Large Solar Flares Research Articles

Large solar flares - Analysis of the events recorded by the Mont Blanc neutrino detector

view Abstract Citations (9) References (7) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Large Solar Flares: Analysis of the Events Recorded by the Mont Blanc Neutrino Detector Aglietta, M. ; Badino, G. ; Bologna, G. ; Castagnoli, C. ; Castellina, A. ; Dadykin, V. L. ; Fulgione, W. ; Galeotti, P. ; Kalchukov, F. F. ; Korolkova, I. V. ; Kortchaguin, P. V. ; Kudryavtsev, V. A. ; Malguin, A. S. ; Periale, L. ; Ryassny, V. G. ; Ryazhskaya, O. G. ; Saavedra, O. ; Trinchero, G. ; Vernetto, S. ; Yakushev, V. F. ; Zatsepin, G. T. Abstract Analytical results are discussed from events recorded by the Mont Blanc neutrino detector during 19 large solar flares from August 1988 to March 1990, including the powerful flares of September 29 and October 19, 1989. It is found that no significant neutrino signal coincides temporally with solar flares. Upper limits are obtained for the integral neutrino and antineutrino flux of different flavors. Publication: The Astrophysical Journal Pub Date: November 1991 DOI: 10.1086/170722 Bibcode: 1991ApJ...382..344A Keywords: Elementary Particle Interactions; Solar Flares; Solar Neutrinos; Radiation Detectors; Scintillation Counters; Solar Physics; NEUTRINOS; SUN: FLARES; SUN: PARTICLE EMISSION full text sources ADS |

The magnetohydrodynamics of energy release in solar flares

A large solar flare is thought to occur when a sheared magnetic arcade loses equilibrium or goes unstable and erupts, and drives magnetic re-connection in the stretched-out magnetic field lines. These two key processes of magnetic eruption and magnetic energy conversion by re-connection are reviewed briefly, with an account of recent analytical and numerical models. When the height or length of a prominence in a sheared coronal arcade is too great it may erupt and drive the formation and re-connection of a current sheet below it. Recent progress in fast steady-state re-connection theory has explained many puzzling features of numerical experiments, and has shown how a new process of magnetic flipping can reconnect fields in three dimensions. Also numerical modelling of the formation of flare loops and ribbons by re-connection has accounted for many observational properties.

Solar flare and sudden change of Earth's rotation

It is shown that it is only when, in a shock pair produced by a large solar flare, the velocity of the following shock is clearly greater than that of the leading shock that a sudden change in the Earth's rotation can occur.

The iron-to-calcium abundance ratio in the 20 X 10 to the 6th K plasma of medium and large solar flares

view Abstract Citations (19) References (23) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS The Iron-to-Calcium Abundance Ratio in the 20 X 10 6 K Plasma of Medium and Large Solar Flares Phillips, K. J. H. ; Feldman, U. Abstract The iron-to-calcium abundance ratio during several flares observed by instruments on the P78-1 and Solar Maximum Mission spacecraft are determined using the intensity ratio of a dielectronic satellite line of Fe XXIV and the resonance line of Ca XIX. Values of A(Fe)/A(Ca) equal to 6.8 +/- 1.0 and 6.0 +/- 1.5 were derived from these data sets, respectively, the small difference being attributable to errors in the calculated instrument sensitivities. These values fall between two other determinations from X-ray spectra, but are less than the photospheric value. They are fairly constant from flare to flare, contrasting with other recent work which indicates strong flare-to-flare variations. Publication: The Astrophysical Journal Pub Date: September 1991 DOI: 10.1086/170515 Bibcode: 1991ApJ...379..401P Keywords: Calcium; High Temperature Plasmas; Iron; Metallicity; Solar Flares; Solar X-Rays; Abundance; Metal Ions; Resonance Lines; Solar Corona; Solar Maximum Mission; Solar Physics; SUN: ABUNDANCES; SUN: FLARES; SUN: X-RAYS full text sources ADS |

Importance of energetic solar protons in ozone depletion

CHLORINE-catalysed depletion of the stratospheric ozone layer has commanded considerable attention since 1985, when Farman et al.1 observed a decrease of 50% in the total column ozone over Antarctica in the austral spring. Here we examine the depletion of stratospheric ozone caused by the reaction of ozone with nitric oxide generated by energetic solar protons, associated with solar flares. During large solar flares in March 1989, satellite observations indicated that total column ozone was depleted by ~9% over ~20% of the total area between the South Pole and latitude 70° S. Chlorine-catalysed ozone depletion takes place over a much larger area, but our results indicate that the influence of solar protons on atmospheric ozone concentrations should not be ignored.

Glaciological studies at Siple Station (Antarctica): potential ice-core paleoclimatic record

AbstractThe quality and utility of the records of oxygen-isotopic abundances, dust concentrations and anionic concentrations preserved in the ice at Siple Station (75°55′ S, 84° 15′ W) are assessed from four shallow (20 m) cores. The combination of high accumulation (0.56 m a−1w.e.) and low mean annual temperature (—24°C) preserves the prominent seasonal variations in δ18Ο which are very spatially coherent. Sulfate concentrations vary seasonally and, in conjunction with δ18Ο, will allow accurate dating of deeper cores from Siple Station. The concentrations of insoluble dust are the lowest measured in Antarctica, making Siple Station an excellent location to examine large increases in atmospheric tubidity.The seasonal variations and annual fluxes of the anions are examined for the last two decades (AD 1966–85) with regard to probable sources. An unusually high sulfate flux in 1976 may reflect the February 1975 eruption of Mount Ngauruhoe, New Zealand. No annual signal in nitrate concentration is confirmed and no unusually high nitrate fluxes support the suggestion of nitrate production by large solar flares. However, nitrate flux is higher for the latter half of the 1970s and early 1980s, possibly reflecting the recent loss of stratospheric ozone.Finally, comparison of the δ18O record with available surface-temperature data (AD 1957–85) reveals that multi-year trends along the western coast of the Antarctic Peninsula are recorded at Siple. More importantly, comparison with areally weighted temperature reconstructions suggests that the δ18Ο record may reflect larger-scale, persistent trends in the high southern latitudes. The strong spatial coherence of the preserved records, the potential for accurate dating, and possible relevance to larger-scale processes make Siple Station an excellent site for paleoenvironmental reconstruction from ice cores.

Glaciological studies at Siple Station (Antarctica): potential ice-core paleoclimatic record

AbstractThe quality and utility of the records of oxygen-isotopic abundances, dust concentrations and anionic concentrations preserved in the ice at Siple Station (75°55′ S, 84° 15′ W) are assessed from four shallow (20 m) cores. The combination of high accumulation (0.56 m a−1 w.e.) and low mean annual temperature (—24°C) preserves the prominent seasonal variations in δ18Ο which are very spatially coherent. Sulfate concentrations vary seasonally and, in conjunction with δ18Ο, will allow accurate dating of deeper cores from Siple Station. The concentrations of insoluble dust are the lowest measured in Antarctica, making Siple Station an excellent location to examine large increases in atmospheric tubidity.The seasonal variations and annual fluxes of the anions are examined for the last two decades (AD 1966–85) with regard to probable sources. An unusually high sulfate flux in 1976 may reflect the February 1975 eruption of Mount Ngauruhoe, New Zealand. No annual signal in nitrate concentration is confirmed and no unusually high nitrate fluxes support the suggestion of nitrate production by large solar flares. However, nitrate flux is higher for the latter half of the 1970s and early 1980s, possibly reflecting the recent loss of stratospheric ozone.Finally, comparison of the δ18O record with available surface-temperature data (AD 1957–85) reveals that multi-year trends along the western coast of the Antarctic Peninsula are recorded at Siple. More importantly, comparison with areally weighted temperature reconstructions suggests that the δ18Ο record may reflect larger-scale, persistent trends in the high southern latitudes. The strong spatial coherence of the preserved records, the potential for accurate dating, and possible relevance to larger-scale processes make Siple Station an excellent site for paleoenvironmental reconstruction from ice cores.

Energetic particle composition measurements from Phobos 2: Results of the LET experiment

The Low Energy Telescope (LET) experiment carried on board the Phobos spacecraft measured the flux, spectra and elemental composition of nuclei from hydrogen up to iron, in the energy range ∼ 1–75 MeV nucleon −1. Isotope separation for helium was also achieved. We present the results of a study of solar energetic particle (SEP) composition using LET data acquired during the period July 1988 to March 1989. The set of particle events selected for study comprises six large solar flare events, two 3He-rich events and two energetic storm particle increases associated with interplanetary shocks. Three of the six large flare events occurred during a period of unusually high solar activity in March 1989. In two of these events, large Fe/O ratios were measured (0.44 ± 0.05 and 0.95 ± 0.24). The Fe/O ratios determined for the complete set of large flare events show an inverse correlation with the spectral index of oxygen, suggesting that the acceleration mechanism that produces events showing enhanced heavy-ion abundances is different from that responsible for lower Fe/O ratios. Our results in the case of the 3He-rich events are in agreement with earlier work, showing an enrichment in heavy ions relative to the average SEP composition. The abundances measured for the shock-associated increases are consistent with the acceleration of the ambient population of solar flare particles.

Variation in proton-induced upsets rates from large solar flares using an improved SEU model

Proton integral flux measurements during solar energetic particle (SEP) events, from the CPME instrument onboard the IMP-8 satellite, and the proton detector on the GOES-7 satellite, are utilized to calculate proton-induced single-event upset (SEU). An improved two-parameter SEU cross section model is used for three RAM devices. The log of the 239 actual RAM upsets on the TDRS-1 satellite during the October 19, 1989 SEP event allowed a comparison between the recorded number of upsets/chip per day and those predicted based on the GOES-7 data, the two-parameter model, and the shielding distribution curve. >

The beam-driven chromospheric evaporation model of solar flares - A model not supported by observations from nonimpulsive large flares

Most large solar flares exhibit hard X-ray emission which is usually impulsive, as well as thermal soft X-ray emission, which is gradual. The beam-driven chromospheric evaporation model of solar flares was proposed to explain the origin of the soft X-ray emitting flare plasma. A careful evaluation of the issue under discussion reveals contradictions between predictions from the theoretical chromospheric evaporation model and actual observations from a set of large X- and M-type flares. It is shown that although the soft X-ray and hard X-ray emissions are a result of the same flare, one is not a result of the other.

Acceleration of energetic particles by shock waves from large solar flares

view Abstract Citations (103) References (20) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Acceleration of Energetic Particles by Shock Waves from Large Solar Flares Reames, Donald V. Abstract 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. Publication: The Astrophysical Journal Pub Date: August 1990 DOI: 10.1086/185780 Bibcode: 1990ApJ...358L..63R Keywords: Particle Acceleration; Shock Wave Interaction; Solar Flares; Solar Planetary Interactions; Heavy Elements; Mass Distribution; Solar Protons; Solar Physics; PARTICLE ACCELERATION; SHOCK WAVES; SUN: ABUNDANCES; SUN: FLARES; SUN: SOLAR WIND full text sources ADS |

Solar variability influences on weather and climate: Possible connections through cosmic ray fluxes and storm intensification

The question of the mechanism for solar‐variability effects on weather and climate can be separated into (1) the identification of the carrier of the solar variability and (2) the identification of the physical link between the carrier and the meteorological response. The suggestion that galactic cosmic rays (GCR), as modulated by the solar wind, are the carriers of the component of solar variability that affects weather and climate has been discussed in the literature for 30 years, and considerable evidence for it has now accumulated. Variations of GCR occur with the 11‐year solar cycle, matching the time scale of recent results for atmospheric variations, as modulated by the quasi‐biennial oscillation of equatorial stratospheric winds (QBO). Variations in GCR occur on the time scale of centuries with a well‐defined peak in the coldest decade of the little ice age. Here we present new evidence on the meteorological responses to variations on the time scale of a few days. The occurrence of correlations of GCR and meteorological responses on all three time scales strengthens the hypothesis of GCR as carriers of solar variability to the lower atmosphere. The responses reported here include changes in the vertical temperature profile in the troposphere and lower stratosphere and in the northern hemisphere vorticity area index, associated with Forbush decreases in GCR. The meteorological responses to Forbush decreases are in the opposite sense but otherwise are quite similar to responses that immediately follow solar flares. This is to be expected, based on the hypothesis that particles with energy about 100–1000 MeV are the external forcing function for the tropospheric response, since large solar flares increase the particle flux and ionization and minor species production in the lower stratosphere, whereas Forbush decreases reduce them. The mechanism or mechanisms linking changes in low‐energy GCR and other particles in this energy range of 100–1000 MeV to tropospheric temperature and dynamic responses have not been identified. This can be attributed to current uncertainties regarding the microphysical and electrical properties of aerosols and clouds. One possibility is that changes in clouds lead to changes in cloud radiative forcing. The height distribution of the tropospheric response and the amount of energy involved and the rapidity of the time response suggest that the release of latent heat could also be involved. These could lead to the observed tropospheric responses which are understandable in terms of changes in the intensity of cyclonic disturbances. Theoretical considerations link such changes to the observed latitudinal movement of the jet stream.

High-energy phenomena on the Sun: An introductory review

Large solar flares are often accompanied by both emissions of high-energy quanta and particles. The emissions such as gamma-ray and hard X-ray photons are generated due to the interaction of high-energy nuclei and electrons with gases ambient in the flare regions and the solar atmosphere. Nonthermal radio emissions of wide frequency band are produced from energetic electrons while being decelerated by the action of plasmas and magnetic fields ambient in the flare site and its neighboring region. To understand the emission mechanism of these high-energy quanta on the Sun, it is, therefore, necessary to find the acceleration mechanism for both nuclei and electrons, which begins almost simultaneously with the onset of solar flares. A part of the accelerated nuclei and electrons are later released from the solar atmosphere into the outer space and eventually lost from the space of the solar system. Their behavior in the interplanetary space is considered to study the large-scale structure of plasmas and magnetic fields in this space. The observations and studies of high-energy phenomena on the Sun are thus thought of as giving some crucial hint important to understand the nature of various high-energy phenomena being currently observed in the Universe.

Wave generation in the transport of particles from large solar flares

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.

Large solar flare radiation shielding requirements for manned interplanetary missions

As the 21st century approaches, there is an ever-increasing interest in launching manned missions to Mars. A major concern to mission planners is exposure of the flight crews to highly penetrating and damaging space radiations. Beyond the protective covering of the Earth's magnetosphere, the two main sources of these radiations are galactic cosmic rays and solar particle events. Preliminary analyses of potential exposures from galactic cosmic rays (GCR's) were presented elsewhere. In this Note, estimates of shielding thicknesses required to protect astronauts on interplanetary missions from the effects of large solar flare events are presented. The calculations use integral proton fluences for the February 1956, November 1960, and August 1972 solar particle events as inputs into the NASA Langley Research Center nucleon transport code BRYNTRN. This deterministic computer code transports primary protons and secondary protons and neutrons through any number of layers of target material of arbitrary thickness and composition. Contributions from target nucleus breakup (fragmentation) and recoil are also included. The results for each flare are presented as estimates of dose equivalent [in units of roentgen equivalent man (rem)] to the skin, eye, and bloodforming organs (BFO) behind various thicknesses of aluminum shielding. These results indicate that the February 1956 event was the most penetrating; however, the August 1972 event, the largest ever recorded, could have been mission- or life-threatening for thinly shielded (< or = 5 g/cm2) spacecraft. Also presented are estimates of the thicknesses of water shielding required to reduce the BFO dose equivalent to currently recommended astronaut exposure limits. These latter results suggest that organic polymers, similar to water, appear to be a much more desirable shielding material than aluminum.

Reaction cross section for solar flare neutrinos with Cl-37 and O-16 targets

view Abstract Citations (9) References (14) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Reaction Cross Section for ``Solar Flare Neutrinos'' with 37Cl and 16O Targets Fukugita, M. ; Kohyama, Y. ; Kubodera, K. ; Kuramoto, T. Abstract Neutrino reaction cross sections are calculated for Cl-37 (electron neutrino, electron) Ar-37 and electron neutrino + O-16 yields electron + anything for the neutrino energy range 50-200 MeV. If the excess neutrino captures observed in the Davis experiment, which seem to correspond to the period during which large solar flares were recorded, are ascribed to the solar-flare neutrinos, 5000 (300) recoil electron events are expected in a 1000-ton water Cerenkov detector, if neutrino energy is 100 (50) MeV. Such detectors have a sensitivity to monitor the solar-flare neutrino event to the level of the maximum theoretical estimate for the flare neutrino flux. Publication: The Astrophysical Journal Pub Date: February 1989 DOI: 10.1086/185378 Bibcode: 1989ApJ...337L..59F Keywords: Absorption Cross Sections; Chlorine; Oxygen; Solar Flares; Solar Neutrinos; Cerenkov Counters; Particle Acceleration; Particle Flux Density; Solar Activity; Solar Physics; PARTICLE ACCELERATION; NEUTRINOS; SUN: ACTIVITY; SUN: FLARES full text sources ADS |

Search for correlation of neutrino events with solar flares in Kamiokande.

A search has been made for a correlation between large solar flares and neutrino events observed in Kamiokande for the period of July 1983–July 1988. No significant neutrino signal was found at the time of a solar flare, giving a limit on the time-integrated ‘‘solar-flare’’ νe flux <3.7×107 (2.5×109) /cm−2 per flare at 90% confidence level, for Eν=100 (50) MeV. These limits are 2000 (60) times smaller than the value required for neutrinos with those energies to account for the excess of signal in the Cl37 solar-neutrino experiment of some of the corresponding solar-flare times.Received 12 September 1988DOI:https://doi.org/10.1103/PhysRevLett.61.2653©1988 American Physical Society

Human Population Exposure to Cosmic Radiation

Critical evaluations of existing data on cosmic radiation in the atmosphere and in interplanetary space have been carried out in order to estimate the exposure of the world's population to this important component of natural background radiation. Data on population distribution and mean terrain heights on a 1 x 1 degree grid have been folded in to estimate regional and global dose distributions. The per caput annual dose equivalent at ground altitudes is estimated to be 270 µSv from charged particles and 50 µSv from neutrons. More than 100 million people receive more than 1 mSv in a year, and two million in excess of 5 mSv. Aircraft flight crews and frequent flyers receive an additional annual dose equivalent on the order of 1 mSv, though the global per caput annual dose equivalent from airplane flights is only about 1 µSv. Future space travellers on extended missions are likely to receive dose equivalents in the range 0.1-1 Sv, with the possibility of higher doses at relatively high dose rates from unusually large solar flares. These results indicate a critical need for a better understanding of the biological significance of chronic neutron and heavy charged particle exposure.

Human Population Exposure to Cosmic Radiation

Abstract Critical evaluations of existing data on cosmic radiation in the atmosphere and in interplanetary space have been carried out in order to estimate the exposure of the world's population to this important component of natural background radiation. Data on population distribution and mean terrain heights on a 1 x 1 degree grid have been folded in to estimate regional and global dose distributions. The per caput annual dose equivalent at ground altitudes is estimated to be 270 µSv from charged particles and 50 µSv from neutrons. More than 100 million people receive more than 1 mSv in a year, and two million in excess of 5 mSv. Aircraft flight crews and frequent flyers receive an additional annual dose equivalent on the order of 1 mSv, though the global per caput annual dose equivalent from airplane flights is only about 1 µSv. Future space travellers on extended missions are likely to receive dose equivalents in the range 0.1-1 Sv, with the possibility of higher doses at relatively high dose rates from unusually large solar flares. These results indicate a critical need for a better understanding of the biological significance of chronic neutron and heavy charged particle exposure.

Polar cap and other auroral events observed from Spitsbergen

AbstractA comprehensive visual and photographic record of a wide variety of auroral events was made from Spitsbergen during a prolonged period of clear weather that coincided with a remarkable resurgence in solar activity close to sunspot minimum. Using colour and interference-filter photography, the nature of the different auroral types was established and tentatively correlated with major flare events on the sun. At least three outstanding auroral substorms and three diffuse polar cap glows were generated by four large solar flares in the first half of February 1986. Many discrete polar cap aurorae were also observed in the same period.