Journal: The Astrophysical Journal

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Journal: The Astrophysical Journal

Title: Monitoring Short-Term Cosmic-Ray Spectral Variations using Neutron Monitor Time-Delay Measurements
General Information: Published 20 January 2016, Pages 817-838
Author(s): D. Ruffolo, A. Sáiz, P.-S. Mangeard, N. Kamyan, P. Muangha, N. Gasiprong, T. Nutaro, S. Sumran, C. Channok, C. Wuttiya, M. Rujiwarodom, P. Tooprakai, B. Asavapibhop, P. Evenson, C. Chaiwattana, J. W. Bieber, J. Clem, and K. Munakata
Abstract: Neutron monitors (NMs) are ground-based detectors of cosmic-ray showers that are widely used for high-precision monitoring of changes in the Galactic cosmic-ray (GCR) flux due to solar storms and solar wind variations. In the present work, we show that a single neutron monitor station can also monitor short-term changes in the GCR spectrum, avoiding the systematic uncertainties in comparing data from different stations, by means of NM time-

delay histograms. Using data for 2007–2014 from the Princess Sirindhorn Neutron Monitor, a station at Doi Inthanon, Thailand, with the world’s highest vertical geomagnetic cutoff rigidity of 16.8 GV, we have developed an analysis of time-delay histograms that removes the chance coincidences that can dominate conventional measures of multiplicity. We infer the “leader fraction” L of neutron counts that do not follow a previous neutron count in the same counter from the same atmospheric secondary, which is inversely related to the actual multiplicity and increases for increasing GCR spectral index. After correction for atmospheric pressure and water vapor, we find that L indicates substantial short-term GCR spectral hardening during some but not all Forbush decreases in GCR flux due to solar storms. Such spectral data from Doi Inthanon provide information about cosmic-ray energies beyond the Earth’s maximum geomagnetic cutoff, extending the reach of the worldwide NM network and opening a new avenue in the study of short-term GCR decreases.

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Journal: Journal of Physics: Conference Series

Title: Calculating Hurst Exponent and Neutron Monitor Data in a Single Parallel Algorithm
General Information: Volume 633, Conference 1, 2015
Author(s): A. S. Kussainov, S. G. Kussainov
Abstract: We implemented an algorithm for simultaneous parallel calculation of the Hurst exponent H and the fractal dimension D for the time series of interest. Parallel programming environment was provided by OpenMPI library installed on three machines networked in the virtual cluster and operated by Debian Wheeze operating system. We applied our program for a comparative analysis of week and a half long, one minute resolution, six channels data from neutron monitor. To ensure a faultless functioning of the written code we applied it to analysis of the random Gaussian noise signal and time series with manually introduced self-affinity features. Both of them have the well-known values of H and D. All results are in good correspondence with each other and supported by the modern theories on signal processing thus confirming the validity of the implemented algorithms. Our code could be used as a standalone tool for the different time series data analysis as well as for the further work on development and optimization of the parallel algorithms for the time series parameters calculations.



Mason, Paolo. "Estimating ground-level neutron-flux enhancements in the extreme cosmic-ray events of the next 100, 1000 and 10000 years." Journal of Atmospheric and Solar-Terrestrial Physics 135 (2015): 92+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: Estimates are proposed of the enhancement in neutron flux which may be experienced at ground level in cosmic-ray events of extreme magnitude over the next century, millennium and ten millennia. The estimates are based on a points-over-threshold analysis of hourly neutron counts measured over the last decades by nine neutron-monitor stations located in Europe, North America and Antarctica. The present results are in good agreement with recent studies of extreme solar events based on the direct observation of flares and the abundance of cosmogenic nuclides in terrestrial and lunar archives.



"Solar cycles and depositional processes in annual.sup.10Be from two varved lake sediment records." Earth and Planetary Science Letters 428 (2015): 44+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: Beryllium 10 concentrations (.sup.10Be.sub.con) were measured at annual resolution from varved sediment cores of Lakes Tiefer See (TSK) and Czechowskie (JC) for the period 1983-2009 ([approximately equal to]solar cycles 22 and 23). Calibrating the.sup.10Be.sub.con time-series against complementing proxy records from the same archive as well as local precipitation and neutron monitor data, reflecting solar forced changes in atmospheric radionuclide production, allowed (i) identifying the main depositional processes and (ii) evaluating the potential for solar activity reconstruction..sup.10Be.sub.con in TSK and JC sediments are significantly correlated to varying neutron monitor counts (TSK: r=0.5, p=0.05, n=16; JC: r=0.46, p=0.03, n=22). However, the further correlations with changes in organic carbon contents in TSK as well as varying organic carbon and detrital matter contents in JC point to catchment specific biases in the.sup.10Be.sub.con time-series. In an attempt to correct for these biases multiple regression analysis was applied to extract an atmospheric.sup.10Be production signal (.sup.10Be.sub.atmosphere). To increase the signal to noise ratio a.sup.10Be composite record (.sup.10Be.sub.composite) was calculated from the TSK and JC.sup.10Be.sub.atmosphere time-series..sup.10Be.sub.composite is significantly correlated to variations in the neutron monitor record (r=0.49, p=0.01, n=25) and matches the expected amplitude changes in.sup.10Be production between solar cycle minima and maxima. This calibration study on.sup.10Be from two sites indicates the large potential but also, partly site-specific, limitations of.sup.10Be in varved lake sediments for solar activity reconstruction.



SARKAR, RUPA, PRASANNA KUMAR MONDAL, and BARUN KUMAR CHATTERJEE. "An alternative method for the measurement of neutron flux." Pramana 85.4 (2015): 685+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: A simple and easy method for measuring the neutron flux is presented. This paper deals with the experimental verification of neutron dose rate--flux relationship for a non-dissipative medium. Though the neutron flux cannot be obtained from the dose rate in a dissipative medium, experimental result shows that for non-dissipative medium one can obtain the neutron flux from dose rate. We have used a .sup.241 AmBe neutron source for neutron irradiation, and the neutron dose rate and count rate were measured using a NM2B neutron monitor and R-12 superheated droplet detector (SDD), respectively. Here, the neutron flux inferred from the neutron count rate obtained with R-12 SDD shows an excellent agreement with the flux inferred from the neutron dose rate in a non-dissipative medium.



Parnahaj, I., and K. Kudela. "Forbush decreases at a middle latitude neutron monitor: relations to geomagnetic activity and to interplanetary plasma structures." Astrophysics and Space Science 359.1 (2015): 1+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: Results of statistical study on relations between Forbush decreases (FDs) as observed at a middle-latitude, high mountain cosmic ray (CR) neutron monitor (NM), and the geomagnetic storms (GS), as well as on connections of FDs to interplanetary plasma structures, are presented. Study confirms and extends (until 2014) earlier results based on NM data from different geomagnetic cut-off positions and covering earlier periods, namely that FDs associated with halo coronal mass ejections (CMEs) and those related with the shocks correspond to higher amplitudes of FDs than those without the mentioned features.



Bentoutou, Youcef, and El-Habib Bensikaddour. "Analysis of radiation induced effects in high-density commercial memories on-board Alsat-1: The impact of extreme solar particle events." Advances in Space Research 55.12 (2015): 2820+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: This paper presents a long-term study on radiation effects in non-hardened high density memory devices operating within the main on-board computer system of the Algerian microsatellite Alsat-1 in Low Earth Orbit (LEO). A statistical analysis of single-event upset (SEU) activity is presented for commercial SRAM devices, and their response to extreme solar events shows SEU rate significant increases correlated with high-energy protons (E 100MeV). Ground based neutron monitor data are used to illustrate the long-term correlation between galactic cosmic rays and Alsat-1 upsets. The short-term effects of energetic solar particles are illustrated with space environment data from GOES-11. The Alsat-1 observed SEU rates are compared to the predicted rates based on ground test data and environment models. The prediction results are in good agreement with in-flight data.



"Force-field parameterization of the galactic cosmic ray spectrum: Validation for Forbush decreases." Advances in Space Research 55.12 (2015): 2940+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: A useful parametrization of the energy spectrum of galactic cosmic rays (GCR) near Earth is offered by the so-called force-field model which describes the shape of the entire spectrum with a single parameter, the modulation potential. While the usefulness of the force-field approximation has been confirmed for regular periods of solar modulation, it was not tested explicitly for disturbed periods, when GCR are locally modulated by strong interplanetary transients. Here we use direct measurements of protons and [alpha]-particles performed by the PAMELA space-borne instrument during December 2006, including a major Forbush decrease, in order to directly test the validity of the force-field parameterization. We conclude that (1) The force-field parametrization works very well in describing the energy spectra of protons and [alpha]-particles directly measured by PAMELA outside the Earths atmosphere; (2) The energy spectrum of GCR can be well parameterized by the force-field model also during a strong Forbush decrease; (3) The estimate of the GCR modulation parameter, obtained using data from the world-wide neutron monitor network, is in good agreement with the spectra directly measured by PAMELA during the studied interval. This result is obtained on the basis of a single event analysis, more events need to be analyzed.



Belov, A. V., et al. "Possible ground level enhancements of solar cosmic rays in 2012." Bulletin of the Russian Academy of Sciences: Physics 79.5 (2015): 561+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: It is commonly accepted that two ground level enhancements of solar cosmic rays (GLEs) have so far been recorded in solar cycle 24: one on May 17, 2012, and one on January 6, 2014. The current solar activity cycle is considered to lag behind previous cycles in both quantity and magnitude of GLEs. Considerably more (around 30) solar proton events have been recorded from satellites. In this work, we analyze the patterns of cosmic ray intensity over the worldwide neutron monitor network during those events of 2012 in which considerable increases in the integral proton fluxes with energies of >100 MeV were observed, i.e., the events of January 27, March 7, and March 13, 2012. All of these events may be considered possible GLEs. More GLEs have apparently been observed during solar cycle 24 than is widely recognized.



Makhmutov, V. S., et al. "Analysis of cosmic ray variations recorded in October--December 2013." Bulletin of the Russian Academy of Sciences: Physics 79.5 (2015): 570+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: Results from analyzing variations in cosmic ray and solar activities in October--November 2013 are described. Data from observations using a Kover/GCR cosmic ray detector (CERN, Switzerland) and the neutron monitor worldwide network are used. Solar flare activity is analyzed using results on H.sub.[alpha], X-ray, gamma, and radio emissions observed at ground-based installations and on board spacecraft (e.g., GOES and FERMI). Attention is focused on the cosmic ray increases detected by the Kover/GCR detector on October 15 and November 19, 2013. Features of these events are similar to increases detected earlier on March 7, 2011, and January 23, 2012, by the Kover/CASLEO detector at the CASLEO astronomical complex in Argentina. Possible correlations between the observed cosmic ray intensity increases and flare solar activity or processes in the Earth's atmosphere are considered.


Grigoryev, V. G., and S. A. Starodubtsev. "Global survey method in real time and space weather forecasting." Bulletin of the Russian Academy of Sciences: Physics 79.5 (2015): 649+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: With the creation of the database of neutron monitor stations (NMDB) it became the possible to study in real time the dynamics of daily cosmic ray anisotropy by the method of a global survey. The results of the authors' investigations show that this approach can improve the accuracy of forecasting the Earth's entry into geoeffective disturbances of the solar wind.


Pacini, A. A., and I. G. Usoskin. "An Unusual Pattern of Cosmic-Ray Modulation During Solar Cycles 23 and 24." Solar Physics 290.3 (2015): 943+. Academic OneFile. Web. 6 Jan. 2016.
Abstract: By means of an analysis of data from eight neutron monitor (NM) stations with different geomagnetic cutoff rigidities, we found an unusual latitudinal effect observed in the cosmic-ray (CR) modulation during the last solar cycles. Since the beginning of the ground-based cosmic-ray monitoring, it is known that the solar-cycle modulation is more evident in data from high latitude than from the medium and low latitudes, showing an expected geomagnetic cutoff rigidity effect. However, a more detailed look shows a new latitudinal effect in cycle 24: while the magnitude of the solar modulation in the low-latitude data remains the same for the last three solar minima, the last solar minimum caused a more intense peak in the polar NM data than in the previous cycles. After correcting the data for the geomagnetic changes of the period, we found an anomalous solar modulation in the last cycle. This suggests a weaker heliospheric modulation at low-energy particles (responsible for the NM counting in polar sites) now than in the previous cycles, while there is no significant difference of the modulation for the more energetic part of the CR spectrum. Our result can be associated with changes of the solar wind turbulence, which would corroborate some recent studies about the last solar minimum phase, and indicates that this new solar modulation feature is still present in the current solar maximum stage.


Journal: Space Weather
Title: Short-Term Variation of Cosmic Radiation Measured by Aircraft under Constant Flight Conditions
General Information: Published 21 November 2015, Volume 13, Issue 11, Pages 797-806
Author(s): Jaejin Lee, Uk-Won Nam, Jeonghyun Pyo, Sunghwan Kim, Yong-Jun Kwon, Jaewon Lee, Inchun Park, Myung-Hee Y. Kim, Tsventan P. Dachev
Abstract: The temporal variations in cosmic radiation on aircraft under constant flight conditions were measured by a Liulin detector. Rather than a commercial long-distance aircraft, we used a military reconnaissance aircraft performing a circular flight at a constant altitude over the Korean Peninsula. At 9144 m (30,000 ft), the mean and standard deviation of the radiation dose rate (among 35 measurements) was 2.3 and 0.17 μSv/h, respectively. The experiment yielded two observational results. First, the dose rate changed over a flight time of 5–7 h; second, no strong correlation was revealed between the cosmic rays observed from the ground-based neutron monitor and the radiation doses at aircraft altitude. These observations can provide insight into the short-term variation of cosmic radiation at aviation altitudes. When discarding various negligible factors, it is postulated that the changes in the geomagnetic field and the air density still could affect the variation of cosmic radiation at aircraft altitude. However, various factors are less known about the dependence on the cosmic radiation. Therefore, investigations of possible factors are also warranted at the monitoring points of space weather.


Journal: Journal of Geophysical Research: Space Physics
Title: Can We Properly Model the Neutron Monitor Count Rate?
General Information: Published 26 September 2015, Volume 120, Issue 9, Pages 7172-7178
Author(s): Agnieszka Gil, Ilya G. Usoskin, Gennady A. Kovaltsov, Alexander L. Mishev, Claudio Corti, Veronica Bindi
Abstract: Neutron monitors provide continuous measurements of secondary nucleonic particles produced in the atmosphere by the primary cosmic rays and form the main tool to study the heliospheric modulation of cosmic rays. In order to study cosmic rays using the world network of neutron monitor and needs to be able to model the neutron monitor count rate. Earlier it was difficult because of the poorly known yield function, which has been essentially revisited recently. We have presented a verification of the new yield function of the standard neutron monitor (NM) using a recently released data on the direct in situ measurements of the galactic cosmic rays energy spectrum during 2006–2009 (the period of the record high cosmic ray flux) by Payload for Antimatter Matter Exploration and Light-nuclei Astrophysics spaceborne spectrometer, and on NM latitude surveys performed during the period of 1994–2007, including periods of high solar activity. We found a very good agreement between the measured count rates of sea level NMs and the modeled ones in very different conditions: from low to high solar activity and from polar to tropical regions. This implies that the count rate of a sea level neutron monitor can be properly modeled in all conditions, using the new yield function.


Journal: Journal of Geophysical Research: Space Physics
Title: Neutrons and Energetic Charged Particles in the inner Heliosphere: Measurements of the MESSENGER Neutron Spectrometer from 0.3 to 0.85 AU
General Information: Published 7 February 2015, Volume 120, Issue 2, Pages 841-854
Author(s): Douglas J. Rodgers, David J. Lawrence, William C. Feldman, Patrick N. Peplowski
Abstract: Energetic charged particle and neutron data from the Neutron Spectrometer (NS) on board the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft have been acquired for solar distances ranging from 0.3 to 0.85 AU. The NS is sensitive to ions with energies greater than 120 MeV/nucleon and has made the first measurements of these energetic ions in the inner heliosphere since the mid-1970s. The high-energy ion measurements are well correlated with Earth-based neutron monitor measurements, which themselves provide a measure of the solar modulation of galactic cosmic rays (GCRs). These measurements provide an explicit demonstration of the expected GCR solar modulation for solar distances to 0.3 AU. These NS data also represent the first interplanetary neutron measurements in the inner heliosphere. The time variability of the neutron measurements are driven by two primary effects: time variable production of neutrons from GCRs interacting with local spacecraft material and small count rate changes due to temperature-driven gain changes in the NS instrument. When these time-dependent variations are removed from the neutron measurements, there is no statistically significant variation of neutron count rates versus solar distance. These data are used to derive an upper limit on solar neutron production of 1024 neutrons[0.5 < E < 9 MeV] sr−1 s−1 during quiescent periods.


Journal: Journal of Geophysical Research: Space Physics
Title: Misidentification of the Source of a Neutron Transient Detected by MESSENGER on 4 June 2011
General Information: Published 12 January 2015, Volume 120, Issue 1, Pages 1-11
Author(s): Gerald H. Share, Ronald J. Murphy, Allan J. Tylka, Brian R. Dennis, James M. Ryan
Abstract: Low-energy (1–10 MeV) neutrons emanating from the Sun provide unique information about accelerated ions with steep energy spectra that may be produced in weak solar flares. However, observation of these solar neutrons can only be made in the inner heliosphere where measurement is difficult due to high background rates from neutrons produced by energetic ions interacting in the spacecraft. These ions can be from solar energetic particle events or produced in passing shocks associated with fast coronal mass ejections. Therefore, it is of the utmost importance that investigators rule out these secondary neutrons before making claims about detecting neutrons from the Sun. The MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) neutron spectrometer recorded an hour-long neutron transient beginning at 15:45 UTC on 4 June 2011 for which Lawrence et al. (2014) claim there is “strong evidence” that the neutrons were produced by the interaction of ions in the solar atmosphere. We studied this event in detail using data from the MESSENGER neutron spectrometer, gamma ray spectrometer, X-ray Spectrometer, and Energetic Particle Spectrometer and from the particle spectrometers on STEREO A. We demonstrate that the transient neutrons were secondaries produced by energetic ions, probably accelerated by a passing shock, that interacted in the spacecraft. We also identify significant faults with the authors' arguments in favor of a solar neutron origin for the transient.


Journal: Journal of Geophysical Research: Space Physics
Title: Long-Duration Neutron Production by Non-Flaring Transients in the Solar Corona
General Information: Published 24 October 2015, Volume 120, Issue 10, Pages 8247-8266
Author(s): William C. Feldman, David J. Lawrence, W. Thomas Vestrand, Daniel N. Baker, Patrick N. Peplowski, Douglas J. Rodgers
Abstract: The purpose of this work is to study neutron enhancements observed using the Neutron Spectrometer aboard MESSENGER in order to identify events that may have been generated at/or near the Sun by solar transients. To securely establish an origin of the observed neutrons that is nonlocal to the MESSENGER spacecraft, a measurement of the energetic ion environment local to MESSENGER is needed. For this purpose, we use energetic ion spectrometers on several spacecraft at 1 AU when they were magnetically connected to MESSENGER during an event. We report strong evidence that for six neutron events studied in detail, the detected neutrons do not likely have a local spacecraft origin. By implication, most of the detected neutrons for these six events may have originated near the Sun, generated by many moderate-level solar eruptive events that produce an extended solar exosphere of moderate-energy neutrons, protons, and electrons.


Journal: Journal of Geophysical Research: Space Physics
Title: The 4 June 2011 Neutron Event at Mercury: A Defense of the Solar Origin Hypothesis
General Information: Published 14 July 2015, Volume 120, Issue 7, Pages 5284-5289
Author(s): David J. Lawrence, William C. Feldman, Patrick N. Peplowski, Sean C. Solomon
Abstract: We address the claim that an increase in the flux of neutrons detected by the Neutron Spectrometer (NS) on the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) spacecraft in orbit about Mercury at 15:45 UTC on 4 June 2011 was generated by the impact of energetic ions onto spacecraft. We find this claim to be unwarranted. The claim is grounded on the erroneous assumption that the NS singles count rate is triggered only by energetic ions. Rather, because any mix of energetic ions, electrons, photons, and neutrons can trigger NS singles, these data do not provide a reliable constraint on the presence of energetic ions. The absence of an enhancement in the count rate of 1635-keV gamma rays, as monitored by the MESSENGER Gamma-Ray Spectrometer, provides independent evidence that a fluence of energetic protons sufficiently high to generate the neutron enhancement was not present during the neutron event. The interpretation that currently best matches the available data is that the neutron enhancement on 4 June 2011 was the result of solar neutrons.


Journal: Journal of Geophysical Research: Space Physics
Title: Comprehensive Survey of Energetic Electron Events in Mercury's Magnetosphere with Data from the MESSENGER Gamma-Ray and Neutron Spectrometer
General Information: Published 27 April 2015, Volume 120, Issue 4, Pages 2851-2876
Author(s): David J. Lawrence, Brian J. Anderson, Daniel N. Baker, William C. Feldman, George C. Ho, Haje Korth, Ralph L. McNutt Jr., Patrick N. Peplowski, Sean C. Solomon, Richard D. Starr, Jon D. Vandegriff, Reka M. Winslow
Abstract: Data from the MErcury Surface, Space ENvironment, GEochemistry, and Ranging (MESSENGER) Gamma-Ray and Neutron Spectrometer have been used to detect and characterize energetic electron (EE) events in Mercury's magnetosphere. This instrument detects EE events indirectly via bremsstrahlung photons that are emitted when instrument and spacecraft materials stop electrons having energies of tens to hundreds of keV. From Neutron Spectrometer data taken between 18 March 2011 and 31 December 2013 we have identified 2711 EE events. EE event amplitudes versus energy are distributed as a power law and have a dynamic range of a factor of 400. The duration of the EE events ranges from tens of seconds to nearly 20 min. EE events may be classified as bursty (large variation with time over an event) or smooth (small variation). Almost all EE events are detected inside Mercury's magnetosphere on closed field lines. The precise occurrence times of EE events are stochastic, but the events are located in well-defined regions with clear boundaries that persist in time and form what we call “quasi-permanent structures.” Bursty events occur closer to dawn and at higher latitudes than smooth events, which are seen near noon-to-dusk local times at lower latitudes. A subset of EE events shows strong periodicities that range from hundreds of seconds to tens of milliseconds. The few-minute periodicities are consistent with the Dungey cycle timescale for the magnetosphere and the occurrence of substorm events in Mercury's magnetotail region. Shorter periods may be related to phenomena such as north-south bounce processes for the energetic electrons.


Journal: Space Weather
Title: Real-Time Prediction of the Occurrence and Intensity of the First Hours of >100 MeV Solar Energetic Proton Events
General Information: Published 27 November 2015, Volume 13, Issue 11, Pages 807-819
Author(s): Marlon Núñez
Abstract: A new model for predicting the occurrence of >100 MeV solar energetic proton (SEP) events and the first hours of the >100 MeV integral proton flux is presented. This model uses a novel approach based on the lag correlation between strong positive derivatives of X-ray flux and proton flux. The new model has been validated with data from January 1994 to September 2013, obtaining a probability of detection of all >100 MeV SEP events of 80.85%, a false alarm ratio of 29.62%, and an average warning time of 1 h and 6 min. The model identifies the associated flare and active region. Currently, there is no other automatic empirical or physics-based system able to predict SEP events of energies in the interval of 100 MeV to ~430 MeV (lower GLE cutoff according to Clem and Dorman (2000)). This paper also proposes the combined use of the new prediction model and the existing one for predicting >10 MeV SEP events. The combined SEP prediction models have been developed to improve mitigation of adverse effects on near-Earth and interplanetary missions.


Journal: Earth and Space Science
Title: Autonomous Identification and Classification of Ionospheric Sporadic E in Digital Ionograms
General Information: Published 14 July 2015, Volume 2, Issue 7, Pages 244-261
Author(s): Payel Ghosh, F. T. Berkey
Abstract: This paper introduces a methodology to autonomously identify and classify ionospheric sporadic E layers (Es) from digital ionograms acquired using a NOAA dynasonde operated at the Bear Lake Observatory (BLO) in northern Utah. This approach uses a windowed-fuzzy clustering technique to group ionospheric echoes present in digital ionograms, employing the transitive property of equivalence. The algorithm introduces a variance constraint to automatically determine the number and size of the clusters present in the data set. Principal component analysis (PCA) of the cluster shapes is employed for curvature estimation and to enable classification of the data into the four principal types of temperate latitude sporadic E. A visual evaluation of the autonomously classified ionograms suggests that the algorithm accurately identifies 95% of the sporadic Eechoes present in the BLO data set. The paper also includes a “proof-of-concept” analysis of the methodology, deriving Esparameters for summer and winter intervals, that explicitly characterizes the diurnal and seasonal variations present in the E region at 42N. This analysis was derived from approximately 34,000 digital ionograms acquired over 4 months. While the experimental data show lower peak Eregion heights than predicted by modeling studies, they are generally consistent with GPS satellite occultation measurements. Our analysis of the temporal variation of foEduring summer and winter intervals is inconsistent with previous results that suggest a seasonal E region density anomaly. The results confirm, however, the ionospheric effect of increased NO densities in both the summer and winter E region, as predicted by modeling studies. The identification of sporadic E using the approach outlined in this work markedly facilitates the analysis of Es parameters, as well as eliminating any human biases from the ionogram analysis process.


Journal: Journal of Geophysical Research: Space Physics
Title: A Link between Solar Events and Congenital Malformations: Is Ionizing Radiation Enough to Explain It?
General Information: Published 19 March 2015, Volume 120, Issue 3, Pages 1537-1542
Author(s): Andrew C. Overholt, Adrian L. Melott, Dimitra Atri
Abstract: Cosmic rays are known to cause biological effects directly and through ionizing radiation produced by their secondaries. These effects have been detected in airline crews and other specific cases where members of the population are exposed to above average secondary fluxes. Recent work has found a correlation between solar particle events and congenital malformations. In this work we use the results of computational simulations to approximate the ionizing radiation from such events as well as longer-term increases in cosmic ray flux. We find that the amounts of ionizing radiation produced by these events are insufficient to produce congenital malformations under the current paradigm regarding muon ionizing radiation. We believe that further work is needed to determine the correct ionizing radiation contribution of cosmogenic muons. We suggest that more extensive measurements of muon radiation effects may show a larger contribution to ionizing radiation dose than currently assumed.


Journal: Geophysical Research Letters
Title: Lightning as a Space-Weather Hazard: UK Thunderstorm Activity Modulated by the Passage of the Heliospheric Current Sheet
General Information: Published 19 November 2015, Volume 42, Issue 22, Pages 9624-9632
Author(s): M. J. Owens, C. J. Scott, A. J. Bennett, S. R. Thomas, M. Lockwood, R. G. Harrison, M. M. Lam
Abstract: Lightning flash rates, RL, are modulated by corotating interaction regions (CIRs) and the polarity of the heliospheric magnetic field (HMF) in near-Earth space. As the HMF polarity reverses at the heliospheric current sheet (HCS), typically within a CIR, these phenomena are likely related. In this study, RL is found to be significantly enhanced at the HCS and at 27 days prior/after. The strength of the enhancement depends on the polarity of the HMF reversal at the HCS. Near-Earth solar and galactic energetic particle fluxes are also ordered by HMF polarity, though the variations qualitatively differ from RL, with the main increase occurring prior to the HCS crossing. Thus, the CIR effect on lightning is either the result of compression/amplification of the HMF (and its subsequent interaction with the terrestrial system) or that energetic particle preconditioning of the Earth system prior to the HMF polarity change is central to solar wind lightning coupling mechanism.


Journal: Journal of Geophysical Research: Space Physics
Title: Intensity of Nightside MARSIS AIS Surface Reflections and Implications for Low-Altitude Ionospheric Densities
General Information: Published 24 April 2015, Volume 120, Issue 4, Pages 3226-3239
Author(s): F. Němec, D. D. Morgan, C. Diéval, D. A. Gurnett
Abstract: Spacecraft radar sounding signals at frequencies higher than the ionospheric peak plasma frequency are not reflected by the ionosphere. Instead, they make it to the ground where they are reflected by the planetary surface. We analyze the intensity of the surface reflections measured by the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) ionospheric radar sounder on board the Mars Express spacecraft. Apart from the surface reflectivity and the spacecraft altitude, the detected intensity of surface reflections is controlled primarily by the signal attenuation during the ionospheric propagation. We focus on the nightside region, where the ionospheric densities in the main layer are too low to cause a significant attenuation and allow sampling of the surface reflections at frequencies down to 3 MHz. The attenuation occurs mainly at altitudes below 100 km, where the electron-neutral collision frequency is a maximum. The intensity of surface reflections can thus serve as a proxy for electron densities at low altitudes not accessible by the direct ionospheric radar sounding. We analyze the intensity of surface reflections as a function of relevant controlling parameters. The intensity of surface reflections is lower at higher solar zenith angles on the nightside and during the periods of larger solar activity. Moreover, it exhibits a seasonal variation that is related to the dust storm occurrence. The intensity of surface reflections is lower in areas of closed magnetic field lines, suggesting that nightside electron densities behave rather differently at low altitudes than at higher altitudes. This is confirmed by comparison with simultaneous observations of the main ionospheric layer.


Journal: American Institute of Physics: Physics of Plasmas
Title: Where is the cosmic-ray modulation boundary of the heliosphere?
General Information: Published online 20 August 2015, Volume 22, Issue 9
Author(s): Ming Zhang, Xi Luo, Nikolai Pogorelov
Abstract: The intensity of Galactic cosmic rays in the heliosphere is modulated by solar activities. The outer boundary where the solar modulation begins has always been a subject matter of debate in the cosmic-ray and heliophysics community. Various experimental methods and theoretical model calculations have been used to determine the boundary. Although the heliopause was always suspected to be the boundary, it is only until very recently after Voyager 1 had crossed the heliopause did we confirm that the boundary is indeed the heliopause. In this paper, we use a model simulation and detailed Voyager observation of cosmic rays at the heliopause crossing to show that the modulation boundary, in fact, is a fraction of an AU beyond the heliopause. Such a conclusion requires a very low turbulence level of the interstellar magnetic field in the outer heliosheath. According to the quasi-linear theory, a low level of turbulence should result in a very large diffusion coefficient parallel to the magnetic field and a very small perpendicular diffusion coefficient. For the first time, we are confident that Voyager 1 has obtained the truly pristine local interstellar cosmic-ray spectra down to the energies below 1 MeV. The cosmic-ray intensity is rapidly filtered by a thin layer of the interstellar magnetic field immediately outside of the heliopause. Its filtration amount depends on the conditions of magnetic field turbulence on the both sides of the heliopause, thus making it solar-cycle dependent as well.


Journal: American Institute of Physics: Physics of Plasmas
Title: Cosmic ray transport in astrophysical plasmas
General Information: Published online 24 August 2015, Volume 22, Issue 9
Author(s): R. Schlickeiser
Abstract: Since the development of satellite space technology about 50 years ago the solar heliosphere is explored almost routinely by several spacecrafts carrying detectors for measuring the properties of the interplanetary medium including energetic charged particles (cosmic rays), solar wind particle densities, and electromagnetic fields. In 2012, the Voyager 1 spacecraft has even left what could be described as the heliospheric modulation region, as indicated by the sudden disappearance of low energy heliospheric cosmic ray particles. With the available in-situ measurements of interplanetary turbulent electromagnetic fields and of the momentum spectra of different cosmic ray species in different interplanetary environments, the heliosphere is the best cosmic laboratory to test our understanding of the transport and acceleration of cosmic rays in space plasmas. I review both the historical development and the current state of various cosmic ray transport equations. Similarities and differences to transport theories for terrestrial fusion plasmas are highlighted. Any progress in cosmic ray transport requires a detailed understanding of the electromagnetic turbulence that is responsible for the scattering and acceleration of these particles.


Journal: American Institute of Physics: Physics of Plasmas
Title: Cosmic Ray Transport in Astrophysical Plasmas
General Information: Published online 24 August 2015
Author(s): R. Schlickeiser
Abstract: Since the development of satellite space technology about 50 years ago the solar heliosphere is explored almost routinely by several spacecrafts carrying detectors for measuring the propertiesof the interplanetary medium including energetic charged particles (cosmic rays), solar wind particle densities, and electromagnetic fields. In 2012, the Voyager 1 spacecraft has even left what could be described as the heliospheric modulation region, as indicated by the sudden disappearance of low energy heliospheric cosmic ray particles. With the available in-situmeasurements of interplanetary turbulent electromagnetic fields and of the momentum spectra of different cosmic ray species in different interplanetary environments, the heliosphere is the best cosmic laboratory to test our understanding of the transport and acceleration of cosmic rays in space plasmas. I review both the historical development and the current state of various cosmic ray transport equations. Similarities and differences to transport theories for terrestrial fusion plasmas are highlighted. Any progress in cosmic ray transport requires a detailed understanding of the electromagnetic turbulence that is responsible for the scattering and acceleration of these particles.


Journal: Journal of Physics: Conference Series
Title: Numerical Calculations of Cosmic Ray Cascade in the Earth’s Atmosphere using Different Particle Interaction Models
General Information: 2015, Volume 661, Conference 1
Author(s): A. V. Nesterenok, V. O. Naidenov
Abstract: The interaction of primary cosmic rays with the Earth's atmosphere is investigated using the simulation toolkit GEANT4. Two reference lists of physical processes - QGSP_BIC_HP and FTFP_BERT_HP - are used in the simulations of cosmic ray cascade in the atmosphere. The cosmic ray neutron fluxes are calculated for mean level of solar activity, high geomagnetic latitudes and sea level. The calculated fluxes are compared with the published results of other analogous simulations and with experimental data.


Journal: The Astrophysical Journal
Title: Re-Evaluation of the Neutron Emission from the Solar Flare of 2005 September 7, Detected by the Solar Neutron Telescope at Sierra Negra
General Information: Published 30 November 2015, Volume 814, Number 2
Author(s): L. X. González, J. F. Valdés-Galicia, F. Sánchez, Y. Muraki, T. Sako, K. Watanabe, Y. Matsubara, Y. Nagai, S. Shibata, T. Sakai, O. Musalem, A. Hurtado
Abstract: The X17.0 solar flare of 2005 September 7 released high-energy neutrons that were detected by the Solar Neutron Telescope (SNT) at Sierra Negra, Mexico. In three separate and independent studies of this solar neutron event, several of its unique characteristics were studied; in particular, a power-law energy spectra was estimated. In this paper, we present an alternative analysis, based on improved numerical simulations of the detector using GEANT4, and a different technique for processing the SNT data. The results indicate that the spectral index that best fits the neutron flux is around 3, in agreement with previous works. Based on the numerically calculated neutron energy deposition on the SNT, we confirm that the detected neutrons might have reached an energy of 1 GeV, which implies that 10 GeV protons were probably produced; these could not be observed at Earth, as their parent flare was an east limb event.


Journal: Environmental Research Letters
Title: Focus on High Energy Particles and Atmospheric Processes
General Information: Published 6 October 2015, Volume 10, Number 10
Author(s): R. Giles Harrison, Keri Nicoll, Yukihiro Takahashi, Yoav Yair
Abstract: The letters published in the 'Focus issue on high energy particles and atmospheric processes' serve to broaden the discussion about the influence of high energy particles on the atmosphere beyond their possible effects on clouds and climate. These letters link climate and meteorological processes with atmospheric electricity, atmospheric chemistry, high energy physics and aerosol science from the smallest molecular cluster ions through to liquid droplets. Progress in such a disparate and complex topic is very likely to benefit from continued interdisciplinary interactions between traditionally distinct science areas.


Journal: The Astrophysical Journal Letters
Title: Comparative Morphology of Solar Relativistic Particle Events
General Information: Published 17 September 2015, Volume 811, Number 1
Author(s): Leon Kocharov, Andreas Klassen, Eino Valtonen, Ilya Usoskin, James M. Ryan
Abstract: Time profiles of the 0.25–10 MeV electrons and the ~(0.1–1) GeV nucleon−1 protons and helium associated with two solar coronal mass ejections (CMEs) are analyzed with a newly formulated method based on modeling of the particle transport in the interplanetary medium. With the modeling, we fit the observed angular distribution of solar particles and infer, for a particular particle instrument and magnetic field orientation, the time delay of the particle registration at 1 AU in respect to the solar source. Then, after the time offset removal, intensity re-normalization and background equalization, the time–intensity profiles of high-energy protons, helium and electrons in different energy channels are superposed and compared. The comparison reveals episodes of remarkable coincidence of different profiles, as well as episodes of essentially different behavior. It implies at least three sources of solar high-energy particles operating in a single event. The first, short-duration source emits electrons next to the flare's impulsive phase and CME liftoff. The second source gradually rises and continues for more than an hour, emitting electrons and lower energy protons, which is consistent with shock acceleration on open magnetic field lines extending to solar wind. An another, third source is the main source of relativistic ions in space. It is retarded in respect to the flare's impulsive phase and may be associated with a structure encountered by the shock within a few solar radii from the Sun.


Journal: The Astrophysical Journal
Title: Modulation of Galactic Electrons in the Heliosphere during the Unusual Solar Minimum of 2006-2009: A Modeling Approach
General Information: Published 8 September 2015, Volume 810, Number 2
Author(s): M. S. Potgieter, E. E. Vos, R. Munini, M. Boezio, V. Di Felice
Abstract: The last solar minimum activity period, and the consequent minimum modulation conditions for cosmic rays, was unusual. The highest levels of Galactic protons were recorded at Earth in late 2009 in contrast to expectations. A comprehensive model was used to study the proton modulation for the period from 2006 to 2009 in order to determine what basic processes were responsible for solar modulation during this period and why it differs from proton modulation during previous solar minimum modulation periods. This established model is now applied to studying the solar modulation of electron spectra as observed for 80 MeV–30 GeV by the PAMELA space detector from mid-2006 to the end of 2009. Over this period the heliospheric magnetic field had decreased significantly until the end of 2009 while the waviness of the heliospheric current sheet decreased moderately and the observed electron spectra increased by a factor of ~1.5 at 1.0 GeV to ~3.5 at 100 MeV. In order to reproduce the modulation evident from seven consecutive semesters, the diffusion coefficients had to increase moderately while maintaining the basic rigidity dependence. It is confirmed that the main diffusion coefficients are independent of rigidity below ~0.5 GV, while the drift coefficient had to be reduced below this value. The 2006–2009 solar minimum epoch indeed was different than previously observed minima, at least since the beginning of the space exploration era. This period could be called "diffusion-dominated" as was also found for the modulation of protons.


Journal: The Astrophysical Journal
Title: An Electron-Tracking Compton Telescope for a Survey of the Deep Universe by MeV Gamma-Rays
General Information: Published 26 August 2015, Volume 810, Number 1
Author(s): T. Tanimori, H. Kubo, A. Takada, S. Iwaki, S. Komura, S. Kurosawa, Y. Matsuoka, K. Miuchi, S. Miyamoto, T. Mizumoto, Y. Mizumura, K. Nakamura, S. Nakamura, M. Oda, J. D. Parker, T. Sawano, S. Sonoda, T. Takemura, D. Tomono, K. Ueno
Abstract: Photon imaging for MeV gammas has serious difficulties due to huge backgrounds and unclearness in images, which originate from incompleteness in determining the physical parameters of Compton scattering in detection, e.g., lack of the directional information of the recoil electrons. The recent major mission/instrument in the MeV band, Compton Gamma Ray Observatory/COMPTEL, which was Compton Camera (CC), detected a mere ~30 persistent sources. It is in stark contrast with the ~2000 sources in the GeV band. Here we report the performance of an Electron-Tracking Compton Camera (ETCC), and prove that it has a good potential to break through this stagnation in MeV gamma-ray astronomy. The ETCC provides all the parameters of Compton-scattering by measuring 3D recoil electron tracks; then the Scatter Plane Deviation (SPD) lost in CCs is recovered. The energy loss rate (dE/dx), which CCs cannot measure, is also obtained, and is found to be helpful to reduce the background under conditions similar to those in space. Accordingly, the significance in gamma detection is improved several fold. On the other hand, SPD is essential to determine the point-spread function (PSF) quantitatively. The SPD resolution is improved close to the theoretical limit for multiple scattering of recoil electrons. With such a well-determined PSF, we demonstrate for the first time that it is possible to provide reliable sensitivity in Compton imaging without utilizing an optimization algorithm. As such, this study highlights the fundamental weak-points of CCs. In contrast we demonstrate the possibility of ETCC reaching the sensitivity below 1 
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