ORCID Profile
0000-0001-7463-8267
Current Organisation
University of Tasmania
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Publisher: American Astronomical Society
Date: 10-2022
Abstract: We analyze the cosmic-ray variations during a significant Forbush decrease observed with worldwide networks of ground-based neutron monitors and muon detectors during 2021 November 3–5. Utilizing the difference between primary cosmic-ray rigidities monitored by neutron monitors and muon detectors, we deduce the rigidity spectra of the cosmic-ray density (or omnidirectional intensity) and the first- and second-order anisotropies separately for each hour of data. A clear two-step decrease is seen in the cosmic-ray density with the first ∼2% decrease after the interplanetary shock arrival followed by the second ∼5% decrease inside the magnetic flux rope (MFR) at 15 GV. Most strikingly, a large bidirectional streaming along the magnetic field is observed in the MFR with a peak litude of ∼5% at 15 GV, which is comparable to the total density decrease inside the MFR. The bidirectional streaming could be explained by adiabatic deceleration and/or focusing in the expanding MFR, which have stronger effects for pitch angles near 90°, or by selective entry of GCRs along a leg of the MFR. The peak anisotropy and density depression in the flux rope both decrease with increasing rigidity. The spectra vary dynamically, indicating that the temporal variations of density and anisotropy appear different in neutron monitor and muon detector data.
Publisher: Springer Science and Business Media LLC
Date: 06-1979
DOI: 10.1038/279620A0
Publisher: World Scientific Publishing Company
Date: 08-2009
Publisher: World Scientific Publishing Company
Date: 08-2009
Publisher: Sissa Medialab
Date: 25-07-2023
DOI: 10.22323/1.444.1351
Publisher: American Geophysical Union (AGU)
Date: 12-2019
DOI: 10.1029/2019JA026651
Abstract: Cosmic rays are charged particles whose flux observed at Earth shows temporal variations related to space weather phenomena and may be an important tool to study them. The cosmic ray intensity recorded with ground‐based detectors also shows temporal variations arising from atmospheric variations. In the case of muon detectors, the main atmospheric effects are related to pressure and temperature changes. In this work, we analyze both effects using data recorded by the Global Muon Detector Network, consisting of four multidirectional muon detectors at different locations, in the period between 2007 and 2016. For each Global Muon Detector Network directional channel, we obtain coefficients that describe the pressure and temperature effects. We then analyze how these coefficients can be related to the geomagnetic cutoff rigidity and zenith angle associated with cosmic ray particles observed by each channel. In the pressure effect analysis, we found that the observed barometric coefficients show a very clear logarithmic correlation with the cutoff rigidity ided by the zenith angle cosine. On the other hand, the temperature coefficients show a good logarithmic correlation with the product of the cutoff and zenith angle cosine after adding a term proportional to the sine of geographical latitude of the observation site. This additional term implies that the temperature effect measured in the Northern Hemisphere detectors is stronger than that observed in the Southern Hemisphere. The physical origin of this term and of the good correlations found in this analysis should be studied in detail in future works.
Publisher: Sissa Medialab
Date: 17-08-2023
DOI: 10.22323/1.444.1344
Publisher: Sissa Medialab
Date: 14-08-2023
DOI: 10.22323/1.444.1267
Publisher: American Geophysical Union (AGU)
Date: 22-02-2021
DOI: 10.1029/2020SW002531
Abstract: We demonstrate that global observations of high‐energy cosmic rays contribute to understanding unique characteristics of a large‐scale magnetic flux rope causing a magnetic storm in August 2018. Following a weak interplanetary shock on August 25, 2018, a magnetic flux rope caused an unexpectedly large geomagnetic storm. It is likely that this event became geoeffective because the flux rope was accompanied by a corotating interaction region and compressed by high‐speed solar wind following the flux rope. In fact, a Forbush decrease was observed in cosmic‐ray data inside the flux rope as expected, and a significant cosmic‐ray density increase exceeding the unmodulated level before the shock was also observed near the trailing edge of the flux rope. The cosmic‐ray density increase can be interpreted in terms of the adiabatic heating of cosmic rays near the trailing edge of the flux rope, as the corotating interaction region prevents free expansion of the flux rope and results in the compression near the trailing edge. A northeast‐directed spatial gradient in the cosmic‐ray density was also derived during the cosmic‐ray density increase, suggesting that the center of the heating near the trailing edge is located northeast of Earth. This is one of the best ex les demonstrating that the observation of high‐energy cosmic rays provides us with information that can only be derived from the cosmic ray measurements to observationally constrain the three‐dimensional macroscopic picture of the interaction between coronal mass ejections and the ambient solar wind, which is essential for prediction of large magnetic storms.
Publisher: Springer Science and Business Media LLC
Date: 1983
DOI: 10.1007/BF00661165
Publisher: Sissa Medialab
Date: 18-08-2023
DOI: 10.22323/1.444.1323
Publisher: American Geophysical Union (AGU)
Date: 05-2009
DOI: 10.1029/2008JA013717
Publisher: American Geophysical Union (AGU)
Date: 12-2004
DOI: 10.1029/2004JA010493
Publisher: Cambridge University Press (CUP)
Date: 11-2010
DOI: 10.1017/S1743921310010355
Abstract: This work presents some observations during the period of the Whole Heliosphere Interval (WHI) of the effects of interplanetary (IP) structures on the near-Earth space using three sets of observations: magnetic field and plasma from the Advanced Composition Explorer (ACE) satellite, ground-based cosmic ray data from the Global Muon Detection Network (GMDN) and geomagnetic indices (Disturbance storm-time, Dst, and auroral electrojet index, AE). Since WHI was near minimum solar activity, high speed streams and corotating interaction regions (CIRs) were the dominant structures observed in the interplanetary space surrounding Earth. Very pronounced geomagnetic effects are shown to be correlated to CIRs, especially because they can cause the so-called High-Intensity Long-Duration Continuous AE Activity (HILDCAAs) - Tsurutani and Gonzalez (1987). At least a few high speed streams can be identified during the period of WHI. The focus here is to characterize these IP structures and their geospace consequences.
Publisher: Sissa Medialab
Date: 17-08-2023
DOI: 10.22323/1.444.1228
Publisher: Cambridge University Press (CUP)
Date: 07-2018
DOI: 10.1017/S1743921318000066
Abstract: The Global Muon Detector Network (GMDN) is composed by four ground cosmic ray detectors distributed around the Earth: Nagoya (Japan), Hobart (Australia), Sao Martinho da Serra (Brazil) and Kuwait city (Kuwait). The network has operated since March 2006. It has been upgraded a few times, increasing its detection area. Each detector is sensitive to muons produced by the interactions of ~50 GeV Galactic Cosmic Rays (GCR) with the Earth′s atmosphere. At these energies, GCR are known to be affected by interplanetary disturbances in the vicinity of the earth. Of special interest are the interplanetary counterparts of coronal mass ejections (ICMEs) and their driven shocks because they are known to be the main origins of geomagnetic storms. It has been observed that these ICMEs produce changes in the cosmic ray gradient, which can be measured by GMDN observations. In terms of applications for space weather, some attempts have been made to use GMDN for forecasting ICME arrival at the earth with lead times of the order of few hours. Scientific space weather studies benefit the most from the GMDN network. As an ex le, studies have been able to determine ICME orientation at the earth using cosmic ray gradient. Such determinations are of crucial importance for southward interplanetary magnetic field estimates, as well as ICME rotation.
Publisher: Society of Geomagnetism and Earth, Planetary and Space Sciences
Date: 1990
DOI: 10.5636/JGG.42.1137
Publisher: Springer Science and Business Media LLC
Date: 07-03-2016
Publisher: Society of Geomagnetism and Earth, Planetary and Space Sciences
Date: 1995
DOI: 10.5636/JGG.47.1103
Publisher: Springer Science and Business Media LLC
Date: 11-1996
DOI: 10.1007/BF00171926
Publisher: American Astronomical Society
Date: 07-07-2016
Publisher: Springer Science and Business Media LLC
Date: 05-1977
DOI: 10.1038/267332A0
Publisher: Elsevier BV
Date: 2005
Publisher: American Geophysical Union (AGU)
Date: 12-2016
DOI: 10.1002/2016JA023515
Publisher: Elsevier BV
Date: 03-2006
Publisher: Elsevier BV
Date: 2002
DOI: 10.1016/S0273-1177(02)00496-9
Abstract: The relativistic solar proton event of 6 November 1997 resulted in the first ground-level enhancement (GLE) of solar cycle 23. The earliest onset was around 1215 UT but was up to 15 minutes later at some neutron monitor locations. The time of maximum intensity also varied significantly over the world-wide neutron monitor network. The modeled particle distributions and spectra are presented. The apparent particle arrival direction is found to be largely consistent with propagation outward from the sun along interplanetary magnetic field lines.
Publisher: Cambridge University Press (CUP)
Date: 08-1995
DOI: 10.1017/S1323358000020191
Abstract: The radial density gradient (G r ) of Galactic cosmic rays in the ecliptic plane points outward from the Sun. This indicates an increasing density of cosmic ray particles beyond the Earth’s orbit. Due to this gradient and the direction of the Sun’s interplanetary magnetic field (IMF) above and below the IMF wavy neutral sheet, there exists an anisotropic flow of cosmic ray particles approximately perpendicular to the ecliptic plane (i.e. in the direction parallel to B IMF × G r ). This effect is called the north–south anisotropy (ξ NS ) and manifests as a diurnal variation in sidereal time in the particle intensity recorded by a cosmic ray detector. By analysing the yearly averaged sidereal diurnal variation recorded by five neutron monitors and six muon telescopes from 1957 to 1990, we have deduced probable values of the average rigidity spectrum and magnitude of ξ NS . Furthermore, we have used determined yearly litudes of ξ NS to infer the magnitude of G r for particles with rigidities in excess of 10 GV.
Publisher: Elsevier BV
Date: 10-2005
Publisher: American Astronomical Society
Date: 14-10-2016
Publisher: American Astronomical Society
Date: 03-08-2018
Publisher: Sissa Medialab
Date: 25-07-2023
DOI: 10.22323/1.444.1336
Publisher: Sissa Medialab
Date: 18-08-2023
DOI: 10.22323/1.444.1279
Publisher: American Geophysical Union (AGU)
Date: 10-2004
DOI: 10.1029/2004GL020803
Publisher: American Geophysical Union (AGU)
Date: 09-2018
DOI: 10.1029/2017JA025135
Publisher: Society of Geomagnetism and Earth, Planetary and Space Sciences
Date: 1995
DOI: 10.5636/JGG.47.1079
No related grants have been discovered for Marcus Duldig.