Energy and nuclear charge dependence of abundance enhancements of solar cosmic ray heavy ions in three large solar events

The differential flux and energy spectra of solar cosmic ray heavy ions of He, C, O, Ne, Mg, Si, and Fe were determined in the energy interval E = 3–30 MeV amu^-1 for two large solar events of January 24, 1971 and September 1, 1971 in rocket flights made from Ft. Churchill. From these data the relative abundances and the abundance enhancement factors, ξ, relative to photospheric abundances were obtained for these elements. Similar results were obtained for a third event on August 4, 1972 from the available published data. Characteristic features of ξ vs nuclear charge dependences were deduced for five energy intervals. The energy dependence of ξ for He shows a moderate change by a factor of about 3, whereas for Fe, ξ shows a very dramatic decrease by a factor of 10–20 with increasing energy. It is inferred that these abundance enhancements of solar cosmic ray heavy ions at low energies seem to be related to their ionization states (Z ^*) and hence studies of Z ^* can give information on the important parameters such as temperature and density in the accelerating region in the Sun.     

Element Abundances in Solar Energetic Particles and the Solar Corona

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.     

Abundance Enhancements in Impulsive Solar Energetic-Particle Events with Associated Coronal Mass Ejections

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.     

CRRES Measurements of Energetic Helium During the 1990–1991 Solar Maximum

During the 1990–1991 solar maximum, the CRRES satellite measured helium from 38 to 110 MeV n^–1, with isotopic resolution, during both solar quiet periods and a number of large solar flares, the largest of which were seen during March and June 1991. Helium differential energy spectra and isotopic ratios are analyzed and indicate that (1) the series of large solar energetic particle (SEP) events of 2–22 June display characteristics consistent with CME-driven interplanetary shock acceleration; (2) the SEP events of 23–28 March exhibit signatures of both CME-driven shock acceleration and impulsive SEP acceleration; (3) below about 60 MeV n^–1, the helium flux measured by CRRES is dominated by solar helium even during periods of least solar activity; (4) the solar helium below 60 MeV n^–1 is enriched in ³He, with a mean ³He/⁴He ratio of about 0.18 throughout most of the CRRES mission `quiet' periods; and (5) an association of this solar component with small CMEs occurring during the periods selected as solar `quiet' times.     

Solar flare neutrons and their capture gamma ray emission

We briefly describe our recent Monte Carlo calculations of the energy and angular distributions of neutrons escaping from the solar atmosphere. Comparing the calculation results with measurements of the neutron flux from the flares, we determined the angular distribution and energy spectrum of the accelerated ions. We also describe our calculations of the time dependence of the 2.223 MeV line emission, which provide a sensitive measure of the photospheric ³He abundance. We find that the SMM measurements of the time dependence of the 2.2 MeV line emission from the flare of 1982 June 3 imply a ³He/H ratio of (2.3±1.2)×10^–5 at the 90% confidence level.     

Ionization states and the origin of low energy cosmic ray nuclei

The origin of the new component of cosmic ray nuclei in 1–30 MeV amu^–1 recently detected through space vehicles in interplanetary space is investigated in detail. It is assumed that these particles may originate from nearby sources, e.g., from novae type explosions, which have peculiar C, N and O compositions. These particles are further assumed to be accelerated and modulated within the heliosphere. The charged states of these ions in the interstellar space have been calculated in detail and it is shown that the same charged states are preserved in the heliosphere when they are accelerated to energies of the order of 10⁷eV amu^–1 from energies of 10⁵ ev amu^–1. Modulation of these ions are calculated and it is found that because of low charged states of the ions these have high rigidities and are modulated in such a way as to enhance the O-ion abundances as compared to C-ions. A comparison is made of the demodulated composition of C to Si-ions with available abundance data of some novae.     

Solar particle events with helium-over-hydrogen enhancement in the energy range up to 100 MeV nucl−1

Flux measurements of solar energetic particles (SEPs) in the ERNE instrument onboard SOHO indicate that the abundance of ⁴He-nuclei compared to protons in the energy range up to 100 MeV nucl^–1 was exceptionally high during the particle events on 27 May 1998 and 28 December 1999. The ⁴He/p ratio stayed between 0.15–0.50 for more than ten hours. There was also a prolonged enhancement in helium-3, ³He/⁴H 1%. Observations of EIT and LASCO on board SOHO confirm that the originators of both SEP events were western eruptions, flares and coronal mass ejections (CMEs). The onset of the SEP release took place close to the maximum of flares which were probably triggered by the rising CMEs. The observations suggest that the SEP events were started with the flare-(pre)accelerated particles, but impact of the CME-associated shocks might explain the continuation and modification of the helium and proton fluxes well after the flare production. These observations support the idea that the helium enhancements in the CME-associated events reflect the availability of seed particles that originate previously in flares.     

Enhancement of solar heavy nuclei at high energies in the 4 July 1974 event

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.     

Solar cosmic ray composition above 10 MeV/nucleon and its energy dependence in the 4 August 1972 event

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.NASA/NAS Senior Resident Research Associate, on leave from TATA Institute of Fundamental Research, Bombay.     

Solar energetic particle events at the rise phase of the 23rd solar activity cycle registered aboard the spacecraft &;#x201C;INTERBALL-2&;#x201D;

The experiment with 10K-80 aboard the INTER-BALL-2 (which detects protons with energies &amp;gt; 7, 27&amp;#x2013;41, 41&amp;#x2013;58, 58&amp;#x2013;88, 88&amp;#x2013;180 and 180&amp;#x2013;300 MeV) registered six events of the solar energetic particle (SEP) increase. These events are during the initial rise phase of the 23rd solar activity cycle. Solar flares with the SEP generation are accompanied by coronal mass ejection (CME). Here we analyze the dynamics of the differential energy spectrum at different phases of the SEP increase.     

A search for neutrons of solar origin using balloon borne detectors 1967–69

A series of telescopes having approximately a 30° half opening angle and responding to neutrons in the energy range 50 MeV to 350 MeV has been flown to the top of the atmosphere on balloons released from an equatorial launching site at Kampala, Uganda, between 1967 and 1969. The aim of the experiment was to attempt to detect solar neutrons during periods of enhanced solar activity. No neutrons of solar origin were detected, but an upper limit of the order of 30 neutrons m^–2 s^–1 at the Earth has been placed on the continuous solar neutron flux in the above energy range, and a limit of four photons m^–2 s^–1 has also been placed on the corresponding -ray flux above 80 MeV. Limits have likewise been placed on the total emission from various flares. For a 1B flare the values were 23 × 10⁴ neutrons m^–2 and 6 × 10⁴ photons m^–2.     

A search for solar neutrons during solar flares

The upper limit on the solar neutron flux from 1–20 MeV has been measured, by a neutron detector on the OGO-6 satellite, to be less than 5 × 10^–2 n cm^–2 s^–1 at the 95% confidence level for several flares including two flares of importance 3B and a solar proton event of importance 3B. The measurements are consistent with the models proposed by Lingenfelter (1969) and by Lingenfelter and Ramaty (1967) for solar neutron production during solar flares. The implied upper limit on the flux of 2.2 MeV solar gamma rays is about the same as the 2.2 MeV flux observed by Chupp et al. (1973).     

Space-based measurements of elemental abundances and their relation to solar abundances

The solar wind provides a source of solar abundance data that only recently is being fully exploited. The Ion Composition Instrument (ICI) aboard the ISEE-3/ICE spacecraft was in the solar wind continuously from August 1978 to December 1982. The results have allowed us to establish long-term average solar wind abundance values for helium, oxygen, neon, silicon, and iron. The Charge-Energy-Mass (CHEM) instrument aboard the CCE spacecraft of the AMPTE mission has measured the abundance of these elements in the magnetosheath and has also added carbon, nitrogen, magnesium, and sulfur to the list. There is strong evidence that these magnetosheath abundances are representative of the solar wind. Other sources of solar wind abundances are Solar Energetic Particle (SEP) experiments and Apollo lunar foils. When comparing the abundances from all of these sources with photospheric abundances, it is clear that helium is depleted in the solar wind while silicon and iron are enhanced. Solar wind abundances for carbon, nitrogen, oxygen, and neon correlate well with the photospheric values. The incorporation of minor ions into the solar wind appears to depend upon both the ionization times for the elements and the Coulomb drag exerted by the outflowing proton flux.     

A search for energetic neutrons emitted during solar flares

On the basis of solar flare forecasts, balloon flights were made from Hyderabad, India (vertical geomagnetic threshold rigidity of 16.9 GV), to detect the possible emission of high energy neutrons during solar flares. The detector comprised of a central plastic scintillator, completely surrounded by an anticoincidence plastic scintillator shield. The instrument responds to neutrons of about 15–150 MeV and gamma rays of about 5–30 MeV with about the same efficiency. The detector was flown to an atmospheric depth of 25 g cm^-2 on February 26, 1969; while the balloon was at ceiling a flare of importance 2B and one of 1N occurred. No perceptible flare associated increase in the counting rate was observed. Using the observed counting rates, an upper limit of 1.2 × 10^-2 neutrons cm^-2 sec^-1 is obtained for the first time for a flare of importance 2B for neutrons of energy 15–150 MeV. The corresponding upper limit for gamma rays of energy 5–30 MeV is found to be 10^-2 photons cm^-2 sec^-1. The neutron flux limits are compared with the recent calculations of Lingenfelter.     

Variations in Abundance Enhancements in Impulsive Solar Energetic-Particle Events and Related CMEs and Flares

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 (°), slower (?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.     

2.2 MeV gamma-ray line observed during two SN solar flares

On December 15, 1978, an omnidirectional gamma-ray detector for the energy range 0.3 to 10 MeV was flown from São José dos Campos, Brazil at a latitude of about -23°. Around noon time, when the Sun was in the field of view of the detector, various solar flares of importance SN and SF occurred. The 2.2 MeV line flux was monitored during this time. A statistically significant line flux of (1.55 ± 0.50) × 10^–2 photons cm^–2 s^–1 and (9.97 ± 4.85) × 10^–3 photons cm^–2 s^–1 was observed within a few minutes of t maxima of the two long-duration SN flares respectively, whereas during SF flares only upper limits were obtained.     

Magnetic diffusion and flare energy buildup

Photospheric motion shears or twists solar magnetic fields to increase magnetic energy in the corona, because this process may change a current-free state of a coronal field to force-free states which carry electric current. This paper analyzes both linear and nonlinear two-dimensional force-free magnetic field models and derives relations of magnetic energy buildup with photospheric velocity field. When realistic data of solar magnetic field (B ₀ 10³ G) and photospheric velocity field (v _max 1 km s^–1) are used, it is found that 3–4 hours are needed to create an amount of free magnetic energy which is of the order of the current-free field energy. Furthermore, the paper studies situations in which finite magnetic diffusivities in photospheric plasma are introduced. The shearing motion increases coronal magnetic energy, while the photospheric diffusion reduces the energy. The variation of magnetic energy in the coronal region, then, depends on which process dominates.     

The Interplanetary Responses to the Great Solar Activities in Late October 2003

Based on the observations of the Sun and the interplanetary medium, a series of solar activities in late October 2003 and their consequences are studied comprehensively. Thirteen X-ray flares with importance greater than M-class, six frontside halo coronal mass ejections (CMEs) with span angle larger than 100 and three associated eruptions of filament materials are identified by examining lots of solar observations from October 26 to 29. All these flares were associated with type III radio bursts, all the frontside halo CMEs were accompanied by type II or type II-like radio bursts. Particularly, among these activities, two major solar events caused two extraordinary enhancements (exceeding 1000 particles/(cm²s^–1sterMev^–1) of solar energetic particle (SEP) flux intensity near the Earth, two large ejecta with fast shocks preceding, and two great geomagnetic storms with Dst peak value of –363 and –401 nT, respectively. By using a cross correlation technique and a force-free cylindrical flux rope model, the October 29 magnetic cloud associated with the largest CME are analyzed, including its orientation and the sign of its helicity. It is found that the helicity of the cloud is negative, contrary to the regular statistical pattern that negative- and positive-helical interplanetary magnetic clouds would be expected to come from northern and southern solar hemisphere. Moreover, the relationship between the orientation of magnetic cloud and associated filament is discussed. In addition, some discussion concerning multiple-magnetic-cloud structures and SEP events is also given.     

Anomalous Cosmic-Ray Helium,Nitrogen and Oxygen in 1996 – Measurements of the ERNE Instrument on-board SOHO

The energy spectra of the anomalous components of helium, nitrogen and oxygen have been measured by the ERNE experiment on board the SOHO spacecraft. During February 28–April 30, 1996, the maximum intensity of anomalous helium was found to be 3.8 × 10^-5 cm^-2 sr^-1 s^-1 (MeV nucl^-1)^-1 in the energy range 10–15 MeV nucl^-1. During the period January 26–April 30, 1996, the maximum oxygen intensity was 1.2 × 10^-5 cm^-2 sr^-1 s^-1 (MeV nucl^-1)^-1 at 4–7 MeV nucl^-1, and the maximum nitrogen intensity 1.7 × 10^-6 cm^-2 sr^-1 s^-1 (MeV nucl^-1)^-1 at 4–9 MeV nucl^-1. These peak intensities are at the same level as two solar cycles ago in 1977, but significantly higher than in 1986. This gives observational evidence for a 22-year solar modulation cycle. A noteworthy point is that the spectra of anomalous nitrogen and oxygen appear to be somewhat broader than in 1977.     

Isotopic composition of primary cosmic-ray nitrogen and oxygen with consequences for source models

An experimental investigation of the isotopic composition of cosmic-ray nitrogen and oxygen is reported. The detector is a stack of nuclear emulsions exposed at about 3 g cm^–2 atmospheric depth. The mass determinations are based on photometric track width measurements on stopping nuclei. The standard deviation of the mass measurements is 0.46 AMU for nitrogen and 0.50 AMU for oxygen. The energy of the measured nuclei falls in the interval 220–450 MeV nucleon^–1 at the top of the atmosphere.The measured isotopic quotients have been extrapolated to near interstellar space with standard methods. The extrapolated quotients are¹⁵N/N=0.34±0.10,¹⁷O/O=0.02±0.03,¹⁸O/O=0.07±0.03. The nitrogen quotient extrapolated to the cosmic-ray source shows that the nitrogenoxygen abundance ratio is approximately the same in the source as in the solar system. The result has been compared with different hypotheses about the source composition and is found to be in best agreement with a hypothesis which states that source matter has approximately the composition of the solar system and that a selection mechanism, which depends on the atomic properties of the elements, is working in the source.