contrast,
true gyroresonant interaction must 'relay' the influence of amplified
waves from low-P large-μ SEPs to high-P low-μ SEPs, leading to fast
acceleration. Model results will be presented and dependence on model
parameters will be discussed.
Title: The Unusual Time History of Galactic and Anomalous Cosmic
Rays at 1 AU over the Solar Minimum of Cycle 23
Authors: McDonald, F. B.; Webber, W. R.; Reames, D. V.
Bibcode: 2008AGUFMSH21C..06M
Altcode:
Studies of the galactic cosmic rays temporal variations (GCRs) over
the "Modern Era" (from 1950s) establish the existence of a 22-year
cosmic ray modulation cycle that is dominated by the 11-year solar
activity cycle but is significantly influenced by gradient and curvature
drifts in the interplanetary magnetic field (IPB) in association with
changes in the tilt of the heliospheric neutral current sheet over
the heliomagnetic cycle. In qA<0 epochs (when positive ions flow in
along the neutral sheet and out over the solar poles), the solar minimum
cosmic rays intensity is peaked over a period of several months (1965,
1987) in contrast to the 3 - 4 year plateau periods for qA>0 minima
when the flow pattern is reversed. However, for 200 MeV/n GCR HE at 1
AU there is a quasi-plateau region for the cycle 23 solar minimum that
now extends over some 12 months. The intensity level of this component
is essentially the same as that of 1965 and 1987, as is the large
depression of anomalous cosmic ray ACR He (10 - 40 MeV/n) relative to
the qA>0 minima. There appears to be two different solar effects,
the current sheet tilt in 2007 is less than in 1987 while the magnitude
of the 1P B field is at its lowest value since essentially continuous
measurements began in 1963. These will have off-setting effects on the
GCR intensity. 10 Be and 14 C studies have shown that previous epochs of
low solar activity [Oort (1050 AD); Spoerer (1420-1540); and Maunder
(1615-1715)] have been marked by high cosmic ray intensity. There
were other periods of reduced solar activity [Wolf (1320) and Dalton
(1810)] which were associated with more moderate enhancements of the
GCR intensity. Studies using data from the Cosmic Ray Network [IMP,
ACE, neutron monitors at 1 AU, and Pioneer, Voyager, and Ulysses at
greater heliocentric distances] are providing a better understanding
of the solar phenomena that produce the cosmic ray modulation and
should lead to an understanding of the solar changes in the distant
past associated with the epochs of enhanced GCR intensity.
Title: Shock Acceleration of Solar Energetic Protons: The First
10 Minutes
Authors: Ng, C. K.; Reames, D. V.
Bibcode: 2008ApJ...686L.123N
Altcode:
Proton acceleration at a parallel coronal shock is modeled with
self-consistent Alfvén wave excitation and shock transmission. 18-50
keV seed protons at 0.1% of plasma proton density are accelerated
in 10 minutes to a power-law intensity spectrum rolling over at 300
MeV by a 2500 km s-1 shock traveling outward from 3.5
r⊙, for typical coronal conditions and low ambient wave
intensities. Interaction of high-energy protons of large pitch angles
with Alfvén waves amplified by low-energy protons of small pitch angles
is key to rapid acceleration. Shock acceleration is not significantly
retarded by sunward streaming protons interacting with downstream
waves. There is no significant second-order Fermi acceleration.
Title: SEP Acceleration by Traveling Coronal Shock
Authors: Ng, C. K.; Reames, D. V.; Tylka, A. J.
Bibcode: 2008AGUSMSH41A..09N
Altcode:
We present simulations from a numerical model of
solar-energetic-particle (SEP) acceleration at a coronal-
mass-ejection-driven shock traveling through the solar corona. The
model includes full pitch-angle dependence, self-consistent resonant
wave-particle interaction, focusing, convection, adiabatic deceleration,
wave propagation and wave transmission at shock. The model is solved
with a new accurate finite-difference method. Outward streaming
SEPs amplify upstream outward Alfvén waves, which are further
enhanced by the wave transmission process as they travel downstream
of the advancing shock. The explosively growing waves bootstrap SEP
acceleration. However, shock accelerated SEPs also stream downstream,
damping outward waves and enhancing inward waves there. Particles
scattered between upstream outward waves and downstream inward waves
experience less compression than SEPs scattered between upstream
outward waves and downstream outward waves. Thus SEPs streaming
inward downstream tend to slow shock acceleration and to produce
a softer SEP energy spectrum. We will illustrate these opposing
processes with computed results and discuss how SEP acceleration
depends on model assumptions and physical parameters, e.g., shock
speed, Alfvén speed, ambient wave intensity, seed particle energy and
density. Acknowledgment: this work was supported by NASA LWS04-0000-0076
and SHP04-0016-0024.
Title: A Comparison of Elemental Abundance Ratios in SEP Events in
Fast and Slow Solar Wind Regions
Authors: Kahler, S.; Tylka, A.; Reames, D.
Bibcode: 2008AGUSMSH43C..01K
Altcode:
The solar energetic (E > 1 MeV) particles (SEP) observed in gradual
events at 1 AU are generally assumed to be accelerated from ambient
suprathermal particles. If so, then the elemental abundances of SEPs
produced in fast wind regions might be systematically distinguished
from the abundances of those from slow wind regions. We look for these
differences using the Mg/Ne ratios in a large number of SEP events
from the past solar cycle. The solar wind regions are characterized
by O7/O6 ratios and by the three-component wind stream classification
of Richardson et al. (JGR, 2002). The Mg/Ne ratio provides a low/high
first ionization potential (FIP) element ratio with comparable particle
rigidities to minimize propagation effects. Our initial survey shows no
significant differences in the 5-10 MeV/nucleon range for fast and slow
wind SEP events. This result supplements the earlier finding that SEP
events are observed frequently in fast wind and are not associated with
unusually higher CME speeds, although the higher Alfven and solar wind
flow speeds in fast wind regions should mitigate against the production
of CME-driven shocks in those regions. We discuss the implications of
our results for shock seed populations and cross-field propagation. AJT
was supported by the Office of Naval Research and NASA DPR NNG06EC55I.
Title: Ion Anisotropy and High-Energy Variability of Large Solar
Particle Events: A Comparative Study
Authors: Tan, Lun C.; Reames, Donald V.; Ng, Chee K.
Bibcode: 2008ApJ...678.1471T
Altcode:
We have made comparative studies of ion anisotropy and high-energy
variability of solar energetic particle (SEP) events previously examined
by the Solar, Heliospheric, and Interplanetary Environment (SHINE)
Workshop campaign. We have found distinctly different characteristics of
SEPs in two large "gradual" events having very similar solar progenitors
(the 2002 April 21 and August 24 events). Since the scattering centers
of SEPs are approximately frozen in the solar wind, we emphasize
work in the solar-wind frame, where SEPs tend to be isotropized and
small anisotropies are easier to detect. While in the August event
no streaming reversal occurred, in the April event the field-aligned
anisotropy of all heavy ions showed signs of streaming reversal. The
difference in streaming reversal was consistent with the difference in
the presence of the outer reflecting boundary. In the April event the
magnetic mirror, which was located behind the interplanetary shock
driven by the preceding coronal mass ejection (CME), could block
the stream of SEPs, while in the August event SEPs escaped freely in
the absence of any nearby boundary. The magnetic mirror was formed
at the bottleneck of magnetic field lines draped around a flank of
the preceding CME. In previous SHINE event analysis, the contrasting
event durations and Fe/O ratios of the both events were explained as
the interplay between shock geometry and seed population. Our new
findings, however, indicate that event duration and time, as well
as spectral variation, are also affected by the presence of a nearby
reflecting boundary.
Title: The High Energy Telescope for STEREO
Authors: von Rosenvinge, T. T.; Reames, D. V.; Baker, R.; Hawk,
J.; Nolan, J. T.; Ryan, L.; Shuman, S.; Wortman, K. A.; Mewaldt,
R. A.; Cummings, A. C.; Cook, W. R.; Labrador, A. W.; Leske, R. A.;
Wiedenbeck, M. E.
Bibcode: 2008SSRv..136..391V
Altcode: 2008SSRv..tmp...20V
The IMPACT investigation for the STEREO Mission includes a complement
of Solar Energetic Particle instruments on each of the two STEREO
spacecraft. Of these instruments, the High Energy Telescopes (HETs)
provide the highest energy measurements. This paper describes the
HETs in detail, including the scientific objectives, the sensors,
the overall mechanical and electrical design, and the on-board
software. The HETs are designed to measure the abundances and energy
spectra of electrons, protons, He, and heavier nuclei up to Fe in
interplanetary space. For protons and He that stop in the HET, the
kinetic energy range corresponds to ∼13 to 40 MeV/n. Protons that
do not stop in the telescope (referred to as penetrating protons)
are measured up to ∼100 MeV/n, as are penetrating He. For stopping
He, the individual isotopes 3He and 4He can be
distinguished. Stopping electrons are measured in the energy range
∼0.7 6 MeV.
Title: Theoretical modeling for the stereo mission
Authors: Aschwanden, Markus J.; Burlaga, L. F.; Kaiser, M. L.; Ng,
C. K.; Reames, D. V.; Reiner, M. J.; Gombosi, T. I.; Lugaz, N.;
Manchester, W.; Roussev, I. I.; Zurbuchen, T. H.; Farrugia, C. J.;
Galvin, A. B.; Lee, M. A.; Linker, J. A.; Mikić, Z.; Riley, P.;
Alexander, D.; Sandman, A. W.; Cook, J. W.; Howard, R. A.; Odstrčil,
D.; Pizzo, V. J.; Kóta, J.; Liewer, P. C.; Luhmann, J. G.; Inhester,
B.; Schwenn, R. W.; Solanki, S. K.; Vasyliunas, V. M.; Wiegelmann, T.;
Blush, L.; Bochsler, P.; Cairns, I. H.; Robinson, P. A.; Bothmer,
V.; Kecskemety, K.; Llebaria, A.; Maksimovic, M.; Scholer, M.;
Wimmer-Schweingruber, R. F.
Bibcode: 2008SSRv..136..565A
Altcode: 2006SSRv..tmp...75A
We summarize the theory and modeling efforts for the STEREO mission,
which will be used to interpret the data of both the remote-sensing
(SECCHI, SWAVES) and in-situ instruments (IMPACT, PLASTIC). The
modeling includes the coronal plasma, in both open and closed magnetic
structures, and the solar wind and its expansion outwards from the Sun,
which defines the heliosphere. Particular emphasis is given to modeling
of dynamic phenomena associated with the initiation and propagation
of coronal mass ejections (CMEs). The modeling of the CME initiation
includes magnetic shearing, kink instability, filament eruption, and
magnetic reconnection in the flaring lower corona. The modeling of CME
propagation entails interplanetary shocks, interplanetary particle
beams, solar energetic particles (SEPs), geoeffective connections,
and space weather. This review describes mostly existing models of
groups that have committed their work to the STEREO mission, but is by
no means exhaustive or comprehensive regarding alternative theoretical
approaches.
Title: STEREO IMPACT Investigation Goals, Measurements, and Data
Products Overview
Authors: Luhmann, J. G.; Curtis, D. W.; Schroeder, P.; McCauley, J.;
Lin, R. P.; Larson, D. E.; Bale, S. D.; Sauvaud, J. -A.; Aoustin, C.;
Mewaldt, R. A.; Cummings, A. C.; Stone, E. C.; Davis, A. J.; Cook,
W. R.; Kecman, B.; Wiedenbeck, M. E.; von Rosenvinge, T.; Acuna,
M. H.; Reichenthal, L. S.; Shuman, S.; Wortman, K. A.; Reames, D. V.;
Mueller-Mellin, R.; Kunow, H.; Mason, G. M.; Walpole, P.; Korth, A.;
Sanderson, T. R.; Russell, C. T.; Gosling, J. T.
Bibcode: 2008SSRv..136..117L
Altcode:
The IMPACT (In situ Measurements of Particles And CME Transients)
investigation on the STEREO mission was designed and developed to
provide multipoint solar wind and suprathermal electron, interplanetary
magnetic field, and solar energetic particle information required to
unravel the nature of coronal mass ejections and their heliospheric
consequences. IMPACT consists of seven individual sensors which are
packaged into a boom suite, and a SEP suite. This review summarizes
the science objectives of IMPACT, the instruments that comprise
the IMPACT investigation, the accommodation of IMPACT on the STEREO
twin spacecraft, and the overall data products that will flow from
the IMPACT measurements. Accompanying papers in this volume of Space
Science Reviews highlight the individual sensor technical details and
capabilities, STEREO project plans for the use of IMPACT data, and
modeling activities for IMPACT (and other STEREO) data interpretation.
Title: The High Energy Telescopes for the STEREO Mission
Authors: von Rosenvinge, T. T.; Cummings, A. C.; Leske, R. A.; Mewaldt,
R. A.; Reames, D. V.; Stone, E. C.; Wiedenbeck, M. E.
Bibcode: 2008ICRC....1..103V
Altcode: 2008ICRC...30a.103V
We describe the High Energy Telescopes (HETs), which are part of the
IMPACT investigation for the STEREO mission (Principal Investigator:
Janet Luhmann, University of California at Berkeley). The two STEREO
spacecraft were launched from Cape Canaveral, FL on October 25,
2006. High energy electrons (~ 0.7 -6 MeV) and nuclei from hydrogen
to iron (~ 13 - 200 MeV/nucleon) are detected by the HETs, one on
each spacecraft. Observations from one pass through the Earth’s
magnetosphere and from four X-class solar events in December,
2006 are presented to illustrate the capabilities of the HETs. The
HET observations are also compared with observations from other
spacecraft. The event of December 13th was the first Ground Level
Event in almost two years. We will compare the elemental composition
of this event with that of the previous Ground Level Event on January
20, 2005. This work was supported by NASA (at Caltech and JPL under
contract NAS5-00133 and grant NAG5-12929).
Title: Bulk Flow Velocity and First-Order Anisotropy of Solar
Energetic Particles Observed on the Wind Spacecraft: Overview of Three
``Gradual'' Particle Events
Authors: Tan, Lun C.; Reames, Donald V.; Ng, Chee K.
Bibcode: 2007ApJ...661.1297T
Altcode:
We have developed techniques to calculate bulk flow velocity and
first-order anisotropy of solar energetic particles (SEPs) with MeV
nucleon-1 energies as recorded on the Wind spacecraft. Using
the techniques we selected and analyzed three gradual SEP events having
different solar longitudes. Since upstream of interplanetary (IP)
shocks during our selected events the interplanetary magnetic field is
nearly perpendicular to the solar wind, the diffusive transport of SEPs
along the magnetic field line is conveniently decoupled from solar-wind
streaming. We present the bulk flow velocity measurements of H, He, O,
and Fe ions at different energies. In two of the three events studied,
it is seen that the flow directions of heavy ions reverse in sequence,
i.e., faster ions reverse their direction earlier. Several hours
before the IP shock passage, the bulk flows of all heavy ions become
opposite to the proton flow. Thus, in the upstream region we mainly
observe shock-accelerated protons that continue to flow away from
the shock, while higher rigidity heavy ions predominantly come from
strong acceleration near the Sun. The reversed ion direction appears
also to involve a reflecting boundary beyond 1 AU, from which higher
velocity ions return earlier. The preferred geometry of the selected
2001 September 24 event also allows us to determine the propagating
direction of proton-generated Alfvén waves based on flow velocity
measurements of heavy ions.
Title: Recent Results of the 2005 LWS TR&T Focus Team for Solar
Energetic Particles
Authors: Desai, M. I.; Cohen, C. M.; Smith, C. W.; Lee, M. A.;
Litvinenko, Y.; Reames, D. V.; Ng, C. K.; Tylka, A. J.; Kota, J.;
Giacalone, J.; Jokipii, J. R.; Sokolov, I.; Gombosi, T.; Roussev,
I. I.; Li, G.; Zank, G. P.; Tessein, J.
Bibcode: 2006AGUFMSH23C..03D
Altcode:
Shock waves driven by coronal mass ejections are presently believed
to be responsible for producing large gradual solar energetic
particle (SEP) events that can pose significant radiation hazard
for humans and technological systems near Earth. However, our
present ability to accurately predict various properties of SEP
events (e.g., peak intensities, energy spectra, and composition)
is somewhat limited. Reliable prediction of these properties depends
on a multitude of observational and theoretical cross-disciplinary
studies that include: (1) Understanding and modeling the initiation and
propagation of fast CMEs and the evolution of shock characteristics
as they travel through the corona and interplanetary medium, (2)
Characterizing the ambient coronal and solar wind plasma, the solar
and interplanetary magnetic field, and the suprathermal ion population
through which the CMEs and their shocks propagate en route to Earth,
and (3) Developing a detailed understanding of particle injection and
acceleration at CME-driven shocks and their subsequent transport out
to 1 AU. Such studies are being routinely conducted both, individually
and collectively by members of the 2005 LWS TR&T Focus Team for
SEPs. In this talk we will summarize the SEP Team's ongoing efforts,
highlight the key new results, and discuss some of the main scientific
challenges that we need to overcome in order to improve current
understanding of the physical processes occurring in large SEP events.
Title: Bulk Flow Velocity and First-Order Anisotropy of Solar
Energetic Particles Observed on Wind Spacecraft
Authors: Tan, L. C.; Reames, D. V.; Ng, C. K.
Bibcode: 2006AGUFMSH43B1515T
Altcode:
We have developed a technique to calculate the bulk flow velocity
and first-order anisotropy of solar energetic particles (SEPs) with
MeV per nucleon energies. Using the technique we have selected and
analyzed three "gradual" SEP events recorded by the Low-Energy Matrix
Telescope (LEMT) of the Energetic Particles: Acceleration, Composition,
and Transport experiment (EPACT) on the Wind spacecraft. Since in
our selected events, the interplanetary magnetic field upstream of
interplanetary (IP) shock is nearly perpendicular to the solar-wind
velocity, the effect of SEP scattering centers can be clearly
discerned. From the observations of H, He, O, and Fe ions at different
energies, we find that upstream of IP shock the bulk flow direction
of heavy ions is opposite to that of protons. In addition, the ion
velocity/rigidity dependence of the first-order anisotropy of SEPs is
different between the onset and the upstream region. The implication
of our observations will be discussed.
Title: The Disappearance of Large, Fe-Rich Solar Energetic Particle
Events in the Declining Phase of Cycle 23: Implications for the Role
of Flares
Authors: Dietrich, W. F.; Tylka, A. J.; Cliver, E. W.; Cohen, C. M.;
Mewaldt, R. A.; Reames, D. V.
Bibcode: 2006AGUFMSH41B..03D
Altcode:
Solar energetic particle (SEP) events are generally divided into two
categories, "gradual" and "impulsive". corresponding, respectively, to
acceleration by shocks driven by fast coronal mass ejections (CMEs) or
acceleration at sites associated with flares, probably through resonant
wave-particle interactions following magnetic reconnection. One of the
defining distinctions between the two types is the event-integrated
Fe/O ratio, with gradual events at a few MeV/nucleon exhibiting
typical coronal values while impulsive events generally show strong
enhancements. But the precise, comprehensive observations from a fleet
of new spacecraft at the start of Cycle 23 immediately challenged this
neat picture: Fe/O ratios generally varied with energy, and a large
fraction of the nominally "gradual" events, when observed at energies
above the few MeV/nucleon where the two categories were originally
developed, showed enhanced Fe/O ratios approaching those typically
associated with impulsive events. In 1997-2002, 13 out of the 38 very
large SEP events (identified by >30 MeV proton fluence above 2 x
105/cm2-sr) had an Fe/O ratio above 30 MeV/nucleon that was at least
four times the nominal coronal value. But in 2003-2005, zero out of the
20 events satisfying the same selection criterion displayed comparably
large Fe/O enhancements. This dramatic shift clearly indicates that
the condition(s) that allow flares to contribute to large SEP events
have changed in some fundamental way in the declining phase of Cycle
23. In particular, three hypotheses (direct-flare; shock- acceleration
of escaping suprathermals from the accompanying flare; or shock
acceleration of remnant suprathermals from previous flare activity)
have been proposed in order to explain the flare-like composition seen
at high energies in some large gradual events. Based on comparisons
of the reported flare, CME, and suprathermal characteristics in the
two time periods, we show that the third hypothesis appears to be most
likely to be able to accommodate the late-Cycle disappearance of the
large Fe-rich events. We also examine open issues surrounding this
explanation that Sentinels will be able to address.
Title: Solar Sources of Impulsive Solar Energetic Particle Events
and Their Magnetic Field Connection to the Earth
Authors: Nitta, Nariaki V.; Reames, Donald V.; De Rosa, Marc L.; Liu,
Yang; Yashiro, Seiji; Gopalswamy, Natchimuthuk
Bibcode: 2006ApJ...650..438N
Altcode:
This paper investigates the solar origin of impulsive solar energetic
particle (SEP) events, often referred to as 3He-rich flares,
by attempting to locate the source regions of 117 events as observed
at ~2-3 MeV amu-1. Given large uncertainties as to when
ions at these energies were injected, we use type III radio bursts
that occur within a 5 hr time window preceding the observed ion onset,
and search in EUV and X-ray full-disk images for brightenings around
the times of the type III bursts. In this way we find the solar sources
in 69 events. High cadence EUV images often reveal a jet in the source
region shortly after the type III burst. We also study magnetic field
connections between the Earth and the solar sources of impulsive SEP
events as identified above, combining the potential field source
surface (PFSS) model for the coronal field and the Parker spiral
for the interplanetary magnetic field. We find open field lines in
and around ~80% of the source regions. But only in ~40% of the cases,
can we find field lines that are both close to the source region at the
photosphere and to the Parker spiral coordinates at the source surface,
suggesting challenges in understanding the Sun-Earth magnetic field
with observations available at present and in near future.
Title: A Comparative Study of Ion Characteristics in the Large Gradual
Solar Energetic Particle Events of 2002 April 21 and 2002 August 24
Authors: Tylka, A. J.; Cohen, C. M. S.; Dietrich, W. F.; Lee, M. A.;
Maclennan, C. G.; Mewaldt, R. A.; Ng, C. K.; Reames, D. V.
Bibcode: 2006ApJS..164..536T
Altcode:
Solar energetic particles (SEPs) provide an opportunity to study in
detail the processes of particle acceleration and transport that are
ubiquitous in astrophysical plasmas. Tylka et al. focused on the problem
of SEP spectral and compositional variability at energies above a few
tens of MeV per nucleon. They motivated their study with two large,
gradual SEP events, 2002 April 21 and 2002 August 24, which have
similar fast coronal mass ejections (CMEs) and flares but nevertheless
illustrate the extremes of high-energy behavior. In this paper, we
present additional detailed comparisons between the ion characteristics
of these events. These results should be helpful in developing and
testing new SEP models, which are currently under development.
Title: Shock Geometry, Seed Populations, and the Origin of Variable
Elemental Composition at High Energies in Large Gradual Solar
Particle Events
Authors: Tylka, A. J.; Cohen, C. M. S.; Dietrich, W. F.; Lee, M. A.;
Maclennan, C. G.; Mewaldt, R. A.; Ng, C. K.; Reames, D. V.
Bibcode: 2005ApJ...625..474T
Altcode:
Above a few tens of MeV per nucleon, large, gradual solar
energetic particle (SEP) events are highly variable in their
spectral characteristics and elemental composition. The origin
of this variability has been a matter of intense and ongoing
debate. In this paper, we propose that this variability arises
from the interplay of two factors-shock geometry and a compound
seed population, typically comprising both solar-wind and flare
suprathermals. Whereas quasi-parallel shocks generally draw their
seeds from solar-wind suprathermals, quasi-perpendicular shocks-by
requiring a higher initial speed for effective injection-preferentially
accelerate seed particles from flares. Solar-wind and flare seed
particles have distinctive compositional characteristics, which are
then reflected in the accelerated particles. We first examine our
hypothesis in the context of particles locally accelerated near 1 AU
by traveling interplanetary shocks. We illustrate the implications
of our hypothesis for SEPs with two very large events, 2002 April 21
and 2002 August 24. These two events arise from very similar solar
progenitors but nevertheless epitomize extremes in high-energy SEP
variability. We then test our hypothesis with correlation studies
based on observations of 43 large SEP events in 1997-2003 by the
Advanced Composition Explorer, Wind, the Interplanetary Monitoring
Platform 8, and GOES. We consider correlations among high-energy Fe/O,
event size, spectral characteristics, the presence of GeV protons,
and event duration at high energies. The observed correlations are
all qualitatively consistent with our hypothesis. Although these
correlation studies cannot be construed as proof of our hypothesis,
they certainly confirm its viability. We also examine the alternative
hypothesis in which a direct flare component-rather than flare particles
subsequently processed through a shock-dominates at high energies. This
alternative would produce compositional characteristics similar to
those of our hypothesis. However, the observed longitude distribution
of the enhanced Fe/O events, their spectral characteristics, and
recent timing studies all pose serious challenges for a direct flare
component. We also comment on measurements of the mean ionic charge
state of Fe at high energies. We conclude that shock geometry and
seed population potentially provide a framework for understanding
the overall high-energy variability in large SEP events. We suggest
additional studies for testing this hypothesis.
Title: IMPACT: Science goals and firsts with STEREO
Authors: Luhmann, J. G.; Curtis, D. W.; Lin, R. P.; Larson, D.;
Schroeder, P.; Cummings, A.; Mewaldt, R. A.; Stone, E. C.; Davis, A.;
von Rosenvinge, T.; Acuna, M. H.; Reames, D.; Ng, C.; Ogilvie, K.;
Mueller-Mellin, R.; Kunow, H.; Mason, G. M.; Wiedenbeck, M.; Sauvaud,
A.; Aoustin, C.; Louarn, P.; Dandouras, J.; Korth, A.; Bothmer, V.;
Vasyliunas, V.; Sanderson, T.; Marsden, R. G.; Russell, C. T.; Gosling,
J. T.; Bougeret, J. L.; McComas, D. J.; Linker, J. A.; Riley, P.;
Odstrcil, D.; Pizzo, V. J.; Gombosi, T.; DeZeeuw, D.; Kecskemety, K.
Bibcode: 2005AdSpR..36.1534L
Altcode:
The in situ measurements of particles and CME transients (IMPACT)
investigation on the twin STEREO spacecraft focuses on the solar
energetic particle, solar wind and suprathermal electron, and magnetic
field measurements needed to address STEREO's goals. IMPACT will provide
regular, identical, in situ multipoint measurements bracketing Earth
as each spacecraft separates from it at a rate of ∼22°/yr along
Earth's orbit. Combined with the PLASTIC and SWAVES investigations,
IMPACT fills a critical role in the STEREO quest to connect SECCHI's
3D coronal images to their interplanetary consequences.
Title: Solar Flare Nuclear Gamma Rays and Energetic Particles in
Space, 1980-198
Authors: Cliver, E. W.; Vestrand, W. T.; Reames, D. V.
Bibcode: 2005ICRC....1...53C
Altcode: 2005ICRC...29a..53C
No abstract at ADS
Title: The Solar Energetic Particle Event of 16 August 2001: ~
400 MeV Protons Following an Eruption at ~ W180
Authors: Cliver, E. W.; Thompson, B. J.; Lawrence, G. R.; Zhukov,
A. N.; Tylka, A. J.; Dietrich, W. F.; Reames, D. V.; Reiner, M. J.;
MacDowall, R . J.; Kosovichev, A. G.; Ling, A. G.
Bibcode: 2005ICRC....1..121C
Altcode: 2005ICRC...29a.121C
No abstract at ADS
Title: Association of Coronal Mass Ejections and Type II Radio Bursts
with Impulsive Solar Energetic Particle Events
Authors: Yashiro, S.; Gopalswamy, N.; Cliver, E. W.; Reames, D. V.;
Kaiser, M. L.; Howard, R. A.
Bibcode: 2004ASPC..325..401Y
Altcode:
We report the association of impulsive solar energetic particle (SEP)
events with coronal mass ejections (CMEs) and metric type II radio
bursts. We identified 38 impulsive SEP events using the WIND/EPACT
instrument and their CME association was investigated using white
light data from SOHO/LASCO. We found that (1) at least ∼ 28--39 % of
impulsive SEP events were associated with CMEs, (2) only 8--13 % were
associated with metric type II radio bursts. The statistical properties
of the associated CMEs were investigated and compared with those of
general CMEs and CMEs associated with large gradual SEP events. The
CMEs associated with impulsive SEP events were significantly slower
(median speed of 613 kmps) and narrower (49 deg) than those of CMEs
associated with large gradual SEP events (1336 kmps, 360 deg), but
faster than the general CMEs (408 kmps).
Title: The unusual signatures at and near 2018 UT (Wind in situ
observations) of the travelling, fast forward interplanetary shock
on September 25, 2001
Authors: Berdichevsky, D. B.; Desch, M. D.; Lepping, R. P.; Larson,
D. E.; Lin, R.; Kasper, J.; Nagai, T.; Reames, D. V.
Bibcode: 2004AGUFMSH33A1197B
Altcode:
We show that at 2018 UT on September 25, 2001, a velocity discontinuity
of [-300, -200, -200] kms-1 (in GSE coordinates) passes Wind. However,
the downstream shock candidate region appears to be far from thermal
equilibrium. Henceforth it is our purpose to show that it is not a
shock discontinuity amenable to the Rankine-Hugoniot based techniques. A
possible shock related thermalization (at Wind) appears approximately
90 seconds later, at 2019:31UT, behind a magnetic hole showing a large
rotational discontinuity. Timing using Wind and other spacecraft located
tens to hundreds of earth radii apart allows the preliminary assessment
of an overall shock normal. In the context of Sun-Earth connections, the
disturbance appears related to the Sept 24,1030UT halo-CME [EIT observed
a CME starting in AR9632 located at [S18; E27] at 09:12 UT], which
was moving at 2240 kms-1 in the plane of the sky. In most events we
put special value on the identification of the plasma density by using
the electron plasma thermal line. However, there is a loss of detection
of the plasma line between 2010 and 2016 UT. This shock is important,
because strong particle and wave intensities appear to be associated
with it. Candidate compressional waves are identified upstream of the
shock. Their presence suggests that they are an additional source of
turbulence. This is so, because the compressional waves are likely
being created by the shock accelerated particles and subsequently
overtaken by the shock, probably, in an almost continuous process.
Title: Heavy-Element Abundances in Solar Energetic Particle Events
Authors: Reames, D. V.; Ng, C. K.
Bibcode: 2004ApJ...610..510R
Altcode:
We survey the relative abundances of elements with 1<=Z<=82
in solar energetic particle (SEP) events observed at 2-10 MeV
amu-1 during nearly 9 years aboard the Wind spacecraft,
with special emphasis on enhanced abundances of elements with
Z>=34. Abundances of Fe/O again show a bimodal distribution with
distinct contributions from impulsive and gradual SEP events, as seen
in earlier solar cycles. Periods with greatly enhanced abundances of
(50<=Z<=56)/O, just as those with enhanced 3He/
4He, fall prominently in the Fe-rich population of the impulsive
SEP events. In a sample of the 39 largest impulsive events, 25 have
measurable enhancements in (50<=Z<=56)/O and (76<=Z<=82)/O,
relative to coronal values, ranging from ~100 to 10,000. By contrast,
in a sample of 45 large gradual events the corresponding enhancements
vary from ~0.2 to 20. However, the magnitude of the heavy-element
enhancements in impulsive events is less striking than their strong
correlation with the Fe spectral index and flare size, with the
largest enhancements occurring in flares with the steepest Fe spectra,
the smallest Fe fluence, and the lowest X-ray intensity, as reported
here for the first time. Thus, it seems that small events with low
energy input can produce only steep spectra of the dominant species
but accelerate rare heavy elements with great efficiency, probably
by selective absorption of resonant waves in the flare plasma. With
increased energy input, enhancements diminish as heavy ions are
depleted, and spectra of the dominant species harden.
Title: Coronal Shocks and Solar Energetic Proton Events
Authors: Cliver, E. W.; Kahler, S. W.; Reames, D. V.
Bibcode: 2004ApJ...605..902C
Altcode:
From 1996 July through 2001 June, less than half (43/98) of all
favorably located (from solar western hemisphere sources) metric type
II radio bursts were associated with solar energetic proton (SEP)
events observed at Earth. When western hemisphere metric type IIs were
accompanied by decametric-hectometric (DH; 1-14 MHz) type II emission
(observed by Wind/WAVES) during this period, their association with
~20 MeV SEP events (with peak fluxes >=10-3 protons
cm-2 s-1 sr-1 MeV-1)
was 90% (26/29), versus only 25% (17/69) for metric IIs without a DH
counterpart. Overall, 82% (63%) of all SEP events with visible disk
origins were associated with metric (DH) type II bursts, with the
percentage associations increasing with SEP event size to 88% (96%) for
~20 MeV SEP events with peak intensities of >=10-1 protons
cm-2 s-1 sr-1 MeV-1. Our
results are consistent with the following possibilities (which are not
mutually exclusive): (1) large ~20 MeV SEP events result from strong
shocks that are capable of persisting well beyond ~3 Rsolar
(the nominal 14 MHz plasma level); (2) shock acceleration is most
efficient above ~3 Rsolar and (3) shocks that survive
beyond ~3 Rsolar are more likely to have broad longitudinal
extents, enabling less well connected shocks to intercept open field
lines connecting to Earth.
Title: Solar energetic particle variations
Authors: Reames, D. V.
Bibcode: 2004AdSpR..34..381R
Altcode:
In the largest solar energetic-particle (SEP) events, acceleration
occurs at shock waves driven out from the Sun by coronal mass ejections
(CMEs). In fact, the highest proton intensities directly measured near
Earth at energies up to ∼1 GeV occur at the time of passage of shocks,
which arrive about a day after the CMEs leave the Sun. CME-driven shocks
expanding across magnetic fields can fill over half of the heliosphere
with SEPs. Proton-generated Alfvén waves trap particles near the shock
for efficient acceleration but also throttle the intensities at Earth to
the "streaming limit" early in the events. At high energies, particles
begin to leak from the shock and the spectrum rolls downward to form an
energy-spectral "knee" that can vary in energy from ∼1 MeV to ∼1
GeV in different events. All of these factors affect the radiation
dose as a function of depth and latitude in the Earth's atmosphere
and the risk to astronauts and equipment in space. SEP ionization
of the polar atmosphere produces nitrates that precipitate to become
trapped in the polar ice. Observations of nitrate deposits in ice cores
reveal individual large SEP events and extend back ∼400 years. Unlike
sunspots, SEP events follow the ∼80-100 year Gleissberg cycle rather
faithfully and are now at a minimum in that cycle. The largest SEP event
in the last 400 years appears to be related to the flare observed by
Carrington in 1859, but the probability of SEP events with such large
fluences falls off sharply because of the streaming limit.
Title: Global heliospheric disturbances near 1 AU caused by the
launch of solar transients on January 1 and September 23, 1978.
Authors: Berdichevsky, D. B.; Reames, D. V.; Wu, C.; Schwenn, R.;
Lepping, R. P.; Farrugia, C. J.; MacDowall, R. J.; Bougeret, J.; Ng,
C. K.; Lazarus, A. J.; Richardson, I. G.
Bibcode: 2003AGUFMSM22A0219B
Altcode:
We revisit the transient events of January and September 1978. In
the January event the ejecta (an interplanetary magnetic cloud, IMC)
was studied using multiple spacecraft observations [Burlaga et al.,
1981]. In the September event Reames et al., 1997 studied the spectral
characteristics of the energetic particles of this big particle
event with a driven shock passage observed at longitudes nearly 180°
apart. Here we present a combined analysis of the overall solar wind
and energetic particles (EP) features of the shock and the driver,
observed at different locations in longitude. We further evaluate the
Rankine-Hugoniot properties of the shock at the locations its passage is
observed and add modeling of the driven shock using a three dimensional
MHD code which, at this stage of the analysis, does not include the
magnetic structure of the ejecta. For the study of the shock velocity
we use remote type II radio burst observations from near Earth (the
September event), and at different longitude locations we examine:
(a) flux intensity of the energetic particles, (b) shock strength,
(c) timing of the shock structure and the driver passage at each
spacecraft to infer the possible location of the nose of the shock. A
preliminary assessment on the connection between the global nature
of the shock and the observed level of energetic particle flux will
be presented. The data sets include the kilometric radio measurements
on ISEE3, and the 3 to 80 MeV energetic proton flux data from IMP-8,
and a similar energy range from Helios at wide longitudinal locations
relative to Earth. For the solar wind parameters we use magnetic field
and plasma parameters from instruments at Helios 1, and 2, and ISEE3
and IMP-8. The data set is completed with the Dst index (Kyoto). We
acknowledge partial support from NSF and NASA grants, and the NSSDC
for on-line access to their space science data archives. Burlaga
LF, E. Sittler, F. Mariani, and R. Schwenn, Magnetic loop behind
an interplanetary shock: Voyager, Helios, and IMP-8 observations,
J. Geophys. Res., 86, 6673, 1981. Reames, DV, SW Kahler,, and CK Ng,
Spatial and temporal invariance in the spectra of gradual particles
in gradual solar events, Astrophys. J., 491, 414, 1997.
Title: Solar-Heliospheric-Magnetospheric Observations on March
23-April 26, 2001: Similarities to Observations in April 1979
Authors: Berdichevsky, D. B.; Farrugia, C. J.; Lepping, R. P.;
Richardson, I. G.; Galvin, A. B.; Schwenn, R.; Reames, D. V.; Ogilvie,
K. W.; Kaiser, M. L.
Bibcode: 2003AIPC..679..758B
Altcode:
We discuss the similarities and differences of two intervals of extreme
interplanetary solar wind conditions, separated almost precisely by
two solar cycles, in April 1979 and March-April 2001. The similarities
extend to various data-sets: Energetic particles, solar wind plasma
and interplanetary magnetic field. In April 1979 observations were made
by three spacecraft covering a wide longitudinal range (~ 70°) in the
heliosphere. Data are presented from Helios 2, located 28° East of the
Sun-Earth line at ~ 2/3 AU, and from near the Earth. Observations of
the 2001 interval are from Wind. We examine the geomagnetic activity
during each interval.
Title: Effect of CME Interactions on the Production of Solar
Energetic Particles
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Kaiser, M. L.;
Howard, R. A.; Leske, R.; von Rosenvinge, T.; Reames, D. V.
Bibcode: 2003AIPC..679..608G
Altcode:
We analyzed a set of 52 fast and wide, frontside western hemispheric
(FWFW) CMEs in conjunction with solar energetic particle (SEP) and
radio burst data and found that 42 of these CMEs were associated
with SEPs. All but two of the 42 SEP-associated FWFW CMEs (95%)
were interacting with preceding CMEs or dense streamers. Most of
the remaining 10 SEP-poor FWFW CMEs had either insignificant or no
interaction with preceding CMEs or streamers, and were ejected into
a tenuous corona. There is also a close association between type II
radio bursts in the near-Sun interplanetary medium and SEP-associated
FWFW CMEs suggesting that electron accelerators are also good proton
accelerators.
Title: Coronal Shocks and Solar Energetic Proton Events
Authors: Cliver, Edward W.; Kahler, S. W.; Reames, D. V.
Bibcode: 2003ICRC....6.3331C
Altcode: 2003ICRC...28.3331C
From July 1996 June 2001, < 50% of favorably-lo cated metric type I I
radio bursts had associated solar energetic protons (SEPs). When western
hemisphere metric I Is were accompanied by decametric-hectometric (DH;
1-14 MHz) type I I emission, their association with ∼20 MeV SEP events
was 90% vs. only 25% for metric I Is without a DH counterpart. Overall,
82% (63%) of all SEP events with visible disk origins were associated
with metric (DH) type I Is, with percentage associations increasing
with SEP event size to 88% (96%), respectively, for ∼20 MeV SEP events
with peak intensities ≥ 10-1 pr cm-2 s-1 sr-1 MeV-1 . Our results are
consistent with the following (not mutually exclusive) possibilities:
(1) large ∼20 MeV SEP events result from strong shocks that can
persist well beyond ∼3 R ; (2) shock acceleration is most efficient
above ∼3 R ; (3) shocks that survive to ∼3 R are more likely to
have broad longitudinal extents.
Title: Onsets and Release Times in Solar Particle Events
Authors: Tylka, A. J.; Cohen, C. M. S.; Dietrich, W. F.; Krucker, S.;
McGuire, R. E.; Mewaldt, R. A.; Ng, C. K.; Reames, D. V.; Share, G. H.
Bibcode: 2003ICRC....6.3305T
Altcode: 2003ICRC...28.3305T
The time at which solar energetic particles (SEPs) are first released
into interplanetary space, and its relation to CMEs and various
photon emissions, are important clues to the site and nature of the
SEP acceleration mechanism [15,7,8,10,11]. We examine velocity disp
ersion among onsets in electrons and ions from Wind, ACE, and IMP8,
as well as available neutron monitors, to determine the solar release
time. We present results for two large impulsive events (1 May 2000
and 14 April 2001) and three western ground level events (GLEs;
6 November 1997, 6 May 1998, and 15 April 2001). In the impulsive
events, the particle release coincides with hard x-ray emission. But
the large GLEs show delayed release with respect to γ -ray emission,
consistent with acceleration by the CME-driven shock.
Title: Modeling Shock-accelerated Solar Energetic Particles Coupled
to Interplanetary Alfvén Waves
Authors: Ng, C. K.; Reames, D. V.; Tylka, A. J.
Bibcode: 2003ApJ...591..461N
Altcode:
We present an idealized model simulating the coupled evolution of the
distributions of multispecies shock-accelerated energetic ions and
interplanetary Alfvén waves in gradual solar energetic particle (SEP)
events. Particle pitch-angle diffusion coefficients are expressed in
terms of wave intensities, and wave growth rates in terms of momentum
gradients of SEP distributions, by the same quasilinear theory augmented
with resonance broadening. The model takes into consideration various
physical processes: for SEPs, particle motion, magnetic focusing,
scattering by Alfvén waves, solar wind convection, and adiabatic
deceleration; for the waves, WKB transport and amplification by
streaming SEPs. Shock acceleration is heuristically represented
by continuous injection of prescribed spectra of SEPs at a moving
shock front. We show the model predictions for two contrasting sets
of SEP source spectra, fast weakening and softening in one case and
long lasting and hard in the other. The results presented include
concurrent time histories of multispecies SEP intensities and elemental
abundance ratios, as well as sequential snapshots of the following:
SEP intensity energy spectra, Alfvén wave spectra, particle mean
free paths as functions of rigidity, and spatial profiles of SEP
intensities and mean free paths. Wave growth plays a key role in both
cases, although the magnitude of the wave growth differs greatly,
and quite different SEP abundance variations are obtained. In these
simulations, the maximum wave growth rate is large, but small relative
to the wave frequency, and everywhere the total wave magnetic energy
density remains small relative to that of the background magnetic
field. The simulations show that, as the energetic protons stream
outward, they rapidly amplify the ambient Alfvén waves, by several
orders of magnitude in the inner heliosphere. Energetic minor ions find
themselves traveling through resonant Alfvén waves previously amplified
by higher velocity protons. The nonuniformly growing wave spectra alter
the rigidity dependence of particle scattering, resulting in complex
time variations of SEP abundances at large distances from the Sun. The
greatly amplified waves travel outward in an expanding and weakening
``shell,'' creating an expanding and falling ``reservoir'' of SEPs with
flat spatial intensity profiles behind, while in and beyond the shell
the intensities drop steeply. The wave-particle resonance relation
dynamically links the evolving characteristics of the SEP and Alfvén
wave distributions in this new mode of SEP transport. We conclude that
wave amplification, the counterpart to the scattering of streaming
particles required by energy conservation, plays an essential role in
the transport of SEPs in gradual SEP events. The steep proton-amplified
wave spectra just upstream of the shock suggest that they may also be
important in determining the elemental abundances of shock-accelerated
SEP sources.
Title: Solar Energetic Particle Driven Alfvén Wave Growth and
Consequences
Authors: Ng, Chee K.; Reames, D. V.; Tylka, A. J.
Bibcode: 2003ICRC....6.3339N
Altcode: 2003ICRC...28.3339N
Our model shows that in large solar energetic particle (SEP) events,
streaming protons amplify interplanetary (IP) Alfv´n waves by orders
of magnitude near e the Sun. The wave intensity varies strongly and
non-monotonically in wavenumb er, time, and space. It falls steeply with
distance and may be difficult to observe at 1 AU. Wave amplification
dynamically modifies the rigidity and radial dependence of SEP
scattering and throttles SEP transport. It is essential in understanding
the time and energy variations of SEP elemental abundances.
Title: A comparative analysis of the helios and istp era sun-earth
connection during solar minimum
Authors: Berdichevsky, D.; Reames, D.; Schwenn, R.; Lepping, R.;
Farrugia, C.; Richardson, I.; Wu, C. -C.
Bibcode: 2003EAEJA....13892B
Altcode:
We discuss the similarities and differences of two intervals of extreme
interplanetary solar wind conditions, separated almost precisely by
two solar cycles, in Feb-Apr 1976 and Jan-Apr 2001. The similarities
extend to various data-sets: Energetic particles, solar wind plasma
and interplanetary magnetic field. In Jan-April 1979 observations were
made by spacecraft at three locations covering a wide longitudinal range
(from ~30 to 70°) in the heliosphere. Data are presented from Helios 2,
Helios 1, and from near the Earth. Observations of the 1997 interval are
from Wind, and solar conditions from SOHO. We examine the geomagnetic
activity during each interval. This Study is partially supported by the
following Grants: ATM-0208414 (NSF), and NASA NASW-02025 and NAG 5-10883
Title: Wind Observations of Anomalous Cosmic Rays from Solar Minimum
to Maximum
Authors: Reames, D. V.; McDonald, F. B.
Bibcode: 2003ApJ...586L..99R
Altcode:
We report the first observation near Earth of the time behavior of
anomalous cosmic-ray N, O, and Ne ions through the period surrounding
the maximum of the solar cycle. These observations were made by the
Wind spacecraft during the 1995-2002 period spanning times from solar
minimum through solar maximum. Comparison of anomalous and Galactic
cosmic rays provides a powerful tool for the study of the physics of
solar modulation throughout the solar cycle.
Title: Solar Energetic Particle Production by Coronal Mass
Ejection-driven Shocks in Solar Fast-Wind Regions
Authors: Kahler, S. W.; Reames, D. V.
Bibcode: 2003ApJ...584.1063K
Altcode:
Gradual solar energetic particle (SEP) events at 1 AU are produced
by coronal/interplanetary shocks driven by coronal mass ejections
(CMEs). Fast (vCME>~900 km s-1) CMEs might
produce stronger shocks in solar slow-wind regions, where the flow and
fast-mode MHD wave speeds are low, than in fast-wind regions, where
those speeds are much higher. At 1 AU the O+7/O+6
ratios distinguish between those two kinds of wind streams. We use
the 20 MeV proton event intensities from the EPACT instrument on Wind,
the associated CMEs observed with the LASCO coronagraph on SOHO, and
the ACE SWICS solar wind values of O+7/O+6
to look for variations of peak SEP intensities as a function
of O+7/O+6. No significant dependence of
the SEP intensities on O+7/O+6 is found for
either poorly connected or well-connected CME source regions or for
different CME speed ranges. However, in the 3 yr study period we
find only five cases of SEP events in fast wind, defined by regions
of O+7/O+6<0.15. We suggest that in coronal
holes SEP acceleration may take place only in the plume regions, where
the flow and Alfvén speeds are low. A broad range of angular widths
are associated with fast (vCME>=900 km s-1)
CMEs, but we find that no fast CMEs with widths less than 60° are
associated with SEP events. On the other hand, nearly all fast halo CMEs
are associated with SEP events. Thus, the CME widths are more important
in SEP production than previously thought, but the speed of the solar
wind source regions in which SEPs are produced may not be a factor.
Title: Unusual Plasma Conditions during may 23-25, 2002
Authors: Berdichevsky, D. B.; Lepping, R. P.; Bougeret, J.; Farrugia,
C. J.; Perche, C.; Vinas, A. F.; Lacombe, C.; Maksimovic, M.; Reames,
D. V.; Scudder, J. D.; Evans, D. S.
Bibcode: 2002AGUFMSH72C..04B
Altcode:
We present an overview of the plasma conditions under the extreme
tenuous plasma (Ne < 0.2 part/cm3) which started on May
23, 2002 and lasted for almost three days. During this unusual interval
at times the magnetosonic speed is well above 300 km/s, and unusual
close values in the ratio of plasma to cyclotron electron frequencies
(fpe/fce ~ 10). Using waves and solar wind parameters from the Wind
WAVES, EPAC, MFI and SWE experiments, we compare this event with other
intervals during this solar cycle which also showed strong hindrance in
the flow of the interplanetary solar wind. We further inquire on the
nature of the event by looking at the earth's polar cusps response to
the solar wind conditions, as illustrated by observations by satellites
POLAR and POES, and investigate, using flux-rope models and energetic
particles, the nature of this intriguing interplanetary structure.
Title: Flare- and Shock-accelerated Energetic Particles in the Solar
Events of 2001 April 14 and 15
Authors: Tylka, A. J.; Boberg, P. R.; Cohen, C. M. S.; Dietrich,
W. F.; Maclennan, C. G.; Mason, G. M.; Ng, C. K.; Reames, D. V.
Bibcode: 2002ApJ...581L.119T
Altcode:
We report heavy-ion composition and spectra for the solar
energetic particle (SEP) events of 2001 April 14 and 15, using
the combined capabilities of the Advanced Composition Explorer
(ACE), Wind, and the Interplanetary Monitoring Platform 8 (IMP-8)
to cover the energy range from ~30 keV nucleon-1 to ~400
MeV nucleon-1. These two events are, respectively, the
largest impulsive event and the largest ground-level event observed
so far in solar cycle 23. These events arose from the same active
region and launched into similar interplanetary conditions. Both were
associated with large western flares and fast coronal mass ejections
(CMEs). However, the two events are distinctly different, thereby
providing useful reminders of the fundamental differences between flare-
and shock-accelerated SEPs. The detailed observations present challenges
for our theoretical understanding of SEP production. Of particular
note is the fact that iron has a harder power-law energy spectrum than
oxygen above ~3 MeV nucleon-1 in the shock-dominated April
15 event. This spectral difference, which is seen in many other gradual
events of various sizes and heliolongitudes, leads to enhanced Fe/O
at high energies. Simple shock acceleration models predict the same
power-law index for all species. Thus, understanding the origin of this
spectral difference will significantly contribute to the resolution
of the ongoing debate about the relative roles of CME-driven shocks
and flares in producing high-energy solar heavy ions.
Title: Rise Times of Solar Energetic Particle Events and Speeds
of CMEs
Authors: Kahler, S.; Reames, D.
Bibcode: 2002AGUFMSH62A..08K
Altcode:
Gradual solar energetic particle (SEP) events are assumed to be
produced in coronal and interplanetary shocks driven by fast coronal
mass ejections (CMEs). These fast CMEs are decelerated as they move
through the slower ambient solar wind. However, the Alfven speed is
decreasing with increasing distance. Faster CMEs may therefore continue
to drive strong shocks for longer characteristic times than do the
slower CMEs, such that shock production and injection of SEPs of a
given energy will also continue longer with the faster CMEs. We test
this proposition observationally by comparing the times to maxima of 20
MeV SEP events with the observed speeds of associated CMEs. The SEP/CME
events are sorted by solar longitude to factor out the longitudinal
dependence of the SEP rise times. A preliminary analysis comparing 20
MeV protons from the GSFC EPACT detector on the Wind satellite with
CMEs observed by the LASCO coronagraph on the SOHO spacecraft showed
a correlation between SEP rise times and CME speeds. We expand the
database to include the 1996-2001 period for a more definitive test
of the correlation. The implications of the results will be discussed.
Title: Angular Distributions of Fe/O from Wind: New Insight into
Solar Energetic Particle Transport
Authors: Reames, D. V.; Ng, C. K.
Bibcode: 2002ApJ...577L..59R
Altcode:
We examine the angular distributions of He, O, and Fe in large solar
energetic particle (SEP) events measured on the Wind spacecraft. We
report, for the first time, that in a fixed velocity interval, Fe/O
is often larger for particles flowing sunward along the magnetic
field than for particles flowing outward from the Sun in many SEP
events. This occurs because the anisotropy for O exceeds that for Fe,
even though both species are streaming outward. There are no examples
of events for which the outward Fe/O dominates. The behavior of Fe
and O conflicts with the expectations of simple diffusion theory,
that angular distributions should be independent of species. It also
seems to conflict with the idea that energetic Fe scatters less than O
of the same velocity. However, preliminary modeling suggests that the
presence of a reflecting magnetic boundary beyond 1 AU, together with
the increased scattering of O over Fe due to proton-generated Alfvén
waves, can explain the direction and magnitude of the effect. These
observations add a new dimension to the study of SEP transport.
Title: Energetic Particle Abundances as Probes of an Interplanetary
Shock Wave
Authors: Reames, D. V.; Tylka, A. J.
Bibcode: 2002ApJ...575L..37R
Altcode:
We examine the unique abundance variations of Fe/O and He/H in solar
energetic particles from a W09 event of 2001 April 10 that have leaked
through the flank of an interplanetary shock launched from W04 on April
9. Shock waves from both events reached the Wind spacecraft on April
11. During the second event, both Fe/O and He/H began at low values and
rose to maxima near the time of passage of the shock waves, indicating
greater scattering for the species with the highest rigidity at a given
velocity. Strong modulation of Fe/O suggests preferential scattering
and trapping of Fe by the wave spectrum near and behind the intermediate
shock. A significant factor may be the residual proton-generated waves
from the very hard proton spectrum accelerated by the early shock wave
prior to the onset of the second event. Thus, ion abundances from the
later event probe the residual wave spectrum at the earlier shock.
Title: Relative recovery of galactic and anomalous cosmic rays at
1 AU: Further evidence for modulation in the heliosheath
Authors: McDonald, F. B.; Klecker, B.; McGuire, R. E.; Reames, D. V.
Bibcode: 2002JGRA..107.1156M
Altcode:
For solar cycle 22 the large-scale interplanetary disturbances produced
by the intense solar activity of March/June 1991 had a long-term effect
on the recovery of galactic cosmic rays throughout the heliosphere that
persisted for almost 5 years. At 1 AU, the recovery of 13 MeV/nucleon
anomalous cosmic ray oxygen (ACR O+) is much more rapid
than that of 265 MeV/nucleon galactic cosmic ray helium (GCR He),
consistent with previous observations in the distant heliosphere
[McDonald et al., 2000] and strengthening the concept that the
region of the heliosheath plays an important role in the modulation
of galactic cosmic rays. A comparison of the time histories of GCR
He and ACR O+ at 1 and 44 AU observations suggest the
recovery moves from the distant heliosphere inward toward 1 AU for
this particular phase of the heliomagnetic cycle. There is a very low
relative modulation potential, Φ, between 1 and 70 AU of 116 +/- 6 MV
for GCR He at solar minimum using the force field approximation. When
combined with the small radial intensity gradients in the distant
heliosphere, a much lower modulation potential is implied between 1
AU and the termination shock at solar minimum than had been assumed
previously. There is no effect on the 13 MeV/nucleon ACR O+
intensity as the inclination of the heliospheric neutral current sheet
decreases from 32° to its minimum value of 8°.
Title: Halo-coronal mass ejections near the 23rd solar minimum:
lift-off, inner heliosphere, and in situ (1 AU) signatures
Authors: Berdichevsky, D. B.; Farrugia, C. J.; Thompson, B. J.;
Lepping, R. P.; Reames, D. V.; Kaiser, M. L.; Steinberg, J. T.;
Plunkett, S. P.; Michels, D. J.
Bibcode: 2002AnGeo..20..891B
Altcode:
The extreme ultraviolet (EUV) signatures of a solar lift-off, decametric
and kilometric radio burst emissions and energetic particle (EP)
inner heliospheric signatures of an interplanetary shock, and in
situ identification of its driver through solar wind observations
are discussed for 12 isolated halo coronal mass ejections (H-CMEs)
occurring between December 1996 and 1997. For the aforementioned twelve
and the one event added in the discussion, it is found that ten passed
several necessary conditions for being a "Sun-Earth connection". It
is found that low corona EUV and Ha
Title: Interacting Coronal Mass Ejections and Solar Energetic
Particles
Authors: Gopalswamy, N.; Yashiro, S.; Michałek, G.; Kaiser, M. L.;
Howard, R. A.; Reames, D. V.; Leske, R.; von Rosenvinge, T.
Bibcode: 2002ApJ...572L.103G
Altcode:
We studied the association between solar energetic particle (SEP) events
and coronal mass ejections (CMEs) and found that CME interaction is
an important aspect of SEP production. Each SEP event was associated
with a primary CME that is faster and wider than average CMEs and
originated from west of E45°. For most of the SEP events, the primary
CME overtakes one or more slower CMEs within a heliocentric distance of
~20 Rsolar. In an inverse study, we found that for all the
fast (speed greater than 900 km s-1) and wide (width greater
than 60°) western hemispheric frontside CMEs during the study period,
the SEP-associated CMEs were ~4 times more likely to be preceded by
CME interaction than the SEP-poor CMEs; i.e., CME interaction is a
good discriminator between SEP-poor and SEP-associated CMEs. We infer
that the efficiency of the CME-driven shocks is enhanced as they
propagate through the preceding CMEs and that they accelerate SEPs
from the material of the preceding CMEs rather than from the quiet
solar wind. We also found a high degree of association between major
SEP events and interplanetary type II radio bursts, suggesting that
proton accelerators are also good electron accelerators.
Title: Solar Energetic Particle Production by Shocks in Fast and
Slow Solar Wind Structures
Authors: Kahler, S. W.; Reames, D. V.; Sheeley, N. R., Jr.
Bibcode: 2002AAS...200.3702K
Altcode: 2002BAAS...34..694K
Gradual solar energetic particle (SEP) events at 1 AU are produced
by coronal and interplanetary shocks driven by coronal mass ejections
(CMEs). Shocks from fast (V > 900 km/s) CMEs should be produced more
easily in slow solar wind regions where the flow and fast-mode MHD wave
speeds are low and less easily in fast solar wind regions where those
speeds are high. We might therefore expect to observe more intense SEP
events at 1 AU when the Earth lies in a slow wind region than when it
lies in a fast wind region. While stream-stream interactions wash out
the slow-fast stream boundaries in the solar wind speed profiles at
1 AU, the O+7/O+6 signatures of the streams are unchanged at 1 AU. We
use the 20 MeV proton intensities from the EPACT instrument on Wind,
the associated CMEs observed with the Lasco coronagraph on SOHO,
and the ACE SWICS/SWIMS solar wind values of O+7/O+6 to look for
variations of peak SEP intensities as a function of O+7/O+6. We find
no significant dependence of the SEP intensities on O+7/O+6 for either
poorly connected or well connected CME source regions or for different
CME speed ranges. While a broad range of angular widths are associated
with fast (V > 900 km/s) CMEs, we find that no fast CMEs with widths
< 60 degrees are associated with SEP events. On the other hand,
nearly all fast halo CMEs are associated with SEP events. Thus the CME
widths are more important in SEP production than previously thought,
but the solar wind source regions in which SEPs are produced are not
a significant factor.
Title: Variability in Elemental Composition in Large Solar Particle
Events of Cycle 23
Authors: Tylka, A. J.; Boberg, P. R.; Cohen, C. M.; Dietrich, W. F.;
Maclennan, C. G.; Mason, G. M.; Ng, C. K.; Reames, D. V.
Bibcode: 2002AGUSMSH42B..05T
Altcode:
Through December 2001, Cycle 23 has produced ~45 large solar
energetic particle (SEP) events, in which the proton intensity above
10 MeV exceeds galactic background rates by a factor of at least
104. We use these events to make a systematic study of SEP
elemental composition in Cycle 23. Preliminary results show no strong
evidence for systematic differences between the early and later phases
of Cycle 23, at least in data at ~5-10 MeV/nucleon, the same energy
range as used for most previous studies of SEP composition. However,
comparing events over the wide range of energies covered by various
instruments on Wind and ACE reveals a number of acceleration, transport,
and seed population effects which are strongly dependent on the species'
charge-to-mass (Q/A) ratio. We will discuss these effects and their
potential importance for understanding the relative roles of flares and
fast CMEs in producing large SEP events. We will also compare results
from Cycle 23 with elemental composition results from Cycles 21 and 22.
Title: Influence of CME Interaction on Solar Proton Events During
Cycle 23
Authors: Gopalswamy, N.; Yashiro, S.; Michalek, G.; Kaiser, M. L.;
Howard, R. A.; Reames, D. V.; Leske, R. A.; Von Rosenvinge, T.
Bibcode: 2002AGUSMSH41A..06G
Altcode:
We studied the association between solar proton events and white-light
coronal mass ejections (CMEs) that occurred during the solar cycle
23 until November 2001. Each of the SEP events was associated with
a large-scale primary CME, that were faster and wider than average
CMEs. For most of the proton events, the primary CME overtakes one or
more slower CMEs. In order to confirm this result, we examined the
association and CME interaction and energetic proton events for all
the fast (speed > 900 km~s-1) and wide (width > 60
deg) western hemispheric and halo CMEs during the study period. CMEs
with energetic protons are 3 times more likely to be preceded by CME
interaction than those without. We conclude that CME interaction is an
important aspect of SEP acceleration. We infer that CME-driven shocks
accelerate SEPs from the material of the preceding CMEs rather than
from the quiet solar wind.
Title: Magnetic Topology of Impulsive and Gradual Solar Energetic
Particle Events
Authors: Reames, Donald V.
Bibcode: 2002ApJ...571L..63R
Altcode:
We examine the magnetic topology at the Sun that leads to the two
classes of impulsive and gradual solar energetic particle (SEP)
events so as to address new observations that seem to blur this
classification, for example, that coronal mass ejections (CMEs) can
accompany events of both classes. In our model, the unusual element
abundances in impulsive SEP events result from resonant stochastic
acceleration in magnetic reconnection regions that incorporate open
magnetic field lines, allowing both accelerated ions and ejected
plasma to escape. In the large gradual events that produce classic
CMEs, reconnection occurs on closed field lines beneath the CME where
the accelerated particles are trapped so they plunge into the solar
atmosphere to produce a flare; they cannot escape. The SEPs seen at
1 AU in these large gradual events are accelerated by the shock wave
driven outward by the CME. The shock-accelerated particles are derived
from the local plasma and from reaccelerated suprathermal ions from
previous impulsive or gradual SEP events.
Title: A comparative study of Solar-Heliospheric Observations during
very active Sun intervals in the 21st and 23rd solar cycles (April
1979 and March-April, 2001)
Authors: Berdichevsky, D. B.; Farrugia, C. J.; Lepping, R. P.;
Richardson, I. G.; Galvin, A. B.; Schwenn, R.; Reames, D. V.
Bibcode: 2002AGUSMSH51A..01B
Altcode:
On March 24, 2001, the largest sun spot group in 10 years, consisting
of three or more active regions (ARs) centered near AR 9393, emerged
from behind the eastern limb of the Sun and began a 2-week passage
across the visible hemisphere. During the same time, the Sun showed
several other ARs so this period constituted a phase of unusually
intense solar activity that continued almost 18 days beyond the
disk passage of the largest sun spot group and included possibly
the most energetic solar flare event in modern records (a > X20
flare in soft X-rays). We shall present an overview of the associated
solar energetic particle events and an analysis of the thermodynamic
characteristics of the shocks observed in the Earth's vicinity. The
investigation includes cross-correlation analysis of interplanetary
plasma and magnetic field observations at ACE (SWEPAM/MAG level-2 data)
situated 250 Re upstream of Earth and at Wind (SWE/MFI data), which
was ahead of Earth and executing a distant prograde orbit with large
Y-coordinate. The interval under study bears a close resemblance to a
similar active period during April 1979 (i.e., 2 solar cycles earlier)
observed by the Helios 1/2 probes and Earth solar wind monitors (ISEE-3,
IMP). The similarities and differences between the two intervals are
examined further.
Title: Colliding coronal mass ejections and particle acceleration
Authors: Gopalswamy, N.; Yashiro, S.; Kaiser, M.; Reames, D.;
Howard, R.
Bibcode: 2002cosp...34E1253G
Altcode: 2002cosp.meetE1253G
Colliding Coronal Mass Ejections (CMEs) have important implications to
a number of physical processes in the near-Sun interplanetary medium:
Shock propagation, particle acceleration and solar wind composition. We
present statistical results on large solar energetic particle events,
associated CMEs and CME interaction during solar cycle 23. We show
that most of the large SEP events are preceded by CME interaction. As
an inverse study, we identified all the fast and wide front side CMEs
from the western hemisphere and examined the SEP association and
CME interaction. We found that fast and wide CMEs interacting with
preceding CMEs are more likely to be associated with SEPs. We discuss
the implications of the statistical results to the understanding of
particle acceleration by CME-driven shocks.
Title: Solar Wind: Energetic Particles
Authors: Reames, D.
Bibcode: 2002eaa..bookE2312R
Altcode:
The energetic particle populations that we observe in the SOLAR
WIND are accelerated in a variety of local and distant sources. We
distinguish different populations by their temporal, spatial and angular
distributions, energy spectra, abundances and ionization states. They
tell us the physics of acceleration mechanisms and the properties of
remote sites that are otherwise invisible or inaccessibl...
Title: Solar energetic particle variations
Authors: Reames, D.
Bibcode: 2002cosp...34E.491R
Altcode: 2002cosp.meetE.491R
In recent years we have learned that in the largest solar energetic
particle (SEP) events, acceleration occurs at shock waves driven out
from the Sun by coronal mass ejections (CMEs). In fact, the highest
proton intensities directly measured near Earth at energies below
~1 GeV occur at the time of passage of shocks, which arrive about a
day after the CMEs leave the Sun. CME-driven shocks can expand across
magnetic fields to fill more than half of the heliosphere with SEPs;
intensity-time profiles of the SEPs depend upon the observer's location
relative to the CME source. Proton-generated Alfven waves trap particles
near the shock for efficient acceleration but also bound intensities
near Earth at the "streaming limit" early in the events. At high
energies, particles begin to leak from the shock and the spectrum rolls
downward to form an energy-spectral "knee." Knee energies can vary from
~10 MeV to ~1 GeV in different SEP events. All of these factors affect
the radiation dose as a function of depth and latitude in the Earth's
atmosphere and the risk to astronauts and equipment in space. Direct
observations of SEP events show a rough correlation with the solar
cycle for the last ~40 years. Observations of nitrate deposits in ice
cores (~400 y) and radioactive isotopes in moon rocks (~1 My) extend
the historic record and address the probability of occurrence of much
larger SEP events.
Title: The Bastille day Magnetic Clouds and Upstream Shocks:
Near-Earth Interplanetary Observations
Authors: Lepping, R. P.; Berdichevsky, D. B.; Burlaga, L. F.; Lazarus,
A. J.; Kasper, J.; Desch, M. D.; Wu, C. -C.; Reames, D. V.; Singer,
H. J.; Smith, C. W.; Ackerson, K. L.
Bibcode: 2001SoPh..204..285L
Altcode:
The energetic charged particle, interplanetary magnetic field, and
plasma characteristics of the `Bastille Day' shock and ejecta/magnetic
cloud events at 1 AU occurring over the days 14-16 July 2000 are
described. Profiles of MeV (WIND/LEMT) energetic ions help to organize
the overall sequence of events from the solar source to 1 AU. Stressed
are analyses of an outstanding magnetic cloud (MC2) starting late on
15 July and its upstream shock about 4 hours earlier in WIND magnetic
field and plasma data. Also analyzed is a less certain, but likely,
magnetic cloud (MC1) occurring early on 15 July; this was separated
from MC2 by its upstream shock and many heliospheric current sheet
(HCS) crossings. Other HCS crossings occurred throughout the 3-day
period. Overall this dramatic series of interplanetary events caused
a large multi-phase magnetic storm with min Dst lower than −300
nT. The very fast solar wind speed (≥ 1100 km s−1)
in and around the front of MC2 (for near average densities) was
responsible for a very high solar wind ram pressure driving in the
front of the magnetosphere to geocentric distances estimated to be as
low as ≈ 5 RE, much lower than the geosynchronous orbit
radius. This was consistent with magnetic field observations from two
GOES satellites which indicated they were in the magnetosheath for
extended times. A static force-free field model is used to fit the two
magnetic cloud profiles providing estimates of the clouds' physical
and geometrical properties. MC2 was much larger than MC1, but their
axes were nearly antiparallel, and their magnetic fields had the same
left-handed helicity. MC2's axis and its upstream shock normal were
very close to being perpendicular to each other, as might be expected
if the cloud were driving the shock at the time of observation. The
estimated axial magnetic flux carried by MC2 was 52×1020
Mx, which is about 5 times the typical magnetic flux estimated for
other magnetic clouds in the WIND data over its first 4 years and is
17 times the flux of MC1. This large flux is due to both the strong
axially-directed field of MC2 (46.8 nT on the axis) and the large
radius (R0=0.189 AU) of the flux tube. MC2's average speed
is consistent with the expected transit time from a halo-CME to which
it is apparently related.
Title: On the Phase of the 27 Day Modulation of Anomalous and Galactic
Cosmic Rays at 1 AU during Solar Minimum
Authors: Reames, D. V.; Ng, C. K.
Bibcode: 2001ApJ...563L.179R
Altcode:
We report on the 27 day oscillations in the intensities of He and O
ions of the anomalous cosmic rays (ACRs) observed near Earth by the
Wind spacecraft during the 1995-1997 solar minimum period. Oscillations
persist throughout the period with amplitudes as large as 50%. Galactic
cosmic ray (GCR) oscillations, observed by neutron monitors, are in
phase with the ACRs, but with much smaller amplitude (2%-3%). For
a sustained period of almost a year, peak intensities occur near
north-to-south crossings of the heliospheric current sheet and
valleys near south-to-north crossings. In GCR observations in the
1974-1976 solar minimum, 27 day oscillations with a similar phase
are seen. Understanding these observations poses a severe challenge
for models of solar modulation as well as for models of the solar and
heliospheric magnetic fields.
Title: Coronal Mass Ejections Associated with Impulsive Solar
Energetic Particle Events
Authors: Kahler, S. W.; Reames, D. V.; Sheeley, N. R., Jr.
Bibcode: 2001ApJ...562..558K
Altcode:
An impulsive solar energetic particle (SEP) event observed on the
Wind spacecraft on 2000 May 1 was associated with an impulsive solar
active region M1 X-ray flare. The timing and position of a fast (v=960
km s-1), narrow CME observed in the LASCO coronagraph on
SOHO make clear the connection between the CME and the flare and SEP
event. Impulsive SEP events have long been associated with impulsive
flares, but only gradual SEP events have thus far been found to be
associated with CMEs. A comparison of impulsive SEP events with CME
observations from the Solwind and LASCO coronagraphs revealed further
good cases of narrow (10°-40°) CMEs associated with impulsive SEP
events. A recent model of impulsive flares includes jets or plasmoids
that are ejected upward from magnetic reconnection sites over active
regions and might therefore be expected to appear in exceptional
cases as faint and narrow CMEs in coronagraphs. We suggest that this
model allows us to understand better SEP production and propagation
in impulsive flares.
Title: Energetic particle composition
Authors: Reames, Donald V.
Bibcode: 2001AIPC..598..153R
Altcode: 2001sgc..conf..153R
Abundances of elements and isotopes have been essential for identifying
and measuring the sources of the energetic ions and for studying the
physical processes of acceleration and transport for each particle
population in the heliosphere. Many of the sources are surprising, in
a few cases the acceleration bias is extreme, but an understanding of
the fundamental physics allows us to use energetic ions to determine
abundances for the average solar corona, the high-speed solar wind,
and the local interstellar medium. .
Title: Evidence for Remnant Flare Suprathermals in the Source
Population of Solar Energetic Particles in the 2000 Bastille Day Event
Authors: Tylka, A. J.; Cohen, C. M. S.; Dietrich, W. F.; Maclennan,
C. G.; McGuire, R. E.; Ng, C. K.; Reames, D. V.
Bibcode: 2001ApJ...558L..59T
Altcode:
The energy spectra of Fe in the very large solar energetic particle
(SEP) event of 2000 July 14 are strikingly different from those
of lighter species. We show that this difference can be explained
by shock acceleration from a two-component source population,
comprising solar wind suprathermals and a small (~5%) admixture of
remnant flare particles, as previously proposed to explain enhanced
3He/4He in some gradual SEP events. Flare
remnants can also account for several previously unexplained features
of high-energy solar heavy ions as well as important aspects of SEP
event-to-event variability. These results offer a new perspective on
the enduring controversy over the relative roles of flares and coronal
mass ejections (CMEs) in producing SEPs. Flare activity clearly makes
a unique and critical contribution to the source population. But
the predominate accelerator in large gradual SEP events is the
CME-driven shock, and many spectral, compositional, and charge state
characteristics of high-energy heavy ions can be understood without
invoking other acceleration mechanisms.
Title: A Comparative Study of the Cosmic Ray Recovery Process in
the Inner and Outer Heliosphere
Authors: McDonald, F. B.; Klecker, B.; McGuire, R. E.; Reames, D. V.
Bibcode: 2001ICRC....9.3762M
Altcode: 2001ICRC...27.3762M
The cosmic ray recovery of galactic and anomalous cosmic rays for cycle
22 over the 1991-1997 time period is strongly affected by the intense
solar activity of March/June 1991. This results in a recovery that
differ from that of cycle 20 and both in turn differs significantly
from the cycle 21 recovery (1981-1987) in a qA<0 epoch. For cycle 22
it is found that the recovery time constants for 265 MeV/n GCR He are
the same at 1 and 44 AU (τ = 1.9 years) which is much longer than the
0.95 year time constant measured at these distances for ACR 0+ . This
has previously been interpreted as evidence for cosmic ray modulation
in the heliosheath. There is no evidence for similar effects in cycle
21 following the large outburst of solar activity in mid 1982. What
is most puzzling about the cycle 22 recovery is that the net increase
in 150-380 MeV/n He between 1990 and 1997 is the same at 1 AU and at
44 AU. However, for ACR 0+ the net increase at 44 AU is appreciably
larger than at 1 AU. This analysis suggests that after 1993.2 (i.e.,
following the passage of the global merged interaction region produced
by the March/June activity) the continuing recovery of galactic cosmic
rays proceed from the outer into the inner heliosphere. Again, this is
different from the 1982 - 1987 recovery which appeared to be strongly
controlled by changes in the inclination of the heliospheric neutral
current sheet (HNCS).
Title: Abundances, spectra, and anisotropies in the 1998 Sep 30 and
2000 Apr 4 large Sep events
Authors: Ng, C. K.; Reames, D.; Tylka, A. J.
Bibcode: 2001ICRC....8.3140N
Altcode: 2001ICRC...27.3140N
The 1998 Sep 30 and 2000 Apr 4 events are both large western solar
energetic particle (SEP) events, in which ∼ 1 MeV proton intensities
exceed 103 particles (cm2 s sr MeV)-1 . Yet they exhibit quite different
time variations of elemental abundance ratios and energy spectra. Using
a model of SEP transport through self-amplified interplanetary Alfv´en
waves, we fit the simultaneous observations of protons and ions of
helium, oxygen, and iron. We conclude that wave amplification by high
energy protons largely account for the differences in the observed
time histories.
Title: A CME associated with an impulsive SEP event
Authors: Kahler, S.; Reames, D.; Sheeley, N., Jr.
Bibcode: 2001ICRC....8.3443K
Altcode: 2001ICRC...27.3443K
An impulsive solar energetic particle (SEP) event observed on the Wind
spacecraft on 2000 May 1 was associated with an impulsive solar active
region M1 X-ray flare. The timing and position of a fast (v = 960 km s-1
), narrow CME observed in the Lasco coronagraph on SOHO make clear the
connection between the CME and the flare and SEP event. Impulsive SEP
events have long been associated with impulsive flares, but only gradual
SEP events have thus far been found to be associated with CMEs. This is
the first clear case of an impulsive SEP event with an associated CME.
Title: Energy Spectra of Very Large Gradual Solar Particle Events
Authors: Tylka, A. J.; Boberg, P. R.; Cohen, C. M. S.; Dietrich,
W. F.; Maclennan, C. G.; Mason, G. M.; Reames, D. V.; McGuire, R. E.;
Ng, C. K.
Bibcode: 2001ICRC....8.3189T
Altcode: 2001ICRC...27.3189T
Energy spectra provide a powerful tool in understanding solar energetic
particle (SEP) events, in that spectra contain information on all
aspects of SEP production, including source plasma, interplanetary
transport effects, and characteristics of the accelerator. We compare
energy spectra of two very large gradual events (1998 April 20 and
2000 July 14), produced by shocks driven by fast coronal mass ejections
(CMEs). We show that differences in their Fe spectra can be understood
in terms of a small, variable admixture of remant flare suprathermals
in the SEP source population.
Title: Associations of Accelerating CMEs with Solar Energetic
Particle Events
Authors: Kahler, S.; Sheeley, N.; Reames, D.
Bibcode: 2001AGUSM..SH22B03K
Altcode:
Gradual solar energetic particle (SEP) events are well associated with
fast coronal mass ejections (CMEs). The times of significant E >
10 MeV SEP events observed with the Goddard Space Flight Center EPACT
detector on the Wind spacecraft have been compared with CME observations
from the Lasco coronagraph on the SOHO spacecraft. As earlier studies
have shown, a correlation exists between peak SEP intensities and
the measured speeds of associated CMEs. Of the CMEs associated with
SEP events in the period 1996 to 2000, we find 9 CMEs for which the
height-time plots of the leading edges show accelerations of at least
13 m/s/s. The heights at which those CMEs attained speeds of 600 km/s
ranged from 7 to 20 Ro. The peak 20 MeV intensities of the 9 SEP events
are relatively low compared with all gradual SEP events of the same
period. We compare the energy spectra and solar event associations of
these 9 SEP events with those of the SEP events associated with CMEs
of uniform speeds.
Title: Angular Distributions of Solar Energetic Particles
Authors: Reames, D. V.; Ng, C. K.; Berdichevsky, D.
Bibcode: 2001ApJ...550.1064R
Altcode:
We report observations, using data from the Wind spacecraft, of temporal
variations in the angular distributions of H, He, O, and Fe ions at MeV
energies during solar energetic particle (SEP) events under a variety
of conditions. Detailed time-dependent angular distributions of O
and Fe during SEP events are reported for the first time. Extended
periods of particle streaming in small gradual events are consistent
with continued acceleration that is expected at shock waves driven from
the Sun by coronal mass ejections (CMEs). Particles accelerated from
SEP events of moderate size show especially strong streaming along the
magnetic fields inside an old CME. For the largest events, however,
streaming rapidly diminishes, showing behavior that is qualitatively
consistent with the theory of Ng et al. In very intense events, that
theory predicts rapid growth of proton-generated Alfvén waves, even
near and beyond 1 AU, that soon scatter and isotropize the particles. We
show, for the first time, cases where SEP streaming is organized by
the value of the plasma beta βp, the ratio of the proton
thermal energy to magnetic energy. Higher initial turbulence in the
high-βp plasma may require less additional wave growth to
reach significant levels of scattering in the largest SEP events.
Title: Heavy Ion Abundances and Spectra and the Large Gradual Solar
Energetic Particle Event of 2000 July 14
Authors: Reames, D. V.; Ng, C. K.; Tylka, A. J.
Bibcode: 2001ApJ...548L.233R
Altcode:
We compare the spectra and abundances of heavy elements of atomic
number Z in the range 34<=Z<=40 with those of He, C, O, Ne, Si,
and Fe, as observed on the Wind spacecraft, in the large solar energetic
particle (SEP) events of 1998 April 20 and 2000 July 14. This is the
first time that spectra of the rare, trans-Fe, 34<=Z<=40 ions
have been measured in SEP events. We use the systematic dependence of
the spectral e-folding energies on the charge-to-mass ratio (Q/A) of
the species to estimate ionization states of each species. Ionization
states of Q~11 for ions with 34<=Z<=40 are comparable to those
for Si and Fe.
Title: Solar energetic particles and space weather
Authors: Reames, Donald V.; Tylka, Allan J.; Ng, Chee K.
Bibcode: 2001AIPC..552.1185R
Altcode: 2001stai.conf.1185R
The solar energetic particles (SEPs) of consequence to space weather
are accelerated at shock waves driven out from the Sun by fast coronal
mass ejections (CMEs). In the large events, these great shocks fill
half of the heliosphere. SEP intensity profiles change appearance with
longitude. Events with significant intensities of >10 MeV protons
occur at an average rate of ~13 yr-1 near solar maximum
and several events with high intensities of >100 MeV protons occur
each decade. As particles stream out along magnetic field lines from
a shock near the Sun, they generate waves that scatter subsequent
particles. At high intensities, wave growth throttles the flow
below the ``streaming limit.'' However, if the shock maintains its
strength, particle intensities can rise above this limit to a peak
when the shock itself passes over the observer creating a `delayed'
radiation hazard, even for protons with energies up to ~1 GeV. The
streaming limit makes us blind to the intensities at the oncoming
shock, however, heavier elements such as He, O, and Fe probe the shape
of the wave spectrum, and variation in abundances of these elements
allow us to evade the limit and probe conditions at the shock, with
the aid of detailed modeling. At high energies, spectra steepen to
form a spectral `knee.' The location of the proton spectral knee can
vary from ~10 MeV to ~1 GeV, depending on shock conditions, greatly
affecting the radiation hazard. Hard spectra are a serious threat to
astronauts, placing challenging requirements for shielding, especially
on long-duration missions to the moon or Mars. .
Title: The observational consequences of proton-generated waves
at shocks
Authors: Reames, Donald V.
Bibcode: 2000AIPC..528...79R
Altcode: 2000atep.conf...79R
In the largest solar energetic particle (SEP) events, acceleration
takes place at shock waves driven out from the Sun by fast coronal
mass ejections. Protons streaming away from strong shocks generate
Alfvén waves that trap particles in the acceleration region, limiting
outflowing intensities but increasing the efficiency of acceleration
to higher energies. Early in the events, with the shock still near
the Sun, intensities at 1 AU are bounded and spectra are flattened
at low energies. Elements with different charge-to-mass ratios, Q/A,
differentially probe the wave spectra near shocks, producing abundance
ratios that vary in space and time. An initial rise in He/H, while Fe/O
declines, is a typical symptom of the non-Kolmogorov wave spectra in the
largest events. Strong wave generation can cause cross-field scattering
near the shock and unusually rapid reduction in anisotropies even far
from the shock. At the highest energies, shock spectra steepen to form
a ``knee.'' For protons, this spectral knee can vary from ~10 MeV to
~1 GeV depending on shock conditions for wave growth. In one case, the
location of the knee scales approximately as Q/A in the energy/nucleon
spectra of other species. .
Title: Abundances of Trans-Iron Elements in Solar Energetic Particle
Events
Authors: Reames, Donald V.
Bibcode: 2000ApJ...540L.111R
Altcode:
We report the first comprehensive observation of the abundances
of heavy elements of atomic number Z in the range 34<=Z<=82
in solar energetic particle (SEP) events as observed on the Wind
spacecraft. In large gradual SEP events, abundances of the element
groups 34<=Z<=40, 50<=Z<=56, and 70<=Z<=82, relative
to Fe, are similar to corresponding coronal abundances within a factor
of ~2 and vary little with time during the events. However, in sharp
contrast, abundances of these ions from impulsive flares increase
dramatically with Z so that abundances of Fe, 34<=Z<=40, and
50<=Z<=56, relative to O, are seen at ~10, ~100, and ~1000 times
their coronal values, respectively.
Title: Temporal evolution in the spectra of gradual solar energetic
particle events
Authors: Tylka, Allan J.; Boberg, Paul. R.; McGuire, Robert. E.; Ng,
Chee K.; Reames, Donald. V.
Bibcode: 2000AIPC..528..147T
Altcode: 2000atep.conf..147T
We examine solar energetic particle (SEP) spectra in two very large
``gradual'' events (20 April 1998 and 25 August 1998), in which
acceleration is caused by fast CME-driven shocks. By combining
data from ACE/SIS, Wind/EPACT/LEMT, and IMP8/GME, we examine all
major species from H to Fe, from ~2 MeV/nuc to the highest energies
measured. These events last for several days, so we have divided the
events into 8-hour intervals in order to study the evolution of the
spectra. The spectra reveal significant departures from simple power
laws. Of particular note is the behavior at high energies, where the
spectra exhibit exponential rollovers. We demonstrate that the fitted
e-folding energies reflect both ionic charge states and a complex but
orderly temporal evolution. We speculate that this behavior may be
related to evolving rigidity dependence in the near-shock diffusion
coefficient, which is of potentially great importance for models of
SEP acceleration and transport. .
Title: Particle acceleration by CME-driven shock waves
Authors: Reames, Donald V.
Bibcode: 2000AIPC..516..289R
Altcode: 2000ICRC...26..289R
In the largest solar energetic particle (SEP) events, acceleration
occurs at shock waves driven out from the Sun by coronal mass ejections
(CMEs). Peak particle intensities are a strong function of CME speed,
although the intensities, spectra, and angular distributions of
particles escaping the shock are highly modified by scattering on
Alfvén waves produced by the streaming particles themselves. Element
abundances vary in complex ways because ions with different values of
Q/A resonate with different parts of the wave spectrum, which varies
with space and time. Just recently, we have begun to model these
systematic variations theoretically and to explore other consequences
of proton-generated waves. .
Title: Initial Time Dependence of Abundances in Solar Energetic
Particle Events
Authors: Reames, D. V.; Ng, C. K.; Tylka, A. J.
Bibcode: 2000ApJ...531L..83R
Altcode:
We compare the initial behavior of Fe/O and He/H abundance ratios
and their relationship to the evolution of the proton energy spectra
in ``small'' and ``large'' gradual solar energetic particle (SEP)
events. The results are qualitatively consistent with the behavior
predicted by the theory of Ng et al. published in 1999. He/H ratios that
initially rise with time are a signature of scattering by non-Kolmogorov
Alfvén wave spectra generated by intense beams of shock-accelerated
protons streaming outward in large gradual SEP events.
Title: A Role for Ambient Energetic Particle Intensities in Shock
Acceleration of Solar Energetic Particles
Authors: Kahler, S. W.; Reames, D. V.; Burkepile, J. T.
Bibcode: 2000ASPC..206..468K
Altcode: 2000hesp.conf..468K
No abstract at ADS
Title: What We Don't Understand about Ion Accelaration in Flares
Authors: Reames, D. V.
Bibcode: 2000ASPC..206..102R
Altcode: 2000hesp.conf..102R
No abstract at ADS
Title: Effect of Wave Generation on the Evolution of Elemental
Abundances of Solar Energetic Particles
Authors: Ng, C. K.; Reames, D. V.; Tylka, A. J.
Bibcode: 2000ASPC..206..162N
Altcode: 2000hesp.conf..162N
No abstract at ADS
Title: Energy-dependent ionization states of shock-accelerated
particles in the solar corona
Authors: Reames, D. V.; Ng, C. K.; Tylka, A. J.
Bibcode: 1999GeoRL..26.3585R
Altcode:
We examine the range of possible energy dependence of the ionization
states of ions that are shock-accelerated from the ambient plasma of the
solar corona. If acceleration begins in a region of moderate density,
sufficiently low in the corona, ions above ∼0.1 MeV/amu approach
an equilibrium charge state that depends primarily upon their speed
and only weakly on the plasma temperature. We suggest that the large
variations of the charge states with energy for ions such as Si and Fe
observed in the 1997 November 6 event are consistent with stripping
in moderately dense coronal plasma during shock acceleration. In the
large solar-particle events studied previously, acceleration occurs
sufficiently high in the corona that even Fe ions up to 600 MeV/amu
are not stripped of electrons.
Title: Particle acceleration at the Sun and in the heliosphere
Authors: Reames, Donald V.
Bibcode: 1999SSRv...90..413R
Altcode:
Energetic particles are accelerated in rich profusion at sites
throughout the heliosphere. They come from solar flares in the low
corona, from shock waves driven outward by coronal mass ejections
(CMEs), from planetary magnetospheres and bow shocks. They come
from corotating interaction regions (CIRs) produced by high-speed
streams in the solar wind, and from the heliospheric termination
shock at the outer edge of the heliospheric cavity. We sample many
populations near Earth, but can distinguish them readily by their
element and isotope abundances, ionization states, energy spectra,
angular distributions and time behavior. Remote spacecraft have
probed the spatial distributions of the particles and examined new
sources in situ. Most acceleration sources can be ‘seen’ only
by direct observation of the particles; few photons are produced at
these sites. Wave-particle interactions are an essential feature in
acceleration sources and, for shock acceleration, new evidence of
energetic-proton-generated waves has come from abundance variations
and from local cross-field scattering. Element abundances often tell
us the physics of the source plasma itself, prior to acceleration. By
comparing different populations, we learn more about the sources, and
about the physics of acceleration and transport, than we can possibly
learn from one source alone.
Title: Observations of systematic temporal evolution in elemental
composition during gradual solar energetic particle events
Authors: Tylka, Allan J.; Reames, Donald V.; Ng, Chee K.
Bibcode: 1999GeoRL..26.2141T
Altcode:
The WIND/EPACT experiment offers a ∼100 fold increase in collecting
power over instruments flown in previous solar cycles, thus allowing
unprecedented detailed studies of temporal evolution in gradual
solar energetic particle (SEP) events. We present hourly WIND/EPACT
observations at ∼2-10 MeV/nuc from the 20 April 1998 and 26 August
1998 SEP events. These observations show striking patterns in elemental
composition which evolve in a systematic fashion throughout the events'
several-day durations. These data, combined with theoretical modeling
in a companion Letter [Ng et al. 1999], suggest that a dynamic Alfvén
wave field, generated primarily by streaming energetic protons, is
responsible for the complex behavior which is observed.
Title: Effect of proton-amplified waves on the evolution of solar
energetic particle composition in gradual events
Authors: Ng, Chee K.; Reames, Donald V.; Tylka, Allan J.
Bibcode: 1999GeoRL..26.2145N
Altcode:
We present a model of the coupled evolution of energetic ions and
Alfvén waves, incorporating magnetic focusing, pitch-angle diffusion,
wave amplification, and a traveling ion source. Ion transport through
proton-amplified waves with non-Kolmogorov spectra produces the
contrasting three-stage evolution of Fe/O and He/H ratios at several
MeV/amu observed by Wind/EPACT in the 20 April 1998 gradual solar
energetic particle event [Tylka et al., 1999].
Title: Quiet-Time Spectra and Abundances of Energetic Particles
During the 1996 Solar Minimum
Authors: Reames, Donald V.
Bibcode: 1999ApJ...518..473R
Altcode:
We report the energy spectra and abundances of ions with atomic
number, Z, in the interval 2<=Z<=36 and energies ~3-20 MeV
amu-1 for solar and interplanetary quiet periods between 1994
November and 1998 April, as measured by the large-geometry Low-Energy
Matrix Telescope on the Wind spacecraft near Earth. The energy spectra
show the presence of galactic and ``anomalous'' cosmic-ray components
(GCR and ACR, respectively), depending on the element. ACR components
are reported for Mg and Si for the first time at 1 AU, and the previous
observation of S and Ar is confirmed. However, only GCR components are
clearly apparent for the elements Ca, Ti, Cr, Fe, as well as for C. New
limits are placed on a possible ACR contribution for other elements,
including Kr.
Title: Quiet-Time Spectra and Abundances of Energetic Particles
During the 1996 Solar Minimum
Authors: Reames, Donald V.
Bibcode: 1999STIN...9941072R
Altcode:
We report the energy spectra and abundances of ions with atomic number,
Z, in the interval Z is greater than or equal to 2 and Z is less than
or equal to 36 and energies approximately 3-20 MeV/amu for solar and
interplanetary quiet periods between 1994 November and 1998 April
as measured by the large-geometry Low Energy Matrix Telescope (LEMT)
telescope on the Wind spacecraft near Earth. The energy spectra show the
presence of galactic (GCR) and "anomalous" cosmic ray (ACR) components,
depending on the element. ACR components are reported for Mg and Si
for the first time at 1 AU and the previous observation of S and Ar
is confirmed. However, only GCR components are clearly apparent for
the elements Ca, Ti, Cr, Fe, as well as for C. New limits are placed
on a possible ACR contribution for other elements, including Kr.
Title: Coronal Abundances
Authors: Fludra, A.; Saba, J. L. R.; Henoux, J. -C.; Murphy, R. J.;
Reames, D. V.; Lemen, J. R.; Strong, K. T.; Sylwester, J.; Widing,
K. G.
Bibcode: 1999mfs..conf...89F
Altcode:
Flare X-Ray Measurements from BCS Calcium Abundance Fe/H and Fe/Ca
Abundance Relative Abundances of Ar. Ca. and Fe in Flares Factors
Affecting Abundance Determinations from X-Ray Spectra FCS Abundances
FCS Active-Region Abundances Abundance Variability in Active Regions
Impact of Resonance Scattering Assessment of FCS Active-Region Abundance
Results FCS Flare Abundance Studies Coronal CI/S and Ar/S Measurements
Dem Studies of Flare Abuncances Determination of Solar Abundances
by Solar Flare γ-Ray Spectrometry γ-Ray Spectral Analysis γ-Ray
Results Solar Energetic Particles Major Proton Events CIR Events from
Coronal Holes Impulsive Flare Events Theory of Abundance Fractionation
Gravitational Settling Pressure Gradient and Stationary Diffusion
Ion-Neutral Separation Due to Currents Ion-Neutral Separation Due to
Electromagnetic Forces Discussion Summary
Title: Coronal/Interplanetary Factors Contributing to the Intensities
of E > 20 MeV Gradual Solar Energetic Particle Events
Authors: Kahler, Stephen; Burkepile, Joan; Reames, Donald
Bibcode: 1999ICRC....6..248K
Altcode: 1999ICRC...26f.248K
Gradual solar energetic particle (SEP) events are produced in coronal
and interplanetary shocks driven by fast coronal mass ejections
(CMEs). There is a correlation between peak ∼ 20 MeV proton
intensities of SEP events at 1 AU and the associated CME speeds measured
in coronagraph white light images. However, a considerable scatter
is found in that correlation, suggesting that factors other than CME
speeds play significant roles in the production of SEP events. To
search for these additional factors, we use peak 28 to 43 MeV proton
intensities of 17 SEP events from IMP-8 and associated west limb CMEs
from SMM with a restricted 650 to 850 km/s CME speed range. Despite
the narrow CME speed range, the 17 SEP events ranged over more than 4
orders of magnitude. We find that the SEP intensity does not depend on
the CME latitude or even whether the CME lies in the ecliptic plane. SEP
intensities are also independent of CME location in or out of coronal
streamers. There is a weak correlation of SEP intensities with CME
angular width and a strong correlation with ambient SEP intensity.
Title: Streaming-limited Intensities of Solar Energetic Particles
Authors: Reames, D. V.; Ng, C. K.
Bibcode: 1998ApJ...504.1002R
Altcode:
Energetic particles streaming outward from an intense source near the
Sun reach a maximum-intensity plateau when scattering by self-generated
waves restricts the streaming. We compare calculated theoretical values
of the streaming-limited intensities with observations from the Helios
1 and 2 and the NOAA Geostationary Operational Environmental Satellites
(GOES) spacecraft and examine the energy dependence and radial gradient
of the intensities.
Title: Evidence for multiple ejecta: April 7-11, 1997, ISTP Sun-Earth
connection event
Authors: Berdichevsky, D.; Bougeret, J. -L.; Delaboudinière, J. -P.;
Fox, N.; Kaiser, M.; Lepping, R.; Michels, D.; Plunkett, S.; Reames,
D.; Reiner, M.; Richardson, I.; Rostoker, G.; Steinberg, J.; Thompson,
B.; von Rosenvinge, T.
Bibcode: 1998GeoRL..25.2473B
Altcode:
Evidence is presented that the enhanced geomagnetic activity, on
April 10-11, 1997, was caused by one of two ejecta that left the
Sun at ≈ 14 UT on April 7. This ejecta was not directly detected
at the Earth. The evidence for this interpretation is based on WIND
spacecraft observations in the solar wind (SW). It is consistent with:
(i) measured velocities of the coronal mass ejections from the SOHO
coronagraph; (ii) the initial propagation speed of the shock generated
in this event, estimation from type II radio burst observations from the
WAVES instrument on WIND, and (iii) the time profile of energetic ions
observed by EPACT on WIND. This locally unobserved ejecta (moving at 600
to 700 kms-1) generated a fast shock which accelerated ions
to several tens of MeV/amu. The inferred passage of the first ejecta
close to Earth (on April 10 to 11) is based on the observation of an
interplanetary shock (IS) ahead of a field and plasma compressional
region where the draping of the SW flow and possibly the changes in
the direction of the IMF are consistent with a location northward of a
faster ejecta. This ejecta was responsible for disturbed SW conditions
including approximately ten hours of southward orientation of the
interplanetary magnetic field (IMF) and a ram pressure many times
above normal. The slower moving ejecta was directed toward Earth and
was observed with WIND from about 0550 until 1500 UT on April 11. It
had a strong northward IMF and produced density enhancements which
elevated the ram pressure to more than four times above normal.
Title: Solar Energetic Particles: Sampling Coronal Abundances
Authors: Reames, Donald V.
Bibcode: 1998SSRv...85..327R
Altcode:
In the large solar energetic particle (SEP) events, coronal mass
ejections (CMEs) drive shock waves out through the corona that
accelerate elements of the ambient material to MeV energies in
a fairly democratic, temperature-independent manner. These events
provide the most complete source of information on element abundances
in the corona. Relative abundances of 22 elements from H through Zn
display the well-known dependence on the first ionization potential
(FIP) that distinguishes coronal and photospheric material. For most
elements, the main abundance variations depend upon the gyrofrequency,
and hence on the charge-to-mass ratio, Q/A, of the ion. Abundance
variations in the dominant species, H and He, are not Q/A dependent,
presumably because of non-linear wave-particle interactions of H and
He during acceleration. Impulsive flares provide a different sample of
material that confirms the Ne:Mg:Si and He/C abundances in the corona.
Title: Solar Energetic Particles: Sampling Coronal Abundances
Authors: Reames, D. V.
Bibcode: 1998sce..conf..327R
Altcode:
No abstract at ADS
Title: Spatial and Temporal Invariance in the Spectra of Energetic
Particles in Gradual Solar Events
Authors: Reames, D. V.; Kahler, S. W.; Ng, C. K.
Bibcode: 1997ApJ...491..414R
Altcode:
We show evidence of spatial and temporal invariance in the energy
spectra of ~1-100 MeV protons from large gradual solar energetic
particle (SEP) events. Nearly identical spectra are seen over longitude
intervals of up to 160°, and the intensities at all energies decline
with e-folding time constants of 6-18 hr for periods of ~3 days. The
region of the invariant spectra is associated with acceleration on
the eastern flank of the shock wave driven out from the Sun by a
coronal-mass ejection (CME). The quasi-parallel shock in this region
changes only slowly with time, and a quasi equilibrium is established
for particles stored on field lines in the expanding volume between the
shock and the Sun. On the western flank of the shock, the SEP event is
more dynamic. Here, the nearly quasi-perpendicular shock produces harder
spectra that change more rapidly with time as regions of the shock with
varying speed and angle sweep across the observer's field line. Gradual SEP events arise from large CMEs with sufficient speeds
to generate shocks that are fast enough to accelerate particles. In
our study, shocks with transit speed >750 km s-1
always accelerate particles, while those with speeds of 500-750 km
s-1 sometimes do. However, invariant spectra seem to occur
in all gradual SEP events as a consequence of the structure and topology
of the CME and shock.
Title: Late-phase acceleration of energetic ions in corotating
interaction regions
Authors: Reames, D. V.; Ng, C. K.; Mason, G. M.; Dwyer, J. R.; Mazur,
J. E.; von Rosenvinge, T. T.
Bibcode: 1997GeoRL..24.2917R
Altcode:
We report on new high-sensitivity measurements from the WIND spacecraft
of the spatial distributions of 30 keV/amu to 10 MeV/amu ions from
corotating interaction regions (CIRs) that extend far beyond the
confines of the parent high-speed solar-wind stream. Not only do
late-phase MeV ions persist far into the declining solar wind,
but they also show a continual gain in energy, even after sector
boundary passage, until the next small increase in solar wind speed
occurs. These ions are accelerated in the distant heliosphere as the
reverse shock from the CIR propagates completely across the rarefaction
region produced by the declining solar wind, growing in acceleration
efficiency as it propagates. Energetic ions from a single CIR event
are seen for a period of 17 days and ∼225° in solar longitude. The
observed energy spectra can be fit to the theory of Fisk and Lee
[1980] only if shock compression increases with time so that the
spectra harden significantly.
Title: New Spectral and Abundance Features of Interplanetary Heavy
Ions in Corotating Interaction Regions
Authors: Mason, G. M.; Mazur, J. E.; Dwyer, J. R.; Reames, D. V.;
von Rosenvinge, T. T.
Bibcode: 1997ApJ...486L.149M
Altcode:
We have surveyed the composition and energy spectra of heavy ions
accelerated in 17 corotating interaction regions (CIRs) during
solar minimum conditions between 1992 December and 1995 July. Using
new high-sensitivity instruments on WIND and SAMPEX, we are able to
cover the energy range from approximately 20 keV nucleon-1
to greater than 10 MeV nucleon-1, making it possible to
distinguish differing forms of particle spectra. Previous measurements
down to about 0.5 MeV nucleon-1 found exponential energy
spectra; however, at the even lower energies studied here, we find
that the spectral forms become power laws in kinetic energy per
nucleon. At 150 keV nucleon-1 we find that the C:O and Ne:O
ratios depend on solar wind speed. These variations suggest that in
addition to the solar wind, other sources of heavy ions contribute to
the CIR composition.
Title: Energy Spectra of Ions Accelerated in Impulsive and Gradual
Solar Events
Authors: Reames, D. V.; Barbier, L. M.; Von Rosenvinge; T. T.; Mason,
G. M.; Mazur, J. E.; Dwyer; J. R.
Bibcode: 1997ApJ...483..515R
Altcode:
We report new high-sensitivity measurements of the energy spectra of
ions from five impulsive solar flares and one gradual event observed
during solar minimum by the Energetic Particles, Acceleration,
Composition, and Transport (EPACT) experiment aboard the WIND
spacecraft. All of the impulsive-flare events had intensities too low
to be visible on previous spacecraft such as ISEE 3, which observed
hundreds of impulsive-flare events. Often these events cluster in
or behind a coronal mass ejection (CME) where magnetic field lines
provide an excellent connection to a solar active region where flares
are occurring. In most cases we can see velocity dispersion as the
ions of 20 keV amu-1 to 10 MeV amu-1 streamed out
from the impulsive flare at the Sun, arriving in inverse order of their
velocity. Ions from a large, magnetically well-connected gradual event,
associated with a CME-driven shock, also show velocity dispersion early
in the event but show identical time profiles that last for several days
late in the event. These time-invariant spectra of H, 4He,
C, O, and Fe in this gradual event are well represented as power laws in
energy from 20 keV amu-1 to ~100 MeV amu-1. In the
impulsive-flare events, H, 3He, 4He, C, O, and Fe
have more rounded spectra that flatten somewhat at low energies; yet the
intensities continue to increase down to 20 keV amu-1. Most
of the ion energy content appears to lie below 1 MeV in the impulsive
events, where it would be invisible to γ-ray line observations.
Title: A Comparison of Characteristic Shock Speeds and Interplanetary
Energetic Particle Fluxes
Authors: Kahler, S. W.; Reames, D. V.
Bibcode: 1997SPD....28.0267K
Altcode: 1997BAAS...29..905K
Previous comparisons of solar energetic particle (SEP) events at 1 AU
with associated coronal mass ejections (CMEs) have shown a correlation
between peak SEP fluxes and CME speeds. These results have provided
some of the evidence for acceleration of SEPs by CME-driven shocks. We
compare SEP observations from the Helios spacecraft with associated CME
and shock speeds reported by Sheeley et al. (JGR, 1985). We find that
the 3 < E < 6 MeV peak proton fluxes correlate better with the
in situ shock speeds than with either the CME speeds or the average
transit speeds of the shocks. This establishes a closer physical
connection between SEPs and CME-driven shocks than the previous work
which used CME speeds as rough proxies for the shock speeds. We also
examine the speed profiles of a number of fast CMEs observed with the
SOHO LASCO coronagraph to look for distinguishing characteristics of
CMEs associated with SEPs at 1 AU.
Title: WIND/EPACT observations of anomalous cosmic rays
Authors: Reames, D. V.; Barbier, L. M.; von Rosenvinge, T. T.
Bibcode: 1997AdSpR..19..809R
Altcode:
The Energetic Particles, Acceleration, Composition and Transport (EPACT)
Experiment on the WIND spacecraft, and especially its large-geometry
Low Energy Matrix Telescope (LEMT), is capable of sensitive measurements
of ions of the anomalous cosmic-ray (ACR) component above 2 MeV/amu. We
report on the energy spectra of He, C, N, O, Ne, S, and Ar and estimate
element abundances at the acceleration site.
Title: The First Observation of Sulfur in Anomalous Cosmic Rays by
the GEOTAIL and the WIND Spacecrafts
Authors: Takashima, T.; Doke, T.; Hayashi, T.; Kikuchi, J.; Kobayashi,
M.; Shirai, H.; Takehana, N.; Ehara, M.; Yamada, Y.; Yanagita,
S.; Hasebe, N.; Kashiwagi, T.; Kato, C.; Munakata, K.; Kohno, T.;
Kondoh, K.; Murakami, H.; Nakamoto, A.; Yanagimachi, T.; Reames,
D. V.; von Rosenvinge, T. T.
Bibcode: 1997ApJ...477L.111T
Altcode:
The Geotail high-energy particle instruments have observed cosmic-ray
particles in the energy range from 3 MeV n-1 to 150 MeV
n-1 at 1 AU during the period 1992 September-1995 August. A
remarkable enhancement of anomalous cosmic-ray (ACR) N, O, Ne, and C
is observed during the period. A measurable enhancement of the sulfur
flux below about 20 MeV n-1 was observed. This is the first
evidence showing the existence of sulfur in the anomalous component. The
flux increase of anomalous sulfur, with a first ionization potential
(FIP) of 10.4 eV, is smaller than that of ACR carbon with an FIP
of 11.3 eV and much smaller than those of high-FIP elements, which
suggests that the fractions of neutral carbon and sulfur atoms are
significantly low in the very local interstellar medium.
Title: The Helium Valley: Comparison of Impulsive Solar Flare Ion
Abundances and Gyroresonant Acceleration with Oblique Turbulence in
a Hot Multi-Ion Plasma
Authors: Steinacker, Jürgen; Meyer, Jean-Paul; Steinacker, Adriane;
Reames, Donald V.
Bibcode: 1997ApJ...476..403S
Altcode:
We present a detailed interpretation of the heavy ion abundance
enhancements observed in impulsive flare energetic particles, in terms
of the conditions for gyroresonant acceleration by moderately oblique
waves in a hot solar coronal plasma. On the basis of a realistic
coronal plasma containing its complete set of minor ions, we analyze
first all parallel wave modes in terms of their dispersion relation,
damping timescale, and condition for gyroresonant acceleration of
thermal ions, as a function of temperature. We identify the ``Helium
Valley,'' the region in the frequency-wavenumber plane of strong wave
damping by thermal 4He+2 ions, as crucial for
explaining the observed abundances: any ions with charge-to-mass ratio
in the neighborhood of 0.5 cannot be accelerated preferentially,
relative to 4He+2. Then solving the
dispersion relation equation for oblique waves in a hot e-p-He plasma,
we discuss this general class of waves in terms of polarization and
damping timescale. For waves propagating at moderate angles to the
magnetic field (θ ≉ 90°), our calculations indicate that the first
harmonic n = 1 gyroresonance is dominant, and that the corresponding
He valley narrows down for increasing angle θ. Using this analysis, we
calculate the limits of the He valley and investigate the preferential
gyroresonant acceleration of heavy ions by moderately oblique waves
(θ ≉ 90°) in a solar coronal plasma. Only for nearly perpendicular
waves (θ ~ 90°), are higher order resonances important and regions
of wave damping by interaction with thermal particles vanishingly
narrow in frequency. We estimate the fraction of ions of each
element outside the He valley as a function of temperature and compare
the resulting enhanced abundances with the observed enhancements, for
the case of a spectrum of non-quasi-perpendicular waves, as produced
by a cascading of the general turbulence. The results allow us to
specify the range of possible temperatures for the source plasma of
the accelerated particles to between ~2.4 and ~4.5 × 106
K, i.e., comparable to active region (AR), but not to flaring gas,
temperatures. This points to an acceleration of the ions taking place,
either in the AR gas surrounding the flare itself or within the flaring
loop but before it became heated. Constraints are set on the typical
time Δt over which the ions are accelerated preferentially. We
find times between ~5 × 10-4 and ~3 × 10-2
s (for our nominal plasma with density and field of ne =
1010 cm-3 and B = 100 G); it could be ~10 times
larger, if the typical conditions in quiescent ARs (ne ~ 2
× 109 cm-3 and B ~ 200 G) apply also to the bulk
~3 × 106 K gas of flaring ARs. We discuss another physical
interpretation of Δt, if wave cascading is effective. Preliminary
calculations have shown that the proposed selective acceleration
mechanism can be applied in underdense (ωp/Ωe
< 1) as well as in overdense plasmas (our nominal case), provided
that quasi-perpendicular waves (generated, e.g., by an electron beam)
are not dominant.
Title: Solar Energetic-Particle Spectra and the Structure of Coronal
Mass Ejections
Authors: Reames, D. V.; Kahler, S. W.; Ng, C. K.
Bibcode: 1997ICRC....1..185R
Altcode: 1997ICRC...25a.185R
No abstract at ADS
Title: Intensity Gradients of Anomalous Cosmic Ray Oxygen Throughout
the Heliosphere
Authors: Cummings, A. C.; Stone, E. C.; Klecker, B.; Marsden, R. G.;
Mewaldt, R. A.; Reames, D. V.; Trattner, K. J.; von Rosenvinge, T. T.;
Webber, W. R.
Bibcode: 1997ICRC....2..257C
Altcode: 1997ICRC...25b.257C
No abstract at ADS
Title: New Spectral and Abundance Features in Low Energy CIR He
vy Ions
Authors: Mason, G. M.; Mazur, J. E.; Dwyer, J. R.; Reames, D. V.;
von Rosenvinge, T. T.
Bibcode: 1997ICRC....1..377M
Altcode: 1997ICRC...25a.377M
No abstract at ADS
Title: The First Observation of Sulfur in Anomalous Cosmic Rays by
the GEOTAIL and the WIND Spacecrafts
Authors: Takashima, T.; Doke, T.; Hayashi, T.; Kikuchi, J.; Itsumi,
K.; Kobayashi, M.; Shirai, H.; Takehana, N.; Hasebe, N.; Kohdoh, K.;
Kohno, T.; Numakata, K.; Kato, C.; Yanagita, S.; Yamada, Y.; Reames,
D. V.; von Rosenvinge, T. T.
Bibcode: 1997ICRC....2..285T
Altcode: 1997ICRC...25b.285T
No abstract at ADS
Title: The Spatial Distribution of Particles Accelerated by Coronal
Mass Ejection--driven Shocks
Authors: Reames, D. V.; Barbier, L. M.; Ng, C. K.
Bibcode: 1996ApJ...466..473R
Altcode:
We use multispacecraft observations to examine the spatial and temporal
distributions of energetic particles accelerated by shock waves driven
by coronal mass ejections from the Sun. The behavior of the intensity
time profiles ahead of the shock can depend strongly on the longitude
of the point where the observer's magnetic flux tube connects to
the shock, relative to the nose of the shock where acceleration is
strongest. Particle intensities can increase (decrease) with time
as this point swings eastward through ≥ 50° toward (away from)
the shock nose because of solar rotation. Well behind the shock,
intensities are often constant with longitude and the intensities of
these quasi-trapped particles at all energies decrease continuously with
time over many days as their containment volume expands. Delayed proton
events are produced when shocks expand into slow solar wind so they
suddenly encounter an observer's field line far from the Sun. Sunward
flows are seen when the shock passes over the observer or when it
suddenly strikes his field line at radial distances out beyond him.
Title: Heavy ion acceleration by cascading Alfvén waves in impulsive
solar flares
Authors: Miller, James A.; Reames, Donald V.
Bibcode: 1996AIPC..374..450M
Altcode: 1996hesp.conf..450M
We propose that the heavy ion abundance enhancements that are observed
for impulsive solar flares result from stochastic acceleration by
cascading Alfvén wave turbulence. In our model, Alfvén waves are
generated at some large scale and nonlinearly cascade to higher
wavenumbers and frequencies. As the waves increase in frequency,
they will be able to cyclotron resonate with ions of progressively
lower energy. For a thermal plasma there will be no damping at low
wavenumbers and the waves will freely cascade. However, when the wave
frequency becomes close to an ion cyclotron frequency, thermal ions will
be accelerated out of the background and to relativistic energies. The
first ion species encountered by the waves will be the one with the
lowest cyclotron frequency, namely Fe. Due to the low Fe abundance,
the waves will not be completely damped and will continue to cascade up
to the group of ions with the next higher cyclotron frequency, namely
Ne, Mg, and Si. Again, these ions will be accelerated but the waves
will not be totally damped. After Ne, Mg, and Si the waves encounter
4He, C, N, and O, which do completely dissipate the waves
and halt the cascade. We show that abundance ratios similar to those
observed can result from this process.
Title: Energetic particles from solar flares and coronal mass
ejections
Authors: Reames, Donald V.
Bibcode: 1996AIPC..374...35R
Altcode: 1996hesp.conf...35R
We review the recent evidence that distinguishes particles accelerated
in flares and in shock waves driven by coronal mass ejections
(CMEs). CME-driven shocks, not flares, produce most of the large
particle events at 1 AU and can accelerate protons up to 20 GeV. In
contrast, flare-accelerated ions have characteristic abundances produced
by resonant wave-particle interactions in the flare plasma. Only the
direct particle observations have allowed us to study this new physics
of ion acceleration in flares, since the energetic ion abundances have
been largely invisible in photons.
Title: Pitch Angle Diffusion Coefficient in an Extended Quasi-linear
Theory
Authors: Ng, C. K.; Reames, D. V.
Bibcode: 1995ApJ...453..890N
Altcode:
Using an extended quasi-linear theory that takes account of the
distribution of medium-scale background interplanetary magnetic
field, we calculate the pitch angle diffusion coefficients of
interplanetary energetic ions, for a slab turbulence model consisting
of a superposition of parallel and antiparallel transverse R and L
waves. Our results show that the background variation broadens the
resonance function significantly at pitch angles near 90°, so that
protons down to ≍ 25 keV interact with hydromagnetic waves at all
pitch angles, and the steepening of the magnetic field power spectrum
in the dissipation range does not result in a resonance gap or infinite
scattering mean free path.
Title: Solar energetic particles: A paradigm shift
Authors: Reames, Donald V.
Bibcode: 1995RvGeo..33S.585R
Altcode: 1995RvGeS..33..585R
Laboratory for High Energy Astrophysics, NASA Goddard Space Flight
Center, Greenbelt, MarylandThe first evidence of high-energy particles
from the Sun was obtained 50 years ago when Forbush [1946] used
sea-level ion chambers to study the large solar events of February
and March of 1942. Over the next 20 years, observation of these
solar energetic particle (SEP) events using neutron monitors and
riometers (that measure radio opacity of the ionosphere) and, later,
with detectors on balloons and satellites, led to an extensive body
of knowledge on the time profiles, spectra and particle abundance in
the large events. Meanwhile, there was already a rich history of the
study of solar flares spanning 100 years since the first observations
reported by Carrington [1860]. With no knowledge of the existence of
coronal mass ejections (CMEs) [Kahler 1992], it was tempting to assume
that the particle acceleration somehow occurred in spatial and temporal
conjunction with the solar flare itself. Thus the "solar flare myth"
[Gosling 1993] of particle acceleration began nearly 30 years ago.
Title: Coronal abundances determined from energetic particles
Authors: Reames, D. V.
Bibcode: 1995AdSpR..15g..41R
Altcode: 1995AdSpR..15R..41R
Solar energetic particles (SEPs) provide a measurement of coronal
element abundances that is highly independent of the ionization
states and temperature of the ions in the source plasma. The most
complete measurements come from large `gradual' events where ambient
coronal plasma is swept up by the expanding shock wave from a coronal
mass ejection. Particles from `impulsive' flares have a pattern
of acceleration-induced enhancements superimposed on the coronal
abundances. Particles accelerated from high-speed solar wind streams
at corotating shocks show a different abundance pattern corresponding
to material from coronal holes. Large variations in He/O in coronal
material are seen for both gradual and impulsive-flare events but
other abundance ratios, such as Mg/Ne, are remarkably constant. SEP
measurements now include hundreds of events spanning 15 years of
high-quality measurement.
Title: The Energetic Particles: Acceleration, Composition, and
Transport (EPACT) investigation on the WIND spacecraft
Authors: von Rosenvinge, T. T.; Barbier, L. M.; Karsch, J.; Liberman,
R.; Madden, M. P.; Nolan, T.; Reames, D. V.; Ryan, L.; Singh, S.;
Trexel, H.; Winkert, G.; Mason, G. M.; Hamilton, D. C.; Walpole, P.
Bibcode: 1995SSRv...71..155V
Altcode:
The Energetic Particles: Acceleration, Composition, and Transport
(EPACT) investigation is designed to make comprehensive observations
of solar, interplanetary, and galactic particles over wide ranges of
charge, mass, energy, and intensity using a combination of 8 different
particle telescopes. This paper summarizes the scientific goals of
EPACT and provides a detailed description of the instrument design
and capabilities. Electrons are measured from 0.2 to 10 MeV, primarily
providing time markers for injections of solar particles. Hydrogen is
measured from 1.4 to 120 MeV, and Helium is measured from 0.04 to 500
MeV nucl-1. The collection powers and energy ranges for
heavier nuclei up to iron are ideal for observations of quiet-time
populations such as particles accelerated by interplanetary shocks
and the anomalous cosmic rays (thought to be accelerated at the
boundary of the heliosphere). The large collection power available
is also ideal for observations of3He,4He, and
heavier nuclei in impulsive3He-rich solar events. There
is even the possibility of observing ultra heavy nuclei (Z>30) in
large solar events for the first time. Finally, there is a telescope
designed to measure isotopes from He (3.4 55 MeV nucl-1)
to Fe (12 230 MeV nucl-1), which is intended for solar
particles, the anomalous cosmic rays and galactic cosmic rays. The
overall capabilities of EPACT provide scientifically interesting
measurements over all phases of the solar cycle. There will also be
important opportunities for combined studies with other spacecraft,
such as SAMPEX, Ulysses, and Voyagers 1 and 2.
Title: Multispacecraft Studies of Coronal Mass Ejection Associated
Energetic Particle Events
Authors: Barbier, L. M.; Ng, C. K.; Reames, D. V.
Bibcode: 1995ICRC....4..365B
Altcode: 1995ICRC...24d.365B
No abstract at ADS
Title: Interplanetary Transport Coefficient in an Extended
Quasi-linear Theory
Authors: Ng, C. K.; Reames, D. V.
Bibcode: 1995ICRC....4..253N
Altcode: 1995ICRC...24d.253N
No abstract at ADS
Title: The dark side of the solar flare myth
Authors: Reames, D. V.
Bibcode: 1995EOSTr..76..405R
Altcode:
No abstract at ADS
Title: Solar energetic particles: A paradigm shift (95RG00188)
Authors: Reames, Donald V.
Bibcode: 1995iugg.rept..585R
Altcode:
No abstract at ADS
Title: Helium Spectra in Corotating Energetic Particle Streams
Observed by EPACT on the Wind Spacecraft
Authors: Mazur, J. E.; Mason, G. M.; Reames, D. V.; von Rosenvinge,
T. T.
Bibcode: 1995ICRC....4..460M
Altcode: 1995ICRC...24d.460M
No abstract at ADS
Title: Acceleration of energetic particles which accompany coronal
mass ejections
Authors: Reames, D. V.
Bibcode: 1994ESASP.373..107R
Altcode: 1994soho....3..107R
No abstract at ADS
Title: Recombination energy of atomic oxygen and related species at
the mesopause
Authors: Reames, Donald V.
Bibcode: 1994AdSpR..14d.177R
Altcode: 1994AdSpR..14..177R
Total chemical energy release of seven exothermic reactions involving
odd-oxygen and odd-hydrogen species at mesopause heights is studied
here. Monthly and zonally averaged heating rates are calculated on
the basis of atomic oxygen densities and atomic hydrogen densities as
these were measured by the SME satellite. The resulting heating rates
are found to be rather high. Consequently they could help to balance
the energy budget of the upper mesosphere and lower thermosphere.
Title: Focused Interplanetary Transport of approximately 1MeV Solar
Energetic Protons through Self-generated Alfven Waves
Authors: Ng, C. K.; Reames, D. V.
Bibcode: 1994ApJ...424.1032N
Altcode:
We present a model of the focused transport of approximately 1 MeV
solar energetic protons through interplanetary Alfven waves that the
protons themselves amplify or damp. It is based on the quasi-linear
theory but with a phenomenological pitch angle diffusion coefficient in
the 'resonance gap.' For initial Alfven wave distributions that give
mean free paths greater than approximately 0.5 AU for approximately
1 MeV protons in the inner heliosphere, the model predicts greater
than roughly an order of magnitude amplification (damping) in the
outward (inward) propagating resonant Alfven waves at less than or
approximately equal to o.3 AU heliocentric distance. As the strength of
proton source is increased, the peak differential proton intensity at
approximately 1 MeV at 1 AU increases to a maximum of approximately 250
particles (/(sq cm)(s)(sr)(MeV)) and then decreases slowly. It may be
attenuated by a factor of 5 or more relative to the case without wave
evolution, provided that the proton source is sufficiently intense
that the resulting peak differential intensity of approximately
1 MeV protons at 1 AU exceeds approximately 200 particles (/(sq
cm)(s)(sr)(MeV)). Therefore, in large solar proton events, (1) one
may have to take into account self-amplified waves in studying solar
particle propagation, (2) the number of accelerated protons escaping
from a flare or interplanetary shock may have been underestimated in
past studies by a significant factor, and (3) accelerated protons
escaping from a traveling interplanetary shock at r less than or
approximately equal to 0.3 AU should amplify the ambient hydromagnetic
waves siginificantly to make the shock an efficient accelerator, even
if initially the mean free path is greater than or approximately equal
to 1 AU.
Title: Energetic-Particle Abundances in Impulsive Solar Flare Events
Authors: Reames, D. V.; Meyer, J. P.; von Rosenvinge, T. T.
Bibcode: 1994ApJS...90..649R
Altcode: 1994IAUCo.142..649R
We report on the abundances of energetic particles from impulsive solar
flares, including those from a survey of 228 He-3 rich events, with
He-3/He-4 is greater than 0.1, observed by the International Sun Earth
Explorer (ISEE) 3 spacecraft from 1978 August through 1991 April. The
rate of occurrence of these events corresponds to approximately 1000
events/yr on the solar disk at solar maximum. Thus the resonant plasma
processes that enhance He-3 and heavy elements are a common occurrence
in impulsive solar flares. To supply the observed fluence of He-3
in large events, the acceleration must be highly efficient and the
source region must be relatively deep in the atmosphere at a density
of more than 1010 atoms/cu cm. He-3/He-4 may decrease in
very large impulsive events because of depletion of He-3 in the source
region. The event-to-event variations in He-3/He-4, H/He-4, e/p, and
Fe/C are uncorrelated in our event sample. Abundances of the elements
show a pattern in which, relative to coronal composition, He-4, C, N,
and O have normal abundance ratios, while Ne, Mg, and Si are enhanced
by a factor approximately 2.5 and Fe by a factor approximately 7. This
pattern suggests that elements are accelerated from a region of the
corona with an electron temperature of approximately 3-5 MK, where
elements in the first group are fully ionized (Q/A = 0.5), those in
the second group have two orbital electrons (Q/A approximately 0.43),
and Fe has Q/A approximately 0.28. Ions with the same gyrofrequency
absorb waves of that frequency and are similarly accelerated and
enhanced. Further stripping may occur after acceleration as the ions
begin to interact with the streaming electrons that generated the
plasma waves.
Title: Comparison of CMEs, magnetic clouds, and bidirectionally
streaming proton events in the heliosphere using helios data
Authors: Webb, D.; Jackson, B.; Hick, P.; Schwenn, R.; Bothmer, V.;
Reames, D.
Bibcode: 1993AdSpR..13i..71W
Altcode: 1993AdSpR..13...71W
Coronal Mass Ejections (CMEs) are large, energetic expulsions of mass
and magnetic fields from the Sun; they can significantly affect large
volumes of the heliosphere and appear to be a key cause of geomagnetic
storms. We have compiled a list of all significant CMEs detected by
the HELIOS white light photometers from 1975-1982. We are studying the
characteristics of these CMEs, and present preliminary results of their
associations with in-situ features, especially magnetic ``clouds'' and
periods of bidirectionally streaming ions, two classes of structures
considered indicative of interplanetary loops. Advantages of this data
set include reliable association in the interplanetary medium of the
white light CME plasma with the in-situ features, and observations of
a large number of events over a long time base.
Title: Non-thermal particles in the interplanetary medium
Authors: Reames, Donald V.
Bibcode: 1993AdSpR..13i.331R
Altcode: 1993AdSpR..13..331R
During the past few years we have found that the MeV ion populations
from a variety different of solar and interplanetary sources have quite
distinct abundances and spectra. Particles from impulsive flares are
electron rich, have 3He/4He enhancements of up to
104, and enhancements in heavy elements like Fe/C by factors
of 10, relative to coronal abundances. The high ionization state of Fe,
+20, indicates heating of the material to temperatures up to ~20 MK
(1 MK = 106 K). The enhancements are probably produced by
selective absorption of plasma waves in these events. In contrast,
particles from gradual solar events have strong proton enhancements at
high energies, but element abundances and ionization states are more
typical of ambient coronal material. The abundances, time profiles,
and extended longitude distribution of gradual events indicate that
particles are accelerated from the ambient corona and solar wind by
a shock wave that is driven by a coronal mass ejection.
Title: Bidirectional approximately 1 MeV AMU -1 Ion Intervals in
1973--1991 Observed by the Goddard Space Flight Center Instruments
on IMP 8 and ISEE 3/ICE
Authors: Richardson, I. G.; Reames, D. V.
Bibcode: 1993ApJS...85..411R
Altcode:
Bidirectional energetic ion flows (BIFs) in the solar wind at 1AU
during 1973-1991 are examined on the basis of about 1 MeV/amu data
from the Goddard Space Flight Center instruments on ISEE3/ICE and IMP
8. BIFs are observed more frequently around solar maximum, when they are
observed about 12 percent of the time compared with about 5 percent at
solar minimum. Intervals with durations greater than 4 hr are observed
on average approximately every 3-4 d at solar maximum and every 2 wk
at solar minimum, with about 33 percent of these intervals following
within 2 d of an interplanetary shock. Various coronal mass ejection
signatures and BIFs greater than 1 MeV/amu usually do not coincide
exactly, and additional bidirectional ion events are identified.
Title: The EPACT Experiment
Authors: Barbier, L. M.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1993ICRC....3..222B
Altcode: 1993ICRC...23c.222B
No abstract at ADS
Title: Mean Element Abundances in Energetic Particles from Impulsive
Solar Flares
Authors: Reames, D. V.
Bibcode: 1993ICRC....3..388R
Altcode: 1993ICRC...23c.388R
No abstract at ADS
Title: Heavy Ion Acceleration and Abundance Enhancements in Impulsive
Solar Flares
Authors: Miller, J.; Viñas, A.; Reames, D. V.
Bibcode: 1993ICRC....3...17M
Altcode: 1993ICRC...23c..17M
No abstract at ADS
Title: Corotating MeV/amu ion enhancements at <=1 AU from 1978
to 1986
Authors: Richardson, I. G.; Barbier, L. M.; Reames, D. V.; von
Rosenvinge, T. T.
Bibcode: 1993JGR....98...13R
Altcode:
MeV/amu ion enhancements associated with corotating high-speed
solar wind streams in 1978-1986 during pre-solar maximum to near
solar minimum conditions are studied using ISEE 3/ICE, IMP 8, and
Helios 1 data. Around 50% of corotating streams contain energetic
ion increases. These increases extend to ~25 MeV/amu, where they
merge into the galactic cosmic ray background, and are most evident
approaching solar minimum. Sunward ion streaming in the solar wind
frame (first-order anisotropy ~20%) and positive radial intensity
gradients (~400%/AU) are consistent with acceleration in the
outer heliosphere at corotating shocks followed by streaming into
the inner heliosphere. The spectra and intensities show little
solar cycle variation. The spectra of ions from protons to Fe
at ~2-20 MeV/amu are approximated equally well by exponentials
in momentum dJ/dP~exp(-P/P0), P0=11-16
MeV c-1 amu-1, or by
distribution functions f~exp(-v/v0), v0=0.18-0.25
(MeV/amu)1/2, with equivalent power law in energy slopes
in the range ~-3 to -4. Ion abundances are correlated with the
stream peak solar wind speed. In slower corotating streams
(maximum solar wind speed <600 km/s), mean abundance ratios are
protons/4He=43+/-18 4He/O=54+/-23 C/O =0.62+/-0.06
Mg/O=0.19+/-0.03, and Fe/O=0.14+/-0.02. These show some similarity
to the corresponding ratios for ``solar energetic particles'' (SEP)
(protons/4He=70+/-10 4He/O=55+/-3 C/O=0.48+/-0.02
Mg/O=0.21+/-0.01 and Fe/O=0.16+/-0.02) which are typically accelerated
by shocks passing through slow solar wind. In corotating events in
higher-speed streams, these ratios become protons/4He=19+/-5
4He/O=130+/-35 C/O=0.89+/-0.05 Mg/O=0.14+/-0.01, and
Fe/O=0.10+/-0.01 and more closely resemble the corotating event
abundance ratios measures in high-speed streams during the mid-1970s
solar minimum (protons/4He=17+/-7 4He/O~160+/-50
C/O=0.89+/-0.1 Mg/O=0.13+/-0.03, and Fe/O=0.096+/-0.05). Solar wind
plasma may also show similar variations in composition with solar
wind speed (based on the limited solar wind composition with solar
wind speed (based on the limited solar wind composition measurements
available) so that the energetic ion compositions are consistent with
the acceleration of corotating event ions and SEPs from the solar
wind. The ordering of corotating event and solar wind abundances by
first ionization potential and their variation with solar wind speed
suggest that conditions in the ion-neutral fractionation region in the
upper chromosphere determine the abundances and are associated in some
way with regulation of the solar wind speed.
Title: Recent Observations and the Modeling of Solar Proton Events
Authors: Reames, D. V.
Bibcode: 1993stp2.conf..302R
Altcode:
No abstract at ADS
Title: An On-board Particle Identification Algorithm for the WIND
Spacecraft
Authors: Von Rosenvinge, T. T.; Barbier, L. M.; Reames, D. V.
Bibcode: 1993ICRC....3..400V
Altcode: 1993ICRC...23c.400V
No abstract at ADS
Title: Selective 3He and Fe Acceleration in Impulsive
Solar Flares
Authors: Miller, J.; Viñas, A.; Reames, D. V.
Bibcode: 1993ICRC....3...13M
Altcode: 1993ICRC...23c..13M
No abstract at ADS
Title: Energetic particle observations and the abundances of elements
in the solar corona.
Authors: Reames, Donald V.
Bibcode: 1992ESASP.348..315R
Altcode: 1992cscl.work..315R
During the last few years it has become clear that energetic particles
in the largest solar events, where abundances are commonly measured,
are not accelerated in flares. Rather they are accelerated from
the ambient plasma above active regions by shock waves driven by
coronal mass ejections. The lowest energy particles from these events
have abundances that almost directly reflect those of the source
plasma. Residual effects of acceleration, that depend smoothly on the
ion's coronal Q/A, vanish when abundances are averaged over many events,
yielding the characteristic dependence of the average coronal abundances
on the first ionization potential (FIP) of the elments from H through
Fe. In contrast, energetic ions accelerated out of the high-speed
solar wind from large coronal holes show a reduced FIP effect with a
different pattern.
Title: Particle acceleration in solar flares: Observations
Authors: Reames, Donald V.
Bibcode: 1992AIPC..264..213R
Altcode: 1992pacp.work..213R
Contrary to our historical understanding, the energetic particles in
most major solar proton events do not come from the flare itself. The
particle abundances, ionization states, time evolution and longitude
distributions all indicate that the particles are accelerated from the
ambient plasma by a shock wave driven by a coronal mass ejection in
these events. In contrast, the particles that do come from impulsive
solar flares are unique in character. These particles are electron
rich, have 3He/4He enhancements of up to 104, and enhancements in heavy
elements such as Fe/C by factors of 10. The high ionization state of
Fe, +20, indicates that the material has been heated to temperatures
of ~2×107 K. It is generally believed that preferential heating
by selective absorption of plasma waves is combined with stochastic
acceleration in these events. Recent studies of the broad gamma-ray
lines emitted by energetic particles within the flare loops indicate
that they are also Fe rich, 3He rich and proton poor like the particles
seen at 1 AU. In large impulsive events, particles from the impulsive
phase may be re-accelerated by a coronal blast-wave shock.
Title: Study of CMES Observed in the Heliosphere Using HELIOS
Photometer, Magnetic Field and Plasma Data
Authors: Webb, D. F.; Jackson, B. V.; Reames, D. V.
Bibcode: 1992AAS...180.1105W
Altcode: 1992BAAS...24..747W
The zodiacal light photometers on the two Helios spacecraft have been
used to identify and study the characteristics of solar mass ejections
within 1 AU of the Sun. We have compiled a list of all significant
CMEs detected by the photometers between 1975 and 1985. We examine
the in-situ characteristics of a subset of these CMEs which enveloped
the spacecraft. In particular, we present results of analyses of
structures considered to be manifestations of interplanetary CMEs,
such as magnetic "clouds", shocks and periods of bidirectionally
streaming ions at energies of about 1 MeV. An important advantage of
this data set is that it permits us to make reliable associations in
the interplanetary medium over a long time base between many white
light CMEs and their in-situ proxies.
Title: Energy Spectra of Ions from Impulsive Solar Flares
Authors: Reames, D. V.; Richardson, I. G.; Wenzel, K. -P.
Bibcode: 1992ApJ...387..715R
Altcode:
A study of the energy spectra of ions from impulsive solar flares in
the 0.1-100 MeV region is reported. Most of the events studied are
dominated by He and these He spectra show a persistent steepening or
break above about 10 MeV resulting in an increase in the power-law
spectral indices from about 2 to about 3.5 or more. Spectra of H,
He-3, O, and Fe have spectral indices that are consistent with a
value of about 3.5 above about 2 MeV/amu. One event, dominated by
protons, shows a clear maximum in the spectrum near 1 MeV. If the
rollover in the spectrum below 1 MeV is interpreted as a consequence
of matter traversal in the solar atmosphere, then the source of the
acceleration would lie only about 800 km above the photosphere, well
below the corona. Alternative interpretations are that trapping in
the acceleration region directly causes a peak in the resulting ion
spectrum or that low-energy particles encounter significant additional
scattering during transport from the flare.
Title: Trapping and Escape of the High Energy Particles Responsible
for Major Proton Events
Authors: Reames, D. V.
Bibcode: 1992LNP...399..180R
Altcode: 1992IAUCo.133..180R; 1992esf..coll..180R
During the last few years, we have learned to distinguish the particle
acceleration mechanisms involved in impulsive and gradual flares
directly from particle observations at 1 AU. Energetic particles
from impulsive flares are characterized as rich in electrons, 3He,
and Fe and high ionization states of Fe indicate that the material
has been heated in the flare. Particles from these events are only
seen from magnetically well-connected flares, and the particles reach
maximum intensity in a few hours. Particles from gradual events have
heavy element abundances (e.g. Fe/C) and ionization states that are
near their coronal values but protons are strongly enhanced. Gradual
events come from a wide longitude region and particle intensities remain
high for several days, much longer than the associated phenomena at the
Sun. Most major proton events are gradual events, but some are impulsive
or have both impulsive and gradual phases. The extended evolution of the
major proton events in space and time can no longer be understood in
terms of slow diffusive transport of particles through the corona and
interplanetary medium, since particles from the impulsive events are
found to behave much differently. The observations can be understood
only if the major gradual events involve a large interplanetary shock
wave that accelerates particles over an extended region of longitude
for a long time. Wave-particle interactions play a major role in the
trapping and acceleration of particles in large events. Streaming
particles may be scattered by self-amplified waves that provide a
throttling mechanism that limits the particle intensities from large
events and distributes particles in time as they leak from the source
region. Diffusive containment allows particle acceleration to occur on
open as well as closed field lines in both impulsive and gradual events.
Title: On the Differences in Element Abundances of Energetic Ions
from Corotating Events and from Large Solar Events
Authors: Reames, D. V.; Richardson, I. G.; Barbier, L. M.
Bibcode: 1991ApJ...382L..43R
Altcode:
The abundances of energetic ions accelerated from high-speed solar
wind streams by shock waves formed at corotating interaction regions
(CIRs) where high-speed streams overtake the lower-speed solar wind are
examined. The observed element abundances appear to represent those of
the high-speed solar wind, unmodified by the shock acceleration. These
abundances, relative to those in the solar photosphere, are organized
by the first ionization potential (FIP) of the ions in a way that is
different from the FIP effect commonly used to describe differences
between abundances in the solar photosphere and those in the solar
corona, solar energetic particles (SEPs), and the low-speed solar
wind. In contrast, the FIP effect of the ion abundances in the CIR
events is characterized by a smaller amplitude of the differences
between high-FIP and low-FIP ions and by elevated abundances of He,
C, and S.
Title: Multispacecraft Observations of Solar 3He-rich Events
Authors: Reames, D. V.; Kallenrode, M. -B.; Stone, R. G.
Bibcode: 1991ApJ...380..287R
Altcode:
A systematic search of He isotope observations on the Helios 1 and
2 spacecraft during the occurrence of 66 (He-3)-rich time periods
observed on ISEE 3 over a 4-yr interval is reported. Seven time-periods
show possible event associations but only three show confirmed events
with similar He-3/He-4 ratios on Helios and ISEE 3. Kilometric radio
observations of type III bursts produced by electrons associated with
the (He-3)-rich events are used to map the interplanetary field lines
outward from the events. The observations are best explained in terms
of a narrow cone of emission of the particles from these events.
Title: Element Abundances in Solar 3He-Rich Events
Authors: Reames, D. V.; Cane, H. V.; von Rosenvinge, T. T.; Meyer,
J. -P.
Bibcode: 1991ICRC....3..319R
Altcode: 1991ICRC...22c.319R; 1991icrc...22....7R
The results of a survey of over 228 (He-3)-rich events, with He-3/H-4
of more than 0.1, observed by the ISEE-3 spacecraft from 1978 August
through 1991 April. In these events the elements above C are enhanced
relative to the corresponding abundances in the corona and the degree
of enhancement increases with Z or A. The flare-to-flare variations
in abundances are different in character from those seen in large
proton events. For example, using Fe/C as a parameter to describe these
variations, the slope of the least-squares fits to ln(X/C) vs ln(Fe/C),
where X is the intensity of N, O, Ne, Mg, Si, or S. Slopes of these
abundance-correlation lines are much steeper for the (He-3)-rich events
than for a sample of 36 large proton events, especially for Ne and
heavier ions. The event-to-event variations for the (He-3)-rich events
distinguish 3 groups of elements, He-O, Ne-S, and Fe. The abundances
of all of the species within each group seem to vary in unison.
Title: Size Distributions of Solar Energetic Particle Events
Authors: Cliver, E.; Reames, D.; Kahler, S.; Cane, H.
Bibcode: 1991ICRC....3...25C
Altcode: 1991ICRC...22c..25C; 1991icrc...22....2C
NASA particle detectors on the IMP-8 are employed to determine the size
distributions of the peak fluxes of events related to solar-energetic
particles including protons and electrons. The energetic proton events
show a flatter size distribution which suggests that not all flares
are proton flares. Both the electron and proton events are classified
as either 'impulsive' or 'gradual', and the impulsive events tend to
have a steeper power-law distribution.
Title: Focused Interplanetary Transport of Solar Energetic Particles
Through Self-Generated Alfven Waves
Authors: Ng, C. K.; Reames, D. V.
Bibcode: 1991ICRC....3..209N
Altcode: 1991ICRC...22c.209N; 1991icrc...22....4N
The coupled evolution of solar-flare protons and interplanetary Alfven
waves based on the quasi-linear theory implies an order of magnitude
amplification (damping) in the outward (inward) propagating left helical
resonant Alfven waves at less than 0.4-AU helioradius, if the proton
intensity at 1 AU exceeds 300 particles/(sq cm s sr MeV) at 1 MeV,
and the initial wave intensities give mean free paths of more than 0.5
AU. The wave growth significantly retards solar-particle transport,
and has implications on the nature of solar-wind turbulence.
Title: Bidirectional MeV/n Ion Intervals: Observations from the
Goddard Space Flight Center Instruments on the ISEE 3/ICE, IMP 8,
Helios-1 and Helios-2 Spacecraft
Authors: Richardson, I. G.; Reames, D. V.
Bibcode: 1991ICRC....3..292R
Altcode: 1991icrc...22....6R; 1991ICRC...22c.292R
A search is made for intervals of bidirectional energetic ion streaming
in approximately 1 MeV data from the instruments on ISEE 3/ICE,
IMP 8 and Helios 1 and 2 during 1973 to 1989. The longest duration
intervals are found around solar maximum, consistent with the expected
association with coronal mass ejections. The ISEE 3/ICE intervals are
associated with previously identified bidirectional 35-1000 keV ions
and solar-wind electron heat fluxes, though additional bidirectional
intervals are found.
Title: Radial Propagation of Solar Energetic Particles Assuming
Large Scattering Mean Free Paths in the Interplanetary Medium
Authors: Mason, G. M.; Reames, D. V.; Ng, C. K.
Bibcode: 1991ICRC....3..197M
Altcode: 1991icrc...22....3M; 1991ICRC...22c.197M
Observations of two flares which fit the diffusive model by Beeck
et al. (1987) are employed to determine whether large solar-particle
events can be explained by the mechanisms of small impulsive events. It
is shown that the injection of particles at the source is extended in
time and lasts more than approximately 10 hours. The extended injection
at the sun is hypothesized to be the reason that large solar particles
do not demonstrate the 'pulse/wake' behavior associated with the small
impulsive events.
Title: MeV/n Ions Associated with Corotating High-speed Solar Wind
Streams at < 1 AU during 1978 to 1986
Authors: Richardson, I. G.; Barbier, L. M.; Reames, D. V.; von
Rosenwinge, T. T.
Bibcode: 1991ICRC....3..288R
Altcode: 1991ICRC...22c.288R; 1991icrc...22....5R
Data from the Goddard Space Flight Center experiments on the ISEE 3/ICE,
IMP 8, and Helios 1 spacecraft are used to investigate ion enhancements
of more than 1 MeV/n associated with corotating high-speed solar wind
streams at least 1 AU during 1978-1986. The observations are consistent
with ion acceleration from the solar wind by corotating shocks in the
outer heliosphere.
Title: Energy Spectra of Ions from Impulsive Solar Flares
Authors: Reames, D. V.; Richardson, I. G.; Wenzel, K. -P.
Bibcode: 1991ICRC....3...13R
Altcode: 1991ICRC...22c..13R; 1991icrc...22....1R
A study of the energy spectra of ions from impulsive solar flares
in the 0.1 to 100 MeV region is reported with data from the combined
observations of experiments on the ISEE 3 and IMP 8 spacecraft. Most
of the events studied are dominated by He, and these He spectra show
a persistent steepening or break above about 10 MeV resulting in
an increase in the power-law spectral indices from about 2 to about
3.5 or more. One event, dominated by protons, shows a clear maximum
in the spectrum near 1 MeV. If the rollover in the spectrum below 1
MeV is interpreted as a consequence of matter traversal in the solar
atmosphere, then the source of the acceleration would lie only about
800 km above the photosphere, well below the corona. An alternative
interpretation is that trapping in the acceleration region directly
causes a peak in the spectrum.
Title: Abundance variations in solar energetic particles
Authors: Cane, H. V.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1991ICRC....3..327C
Altcode: 1991ICRC...22c.327C; 1991icrc...22....8C
Abundance variations are examined in a large number of events including
smaller nonimpulsive events not previously considered. Whereas a
comparison at equal energy per nucleon is appropriate for heavy ions
this is not the case when including H. The best representation is
either in terms of rigidity or energy per charge depending on the
type of event under consideration. For the majority of large events,
where particles are primarily accelerated at interplanetary shocks, if
abundances relative to H are evaluated at equal energy per charge then
abundance ratios are compatible with solar wind values and spectral
shapes agree. Furthermore the behavior of H is then compatible with
that of other high FIP elements.
Title: Probing the magnetic topologies of magnetic clouds by means
of solar energetic particles
Authors: Kahler, S. W.; Reames, D. V.
Bibcode: 1991JGR....96.9419K
Altcode:
Magnetic clouds are large (<0.25 AU) interplanetary regions with
topologies consistent with those of magnetic loops. They are of
interest because they may be an interplanetary signature of coronal
mass ejections. Clouds have been identified in solar wind data by
their magnetic properties and by the presence of bidirectional particle
fluxes. Two possible closed magnetic topologies have been considered for
clouds: (1) an elongated bottle with field lines rooted at both ends
in the Sun and (2) a detached magnetic bubble or plasmoid consisting
of closed field lines. The inferred topologies are also consistent
with open field lines that converge beyond 1 AU. We have used solar
energetic particles (SEPs) as probes of the cloud topologies. The rapid
access of SEPs to the interiors of many clouds indicates that the cloud
field lines extend back to the Sun and hence are not plasmoids. The
small modulation of galactic cosmic rays associated with clouds also
suggests that the magnetic fields of clouds are not closed. ©1991
American Geophysical Union
Title: Solar Particle Abundances at Energies Greater than 1 MeV per
Nucleon and the Role of Interplanetary Shocks
Authors: Cane, H. V.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1991ApJ...373..675C
Altcode:
The abundances of elements in large solar energetic-particle events
in the energy range of 2-12 MeV per nucleon are examined. It is
confirmed that the abundances relative to mean values vary approximately
monotonically as a function of mass, except for He-4; some events show
a gradual depletion of heavy ions, whereas a small number displays a
gradual increase. A further organization of abundance data is shown,
which depends on the longitude of the source region. Enhancements in
Fe/C and other heavy elements relative to C occur when source regions
are near west 60 deg; the enhancements are attributed to the sampling
of a flare-heated material. Depletions of these elements are found to
be greatest for source regions near central meridian; they are matched
by a steepening of the spectrum and can be understood in terms of
diffusive shock acceleration.
Title: Solar Abundances from Gamma-Ray Spectroscopy: Comparisons
with Energetic Particle, Photospheric, and Coronal Abundances
Authors: Murphy, R. J.; Ramaty, R.; Kozlovsky, B.; Reames, D. V.
Bibcode: 1991ApJ...371..793M
Altcode:
Accelerated particle and ambient gas abundances have been derived using
solar flare gamma-ray spectroscopy. The results with photospheric
and coronal abundances, as well as with solar energetic particle
abundances. This is the first time that the composition of accelerated
particles interacting in an astrophysical source has been compared with
the composition of particles escaping from the source. The analysis
shows that the derived composition of the accelerated particles is
different from the composition of particles observed in large proton
flares; rather, it resembles the composition observed in He-3-rich
flares. The analysis also suggests an ambient gas composition which
differs from the composition of both the photosphere and the corona.
Title: Quiet-Time Properties of Low-Energy (< 10 MeV per Nucleon)
Interplanetary Ions during Solar Maximum and Solar Minimum
Authors: Richardson, I. G.; Reames, D. V.; Wenzel, K. -P.;
Rodriguez-Pacheco, J.
Bibcode: 1990ApJ...363L...9R
Altcode:
The abundances and spectra of 1-10 MeV per nucleon protons, He-3, He-4,
C, O, and Fe have been exmained during solar quiet periods from 1978
to 1987 in an effort to investigate the recent suggestion by Wenzel et
al. (1990) that the ions may be of solar origin. It is found that the
intensities of the ions, other than O, fall by an order of magnitude
between solar maximum and solar minimum, and that the greater than 1
MeV per nucleon ions exhibit weak streaming away from the sun. More
significantly, the quiet-time ions during solar maximum have He-3-rich
and Fe-rich abundances which are established characteristics of small
impulsive solar flares. Thus, it is suggested that small unresolved
impulsive flares make a substantial contribution to the 'quiet-time'
fluxes. He-4 from these flares may also contribute strongly to the ion
spectra that were reported for the 35-1600 keV energy range by Wenzel
et al.
Title: Acceleration of Energetic Particles by Shock Waves from Large
Solar Flares
Authors: Reames, Donald V.
Bibcode: 1990ApJ...358L..63R
Altcode:
Time-intensity profiles for solar proton events are analyzed with
respect to the acceleration of energetic particles from the ambient
solar wind by an interplanetary shock. The time-intensity profiles
are derived from the Helio 1 particle data base for 1974 to 1984. It
is found that many of the large proton events display a prolonged
plateau. The Fe/O abundances in the large proton events are studied. It
is observed that initially the Fe/O ratio is high (about 1.0), but
after proton intensities increase to about 100 protons/sq cm sr sec
MeV the Fe/O ratio decreases to a value near 0.1.
Title: Energetic Particle Abundances in Solar Electron Events
Authors: Reames, D. V.; Cane, H. V.; von Rosenvinge, T. T.
Bibcode: 1990ApJ...357..259R
Altcode:
The results of a comprehensive search of the ISEE 3 energetic particle
data for solar electron events with associated increases in elements
with atomic number Z = 6 or greater are reported. A sample of 90 such
events was obtained. The events support earlier evidence of a bimodal
distribution in Fe/O or, more clearly, in Fe/C. Most of the electron
events belong to the group that is Fe-rich in comparison with the
coronal abundance. The Fe-rich events are frequently also He-3-rich
and are associated with type III and type V radio bursts and impulsive
solar flares. Fe-poor events are associated with type IV bursts and with
interplanetary shocks. With some exceptions, event-to-event enhancements
in the heavier elements vary smoothly with Z and with Fe/C. In fact,
these variations extend across the full range of events despite inferred
differences in acceleration mechanism. The origin of source material
in all events appears to be coronal and not photospheric.
Title: Energetic Particles from Impulsive Solar Flares
Authors: Reames, Donald V.
Bibcode: 1990ApJS...73..235R
Altcode:
Observations of solar energetic particles from impulsive flares are
reviewed. Consideration is given to observations of electron events,
He-3 rich events, and heavy-nuclei-rich events. It is found that these
observations can be unified into a description of the particles from
impulsive flares. The observations are compared with observations of
gamma-ray line in impulsive flares and particles in flares and compared
with particles in space. A model for accelerating the unique particle
abundances of energetic particles is proposed.
Title: Solar Neutron Decay Proton Observations in Cycle 21
Authors: Evenson, Paul; Kroeger, Richard; Meyer, Peter; Reames, Donald
Bibcode: 1990ApJS...73..273E
Altcode: 1990ApJS...73..272E
Measurement of the flux and energy spectrum of the protons resulting
from the decay of solar flare neutrons gives unique information on the
spectrum of neutrons from 5 to 200 MeV. Neutrons from three flares
have been observed in this manner during solar cycle 21. The use of
the decay protons to determine neutron energy spectra is reviewed,
and new and definitive energy spectra are presented for the two large
flares on June 3, 1982 and April 25, 1984.
Title: The Relationship between Energetic Particles and Flare
Properties for Impulsive Solar Flares
Authors: Cane, H. V.; Reames, D. V.
Bibcode: 1990ApJS...73..253C
Altcode:
The impulsive mode of particle acceleration is studied by searching
for 0.2-2 MeV electron increases associated with intense type
III/V bursts. It is found that the presence of a type III/V burst
in association with a relatively intense flare event indicates the
acceleration and escape of greater than 100 KeV electrons. A list
of type III/V electron events is compiled, showing that the majority
included greater than 10 MeV proton increases, although they were not
followed by a type II burst. The results suggest that there are two
different modes of proton acceleration with the second mode becoming
significant only for larger, gradual flares.
Title: The energetic particles: Acceleration, composition, and
transport (EXPACT) experiment on the ISTP/wind spacecraft
Authors: Reames, D. V.; von Rosenvinge, T. T.; Ramaty, R.; Mason,
G. M.; Hamilton, D. C.; Forman, M. A.; Webber, W. R.
Bibcode: 1990AIPC..203...32R
Altcode: 1990pacr.rept...32R
The EPACT experiment will measure abundances, spectra and angular
distributions of particles from 20 keV/amu to 500 MeV/amu. At high
energies, isotopes will be resolved up through Z=26, at intermediate
energies elements with 1<Z<82 will be observed at at low energies
element abundances above Z=2 will be resolved for the first time.
Title: POsitron Electron Magnet Spectrometer (POEMS) for the Eos
Mission
Authors: Evenson, Paul; Wefel, John P.; Swordy, Simon; Streitmatter,
Robert; Salamon, Michael; Barbier, Louis; Guzik, T. Gregory;
Magee-Sauer, Karen P.; Mitchell, John W.; Ormes, Jonathan; Ramaty,
Reuven; Reames, Donald
Bibcode: 1990AIPC..203...58E
Altcode: 1990pacr.rept...58E
The POsitron Electron Magnet Spectrometer (POEMS) has been selected to
enter definition phase study for flight on one of the Earth Observing
System (Eos) polar platforms. Following launch, which could comes as
early as 1997, POEMS will measure the critical positron and electron
components of the cosmic radiation and utilize this information to trace
processes occurring within our geospace environment, in solar flares,
in the solar wind, and elsewhere in the galaxy. In addition, POEMS will
measure heavier charged particles to complement the electron/positron
measurements. With POEMS data we will investigate the origin (primary
or secondary) of galactic positrons, study the charge sign dependence
of solar modulation over a large fraction of a solar magnetic cycle,
measure positron and neutral particle emission from solar flares,
and monitor the temporal variations of the charged intensities and
energy spectra in the Eos orbit. Two orthogonal charged particle
telescopes are used, each terminating in a shared bismuth germanate
(BGO) detector array that also serves as a calorimeter for neutral
particles, specifically neutrons and gamma-rays from solar flares.
Title: The EPACT Experiment for the WIND Spacecraft
Authors: von Rosenvinge, T. T.; Reames, D. V.
Bibcode: 1990ICRC....5..125V
Altcode: 1989ICRC....5..125V; 1990ICRC...21e.125V
The Energetic Particle: Acceleration, Composition and Transport (EPACT)
experiment for the WIND spacecraft to be launched in late 1992 is
presented. This experiment is designed to study the acceleration,
composition and transport of a wide variety of energetic particle
populations, including particles accelerated in interplanetary shocks,
particles from solar flares, the anomalous component, and the Galactic
cosmic rays.
Title: Coronal Mass Ejections and the Injection Profiles of Solar
Energetic Particle Events
Authors: Kahler, S. W.; Reames, D. V.; Sheeley, N. R., Jr.
Bibcode: 1990ICRC....5..183K
Altcode: 1989ICRC....5..183K; 1990ICRC...21e.183K
Previous studies using Skylab and Solwind coronagraph observations have
shown that almost all E greater than 10 MeV solar energetic proton (SEP)
events are associated with the occurrence of a coronal mass ejection
(CME). These earlier studies did not address the relationship between
the position of the associated CME and the timing of the injection
of particles into the interplanetary medium. Ten cases are selected
in which a SEP event observed with the GSFC detectors on the IMP 8 or
ISEE 3 spacecraft was correlated to a CME well observed by the Solwind
coronagraph. The height of the leading edge of the CME is compared with
the particle injection profiles for several energy ranges using the
solar release times for the particles. The derived injection profiles
are found to be increasing and sometimes reaching maximum while the
associated CMEs are at heights of 2-10 Ro.
Title: The Origin of Solar Particle Events With Low Fe/O
Authors: Cane, H. V.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1990ICRC....5..370C
Altcode: 1990ICRC...21e.370C
The origins of particle events which have low Fe/O are studied, and
it is found that the majority are associated with interplanetary
shocks. Separately Fe/O associated with all strong shocks in the
same time period are examined. The important role played by shocks
is substantiated by establishing that the average Fe/O ratio for days
when a strong shock passes is 0.1, below the average value of 0.2 for
large solar proton events and the solar wind. The variations of other
elements are also shown.
Title: Solar Energetic Particles as Probes of the Structures of
Magnetic Clouds
Authors: Kahler, S. W.; Reames, D. V.
Bibcode: 1990ICRC....5..245K
Altcode: 1990ICRC...21e.245K
Two possible closed magnetic topologies are considered for clouds:
an elongated bottle with field lines rooted at both ends in the
sun and a magnetic bubble or plasmoid consisting of closed field
lines. Solar energetic particles (SEPs) are used as probes of the
cloud topologies. The rapid access of SEPs to clouds in many events
indicates that the cloud field lines extend back to the sun.
Title: Positron Electron Magnet Spectrometer (POEMS) for the Eos
Mission
Authors: Evenson, P.; Wefel, P. J.; Swordy, S.; Streitmatter, R.;
Salamon, M.; Barbier, L.; Guzik, G. T.; Magee-Sauer, P. K.; Mitchell,
W. J.; Ormes, J.; Ramaty, R.; Reames, D.
Bibcode: 1990ICRC....3..265E
Altcode: 1989ICRC....3..265E; 1990ICRC...21c.265E
No abstract at ADS
Title: Energetic-Particle Abundances in Impulsive Solar Flares
Authors: Reames, D. V.; Cane, H. V.; von Rosenvinge, T. T.
Bibcode: 1990ICRC....5..108R
Altcode: 1989ICRC....5..108R; 1990ICRC...21e.108R
The abundances of elements and of He-3 in 90 solar electron events
have been examined. It is found that the events fall into two distinct
groups based upon their F/C ratio. Events in the F-rich group frequently
have high He-3/He-4 ratios and are associated with type III and type
V radio bursts in the parent flare. The F-poor events are associated
with type IV bursts. These results on individual events support the
conclusions of earlier work done with daily-averaged abundances.
Title: Solar Flare Nuclear Gamma Rays and Interplanetary Proton Events
Authors: Cliver, E. W.; Forrest, D. J.; Cane, H. V.; Reames, D. V.;
McGuire, R. E.; von Rosenvinge, T. T.; Kane, S. R.; MacDowall, R. J.
Bibcode: 1989ApJ...343..953C
Altcode:
Gamma-ray line (GRL) and solar energetic proton (SEP) events observed
from February 1980 through January 1985 are compared in order to
substantiate and better characterize the lack of correlation between
GRL fluences and SEP event peak fluxes. The scatter plot of SEP event
peak flux vs. GRL fluence is presented, and the ratio of 'solar' to
'interplanetary', about 10 MeV protons, is presented. It is shown that,
while even large SEP events can originate in flares lacking detectable
GRL emission, the converse case of flares with a significant GRL line
fluence by lacking protons in space is rare. The ratio R of the number
of about 10 MeV protons that produce GRL emission at the flare site
to the number of about 10 MeV protons detected in space can vary from
event to event by four orders of magnitude. There is a clear tendency
for impulsive flares to have larger values of R than long-duration
flares, where the flare time scale is given by the e-folding decay
time of the associated soft X-ray emission.
Title: Wave Generation in the Transport of Particles from Large
Solar Flares
Authors: Reames, Donald V.
Bibcode: 1989ApJ...342L..51R
Altcode:
The growth rate of Alfven waves produced by energetic solar
protons streaming outward from large solar flares is estimated. The
mathematical development is directly analogous to that used to describe
the self-containment of cosmic rays in the Galaxy. It is found that
sufficient intensities of streaming protons can generate Alfven waves
that reduce the scattering mean free path of the particles that produce
the waves. This scattering impedes further flow of particles. The
estimated growth rate of the waves depends linearly upon the particle
intensity so that lower energy particles are much more strongly affected
than high-energy particles for typical solar spectra.
Title: The Properties of Energetic Particles Associated with Type
III Bursts
Authors: Cane, H. V.; Reames, D. V.
Bibcode: 1989BAAS...21..836C
Altcode:
No abstract at ADS
Title: Solar Energetic Particles as Probes of the Structure of
Magnetic Clouds
Authors: Kahler, S. W.; Reames, D. V.; McGuire, R. E.
Bibcode: 1989BAAS...21Q.857K
Altcode:
No abstract at ADS
Title: Solar particle composition, spectra, and frequency of
occurrence
Authors: Reames, D. V.
Bibcode: 1989AIPC..186...86R
Altcode: 1989herb.book...86R
The radiation background from solar-particle events can assume different
forms as the energy and composition of the particles changes from
event to event. It has recently become clear that different particle
composition and spectra arise from different classes of events at
the sun and we have learned how to associate the properties of the
particles with the radio, X-ray and optical observations of the parent
flares or with the related interplanetary shock.
Title: An explanation of the correlation between 3He rich
flares and non-relativistic electron events.
Authors: Cargill, P. J.; Ramadurai, S.; Reames, D. V.
Bibcode: 1989BAAS...21.1027C
Altcode:
No abstract at ADS
Title: The role of interplanetary shocks in the longitude distribution
of solar energetic particles
Authors: Cane, H. V.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1988JGR....93.9555C
Altcode:
A study of solar proton events with well-identified sources has
been carried out using data from Goddard particle experiments on
IMPs 4, 5, 7, and 8 and ISEE 3. The experiments cover the energy
range from about 1 to 300 MeV. The 235 events of our study represent
approximately 70% of all increases above 10-3
particles cm-2 sr-1
MeV-1 at energies >20 MeV detected
in a 19.7-year period commencing mid-May 1967. It is shown that
intensity-time profiles of solar proton events display an organization
with respect to heliolongitude. Whilst it has been known for many years
that the profile of a proton event depends on the longitude of the solar
event relative to the observer, we suggest that the major controlling
agent is the existence of an interplanetary (IP) shock. Furthermore, we
explain the change in shape as a function of heliolongitude within the
framework of a recently derived model for the large-scale structure of
IP shocks. In particular, the long delay to maximum intensity for far
eastern events (a property previously ascribed to coronal processes)
and the overall extended duration can be accounted for by IP shock
acceleration and continued magnetic connection to the shock even after
it has propagated beyond 1 AU.
Title: Solar Neon Abundances from Gamma-Ray Spectroscopy and 3He-rich
Particle Events
Authors: Reames, D. V.; Ramaty, R.; von Rosenvinge, T. T.
Bibcode: 1988ApJ...332L..87R
Altcode:
The authors compare ambient solar atmospheric abundances derived
from gamma-ray spectroscopy with observations of solar energetic
particles. They find agreement between the gamma-ray derived Ne/O ratio
and the corresponding mean ratio for 3He-rich flares. Both
of these values are significantly higher than inferred coronal Ne/O
ratios. It is suggested that the mean Ne/O ratio in 3He-rich
flares reflects the composition of the flare plasma rather than the
acceleration process.
Title: Bimodal Abundances in the Energetic Particles of Solar and
Interplanetary Origin
Authors: Reames, Donald V.
Bibcode: 1988ApJ...330L..71R
Altcode:
This letter reports the first results from an examination of the
daily-averaged abundances of the elements from H through Fe as well
as electrons and isotopes of He in energetic particles observed
in interplanetary space by the ISEE 3 spacecraft over an 8.5 yr
period. The abundances of heavy elements such as Fe/O show, for the
first time, clear evidence of the presence of two distinct populations
of particles. Earlier observations could be interpreted as extreme
variations within a single population. The population with enhanced
Fe/O shows correlated enhancements in He-3/He-4, p/e, and He/H. This
population is consistent with material that has been processed to high
temperatures in the impulsively heated regions of solar flares. The
second population, with more normal abundances, is probably accelerated
from ambient material by coronal and interplanetary shocks.
Title: X-Ray and Radio Properties of Solar 3He-rich Events
Authors: Reames, D. V.; Dennis, B. R.; Stone, R. G.; Lin, R. P.
Bibcode: 1988ApJ...327..998R
Altcode:
Radio and X-ray properties of solar flares associated with a new sample
of individual (He-3) rich solar particle events are examined. Given the
association between kilometric type III bursts and (He-3) rich events,
the timing of the radio events is used to identify the related X-ray
increases. The X-ray events exhibit a rich variety, from the standpoint
of both intensity and complexity. Examination of the events shows
statistically significant anticorrelations between the He-3/He-4 ratio
and the intensity of the event as measured at kilometric wavelengths
and in hard and soft X-rays; larger He-3/He-4 ratios occur in smaller
flares. The result suggests that a coupling may exist between the
preheating phase and the acceleration phase of these events or that
mixing occurs between an enriched particle population accelerated
within the compact flare and a normal population accelerated by a
shock propagating away from an intense flare.
Title: Solar Flare Nuclear Gamma Rays and Interplanetary Proton Events
Authors: Cliver, E. W.; Forrest, D. J.; McGuire, R. E.; von Rosenvinge,
T. T.; Reames, D. V.; Cane, H. V.; Kane, S. R.; MacDowall, R. J.
Bibcode: 1988BAAS...20..740C
Altcode:
No abstract at ADS
Title: Temperature Dependence of the Abundances of Elements in Solar
3He-rich Events
Authors: Reames, D. V.
Bibcode: 1988ApJ...325L..53R
Altcode:
The element abundances in solar He-3-rich events are observed to vary
with the soft X-ray temperature of the parent flare. The observations
are consistent with thermal collisional ionization of the elements to
the equilibrium-charge states expected within the flare-heated plasma at
(10-15) x 10 to the 6th K. Proposed photoionization mechanisms appear
to be excluded. Rapid ionization of the ions requires that the heating
occur sufficiently low in the corona that the electron density exceed
about (1-5) x 10 to the 8th/cu cm. Heavy-element enhancements might
be a signature of material processed in the flash phase of events in
contrast to unheated ambient material accelerated by a coronal shock.
Title: Soft X-Ray Emissions, Meter-Wavelength Radio Bursts, and
Particle Acceleration in Solar Flares
Authors: Cane, H. V.; Reames, D. V.
Bibcode: 1988ApJ...325..895C
Altcode:
A detailed study of the relationship between metric radio bursts and
soft X-ray flares has been made using an extensive data set covering
15 yr. It is found that type IV emission is mainly associated with
long-duration 1-8 A events that are known to be well associated with
coronal mass ejections. In contrast, type II and type III bursts
originate primarily in impulsive soft X-ray events that are not
necessarily accompanied by mass ejection. Strong type III bursts,
in particular, appear to occur only in association with relatively
impulsive flares. It is suggested that coronal shocks responsible for
type II bursts are blast waves generated in impulsive energy releases.
Title: Some Statistics of Solar Radio Bursts of Spectral Types II
and IV
Authors: Cane, H. V.; Reames, D. V.
Bibcode: 1988ApJ...325..901C
Altcode:
The properties of meter wavelength solar emissions are studied using a
sample of all type II and type IV radio bursts detected by the Culgoora
radio observatory during 1968-1983. It is found that type IV emission
generally occurs in conjunction with type II emission. For type III
bursts preceding type II bursts, the delay to type II onset is 6.5
min on average. The intensities and durations of type II bursts are
not dependent on the heliolongitude of the associated flares.
Title: Characteristics of solar coronal source regions producing
3He-rich particle events
Authors: Kahler, S. W.; Lin, R. P.; Reames, D. V.; Stone, R. G.;
Liggett, M.
Bibcode: 1987SoPh..107..385K
Altcode:
We use Hα, X-ray, and kilometric radio data to examine
the solar coronal activity associated with energetic (∼1
MeV/nucl−1) 3He-rich particle events observed
near Earth. The basis of the study is the 12 3He-rich
events observed in association with impulsive 2 to 100 keV electron
events reported by Reames et al. (1985). We find that when Hα and
X-ray brightenings can be associated with 3He/electron
events, they have onsets coinciding to within 1 min of that of the
associated metric type III bursts. In three or four events we found
no associated Hα or X-ray flares, and in two events even the metric
type III bursts were weak or absent. The measured low-energy (2 keV)
electron spectra for these events show no evidence of a flattening due
to Coulomb collisional losses. These results and several other recent
findings are consistent with the idea that the 3He/electron
events are due to particle acceleration in the corona well above the
associated Hα and X-ray flares.
Title: Solar Flare Nuclear Gamma-Rays and Interplanetary Proton Events
Authors: Cane, H. V.; Cliver, E. W.; Forrest, D. J.; Kane, S. R.;
McGuire, R. E.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1987ICRC....3...61C
Altcode: 1987ICRC...20c..61C
No abstract at ADS
Title: The Reappearance of the Anomalous Oxygen Component at 1 A.U.
Authors: von Rosenvinge, T. T.; Reames, D. V.
Bibcode: 1987ICRC....3..434V
Altcode: 1987ICRC....3..434R; 1987ICRC...20c.434V
No abstract at ADS
Title: Solar Energetic Proton Events and Coronal Mass Ejections Near
Solar Minimum
Authors: Kahler, S. W.; Cliver, E. W.; Cane, H. V.; McGuire, R. E.;
Reames, D. V.; Sheeley, N. R., Jr.; Howard, R. A.
Bibcode: 1987ICRC....3..121K
Altcode: 1987ICRC...20c.121K; 1987ICRC....3..121C
No abstract at ADS
Title: X-Ray and Radio Emission in Solar (3)HE-RICH Events
Authors: Reames, D. V.; Lin, R. P.; Sonte, R. L.; Dennis, B. R.
Bibcode: 1987ICRC....3..271R
Altcode: 1987ICRC...20c.271R; 1987ICRC....3..271D
No abstract at ADS
Title: On the Sources of Solar Energetic Particles
Authors: Cane, H. V.; Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1987ICRC....3..217C
Altcode: 1987ICRC...20c.217C
No abstract at ADS
Title: The Identification of Solar 3He-rich Events and the Study of
Particle Acceleration at the Sun
Authors: Reames, D. V.; Stone, R. G.
Bibcode: 1986ApJ...308..902R
Altcode:
Kilometric radio observations are to associate type III radio bursts
with solar He-3-rich events and to identify and study the sources of
those events at the sun and the transport of the particles outward
toward earth. The events exhibit an impulsive behavior that earns
them a natural role in the event classification scheme based upon the
time scale of the particle acceleration process. Multiple He-3-rich
events are observed frequently from a single active region where they
provide a convenient signature to test theories of particle storage
and transport. These multiple events act as impulsive probes of the
condition of the interplanetary medium. Their profiles contrast with
the source-acceleration-induced profiles of the long-duration events
from the same active region that are interspersed among them.
Title: The Heavy-Ion Compositional Signature in 3He-rich Solar
Particle Events
Authors: Mason, G. M.; Reames, D. V.; Klecker, B.; Hovestadt, D.;
von Rosenvinge, T. T.
Bibcode: 1986ApJ...303..849M
Altcode:
A survey of the approx. 1 MeV/nucleon heavy ion abundances
in 66 He-3-rich solar particle events was performed using the
Max-Planck-Institut/University of Maryland and Goddard Space Flight
Center instruments on the ISEE-3 spacecraft. The observations were
carried out in interplanetary space over the period 1978 October
through 1982 June. Earlier observations were confirmed which show an
enrichment of heavy ions in He-3-rich events, relative to the average
solar energetic particle composition in large particle events. For
the survey near 1.5 MeV/nucleon the enrichments compared to large
solar particle events are approximately He4:C:O:Ne:Mg:Si:Fe =
0.44:0.66:1.:3.4:3.5:4.1:9.6. Surprising new results emerging from
the present broad survey are that the heavy ion enrichment pattern
is the same within a factor of approx. 2 for almost all cases, and
the degree of heavy ion enrichment is uncorrelated with the He-3
enrichment. Overall, the features established appear to be best
explained by an acceleration mechanism in which the He-3 enrichment
process is not responsible for the heavy ion enrichment, but rather the
heavy ion enrichment is a measure of the ambient coronal composition
at the sites where the He-3-rich events occur.
Title: The heavy ion compositional signature in 3He-rich solar
particle events
Authors: Mason, G. M.; Reames, D. V.; Klecker, B.; Hovestadt, D.;
von Rosenvinge, T. T.
Bibcode: 1985STIN...8617255M
Altcode:
A survey of the approx. 1 MeV/nucleon heavy ion abundances
in 66 He3-rich solar particle events was performed using the
Max-Planck-Institut/University of Maryland and Goddard Space Flight
Center instruments on the ISEE-3 spacecraft. The observations were
carried out in interplanetary space over the period 1978 October
through 1982 June. Earlier observations were confirmed which show an
enrichment of heavy ions in HE3-rich events, relative to the average
solar energetic particle composition in large particle events. For
the survey near 1.5 MeV/nucleon the enrichments compared to large
solar particle events are approximately He4:C:O:Ne:Mg:Si:Fe =
0.44:0.66:1.:3.4:3.5:4.1:9.6. Surprising new results emerging from
the present broad survey are that the heavy ion enrichment pattern
is the same within a factor of approx. 2 for almost all cases,
and the degree of heavy ion enrichment is uncorrelated with the
He3 enrichment. Overall, the features established appear to be best
explained by an acceleration mechanism in which the He3 enrichment
process is not responsible for the heavy ion enrichment, but rather the
heavy ion enrichment is a measure of the ambient coronal composition
at the sites where the He3-rich events occur.
Title: **3HE in Solar Non-Relativistic Electron Events
Authors: Reames, D. V.; Lin, R. P.; Reames, D. V.
Bibcode: 1985ICRC....4..273R
Altcode: 1985ICRC...19d.273R
The authors report on a systematic study of the presence of
3He in 187 solar electron events observed on the ISEE-3
spacecraft during a 9-month period beginning in Aug 1978. 3He
is present in over half of the events and in 2/3 of events with 19
keV electrons, suggesting that 3He would be found in all
electron events given somewhat greater collection efficiency.
Title: Solar Source Regions of 3**HE-RICH Particle Events
Authors: Kahler, S. W.; Lin, R. P.; Reames, D. V.; Stone, R. G.;
Liggett, M.
Bibcode: 1985ICRC....4..269K
Altcode: 1985ICRC...19d.269K
Hydrogen alpha X-ray, and metric and kilometric radio data to examine
the solar sources of energetic 3He-rich particle events observed near
earth in association with impulsive 2 to 100 keV electron events were
applied. Each 3He/electron event is associated with a kilometric type
3 burst belonging to a family of such bursts characterized by similar
interplanetary propagation paths from the same solar active region. The
3He/electron events correlate very well with the interplanetary low
frequency radio brightnesses of these events, but progressively worse
with signatures from regions closer to the Sun. When H alpha brightnings
can be associated with 3He/electron events, they have onsets coinciding
to within 1 min of that of the associated metric type 3 burst but
are often too small to be reported. The data are consistent with the
earlier idea that many type 3 bursts, the 3He/electron events, are
due to particle acceleration in the corona, well above the associated
H alpha and X-ray flares.
Title: The Heavy Ion Composition in **3HE-RICH Solar Flares
Authors: Mason, G. M.; Reames, D. V.; Hovestadt, D.; von Rosenvinge,
T. T.
Bibcode: 1985ICRC....4..281M
Altcode: 1985ICRC...19d.281M
The 3He-rich flares show a tendency to be enriched in heavy ions, and
that this enrichment covers the charge range through Fe. The discovery
of this association was responsible, in part, for the discarding of
3He enrichment models which involved spallation or thermonuclear
reactions, since such models were unable to produce heavy nuclei
enhancement. Results of a survey of heavy nucleus abundances observed
in 66 3He-rich flares which occurred over the period October 1978 to
June 1982 are presented.
Title: Variation in Elemental Composition of Several Mev/nucleon
Ions Observed in Interplanetary Space
Authors: McGuire, R. E.; von Rosenvinge, T. T.; Reames, D. V.
Bibcode: 1985ICRC....4..225M
Altcode: 1985ICRC...19d.225M
The authors have surveyed six years of accumulated ISEE-3 and IMP-8
data to study variations in elemental relative abundances among the
different populations of energetic (1.5 to >10 MeV/nuc) ions seen in
interplanetary space. They present evidence suggestive that heavy ion
enrichments may be organized (with substantial scatter) by a rigidity
scaling factor A/Z* over the range H to Fe. They also show
some data to support the hypothesis that shock-associated particles
are probably accelerated from ambient energetic fluxes.
Title: Type III Solar Radio Bursts and **3HE-RICH Events
Authors: Reames, D. V.; Stone, R. G.
Bibcode: 1985ICRC....4..265R
Altcode: 1985ICRC...19d.265R
The authors investigate the kilometric radio data for
3He-rich events during the 1979 - 82 time period. Type
III bursts are present for each event as expected from the previous
electron/3He-event association. A list of identified solar
events is presented.
Title: Solar He-3-rich events and nonrelativistic electron events -
A new association
Authors: Reames, D. V.; von Rosenvinge, T. T.; Lin, R. P.
Bibcode: 1985ApJ...292..716R
Altcode:
In 15 months of observation by the ISEE-e spacecraft, it was found
that virtually all solar greater than or approximately equal to
1.3 MeV/nucleon He-3-rich events are associated with impulsive 2
to approximately 100 keV electron events, although many electron
events were not accompanied by detectable He-3 increases. Both the
He-3 and the electrons exhibit nearly scatter-free propagation in the
interplanetary medium, and the times of onset and maximum for the He-3
and electron increases are closely related by velocity dispersion. The
electron events and their related type III solar radio bursts provide,
for the first time, identification of the flares which produce the
He-3-rich events. He-3 appears to be accelerated at the flash phase
of solar flares along with nonrelativistic electrons.
Title: A comparison of solar helium-3-rich events with type II bursts
and coronal mass ejections
Authors: Kahler, S.; Reames, D. V.; Sheeley, N. R., Jr.; Howard,
R. A.; Michels, D. J.; Koomen, M. J.
Bibcode: 1985ApJ...290..742K
Altcode:
The authors ask whether the energetic particles of 3He-rich
events are accelerated in the same process as that resulting in
particles of normal-abundance events. They first present a list
of 66 3He-rich events observed with the Goddard Space
Flight Center particle detector on ISEE 3. It is then shown that
these events are not statistically associated with either of the two
common signatures of normal-abundance events, metric type II bursts
and coronal mass ejections. This indicates that enhanced abundance
events may be produced only in the impulsive phases of flares, while
normal abundance events are produced in subsequent flare shock waves.
Title: Solar He-3-rich events and non-relativistic electron events:
A new association
Authors: Reames, D. V.; von Rosenvinge, T. T.; Lin, R. P.
Bibcode: 1984STIN...8515652R
Altcode:
In 15 months of observation by the ISEE-e spacecraft, it was found
that virtually all solar greater than or approximately equal to
1.3 MeV/nucleon He-3-rich events are associated with impulsive 2 to
approximately 100 keV electron events, although many electron events
were not accompanied by detectable He-3 increases. Both the He-3 and the
electrons exhibit nearly scatter-free propagation in the interplanetary
medium, and the times of onset and maximum for the He-3 and electron
increases are closely related by velocity dispertion. The electron
events and their related type III solar radio bursts provide, for
the first time, identification of the flares which produce He-3-rich
events. He-3 appears to be accelerated at the flash phase of solar
flares along with nonrelativistic electrons.
Title: Associations beteen coronal mass ejections and solar energetic
proton events
Authors: Kahler, S. W.; Sheeley, N. R., Jr.; Howard, R. A.; Michels,
D. J.; Koomen, M. J.; McGuire, R. E.; von Rosenvinge, T. T.; Reames,
D. V.
Bibcode: 1984JGR....89.9683K
Altcode:
We have used data from the Naval Research Laboratory (NRL) white
light coronograph on the P78-1 spacecraft and energetic (E>4 MeV)
proton data from the Goddard Space Flight Center (GSFC) detectors
on the IMP 8 and ISEE 3 spacecraft to investigate the association
between proton events originating in flares and coronal mass ejections
(CME's). The primary data were 50 prompt proton events observed between
April 1979 and February 1982 for which reduced coronograph data were
available. H alpha flares could be confidently associated with 27 of
these events, and in 26 of these 27 cases an associated CME was found,
indicating a high but not perfect association of prompt proton events
with CME's. Peak proton fluxes correlate with both the speeds and the
angular sizes of the associated CME's. We show that the CME speeds do
not significantly correlate with CME angular sizes, so that the peak
proton fluxes are correlated with two independent CME parameters. With
larger angular sizes, CME's are more likely to be loops and fans
rather than jets and spikes and are more likely to intersect the
ecliptic. Which of these factors is important to the peak proton flux
correlation cannot be determined from the data. We find weak evidence
that steeper proton spectra are associated with faster and wider
CME's. Two of the 50 proton events of the study and two additional
events, all with no associated CME's share common characteristics:
relatively short duration (~1) day proton events with low fluxes,
parent flares with short (~10 min) soft x ray duration, close magnetic
connection to the earth, and gamma ray and metric type II emission.
Title: Solar Energetic Proton Events Unassociated with Coronal
Mass Ejections
Authors: Kahler, S.; Evenson, P.; McGuire, R. E.; Reames, D. V.;
von Rosenvinge, T. T.; Sheeley, N. R., Jr.; Howard, R. A.; Koomen,
M. J.; Michels, D. J.
Bibcode: 1984BAAS...16..453K
Altcode:
No abstract at ADS
Title: The Correlation of Coronal Mass Ejections with Energetic
Flare Proton Events
Authors: Kahler, S. W.; McGuire, R. E.; Reames, D. V.; von Rosenvinge,
T. T.; Sheeley, N. R., Jr.; Howard, R. A.; Michels, D. J.; Koomen,
M. J.
Bibcode: 1983ICRC....4....6K
Altcode: 1983ICRC...18d...6K
Proton events of energies of at least 4 MeV presumed due to solar
flares are compared with coronal mass ejections (CMEs) observed with
an orbiting coronagraph. H alpha flares are associated with 27 of
the 50 flare proton events of the study. Each of these 27 flares
is then associated temporally and spatially with a CME, confirming
the earlier conclusion, based on Skylab data, that a CME may be a
necessary condition for a flare proton event. Peak 4-22 MeV proton
fluxes correlate with both the speeds and the angular sizes of the
associated CMEs. CMEs of larger angular sizes are more likely to
be loops or fans rather than jets or spikes and are more likely to
intersect the ecliptic.
Title: Association of interplanetary particles with radio S.A. (shock
acceleration) events.
Authors: von Rosenvinge, T. T.; Reames, D. V.; Cane, H. V.
Bibcode: 1983ICRC....4...10V
Altcode: 1983ICRC...18d..10V
No abstract at ADS
Title: Solar 3HE-RICH Events Observed on ISEE-3
Authors: Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1983ICRC....4...48R
Altcode: 1983ICRC...18d..48R
A scan has been made of ISEE-3 data for all events with He-3/He-4
between 0.20 and 1.3 MeV/nucl. The 67 events found show some evidence
of 27-day recurrence. Larger events show both velocity dispersion
and magneic field-aligned arrival from the solar direction. At
least one third of the events are preceded by increases in about
300 keV electrons, although several larger events show no electron
increases. Spike events also exist suggesting nearly scatter-free
propagation of He-3 from well-connected events.
Title: The delayed energetic particle event of June 6 - 10, 1979.
Authors: von Rosenvinge, T. T.; Reames, D. V.
Bibcode: 1983ICRC...10..373V
Altcode: 1983ICRC...18j.373V
Energetic particle observations carried out with the ISEE-3
Medium-Energy Cosmic Ray experiment during the flare event of June 6-10,
1979 are reported. An expanded time history of the He nuclei particle
spectra is given, and particle trajectory angles are identified with
respect to the earth-sun line. The backward flow of the particle
stream following the shock was analyzed, and it is found that the
shock continued to accelerate particles beyond 1 AU from the sun. Polar
plots of the number of protons counted in each sector of observation
are given with their corresponding magnetic field directions.
Title: The Delayed Energetic Particle Event of June 6, 1979
Authors: Rosenvinge, T. T. V.; Reames, D. V.
Bibcode: 1983ICRC....4..148R
Altcode: 1983ICRC...18d.148R
No abstract at ADS
Title: Association of Interplanetary Particles with Radio S. a. Events
Authors: Rosenvinge, T. T. V.; Reames, D. V.; Cane, H. V.
Bibcode: 1983ICRC....4...10R
Altcode: 1983ICRC...18d..10R
No abstract at ADS
Title: Associations between Coronal Mass Ejections and Solar Energetic
Proton Events
Authors: Kahler, S. W.; Sheeley, N. R., Jr.; Howard, R. A.; Koomen,
M. J.; Michels, D. J.; McGuire, R. E.; von Rosenvinge, T. T.; Reames,
D. V.
Bibcode: 1983BAAS...15..699K
Altcode:
No abstract at ADS
Title: Heavy-Element Abundances in HE3 - Rich Events
Authors: Reames, D. V.; von Rosenvinge, T. T.
Bibcode: 1981ICRC....3..162R
Altcode: 1981ICRC...17c.162R
Abundances of the elements He through Fe observed on the ISEE-3
during He(3) rich events are reported. Ratios of He(3)-He(4) of not
less than about 1, and Fe/O of greater than 1 are found, and rather
large event-to-event variations in C, O, Ne, Mg, Si, and S are seen
superposed upon the general trend of heavy element enhancement. It is
concluded that the discontinuous variation of the neighboring elements
in the He(3) rich events could result from differences in the electron
temperature of the material prior to injection that give rise to
differences in the dominant charge states and cyclotron frequencies
of different elements.
Title: Interplanetary Particle Observations Associated with Solar
Flare Gamma-Ray Line Emission
Authors: von Rosenvinge, T. T.; Ramaty, R.; Reames, D. V.
Bibcode: 1981ICRC....3...28V
Altcode: 1981ICRC...17c..28V
Observations of particle emissions during three solar flares which were
observed to emit 2.22 MeV gamma rays as recorded by the Solar Maximum
Mission are discussed. The 2.22 MeV line is produced by neutron capture
by hydrogen, and additional attention is given to a 4.4 MeV emission
line of June 7, 1980, with estimates made of the particle density 1
AU from the sun assuming a good magnetic connection between the earth
and the sun. The measurements were made from the ISEE-3 and HELIOS-1
spacecraft. The connectedness of the earth and the sun in a magnetic
field leads to conclusions that few particles actually escaped into
interplanetary space.
Title: ISEE-3 Measurements of Solar Energetic Particle Composition
Authors: von Rosenvinge, T. T.; Reames, D. V.
Bibcode: 1979ICRC....5...68V
Altcode: 1980ICRC....5...68V; 1979ICRC...16e..68V
Preliminary observations of energetic particles from solar flares
beginning on September 23 and November 10, 1978 are reported. The
measurements were made from the ISEE-3 spacecraft using very thin, large
area solid-state detectors. Charge composition was measured for all
elements from Z = 2 to Z = 26 above approximately 2 MeV/nucleon. More
than 100,000 nuclei with Z greater than 2 were pulse-height analyzed
during the course of the first event, while the second was substantially
smaller. These good statistics enable the observation of variations
in composition at low energies as a function of time. For example,
the Fe/O ratio (2.0-3.1 MeV/n) was observed in the September event
to decrease by a factor of approximately 5. By contrast, this same
ratio increased by a factor of approximately 1.5 during the November
10 event. Similar variations have been reported earlier by Scholer
et al. (1978). These authors, however were unable to observe the He/O
ratio which has now been observed also to show significant variation.
Title: Enhancement of solar heavy nuclei at high energies in the 4
July 1974 event.
Authors: Bertsch, D. L.; Reames, D. V.
Bibcode: 1977SoPh...55..491B
Altcode:
Relative abundances of energetic nuclei in the 4 July 1974 solar event
are presented. The results show a marked enhancement of abundances
that systematically increase with nuclear charge numbers in the
range of the observation, 6 ≤ Z ≤ 26 for energies above 15 MeV
nucl.−1 While such enhancements are commonly seen below
10 MeV nucl−1, most observations at higher energies
are found to be consistent with solar system abundances. The energy
spectrum of oxygen is observed to be significantly steeper than most
other solar events studied in this energy region. It is proposed
that these observations are characteristic of particle populations at
energies ∼1 MeV nucl−1, and that the anomalous features
observed here may be the result of the high energy extension of such
a population that is commonly masked by other processes or populations
that might occur in larger solar events.
Title: Enhancement of solar heavy nuclei at high energies in the 4
July 1974 event
Authors: Bertsch, D. L.; Reames, D.
Bibcode: 1976STIN...7715970B
Altcode:
Relative abundances of energetic nuclei in the 4 July 1974 solar event
are presented. The results show a marked enhancement of abundances
that systematically increase with nuclear charge numbers in the range
of the observation, 6 less than or equal to Z less than or equal
to 26 for energies above 15 MeV/nucleon. While such enhancements
are commonly seen below 10 MeV/nucleon, most observations at higher
energies are found to be consistent with solar system abundances. The
energy spectrum of oxygen is observed to be significantly steeper than
most other solar events studied in this energy region. It is proposed
that these observations are characteristic of particle populations at
energies approximately 1 MeV/nucleon, and that the anomalous features
observed here may be the result of the high energy extension of such
a population that is commonly masked by other processes or populations
that might occur in larger solar events.
Title: Solar Cosmic Ray Composition above 10 MeV/Nucleon and Its
Energy Dependence in the 4 August 1972 Event
Authors: Bertsch, D. L.; Biswas, S.; Reames, D. V.
Bibcode: 1974SoPh...39..479B
Altcode:
Observations of the proton, helium, (C, N, O) and Fe-group nuclei
fluxes made during the large 4 August 1972 solar particle event are
presented. The results show a small, but significant variation of the
composition of multiply-charged nuclei as a function of energy in the
energy region above 10 MeV nucleon−1. In particular, the
He/(C, N, O) abundance ratio varies by a factor ∼ 2 between 10 and 50
MeV nucleon−1 and the Fe-group/(C, N, O) ratio suggests a
similar variation. Abundance ratios from the 4 August 1972 event are
compared as a function of energy with ratios measured in other solar
events to show that several of the earlier results are consistent with
an energy variation like that observed in August 1972, while certain
other events must have had a substantially different dependence of
composition on energy. At energies ≳50 MeV nucleon−1,
the He/(C, N, O) abundance ratio for August 1972 is consistent with
all earlier measurements made above that energy which suggests that
variations may vanish at high energies.
Title: The Abundances of Nuclei in the Cosmic Radiation
Authors: Reames, D. V.
Bibcode: 1974hepq.conf...54R
Altcode:
No abstract at ADS
Title: Variations of the Relative Abundances of He, (C, N, O) and
Fe-Group Nuclei in Solar Cosmic Rays and Their Relationship to Solar
Particle Acceleration
Authors: Bertsch, D. L.; Biswas, S.; Fichtel, C. E.; Pellerin, C. J.;
Reames, D. V.
Bibcode: 1973SoPh...31..247B
Altcode:
Measurements of the flux of helium nuclei in the 24 January, 1971, event
and of helium and (C, N, O) nuclei in the 1 September, 1971, event are
combined with previous measurements to obtain the relative abundances of
helium, (C, N, O), and Fe-group nuclei in these events. These data are
then summarized together with previously reported results to show that,
even when the same detector system using a dE/dx plus range technique is
used, differences in the He/(C, N, O) value in the same energy/nucleon
interval are observed in solar cosmic ray events. Further, when
the He/(C, N, O) value is lower the He/(Fe-group nuclei) value is
also systematically lower in these large events. When solar particle
acceleration theory is analyzed, it is seen that the results suggest
that, for large events, Coulomb energy loss probably does not play a
major role in determining solar particle composition at higher energies
(> 10 MeV). The variations in multicharged nuclei composition are
more likely due to partial ionization during the acceleration phase.
Title: Measurements of the Iron-Group Abundance in Energetic Solar
Particles
Authors: Bertsch, D. L.; Fichtel, C. E.; Pellerin, C. J.; Reames, D. V.
Bibcode: 1973ApJ...180..583B
Altcode:
The abundance of iron-group nuclei in the energetic solar particles
was measured twice in the 1971 January 24 event and once in the 1971
September 2 event. Including earlier results from the 1966 September
2 event, the experimental series being discussed in this article has
found the iron- group abundance to be in the range from 3-6 percent
of the oxygen nuclei in the energy interval from 21 to 50 MeV per
nucleon, in those events where the iron-group abundance could be
measured. Iron-nuclei have a different charge-to-mass ratio from
that of the C, N, 0 nuclei, so small variations in the Fe abundance
in solar particles are not unexpected due to rigidity-dependent
propagation effects and possibly rigidity-dependent acceleration. In
the three exposures where the statistics were adequate to construct
an energy spectrum, the iron-group nuclei were seen to have an
energy per nucleon spectrum similar to that of the C, N, 0 nuclei;
however, the energy per nucleon range was limited. The abundance for
the iron-group nuclei mentioned above is consistent with the present
solar spectroscopic abundance estimates. Subject headings: abundances,
cosmic-ray abundances, solar
Title: Composition of Cosmic Rays in the January 24 and September 2,
1971 Solar Events
Authors: Fichtel, C. E.; Bertsch, D. L.; Biswas, S.; Pellerin, C. J.;
Reames, D. V.
Bibcode: 1973BAAS....5R.272F
Altcode:
No abstract at ADS
Title: Measurements of Solar Protons, Helium and Heavy Nuclei in
the Aug. 4, 1972 Solar Event
Authors: Biswas, S.; Bertsch, D. L.; Fichtel, C. E.; Pellerin, C. J.;
Reames, D. V.
Bibcode: 1973BAAS....5T.269B
Altcode:
No abstract at ADS
Title: Relative Abundances and Energy Spectra of Solar Cosmic Ray
Nuclei in the August 4, 1972 Event
Authors: Biswas, S.; Bertsch, D. L.; Fichtel, C. E.; Pellerin, C.;
Reames, D. V.
Bibcode: 1973ICRC....2.1543B
Altcode: 1973ICRC...13.1543B
No abstract at ADS
Title: Variations in the Nuclear Abundances in Solar Particle Events
Authors: Bertsch, D. L.; Biswas, S.; Fichtel, C. E.; Pellerin, C. J.;
Reames, D. V.
Bibcode: 1973ICRC....2.1526B
Altcode: 1973ICRC...13.1526B
No abstract at ADS
Title: Solar Cosmic Ray Composition Measured With Nuclear Emulsions
Flown On Sounding Rockets During 1971
Authors: Fichtel, C. E.; Bertsch, D. L.; Pellerin, C. J.; Reames, D. V.
Bibcode: 1972BAAS....4Q.382F
Altcode:
No abstract at ADS
Title: Nuclear Composition and Energy Spectra in the 1969 April 12
Solar-Particle Event
Authors: Bertsch, D. L.; Fichtel, C. E.; Reames, D. V.
Bibcode: 1972ApJ...171..169B
Altcode:
The charge composition for several of the multicharged nuclei and
the energy spectra for hydrogen, helium, and medium (6 < Z < 9)
nuclei were measured in the 1969 April 12 solar-particle event. The
energy/nucleon shape of the medium nuclei was again the same as that of
the helium nuclei, and the ratio of these two species was consistent
with the present best average of 58 * 5. By combining the results
obtained here with previous work, improved estimates of the Ne/O
and Mg/O values of 0.16 * 0.03 and 0.056 i 0.014, respectively, were
obtained. Silicon and sulfur abundances relative to 0 were determined
to be 0.208 i 0.010 and 0.008 i 0.006, respectively, and 85 percent
confidence upper limits for Ar and Ca relative to 0 of 0.017 and 0.010
were obtained. Previously, these last four nuclei had only been listed
as a group.
Title: Solar Particle Composition Measurements
Authors: Reames, Donald V.
Bibcode: 1972NASSP.312..122R
Altcode:
No abstract at ADS
Title: Solar Fe abundance deduced from solar particle measurements
made with nuclear emulsions.
Authors: Fichtel, C. E.; Bertsch, D. L.; Pellerin, C. J.; Reames, D. V.
Bibcode: 1972BAAS....4S.259F
Altcode:
No abstract at ADS
Title: A comparison of measurements of the charge spectrum of solar
cosmic rays from nuclear emulsions and the Explorer 35 solid-state
detector
Authors: Armstrong, T. P.; Krimigis, S. M.; Reames, D. V.; Fichtel,
C. E.
Bibcode: 1972JGR....77.3607A
Altcode:
No abstract at ADS
Title: Charge Composition of Solar Cosmic Rays.
Authors: Bertsch, D. L.; Fichtel, C. E.; Reames, D. V.
Bibcode: 1971ICRC....2..455B
Altcode: 1971ICRC...12..455B
No abstract at ADS
Title: ^{53}Mn and the Age of Galactic Cosmic Rays
Authors: Reames, Donald V.
Bibcode: 1970ApJ...162..837R
Altcode:
A new measurement is suggested for obtaining information on the mean
age of the galactic cosmic rays. The technique is based on a half-life
of 2 X 10' years for 53Mn which may be produced copiously below 200
MeV per nucleon by the fragmentation of cosmic-ray 56Fe during its
passage through interstellar or intergalactic hydrogen.
Title: Statistical Discrete-Source Model of Local Cosmic Rays
Authors: Ramaty, R.; Reames, D. V.; Lingenfelter, R. E.
Bibcode: 1970PhRvL..24..913R
Altcode:
The anisotropy, lifetime, and fluctuations of the cosmic rays are
considered for a model in which the cosmic-ray sources are random
discrete events in space-time.
Title: Chemical Composition of Relativistic Cosmic Rays Detected
above the Atmosphere
Authors: Durgaprasad, N.; Fichtel, C. E.; Guss, D. E.; Reames, D. V.;
O'dell, F. W.; Shapiro, M. M.; Silberberg, R.; Stiller, B.; Tsao, C. H.
Bibcode: 1970PhRvD...1.1021D
Altcode:
Final results on the first satellite experiment on abundances of
cosmic-ray nuclei having a mean energy of several GeV per nucleon
are presented. A nuclear-emulsion detector, exposed on Gemini XI in
a near-equatorial orbit ranging between geographic latitudes +/-29°,
collected 619 high-quality tracks above the earth's atmosphere. Time
resolution (within about 5 min) was provided by movement of a lower
emulsion stack relative to an upper one. The detector was covered by
only 0.07 g/cm2 of aluminum and was favorably oriented for
18 h. The results on abundances, requiring no correction for secondary
production in the atmosphere, are characterized by (a) a pronounced
odd-even effect, with low abundances for elements of atomic number 7,
9, 11, and 13, compared to those of neighboring elements with even Z;
(b) approximately equal fluxes of neon, magnesium, and silicon, each
being about one-fourth that of oxygen; and (c) an abundance gap in the
region 15<=Z<=19. The observed ratios of Be+B, 10<=Z<=19,
and Z>=20 to the medium group, 6<=Z<=9, provide no evidence for
significant variation of composition with rigidity between 3.5 and 30
GV. A primordial composition-prior to interactions of the cosmic rays
with the interstellar medium-is calculated. This source composition
is compared with "universal" and solar abundances.
Title: Discrete Sources and the Statistics of Cosmic-Ray Propagation
Authors: Reames, D. V.; Ramaty, R.
Bibcode: 1970cora.conf...39R
Altcode:
No abstract at ADS
Title: Composition of relativistic cosmic rays detected on Gemini XI
Authors: O'dell, F. W.; Shapiro, M. M.; Silberberg, R.; Stiller, B.;
Tsao, C. H.; Durgaprasad, N.; Fichtel, C. E.; Guss, D. E.; Reames,
D. V.
Bibcode: 1970ICRC....1..457O
Altcode: 1970ICRC...11a.457O
No abstract at ADS
Title: Relative Abundance of Iron-Group Nuclei in Solar Cosmic Rays
Authors: Bertsch, D. L.; Fichtel, C. E.; Reames, D. V.
Bibcode: 1969ApJ...157L..53B
Altcode:
The abundance of the iron-group nuclei relative to oxygen in a solar
cosmic-ray event has been de- termined for the first time in the
event of September 2, 1966; it was found to be (1.1 ± 0.3) X 1O~
above 24.5 MeV nucleon1. This ratio is consistent with the solar value
determined spectroscopically but is over an order of magnitude smaller
than the galactic cosmic-ray ratio. This result is in agreement with
the concept already evolving from measurements on other nuclei that
the relative abundances of solar cosmic rays reflect those of the
solar photosphere for multicharged nuclei with approximately the same
nuclear charge-to-mass ratio
Title: Iron Nuclei in Solar Cosmic Radiation
Authors: Bertsch, D. L.; Fichtel, C. E.; Reames, D. V.
Bibcode: 1969BAAS....1R.273B
Altcode:
No abstract at ADS
Title: The charge composition of solar cosmic rays and solar
abundances
Authors: Reames, D. V.; Fichtel, C. E.
Bibcode: 1969sfsr.conf..277R
Altcode:
No abstract at ADS
Title: Composition of cosmic rays measured in Gemini XI.
Authors: O'Dell, F. W.; Shapiro, M. M.; Silberberg, R.; Stiller, B.;
Tsao, C. H.; Durgaprasad, N.; Fichtel, C. E.; Guss, D. E.; Reames,
D. V.
Bibcode: 1969spre.conf..215O
Altcode:
No abstract at ADS
Title: Nuclear-Charge Spectra and Energy Spectra in the September 2,
1966, Solar-Particle Event
Authors: Durgaprasad, N.; Fichtel, C. E.; Guss, D. E.; Reames, D. V.
Bibcode: 1968ApJ...154..307D
Altcode:
Heavy nuclei (Z »= 3) were detected in the September 2, 1966,
solar-particle event. This brings to five the number of events in which
these particles have been detected. The proton energy spectrum was
measured down to energies as low as 3 MeV and up to energies as high as
100 MeV, with measurements on the helium and heavier nuclei covering
a more restricted range. The relative abundances of helium, light (3
«= Z «= 5), medium (6 «= Z «= 9), and heavier nuclei obtained in
this experiment in the energy range from about 14 to 35 MeV nucleon'
agree with those measured in previous solar-particle events at higher
energies and hence with those of the solar photosphere. This result
strengthens the concept of a multicharged nuclear composition, which
is a characteristic of solar-particle events. Use of the recent solar
spectroscopic data and the ratio of helium to medium nuclei observed
in the solar cosmic rays results in a hydrogen-to-helium ratio of 16
± 2. An examination of the relative abundances of protons and medium
nuclei shows that the propagation of solar particles in this event
cannot be described by a simple diffusion model with a diffusion
coefficient proportional to j3 or 13R
Title: The Composition and Energy Spectra of Energetic Particles.
Authors: Reames, D. V.; Fichtel, C. E.
Bibcode: 1968AJS....73R..74R
Altcode:
The composition and energy spectra of particles observed during
the solar particle event of 2 Sept. 1966 are compared with similar
measurements on previous events. Perhaps the most striking feature
of these measurements is the constancy of the relative abundances of
the multicharged nuclei with time during an event and from event to
event; this composition is apparently the same as that of the solar
photosphere. In contrast the proton to helium ratio is observed to
vary markedly with time and from one event to another. The latter
observation precludes the possibility of a purely velocity-dependent
propagation mechanism, and together with the spectral measurements
shows that any simple diffusion model is probably inadequate.
Title: High-energy galactic cosmic-ray composition measured in
Gemini XI
Authors: O'dell, F. W.; Shapiro, M. M.; Silberberg, R.; Stiller, B.;
Tsao, C. H.; Durgaprasad, N.; Fichtel, C. E.; Guss, D. E.; Reames,
D. V.
Bibcode: 1968CaJPS..46..569O
Altcode: 1968ICRC...10..569O; 1968CaJPh..46S.569O; 1968CaJPh..46..569O
No abstract at ADS
Title: The composition of galactic cosmic rays
Authors: Reames, D. V.; Fichtel, C. E.
Bibcode: 1968CaJPS..46..544R
Altcode: 1968ICRC...10..544R; 1968CaJPh..46S.544R; 1968CaJPh..46..544R
No abstract at ADS
Title: Composition of the September 2, 1966 solar particle event
Authors: Durgaprasad, N.; Fichtel, C. E.; Guss, D. E.; Reames, D. V.
Bibcode: 1968CaJPS..46..749D
Altcode: 1968ICRC...10..749D; 1968CaJPh..46S.749D
No abstract at ADS
Title: Nuclear Cross Sections Required in Studies of Cosmic Rays
Authors: Reames, D. V.
Bibcode: 1967henr.book..273R
Altcode:
No abstract at ADS
Title: Source Spectra and Composition of Cosmic Rays Implied by an
Analysis of Interstellar and Interplanetary Travel
Authors: Fichtel, C. E.; Reames, D. V.
Bibcode: 1966PhRv..149..995F
Altcode:
The implications of a simple set of assumptions related to galactic
cosmic rays are examined and compared with the existing data. These
assumptions are that (a) the multiply charged cosmic-ray nuclei
all have the same spectral shape at the source, (b) the relative
abundances of He3 and light nuclei (3<=Z<=5) are
negligible at the source, and (c) the average amount of interstellar
material traversed is independent of particle energy. The results show
that within the present uncertainties of the experimental data and of
the interaction cross sections, the data agree with the predictions
without additional assumptions if the differential source spectra are
relatively flat at low energies and the average interstellar path is
2.8+/-0.4 g/cm2. In particular, the nearly constant relative
abundances of the helium, medium (6<=Z<=9), and (Z>=10)
nuclei for different values of energy/nucleon can be explained, and
the observed variation of the flux ratio of light to medium nuclei with
energy/nucleon can be brought into fair agreement with predictions. The
calculations also imply that, if the analysis does represent the true
situation, then there is little or no solar modulation of the cosmic
rays near solar minimum, and protons and helium nuclei have different
source spectra.
Title: Very Low Energy Cosmic Bay Heavy Nuclei
Authors: Fichtel, C. E.; Guss, D. E.; Neelakantan, K. A.; Reames, D. V.
Bibcode: 1966crep.conf..121F
Altcode:
No abstract at ADS
Title: An experimental examination of low energy cosmic ray heavy
nuclei
Authors: Fichtel, C. E.; Guss, D. E.; Neelakantan, K. A.; Reames, D. V.
Bibcode: 1965ICRC....1..400F
Altcode: 1965ICRC....9..400F
No abstract at ADS