Rigidity Spectrum Of Cosmic Rays Research Articles

Ground level enhancement of cosmic rays on November 6, 1997: Spectra and anisotropy

Variations of the rigidity spectrum and anisotropy of cosmic rays in the period of the ground-level enhancement (GLE) of cosmic rays on November 6, 1997, according to the data from the worldwide network of ground-based stations and satellites have been studied by the unique spectrographic global survey method developed at the Institute of Solar–Terrestrial Physics, Siberian Branch, Russian Academy of Sciences. Rigidity spectra of cosmic rays in various periods of the event under study have been determined. It has been shown that the acceleration of protons in the period of this GLE event was observed to a rigidity of ~10–12 GV, and neither a power-law nor an exponential function of the rigidity of particles describes the differential rigidity spectra of cosmic rays in the event under consideration. The analysis has indicated that the Earth at the time of the GLE event was in a looplike structure of the interplanetary magnetic field.

Estimation of index of power law rigidity spectrum of cosmic rays using effective rigidity of multidirectional muon detector

We develop a new approach for calculating index of power law for variations in the differential rigidity spectrum of cosmic rays registered by Nagoya multidirectional muon detector. Our approach is based on effective rigidity which we define for the entire instrument, not just for its individual channels. Our definition of effective rigidity can be straightforwardly extended to other multichannel instruments and networks of instruments. As examples, we calculate the power law index under quiet conditions and during 12 Forbush decrease events. We also discuss sensitivity of the Nagoya muon detector to different values of the power law index and different rigidities.

July 2000 Forbush-effect from world network of cosmic rays stations

We studied variations in the galactic cosmic ray (CR) rigidity spectrum and anisotropy during the July 2000 strong magnetic storm from the ground-based observations of cosmic rays within the world network of neutron monitor stations through spectrographic global survey. We show the time history for amplitude variations in the rigidity spectrum of cosmic rays, their anisotropy and planetary system of the geomagnetic cutoff rigidity during the Forbush-effect evolution over that period.

Cosmic ray rigidity spectrum and anisotropy during GLE on 14 July 2000

Using the method of spectrographic global survey, rigidity spectrum and anisotropy of galactic cosmic rays during GLE on 14 July 2000 have been studied with the data from ground-based observations of cosmic rays (CR) at the world-wide network of stations. The CR rigidity spectrum observed during this period over the range 1 to ~ 20 GV is shown to be described not only by power function of particle rigidity: distribution of CRs in the earthward direction varies with time and depends on their energy.

The onset of sunspot cycle 24 and galactic cosmic ray modulation

The annual mean sunspot number (SSN) has a minimum value in 2008, while the monthly mean SSN has a value of zero in August 2009. The galactic cosmic ray modulation for cycle 24 began at earth orbit in January 2010. We study the onset characteristics of the new modulation cycle using data from the global network of neutron monitors. They respond to time variations in different segments of the galactic cosmic ray rigidity spectrum. The corresponding temporal variations in the interplanetary magnetic field intensity ( B) and solar wind velocity ( V) as well as the tilt angle of the heliospheric current sheet are also studied. There is a lag of 3 months between a large, sharp increase of the tilt angle of the heliospheric current sheet and the onset of modulation. Some neutron monitors are undergoing long-term drifts of unknown origin.

Solar proton event in December 2006

The variations in the rigidity spectrum and anisotropy of cosmic rays in December 2006 have been studied based on the surface measurements of the cosmic ray intensity at the global network of stations, using the method of global spectrographic survey. It has been indicated that the highest degree of anisotropy (to ∼50%) with the maximal intensity of particles with a rigidity of 4 GV in the direction from the Sun (an asymptotic direction of about −25° and 160°) was observed at 0400 UT on December 13. The parameters of the cosmic ray rigidity spectrum, which reflect the electromagnetic characteristics of the heliospheric fields during the studied period, have been determined when the surface and satellite measurements of protons in the energy range from several megaelectronvolts to several tens of gigaelectronvolts were jointly analyzed. The observed anisotropy and variations in cosmic rays in a wide energy range have been explained based on an analysis of the results.

Primary and secondary effects in cosmic-ray variations at solar proton events

The variations of the cosmic-ray rigidity spectrum in the energy range from 0.8 MeV to several dozen GeV at solar proton events in January 2005 and December 2006 have been analyzed. A comparison of the observed and model spectra revealed the power range of direct detection of solar cosmic rays and moments of their observations.

The method for predicting solar proton events

Dynamic processes in the interplanetary space have been investigated using time variations in time parameters of the cosmic-ray rigidity spectrum. Change of heliosphere electromagnetic characteristics has been found out to precede sporadic phenomena on the Sun. In particular, it is shown that sporadic phenomena are followed by generation of local polarization electric fields, decrease of the magnetic-field strength in small-scale heliospheric structures, and increase of the potential difference between the pole and the plane of the ecliptic. These features allow prediction of solar proton events in advance (from several hours to several tens of hours) with a high degree of confirmation.

Variations in the cosmic-ray rigidity spectrum during events of January 2005

Variations in the cosmic-ray (CR) rigidity spectrum during events of January 2005 have been investigated on the basis of the ground-based observations of the CR intensity performed at the world network of stations using spectrographic global survey. The parameters of the CR rigidity spectrum reflecting the electromagnetic characteristics of heliospheric fields during the events under study have been determined in the combined analysis of ground-based and satellite measurements of protons with energies from several megaelectronvolts to several tens of gigoelectronvolts. The CR variations in a wide energy range are explained on the basis of the analysis performed.

Possibility of prediction of solar proton events

The dynamic processes in the interplanetary space have been investigated on the basis of the time variations in the parameters of the cosmic-ray rigidity spectrum. It is established that the change in the electromagnetic characteristics of the heliosphere begins before the sporadic phenomena on the Sun. In particular, it is shown that the sporadic phenomena are preceded by generation of local polarization electric fields, a decrease in the magnetic field strength in small-scale heliospheric structures, and an increase in the potential difference between the pole and ecliptic plane. The use of these signs makes it possible to predict solar proton events with a lead time from several hours to several tens of hours with a high degree of confirmation.

Observations of the cosmic ray knee with a polar orbiting ionization chamber

The cosmic ray knee has been observed with the ion chambers on the OGO 2 (October 1965–February 1966) and OGO 4 (August 1967) polar orbiting satellites, using the same graphical definition that applies to balloon observations. The knee is interpreted as a position in the geomagnetic field, which depends on the cosmic ray rigidity spectrum at the time of observation, where the cosmic ray cutoff rigidity has a particular value and is about 1.2 bv for the OGO 2 measurements. The invariant latitude of the knee decreases with altitude of observation at the rate of (2.5±0.5)×10−3 degree/km and had the value 59.1° at the surface of the earth in 1965–1966. This invariant latitude should be independent of longitude; in fact, however, a slight longitude dependence of the order of ±1° is observed. Knee latitudes were 0.6° lower (toward the equator) in 1967, according to OGO 4, and 4° to 5° lower in 1961 as measured by other observers. We find a north-south latitude difference of 0.6°±0.4°, which suggests a seasonal variation with the knee slightly closer to the pole during winter. A small diurnal variation of the knee latitude with amplitude 0.5°±0.4° is indicated; this appears to be consistent with calculations and observations for higher latitudes.

Empirical response functions for a neutron multiplicity monitor

Geomagnetic latitude survey by neutron multiplicity monitor covering threshold rigidity ranges at various elevations, relating data to primary cosmic ray rigidity spectrum

Spectral variation of primary cosmic rays during forbush decreases

Variations of primary cosmic ray rigidity spectrum occurring at typical Forbush decreases in the geomagnetically sensitive range are studied. Selected events are grouped in two classes according to the degree of associated geomagnetic perturbation. It is shown that the systematic differences between the two classes, arising when spectral variation is derived from the latitude effect of the amplitude of nucleonic intensity decrease, do practically vanish when tests independent of any variation on the geomagnetic field are applied. For events of the geomagnetically quiet group an inverse power law δD(R)/D(R)=−BR−k with an exponentk lower than unity is found to approximate well all the analyzed experimental data.

COSMIC-RAY TRAPPING IN INTERPLANETARY SPACE

The existence of long-term variations in cosmic-ray intensity negatively correlated with sunspot activity, a discovery due to Forbush, has been explained by Davis in terms of a cavity in the galactic magnetic field centered about the sun. In the present paper, it is shown that a “diamagnetic” interplanetary region, rather than a “superconducting” one, can account for the cut-off in the primary cosmic-ray rigidity spectrum, as well as for the 11 year variations. The suggested diamagnetic region is an oblate spheroid in shape, with semiaxes of roughly 5×1015 cm and 5×1014 cm, and its effective permeability of 10−4 implies a mean interplanetary field of about 10−9 gauss. The 11-year variations and the rigidity cut-off are analyzed in detail on the basis of this model.