Journal: The Astrophysical Journal

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97) (2)

Journal: American Institute of Physics: Conference Proceedings
Title: Radiation Risks from Large Solar Energetic Particle Events
General Information: Published online 28 August 2007
Author(s): R. A. Mewaldt, C. M. S. Cohen, D. K. Haggerty, G. M. Mason, M. L. Looper, T. T. von Rosenvinge, M. E. Wiedenbeck
Abstract: Solar energetic particles (SEPs) constitute a radiation hazard to both humans and hardware in space. Over the past few years there have been significant advances in our knowledge of the composition and energy spectra of SEP events, leading to new insights into the conditions that contribute to the largest events. This paper summarizes the energy spectra and frequency of large SEP events, and discusses the interplanetary conditions that affect the intensity of the largest events.

98) (2)

Journal: American Institute of Physics: Conference Proceedings
Title: Modeling of the Solar Energetic Particles Recorded at Neutron Monitors
General Information: Published online 11 September 2006
Author(s): Christina G. Plainaki, Helen A. Mavromichalaki, Anatoly V. Belov, Eugenia A. Eroshenko, Victor A. Yanke
Abstract: Last year the worldwide network of neutron monitors recorded a new ground level enhancement (GLE) of cosmic my intensity (CR) on 20th of January 2005, during the recovery phase of a series of Forbush effects taking place at a time‐period very close to the minimum of the current cycle of solar activity. This enhancement seems to be the greatest GLE of the current solar cycle, reaching almost 5000% in some polar stations. A joint analysis of data from ground level stations (neutron monitors) and satellite measurements has been performed in order to calculate the amplitude and the anisotropy of the event as well as the energy of the more fast particles arriving at the Earth. A new GLE — model has been created in order to couple the primary solar cosmic ray flux on the top of the magnetosphere with the flux recorded by neutron monitors and define this way the primary solar cosmic ray spectrum during the event. Moreover, the absorption length of solar energetic particles propagating through the Earth’s atmosphere has been calculated applying the Wilson et al. method (1967). These results have been compared with the respective results calculated for other ground level enhancements. Finally, a comparison between this enhancement and the big GLE of 1956 has been performed.

99) (3)

Journal: American Institute of Physics: Conference Proceedings
Title: Long-Term Cosmic-Ray Modulation during Solar Cycle 23
General Information: Published online 11 September 2006
Author(s): Helen Mavromichalaki, Evagelos Paouris, Theothora Karalidi
The long‐term modulation of the current solar cycle 23 is of great interest, as this cycle is characterized by many peculiarities with double peaks. Many quiet periods (Gnevyshev gaps) are interrupted by extreme solar activity, as for example in April 2001, October–November 2003 and January 2005. Previous works proposed an empirical model to describe the long‐term cosmic‐ray intensity modulation during solar cycles 20, 21 and 22. In this work an attempt to apply this model to the solar cycle 23 is made analyzing monthly cosmic ray data from the Neutron Monitor Stations of Oulu (cut‐off rigidity 0.81 GV) and Moscow (cut‐off rigidity 2.42 GV). An empirical relation obtained from the linear combination of the sunspot number Rz, the solar flares Nf and the geomagnetic index Ap, is outlined incorporating the time‐lag of these parameters against cosmic ray intensity. An extended study of the hysteresis phenomenon of cosmic ray intensity against different solar, interplanetary and terrestrial parameters during the time period 1996–2005 is also presented. This effect was found to have a high value, in average about 14 months, related to the size of the heliosphere and characterizing an odd solar cycle. Analytical modeling and numerical simulations are qualitatively consistent with experimental data. In our days a satisfied long‐term cosmic ray model would be very useful for Space Weather studies given the possibility for cosmic‐ray intensity prediction, especially now where these and satellite data are provided in real time to the Internet. A first evidence for the important role of coronal mass ejections to the long‐term cosmic ray modulation is also discussed.

100) (4)

Journal: American Institute of Physics: Conference Proceedings
Title: The Heliospheric Current Sheet and Galactic Cosmic Rays
General Information: Published online 26 September 2006
Author(s): Edward J. Smith
Abstract: The correlation between galactic cosmic ray intensity (j) and the inclination or tilt angle (α) of the heliospheric current sheet is used to test the cosmic ray drift model that predicts cosmic ray intensity varies more with tilt angle for negative than positive polarity of the heliospheric magnetic field (P). Three solar cycles with three changes in polarity are examined. Plots of j vs. α lead to open contours with a clockwise rotation for both +/− and −/+ cycles contrary to expectation. A major influence is the different dependence of j on α for the asymmetric onset or descending (D) phase and the recovery or ascending (A) phase. Thus, j is a function of α, P and A or D. A hierarchy of dependences is apparent in the j‐α contours that reveals the greater influence of α for P<0 than for P>0 in agreement with drift models. However, the models can be improved by including the dependence on modulation phase (A/D) that may result from a time‐dependent α that gradually increases (decreases) during the descending (ascending) phase from the outer heliosphere to the Sun.

101) (1)

Journal: Effects of Space Weather on Technology Infrastructure
Title: Neutron Monitor Network in Real Time and Space Weather
General Information: Published 2005, Volume 176 of the series NATO Science Series II: Mathematics, Physics and Chemistry, Pages 301-317
Author(s): H. Mavromichalaki, V. Yanke, L. Dorman, N. Iucci, A. Chilingaryan, O. Kryakunova
Abstract: Relativistic cosmic rays (galactic and solar) registered by neutron monitors at the Earth, bring valuable information on their interaction with interplanetary disturbances. Therefore, they can play a useful role in forecasting space weather storms and in specifying magnetic properties of CME shocks and may be derived from ground level cosmic ray (CR) observations well in advance of the onset of geomagnetic storm. This can be used for forecasting. High energy solar particle events during powerful solar flares are registered at the Earth well before the main development of particle profiles recorded onboard GOES. This provides a good chance of a preventive prognosis of dangerous particle flux by ground level observations. To produce real-time prediction of the phenomena, only real time data from Neutron Monitor Network (NMN) should be employed. The increased number of NM stations operating in real-time gives a good basis for using NMN as a single multidirectional tool and for improving the definition of the onset of GLEs in powerful SPEs and to give an immediate forecast of the arrival of the interplanetary disturbance at the Earth. The properties of the Neutron Monitor Network and its possibilities for Space Weather tasks are discussed in this paper. Different real time Neutron Monitor Network topologies, different synchronization methods and the ways of collecting data in a central data server accessible to the users, are also discussed.

102) (2)

Journal: Journal of Geophysical Research: Space Physics

Title: Heliospheric Modulation of Cosmic Rays: Monthly Reconstruction for 1951-2004
General Information: Published 23 December 2005, Volume 110, Issue A12
Author(s): Ilya G. Usoskin, Katja Alanko-Huotari, Gennady A. Kovaltsov, Kalevi Mursula
Abstract: The differential energy spectrum of galactic cosmic rays in the vicinity of the Earth can be parameterized by the so-called force field model which has only one parameter, the modulation potential ϕ, for a given local interstellar spectrum. Here we present the series of monthly values of the modulation potential ϕ since February 1951, reconstructed using the data from the worldwide neutron monitor network and calibrated with precise balloon and space-borne direct measurements of cosmic ray energy spectrum. This work provides a long series of a parameter allowing for a quantitative estimate of the average monthly differential energy spectrum of cosmic rays near the Earth. A comparison with other occasional direct measurements of cosmic ray spectra confirms the reliability of the present reconstruction. The results can be applied in studies of long-term solar-terrestrial relations and the global evolution of the heliosphere.

103) (1)

Journal: Journal of Geophysical Research: Space Physics
Title: Latitude Survey Observations of Neutron Monitor Multiplicity
General Information: Published 17 December 2004, Volume 109, Issue A12
Author(s): J. W. Bieber, J. M. Clem, M. L. Duldig, P. A. Evenson, J. E. Humble, R. Pyle
Abstract: We have recently augmented the electronics for our neutron monitor (NM) latitude survey so as to record the elapsed time (δT) between detected neutrons in each proportional tube, in order to examine time correlations in the data as a function of cutoff rigidity and primary spectrum. We quantify the dependence of counting rate on dead time, with particular focus on the longer dead times that were once employed in FSU/Russian stations. Our observations show that monitor dead time has little influence on the observed depth of Forbush decreases, indicating that the cosmic ray spectral shape is little changed in the decrease. However, the use of a different dead time significantly alters the response of the monitor as a function of cutoff rigidity. In spite of the general success of our calculation in reproducing the data, unexplained discrepancies are still present.
104) (1)

Journal: American Institute of Physics: Conference Proceedings

Title: Time Variations of the Modulation of Anomalous and Galactic Cosmic Rays
General Information: Published online 15 September 2000
Author(s): E. R. Christian, W. R. Binns, C. M. S. Cohen, A. C. Cummings, J. S. George, P. L. Hink, J. Klarmann, R. A. Leske, M. Lijowski, R. A. Mewaldt, P. L. Slocum, E. C. Stone, T. T. von Rosenvinge, M. E. Wiedenbeck, N. Yanasak
Abstract: Between the launch of the Advanced Composition Explorer (ACE) in 1997 and the end of 1999, the intensities of galactic cosmic rays at 1 AU have dropped almost a factor of 2, and the anomalous cosmic rays have decreased by an even larger amount. The large collecting power of the Cosmic Ray Isotope Spectrometer (CRIS) and the Solar Isotope Spectrometer (SIS) instruments on ACE allow us to investigate the changing modulation on short time scales and at different rigidities. Using anomalous cosmic ray (ACR) and galactic cosmic ray (GCR) intensities of He, C, O, Ne, Si, S, and Fe, and energies from ∼6 MeV/nucleon to ∼460 MeV/nucleon, we examine the differences between the short term and long term effects. We observe the expected correlation of these intensities with neutron monitor data, but see little correlation of GCR and ACR intensities with the locally measured magnetic field.

105) (2)

Journal: Cosmic Rays and Earth
Title: Neutron Monitor Response Functions
General Information: Published 2000, Volume 10 of the series Space Sciences Series of ISSI, Pages 335-359
Author(s): John M. Clem, Lev I. Dorman
Abstract: The neutron monitor provides continuous ground-based recording of the hadronic component in atmospheric secondary radiation which is related to primary cosmic rays. Simpson (1948) discovered that the latitude variation of the secondary hadronic component was considerably larger than the muon component suggesting the response of a neutron monitor is more sensitive to lower energies in the primary spectrum. The different methods of determining the neutron monitor response function of primary cosmic rays are reviewed and discussed including early and recent results. The authors also provide results from a new calculation (Clem, 1999) including angle dependent yield functions for different neutron monitor types which are calculated using a simulation of cosmic ray air showers combined with a detection efficiency simulation for different secondary particle species. Results are shown for IGY and NM64 configurations using the standard 10BF3 detectors and the new 3He detectors to be used in the Spaceship Earth Project (Bieber et al., 1995). The method of calculation is described in detail and the results are compared with measurements and previous calculations. A summary of future goals is discussed.
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106) (3)

Journal: American Institute of Physics: Conference Proceedings
Title: Transient Phenomena in the Heliosphere and Terrestrial Effects
General Information: Published online 13 June 2000
Author(s): Marisa Storini
General Information: Published 13 June 2000
Abstract: This paper is an overview of the contributed papers presented at the SH2.1, SH2.2, SH2.3, and SH3.6 sessions of the 26th International Cosmic Ray Conference (Salt Lake City—Utah, August 17–25, 1999). The main subjects covered are observational features and modeling efforts for transient phenomena in the heliosphere and radiation in the terrestrial environment.

107) (4)

Journal: American Institute of Physics: Conference Proceedings
Title: Observations of Anomalous Cosmic Rays at 1 AU
General Information: Published online 15 September 2000
Author(s): R. A. Leske, R. A. Mewaldt, E. R. Christian, C. M. S. Cohen, A. C. Cummings, P. L. Slocum, E. C. Stone, T. T. von Rosenvinge, M. E. Wiedenbeck
Abstract: Anomalous cosmic rays (ACRs) provide a sensitive probe of the access of energetic particles to the inner heliosphere, varying in intensity by more than two orders of magnitude during the course of the solar cycle. New data which are becoming available from the Advanced Composition Explorer (ACE) can provide a detailed record of ACR intensity and spectral changes on short (∼1 day) time scales during the approach to solar maximum, which will help address issues of ACR modulation and transport. The elemental and isotopic composition of ACRs provides important information on the source or sources of these particles, while their ionic charge state composition and its energy dependence serves as a diagnostic of their acceleration time scale. We review measurements of the ACR elemental, isotopic, and charge state composition and spectra as determined at 1 AU by SAMPEX, ACE, Wind, and other spacecraft. These results are important input to models of the acceleration, modulation, and transport of ACRs.

108) (5)

Journal: Space Science Review
Title: Neutron Monitor Design Improvements
General Information: Published July 2000, Volume 93, Issue 1, Pages 361-380
Author(s): Pieter H. Stoker, Lev I. Dorman, John M. Clem
Abstract: The original design by J. A. Simpson of the neutron monitor enabled continuous monitoring of the primary cosmic-ray flux by ground-based recordings of the nucleonic component with only a rather simple correction for atmospheric effects. Simpson (1957) extended the original pile to the 12 counter IGY neutron monitor which was deployed in a world wide network during the International Geophysical Year 1957/8. The desirability for monitors with higher counting rates became evident soon afterwards. Subsequently the NM64 super neutron monitor was designed by H. Carmichael for deployment in time for the International Quiet Sun Year 1964. Using unusually large 10BF3 proportional counters made at Chalk River, Hatton and Carmichael (1964) studied comprehensively the experimental design of the NM64. Consequently the efficiency of neutron counters to record evaporation neutrons produced in the lead of a monitor increased from 1.9% for the IGY to 5.7% for the NM64, an increase of 3.3 times the counting rate per unit area of lead producer. During the years much attention was given to the neutron multiplicity spectrum in neutron monitors. This spectrum is related to the energy spectrum of the nucleonic component incident on the neutron monitor, but is only weakly dependent on the spectrum of galactic cosmic rays at the top of the atmosphere. Contrary to galactic cosmic rays, solar flare protons and neutrons are observed predominantly as single counts per interaction, in multiplicity 1, because of the softness of solar flare particle energy spectra. Neutron monitors have also been specially designed to record solar neutrons with increased sensitivity. Newly developed 3He counters with a largely reduced thermal neutron absorption mean free path should lead to improved efficiency in recording primary cosmic radiation. Design criteria are discussed.

109) (6)

Journal: Cosmic Rays and Earth
Title: Design and Co-Ordination of Multi-Station International Neutron Monitor Networks
General Information: Published 2000, Volume 10 of the series Space Sciences Series of ISSI, Pages 285-303
Author(s): Harm Moraal, A. Belov, J. M. Clem
Abstract: The world’s neutron monitor network was initiated about 50 years ago. It grew to a peak of almost 100 stations towards the end of the 1960s and at present about half of these are still active. Many of the original questions about the production of atmospheric secondaries, geomagnetic effects, and neutron monitor response in general, have been settled satisfactorily. Due to their long-term reliability and automated data acquisition, the remaining neutron monitors in the network are well suited for important future contributions in several areas. Amongst these are (a) spectral measurements, which require an optimal distribution along cutoff rigidities; (b) anisotropy studies, which require a set of neutron monitors with well-defined, narrow cones of acceptance for charged particles, covering all directions as evenly as possible; and (c) solar neutron measurements, which primarily require an even distribution in longitude, at high altitude and near the equator. Steps have already been taken to improve the network with these goals in mind, and to standardize methods. This contribution describes some of these steps and suggests further strategies to achieve the most optimal network.
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110) (1)

Journal: American Institute of Physics: Conference Proceedings
Title: Solar Magnetic Field Variations and Cosmic Ray Modulation
General Information: Published online 16 June 1999
Author(s): H. V. Cane, G. Wibberenz, I. G. Richardson
Abstract: Current modeling of long-term (11-year) cosmic ray modulation incorporates as a major component the so-called “Global Merged Interaction Regions” (GMIRs). GMIRs are assumed to be formed beyond about 10 AU by the merging of systems of coronal mass ejections (CMEs) and existing interaction regions. Merged interaction regions are identified from outer heliospheric magnetic field observations as complex structures and enhancements above the average field strength. We demonstrate that the ∼1 year cosmic ray modulation events supposedly caused by GMIRs are already apparent at 1 AU, with the effects of individual major CMEs superimposed. Thus, GMIRs are unlikely to be the prime cause of long-term cosmic ray modulation. We show that the cosmic ray intensity is anti-correlated with the interplanetary magnetic field strength (IMF). The IMF shows an overall solar-cycle variation of about a factor of 2 together with episodic increases with durations of about a year which do not form in the interplanetary medium but are related to global variations of the solar photospheric magnetic field. We point out, once again, that cosmic rays are important probes of the structure of the interplanetary medium.

111) (2)

Journal: American Institute of Physics: Review of Scientific Instruments
Title: Neutron Monitor using Microfission chambers for the International Thermonuclear Experimental Reactor
General Information: Published 1999
Author(s): T. Nishitani, S. Kasai, L. C. Johnson, K. Ebisawa, C. Walker, T. Ando
Abstract: We are designing microfission chambers, which are pencil size gas counters with fissile material inside, to be installed in the vacuum vessel as neutron flux monitors for the International Thermonuclear Experimental Reactor (ITER). We computed the neutron and gamma flux around the shielding blanket by a two-dimensional neutron calculation, in order to find suitable locations for microfission chambers. We found that the 238U238U microfission chambers are not suitable because the detection efficiency will increase up to 50% during the ITER lifetime by breeding 239U.239U. We propose to install 235U235U microfission chambers on the front side of the back plate in the gap between adjacent blanket modules and behind the blankets at ten poloidal locations. One chamber will be installed in the divertor cassette, just under the dome. Employing both the pulse counting mode and Campbelling mode in the electronics, we can accomplish the ITER requirement of 107107 dynamic range, with 1 ms temporal resolution, and eliminate the effect of gamma rays. An in-vessel neutron monitor will be affected by changes of the detection efficiency due to the change in the plasma position and neutron source profile. Here we demonstrate by neutron Monte Carlo calculation with three-dimensional modeling that we avoid those detection efficiency changes by installing microfission chambers at several poloidal locations inside the vacuum vessel.
112) (3)

Journal: Annales Geophysicae

Title: The World Neutron Monitor Network as a Tool for the Study of Solar Neutrons
General Information: Accepted 26 November 1996, Volume 15, Pages 375-386
Author(s): G. Usoskin, G. A. Kovaltsov, H. Kananen, P. Tanskanen
Abstract: The use of the World Neutron Monitor Network to detect high-energy solar neutrons is discussed in detail. It is shown that the existing network can be used for the routine detection of intense sporadic solar-neutron events whenever they occur. A technique is suggested involving the weighted summation of responses of separate monitors to solar neutrons. It is demonstrated that the use of this method improves the significance of solar-neutron event detection. Different results of the simulation of the neutron-monitor sensitivity to solar neutrons have been tested with respect to their application for practical use. It is shown that the total number of neutrons with energy above 300 MeV injected from the Sun during a solar flare can be estimated directly from the time-integrated neutron monitor response to solar neutrons without any model assumptions. The estimation technique has been developed.
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