CME geometry in relation to cosmic ray anisotropy

Bieber, J. W.; Evenson, P. A.

doi:10.1029/98gl51232

Cited by 48 publications

(42 citation statements)

References 8 publications

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“…In the near upstream region of the CME shock, some particles will already have interacted with the postshock field, and this could be a source of EV-type anisotropies. A second possible source of EV anisotropies could be enhancement of the diumal anisotropy (or first-order anisotropy), as the axis of the diurnal anisotropy is not necessarily aligned with the IMF [Bieber and Evenson, 1998]. …”

Section: Munakata Et Al: Precursors Of Geomagnetic Stormsmentioning

confidence: 99%

“…Somewhat larger pitch angles correspond to ambient cosmic rays that have approached the shock from the upstream region and reflected from it. Detectors viewing these pitch angles may observe a precursory increase (rather than decrease), because the particles receive a small energy boost from the shock reflection Bieber and Evenson, 1998]. Because cosmic rays are fast and have large scattering mean free paths in the solar wind, the information contained in precursory 'anisotropies is carried rapidly to remote locations and may provide useful information for space weather forecasting.…”

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confidence: 99%

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Precursors of geomagnetic storms observed by the muon detector network

Munakata¹,

Bieber²,

Yasue³

et al. 2000

J. Geophys. Res.

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102

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Abstract. We report the first systematic survey of cosmic ray precursors of geomagnetic storms. Our data set comprises the 14 "major" geomagnetic storms (peak Kp > 8-) identified by Gosling et al. [ 1990] together with 25 large storms (peak Kp > 7-) observed from 1992 through 1998. After eliminating events for which the muon detector network had poor coverage of the sunward interplanetary magnetic field (IMF) direction, we determined that 15 of the remaining 22 events (68%) had identifiable cosmic ray precursors with typical lead times ranging from 6 to 9 hours prior to the storm sudde.n commencement (SSC). Of the 15 precursors, 10 were of the "loss cone" (LC) type which is characterized by an intensity deficit confined to a narrow pitch angle region around the sunward IMF direction. Cosmic rays in the loss cone presumably originate in the cosmic-ray-depleted region downstream of the approaching shock. The remaining five precursors were of the "enhanced variance" (EV) type which is characterized by intensity increases or decreases that do not systematically align with the IMF direction. The incidence of precursors increases with storm size; for instance, 89% of storms with peak Kp greater than or equal to 8.0 had precursors. Our results show that the muon detector network can be a useful tool in space weather forecasting. However, new detector(s) installed to fill major gaps in the present network are urgently required for better understanding the nature of precursors and for reliable space weather forecasting. In this paper we examine cosmic ray precursors of large geomagnetic storms by analyzing high-energy cosmic ray intensities observed by ground-level muon detectors. As far as we know, this is the first systematic survey of cosmic ray precursors in which event selection is determined by the occurrence of a geomagnetic storm rather than by a Forbush decrease or other cosmic ray effect. Similar analysis using the high-latitude neutron monitor network will be reported hours prior to the shock arrival, assuming a shock speed of 600 km/s. This also implies that the precursors might be observed much earlier by muon detectors than by neutron monitors, as the muon detector responds to higher-energy (> 50 GeV) cosmic rays for which •.// is expected to be much longer. In this respect, the muon observations at higher-energy regions may supply useful information for forecasting geomagnetic storms. This is a primary motivation of the present analysis. It will be demonstrated that the muon observation network could be a very good tool for space weather forecasting if it has a good coverage of a full range of pitch angles. Data Analysis MethodWe analyze the cosmic ray precursors of geomagnetic storms recorded by a network of ground-level muon detectors at "Nagoya" (Japan), "Hobart" (Australia) and "Mawson-PC" (Antarctica) (see Table 1). Each of these detectors is multidirectional, allowing us to simultaneously record the intensities in various directions of viewing. The total number of directional telescopes used in this...

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Section: Munakata Et Al: Precursors Of Geomagnetic Stormsmentioning

confidence: 99%

mentioning

confidence: 99%

Precursors of geomagnetic storms observed by the muon detector network

Munakata¹,

Bieber²,

Yasue³

et al. 2000

J. Geophys. Res.

Self Cite

102

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show abstract

“…Bieber and Evenson [1] noticed strong enhancements of the cosmic ray anisotropy before and during the January 1997 CME/magnetic cloud. From a multi-station analysis of neutron monitor data, they conclude that B×∇n drift is a primary source of CME-related anisotropies for 5 GeV cosmic rays.…”

Section: Introductionmentioning

confidence: 99%

“…They have studied anisotropies (obtained from neutron monitor data) related to particle effects at shocks and in particular decrease and increase caused by density gradient flows across the shock. The decreases which are sometimes visible prior to shock arrival may have some application in Space Weather forecasting [6][7][8].…”

Section: Introductionmentioning

confidence: 99%

Cosmic ray intensity during the passage of coronal mass ejections

Mishra¹,

Agarwal²

2008

Braz. J. Phys.

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Coronal Mass Ejections are vast structures of plasma and magnetic fields that are expelled from the sun into the heliosphere. This material is detected by remote sensing and in-situ spacecraft observations. The present study deals with the influence of four types of CMEs namely Asymmetric 'Full' Halo CMEs, Partial Halo CMEs, Asymmetric and Complex 'Full' Halo CMEs and 'Full' Halo CMEs on cosmic ray neutron monitor intensity. The data of ground based neutron monitor of Moscow and CME events observed with instruments onboard and Wind spacecraft have been used in the present analysis. The method of superposed epoch (Chree) analysis has been used to the arrival times of these CMEs. It is noteworthy that the frequency of occurrence of Asymmetric 'Full' Halo CMEs is significantly high, whereas frequency of occurrence of Asymmetric and Complex 'Full' Halo CMEs is low compared to other CMEs. Significant enhancement in cosmic ray intensity is observed after 4 days of the onset of asymmetric full halo and 6 days after the onset of full halo CMEs. The fluctuations in cosmic ray intensity are more prior to the onset of both types of the CMEs. However, during Partial Halo CMEs the cosmic ray intensity peaks, 8-9 days prior to the onset of CMEs and depressed 3 days prior to the onset of CMEs, whereas in case of asymmetric and complex full CMEs, the intensity depressed 2 days prior to the onset of CMEs and enhanced 2 days after the onset of CMEs. The deviations in cosmic ray intensity are more pronounced in case for asymmetric and complex full halo CMEs compared to other CMEs.

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“…Ap is also found to related with solar wind velocity, which is related to the convective component of convection-diffusion theory. Agrawal (1983) and Bieber and Evenson (1997) have preferred to investigate the daily variation in cosmic ray intensity on long/short term basis performing the analysis for all days in a year; whereas, Kumar et al (1981Kumar et al ( , 1993 have studied long/short term daily variation on geomagnetically 60 quiet days (QD). Jadhav et al (1983) and Kumar et al (1999) studied daily variation during days of low and high amplitude anisotropic wave trains.…”

Section: Introductionmentioning

confidence: 99%

Modulation of cosmic rays at different cutoff rigidity

Agarwal

Mishra

2008

Braz. J. Phys.

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The present work deals with the study of first three harmonics of cosmic ray intensity on geo-magnetically quiet days over the period [1981][1982][1983][1984][1985][1986][1987][1988][1989][1990][1991][1992][1993] for Deep River and Inuvik neutron monitoring stations having mid and low cutoff rigidity. The amplitude of first harmonic remains high for Deep River having mid cutoff rigidity as compared to Inuvik neutron monitor having low cutoff rigidity on quiet days. The diurnal amplitude significantly decreases and phase shifts towards an earlier time during solar activity minimum years at both Deep River and Inuvik. The amplitude of second harmonic significantly enhanced during solar activity minimum as well as maximum at Deep River and remains low during solar activity maximum at Inuvik, whereas the phase shifts towards an earlier time during solar maximum for both the stations. The amplitude of the third harmonic significantly enhanced during solar activity minimum at Deep River and on solar activity minimum at Inuvik, whereas the phase does not show any significant characteristics and fluctuates quite frequently. The amplitude of semi/tri-diurnal anisotropy has a good positive correlation, while the others (i.e. amplitude and phase) have very weak correlation with solar wind velocity on quiet days at Deep River station during 1981-1993. The solar wind velocity significantly remains in the range 350 to 425 km/s i.e. being nearly average on quiet days. The amplitude and direction of the anisotropy on quiet days are weakly dependent on high-speed solar wind streams for two neutron monitoring station of mid and low cutoff rigidity threshold. The amplitude as well as direction of second harmonic has a good anti-correlation with IMF Bz and the product V x Bz on quiet days at Deep River station. However, the direction of second and third harmonic has a good anti-correlation with IMF Bz and the product V x Bz on quiet days at Inuvik station.

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CME geometry in relation to cosmic ray anisotropy

Cited by 48 publications

References 8 publications

Precursors of geomagnetic storms observed by the muon detector network

Precursors of geomagnetic storms observed by the muon detector network

Cosmic ray intensity during the passage of coronal mass ejections

Modulation of cosmic rays at different cutoff rigidity

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