Increase In Cosmic Ray Intensity Research Articles

The Updated Version of the A.Ne.Mo.S. GLE Alert System: The Case of the Ground-Level Enhancement GLE73 on 28 October 2021

A ground-level enhancement (GLE) event is a sudden increase in cosmic ray intensity originated by solar sources and recorded by ground-based detectors. GLEs are invariably associated with large solar flares that can release and accelerate solar particles at high energies. The minimum kinetic energy of particles reaching the Earth’s surface is >433 MeV at sea level and about 300 MeV/n at high-mountain altitude of about 3000 m a.s.l. Even though these abrupt events linked to solar activity are quite rare, they can have a great impact on technological systems and human health when recorded. Therefore, the accurate and effective prognosis of such events is of great importance. In this paper, an overview of the most recently recorded GLE event and the first of solar cycle 25, i.e., GLE73, as well as a post-event analysis is presented. GLE73 was detected on 28 October 2021 and was associated with the active region AR12887 on the central part of the solar disk, which produced an X1.0 solar flare. The event was registered by several stations of the worldwide ground-based neutron monitor network. An accurate alert was issued successfully by the ESA R-ESC federated product GLE Alert Plus, as well as the updated GLE Alert++ System of the Athens Neutron Monitor Station (A.Ne.Mo.S.). It should be emphasized that the GLE Alert++ signal by NKUA/A.Ne.Mo.S. was issued 45 min earlier than the one issued by GOES. A short description and the advantages of this last system are provided.

Interaction between Multiple Current Sheets and a Shock Wave: 2D Hybrid Kinetic Simulations

Abstract Particle acceleration behind a shock wave due to interactions between magnetic islands in the heliosphere has attracted attention in recent years. The downstream acceleration may yield a continuous increase of particle flux downstream of the shock wave. Although it is not obvious how the downstream magnetic islands are produced, it has been suggested that current sheets are involved in the generation of magnetic islands due to their interaction with a shock wave. We perform 2D hybrid kinetic simulations to investigate the interaction between multiple current sheets and a shock wave. In the simulation, current sheets are compressed by the shock wave and a tearing instability develops at the compressed current sheets downstream of the shock. As the result of this instability, the electromagnetic fields become turbulent and magnetic islands form well downstream of the shock wave. We find a “post-cursor” region in which the downstream flow speed normal to the shock wave in the downstream rest frame is decelerated to ∼ 1V A immediately behind the shock wave, where V A is the upstream Alfvén speed. The flow speed then gradually decelerates to 0 accompanied by the development of the tearing instability. We also observe an efficient production of energetic particles above 100 E 0 during the development of the instability some distance downstream of the shock wave, where E 0 = m p V A 2 and m p is the proton mass. This feature corresponds to Voyager observations showing that the anomalous cosmic-ray intensity increase begins some distance downstream of the heliospheric termination shock.

Criteria for early prediction of geomagnetic disturbances caused by coronal holes during periods of low solar activity based on muon flux variations

Coronal holes generate a high speed solar wind. This wind is the cause of magnetic storms on the Earth during the years of low solar activity. Also a high speed solar wind creates disturbances in the interplanetary magnetic field. The disturbance may reflect cosmic rays hitting them in the direction of the Earth. As a result, it is possible to observe a change in the flux of cosmic rays on the Earth before the arrival of the disturbance. The paper identifies a criterion for early detection of cosmic ray flux increasing by the muon hodoscope URAGAN (MEPhI, Moscow) to coronal holes in years of decreased solar activity (2009-2010, 2018-2019). It was found that increases of cosmic ray intensity are visible before the main sequence of areas of increasing and decreasing cosmic ray intensities in GSE maps in 60% of the cases.

Cosmic Ray Enhancements in Lunar Radiation Environment Observed by CRaTER on the LRO

The Cosmic Ray Telescope for the Effects of Radiation (CRaTER) instrument onboard the Lunar Reconnaissance Orbiter (LRO) characterizes the global lunar radiation environment and its biological impacts by measuring cosmic ray (CR) radiation. By using CRaTER data, we identify the lunar CR enhancements, which are similar to the terrestrial ground level enhancements (GLEs). GLE is a sudden and short increase in CR intensity recorded by the Earth’s ground neutron monitors. We examine the origins and the characteristics of CR enhancements in the lunar space environment by using the CR intensity and dose rate according to CRaTER data. In order to determine origins of CR enhancements, we also use solar proton event (SPE) data, CR data of the Advanced Composition Explorer (ACE) equipped with a Solar Isotope Spectrometer (SIS), and proton flux data of Geostationary Operational Environmental Satellite 15 (GOES15). We identified 96 CRaTER enhancements (CREs) as increases in CR events in the lunar space environment during the period June 2009-December 2017. Unlike terrestrial GLEs, CREs are much longer and more frequent. Of the 96 CREs, 43 events are associated with SPE. The values of their physical characteristics are statistically larger than those of the CREs without associated SPEs. However, such non-SPE CREs are considered to originate from solar ejections. All CREs are associated with an increase in He flux by ACE/SIS. Even though CREs are associated with a small increase in He flux, this does indicate that some materials are ejected from the Sun; rather, it indicates that all CREs are associated with solar eruptions. Because of the very weak magnetic field and extremely rare atmosphere, the lunar space environment responds to even weak solar activity. An increase in He flux observed by ACE/SIS can be useful for monitoring the eruption of energetic particles from the Sun regardless of accompanying SPEs.

Cosmic-Ray Short Burst Observed with the Global Muon Detector Network (GMDN) on 2015 June 22

Abstract We analyze the short cosmic-ray intensity increase (“cosmic-ray burst”: CRB) on 2015 June 22 utilizing a global network of muon detectors and derive the global anisotropy of cosmic-ray intensity and the density (i.e., the omnidirectional intensity) with 10 minute time resolution. We find that the CRB was caused by a local density maximum and an enhanced anisotropy of cosmic rays, both of which appeared in association with Earth’s crossing of the heliospheric current sheet (HCS). This enhanced anisotropy was normal to the HCS and consistent with a diamagnetic drift arising from the spatial gradient of cosmic-ray density, which indicates that cosmic rays were drifting along the HCS from the north of Earth. We also find a significant anisotropy along the HCS, lasting a few hours after the HCS crossing, indicating that cosmic rays penetrated into the inner heliosphere along the HCS. Based on the latest geomagnetic field model, we quantitatively evaluate the reduction of the geomagnetic cutoff rigidity and the variation of the asymptotic viewing direction of cosmic rays due to a major geomagnetic storm that occurred during the CRB and conclude that the CRB is not caused by the geomagnetic storm, but by a rapid change in the cosmic-ray anisotropy and density outside the magnetosphere.

UNUSUAL GALACTIC COSMIC RAY INTENSITY AND SPECTRAL CHANGES OBSERVED BY $V1$ NEAR THE HELIOPAUSE

We discuss here two unusual increases of cosmic ray intensity that were observed by V1 in the last 1.1 AU before it crossed the heliopause in 2012 August, at 121.5 AU. These two increases are roughly similar in amplitude and result in a total increase in ?1 GV cosmic ray nuclei of over 50% and 0.01 GV electrons of a factor ?2. During the first increase the changes in the B field are small. After the first increase the B field changes become large and during the second increase the B field variations and cosmic ray changes are correlated to within ? one day. During these time intervals, the rigidity dependence of the increases of GCR H and He nuclei from 100?600 MeV/nuc resemble those used to describe the solar modulation near the Earth during a large transient decrease but the ratio between the intensity changes of H, He, and electrons are different. The magnitude of these increases at Voyager is ?1/3 of the modulation that is required to produce the total modulation of protons, helium nuclei, and electrons between the local interstellar intensities and those observed at the Earth at the 2009 sunspot minima. This may imply that a significant part of the residual solar modulation at times of sunspot minima occurs near the heliopause itself.

GALACTIC COSMIC-RAY MODULATION NEAR THE HELIOPAUSE

We investigate the modulation of galactic cosmic rays in the inner and outer heliosheaths using three-dimensional numerical simulations. The model is based on the Parker transport equation integrated using a stochastic phase-space trajectory method. Integration is performed on a plasma background obtained from a global three-dimensional magnetohydrodynamic simulations. Our results predict a negligible amount of modulation in the outer heliosheath because of weak scattering of cosmic ray ions owing to very low levels of magnetic fluctuation power at wavenumbers relevant to the transport of cosmic rays with MeV to GeV energies. This means that the heliopause may be treated as a Dirichlet-type boundary for the purpose of energetic particle modeling. We present models with and without drift velocity to facilitate comparison with papers published earlier. We also attempt to reproduce the sudden step-like increases of cosmic-ray intensity observed by Voyager 1 before its encounter with the heliopause. Our results indicate that very slow cross-field diffusion in the outer heliosheath could produce a large gradient of cosmic rays inside the heliospheric boundary. The resulting large gradient in cosmic-ray intensity near the heliopause qualitatively agrees with recent Voyager 1 observations.

Magnetospheric cut-off rigidity variations recorded by neutron monitors in the events from 2001 to 2010

During a geomagnetic storm, many interesting variations in cosmic ray intensity recorded by the worldwide network of neutron monitor stations are observed. More specifically, a characteristic increase of cosmic ray intensity mainly in the middle latitude stations is observed, due to the geomagnetic cut-off rigidity changes. During the declining phase of the last solar cycle, many characteristic geomagnetic effects were observed with the most significant one on November of 2003, which is considered as the largest magnetic storm in the history of neutron monitors. In this work, the magnetic storms of 31 March 2001, 11 April 2001, 8 and 10 November 2004, 15 May 2005 and 24 August 2005 are analyzed using cosmic ray data from a number of neutron monitor stations located at different places worldwide.

Changes of geomagnetic transmissivity in the disturbed magnetosphere: ground-based and CORONAS-F observations

We report increases of cosmic-ray intensity at lowL shells, on the ground as well as on the altitude of 500 km, during the selected intervals when magnetosphere was strongly disturbed. The geomagnetic transmissivity for cosmic ray vertical access has been computed for four events, using two geomagnetic field models. The first event, namely, dated November 20–22, 2003, led to an increase of galactic cosmic-ray intensity due to the improvement of magnetospheric transmissivity at neutron monitors with high nominal cut-off rigidity. Other two events with high-energy solar proton emissions, namely, dated October 28 and November 2, 2003, caused different responses at middle latitudes. The first one followed by the strong geomagnetic disturbance led to the shift of the penetration boundary of protons, having(50–90) MeV at CORONAS-F satellite toL<3, coinciding approximately with the cut-off reduction expected byDst depression, while the other one, without remarkableDst decrease, did not shift the outer boundary of penetration belowL ≈ 4. And the fourth of the events, on November 8, 2004, with strong geomagnetic disturbance, yielded a complicated structure of cosmic-ray time profiles: superimposed on the cosmic-ray decrease, viewed by neutron monitors and by CORONAS-F at high latitude; an increase of intensity at middle latitudes both on the ground and on the altitude of 500 km has been observed during theDst depression.

Galactic cosmic ray modulation and the passage of the heliospheric current sheet at Earth

We have examined the effect of heliospheric current sheet (HCS) crossings on cosmic ray intensity (CRI), solar wind speed, interplanetary magnetic field (IMF) and the cosmic ray solar diurnal anisotropy in free space. Data from eight neutron monitors and three muon telescopes, covering a wide energy and latitude range, were separated into two epochs, 1971–1979 (A > 0) and 1981–1990 (A < 0) according to the solar magnetic polarity. The CRI is more strongly affected during the A > 0 than during the A < 0 epoch. The increase in CRI associated with A-T HSC crossings was larger in magnitude than that of T-A crossings, and the magnitude was dependent on the rigidity of the particles. A symmetric negative cosmic ray gradient was observed with respect to the HCS. HCS crossings have no observable effect on the CRI observed by shallow underground detectors. Changes in solar wind speed and IMF magnitude, near HCS crossings, are related to the distance of the Earth from the sheet. We found no consistent changes in the solar diurnal variation related to HCS crossings.

Cosmic-ray forecasting features for big forbush decreases

It is well known that big geomagnetic storms have an adverse influence on technological devices and radio wave propagation. Major geomagnetic storms, associated with Forbush decreases (FDs) in cosmic ray (CR) intensity, have also been found to increase the incidence of some diseases (in particular, the frequency of myocardial infarction increases by 13 ± 1.4%). We discuss here three phenomena that can be used for forecasting FDs: 1) CR intensity increase, of non solar-flare origin, occurring before sudden commencement of a major geomagnetic storm connected with FD (preincrease effect), 2) CR intensity decrease before FD (predecrease effect), 3) change in CR fluctuations before FD. First we investigate several such events by the global survey method for the years 1989–1991. We analyse the behaviour of the isotropic CR intensity and of the 3-dimensional vector of CR anisotropy before FDs, as well as results on CR scintillation of 1-hour and 5-minute data. We discuss a possible procedure of data treatment for future FD-forecasting analyses.

A high-energy increase in cosmic-ray intensity

The increase in cosmic rays observed by neutron monitors with high-energy cutoff, on April 29, 1973, is interpreted to be a definite high-energy phenomenon. This is not associated with any solar flare or interplanetary disturbance. The association of the increase in intensity with geomagnetic index Dst variation indicates a possibility that the high-energy event was caused by a magnetospheric phenomenon.

The ground-level cosmic-ray event of September 29, 1989 as recorded by the rome detectors

An extraordinary increase in cosmic-ray intensity has been recorded on September 29, 1989 by the Rome detectors (rigidity threshold ∼6.2 GV). We show the time evolution of the event as recorded at Rome in the nucleonic component and in the total ionizing and muon components; as well as at Campo Imperatore (2300 m a.s.l. near Rome) in the nucleonic component by a special monitor designed for the detection of solar-neutron events. The one-minute time resolution of the Campo Imperatore data offers the possibility to follow in detail the development of the event for most of the time. The possible contribution of solar neutrons to the early phase of the Campo Imperatore event has been not clarified so far, further results may be obtained by the analysis of the multiplicity data registered in the event.

Unique series of increases in cosmic-ray intensity due to solar flares

THE second half of 1989 was the most prolific period of relativistic particle production by the Sun since continuous monitoring of cosmic-ray activity by neutron detectors was begun in 1957. Some of last year's events were among the largest bursts of particles observed throughout the last three solar cycles. Only when the particles released by the Sun during flares have energies greater than 0.5 gigaelectronvolt (GeV) are the secondary particles generated through interactions in the upper atmosphere able to reach ground level. Six different ground-level events were detected by the super neutron monitor in Calgary (geomagnetic latitude and longitude 51.08° N 245.91°, altitude 1,128 m, cut-off 1.07 GV) in the period July to October 1989. The intensity of energetic particle fluxes during these ground-level events is high enough to be a potential hazard, especially for passengers in aircraft at altitudes of 10 to 15 km.

Cosmic-ray intensity increase observed on September 29, 1989: the Chilean neutron monitor data

Data obtained in Chile with the standard neutron monitor (Santiago: 6 NM-64; geomagnetic cut-off rigidity: about 11 GV) are reported for the ground-level solar cosmic-ray event registered on September 29, 1989. Possible studies connected with such a rare event are suggested to understand even more solar-interplanetary-terrestrial relations.

Unusual characteristics of the cosmic ray intensity increase of September 17–18, 1979

The data from a number of neutron and meson monitors are examined for the cosmic ray event of September 17–18, 1979. The profiles of the observed cosmic ray intensity increase at various stations exhibit an apparent solar flare origin, if one were to look at a limited amount of data. It is clearly shown that the ‘flare‐type’ increase is unusual and is of nonsolar origin. A suggestion is made for explaining this in terms of interplanetary structures for which supportive evidence is provided by reference to in situ observations.

High-energy cosmic ray intensity increase of nonsolar origin and the unusual Forbush decrease of August 1972

A series of spectacular cosmic ray events, which included two relativistic solar particle enhancements and three major Forbush decreases, was registered by ground-based cosmic ray monitors beginning on August 4, 1972. Among these, the Forbush decrease that occurred on August 4–5 exhibited extremely interesting and complex behavior, the prominent features of which are a preincrease (PI-1) prior to the largest Forbush decrease (FD-2) during the recovery of which an abrupt universal time increase (PI-2) occurred. Large N-S and E-W anisotropies were observed during the entire Forbush decrease event. The rigidity spectra for both FD-2 and PI-2 had practically the same exponent of −1.2±0.2 and an upper cutoff rigidity of about 50–60 GV, and the anisotropy during both PI-1 and PI-2 was from the sunward direction. This paper describes the detailed observational features and presents a unified model to explain these in terms of a transient modulating region associated with the passage of a shock front. In this model, the reflection of particles from the approaching shock front accounts for the preincrease (PI-1), whereas the early onset of FD-2 from the antisun direction is caused by the occultation of particle trajectories reaching the earth from that direction while the detectors looking along the sunward direction are still sampling albedo particles reflected from the shock front. The main Forbush decrease occurs as the shock front, containing tangled magnetic fields with large-scale tangential discontinuities, sweeps past the earth. The particles, diffusing into the cavity as they are swept by the solar wind, get ‘piled up’ behind the tangled field region causing the abrupt increase (PI-2). Evidence from interplanetary plasma, radio, and field measurements is provided in support of the model wherever possible.

Sudden Increases in Cosmic Ray Intensity

At different times during a period of continuous recording of cosmic rays large increases in the intensity of cosmic radiation have been observed. Most of these are associated with formations on the visible side of the Sun. However, there are two exceptions: Carmichael et al. (1961) believe that the November 20,1960 increase in intensity was due to a solar flare on the reverse side of the Sun, and Sud (1968) has shown that the intensity increase of January 28,1967 also may not be connected with chromospheric eruptions on the visible side of the Sun.

Cosmic-ray solar-flare increase of 28 January 1967

The main features of the solar-flare increase in cosmic-ray intensity observed on 28 January 1967 are presented. The flare increase showed no marked anisotropy. It is shown that the onset and decay of this increase can be well accounted for by anisotropic diffusion of particles in a spherically symmetric, inhomogeneous medium with a perfectly absorbing boundary at about 1.3 AU from the sun.

Cosmic Ray Intensity Increase on January 28, 1967

During the present solar cycle, which started in October 1964, the ground-based cosmic ray detectors have so far recorded two increases in the intensity of cosmic rays. The first one was observed on July 7,1966 and the other on January 28,1967. Both these events were somewhat unusual in their characteristics.