Time variations of cosmic-ray intensity

Changes of the energy spectrum of primary cosmic radiation can be followed through the time variations of east-west asymmetry of the μ -meson component at low latitudes. Such a study has been conducted for the first time at Ahmedabad during 1957-8. The changes of east-west asymmetry are associated with changes of the daily variation of cosmic ray intensity, of the daily mean neutron intensity measured at equatorial and middle latitude stations, of the index of geomagnetic disturbance and of the horizontal component of the earth’s magnetic field. The study indicates that days with high east-west asymmetry are associated with geomagnetically quiet days and a cosmic ray daily variation consistent with its being produced by an anisotropy of primary radiation outside the influence of the geomagnetic field. On such days, the daily variation produced by the anisotropy, as observed at an equatorial station, has a significant diurnal as well as a semi-diurnal component. High east-west asymmetry and associated anisotropy occur 3 to 5 days before the arrival of solar corpuscular beams which envelop the earth. Days with low east-west asymmetry occur about 3 to 4 days after the onset of cosmic ray storms associated with geomagnetic storms, usually of the SC type.

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Time variations of directional cosmic ray intensity at low latitudes: I. Comparison of daily variation of the intensity of cosmic rays incident from east and west

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1961.0149 ◽

1961 ◽

Vol 263 (1312) ◽

pp. 101-117 ◽

Cited By ~ 5

Keyword(s):

Geomagnetic Field ◽

Daily Variation ◽

Cosmic Ray ◽

Local Source ◽

Cosmic Ray Intensity ◽

Low Latitudes ◽

Long Term Changes ◽

Time Variations ◽

East And West

A study has been, conducted at Ahmedabad during 1957 and 1958 of the time variations of meson intensity incident from east and west at 45° to the vertical. A characteristic difference of about 6 h in the diurnal time of maximum for the east and west directions is observed to occur on many days and this has been interpreted as signifying an anisotropy of primary radiation caused by a source outside the influence of the geomagnetic field. However, there are many days on which the daily variation has a maximum near noon for both directions. On such days the predominant influence is that of a local source situated within the influence of the geomagnetic field. The local source is associated with geomagnetically disturbed days. Long-term changes in the daily variation are found to be similar for the east, vertical and west directions.

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Reconstructing the long-term cosmic ray intensity: linear relations do not work

Annales Geophysicae ◽

10.5194/angeo-21-863-2003 ◽

2003 ◽

Vol 21 (4) ◽

pp. 863-867 ◽

Cited By ~ 15

Author(s):

K. Mursula ◽

I. G. Usoskin ◽

G. A. Kovaltsov

Keyword(s):

Cosmic Ray ◽

Geomagnetism And Paleomagnetism ◽

Cosmic Ray Intensity ◽

Linear Relations ◽

Cosmic Ray Modulation ◽

Interplanetary Physics ◽

Long Time ◽

Time Variations ◽

Cosmic Ray Flux

Abstract. It was recently suggested (Lockwood, 2001) that the cosmic ray intensity in the neutron monitor energy range is linearly related to the coronal source flux, and can be reconstructed for the last 130 years using the long-term coronal flux estimated earlier. Moreover, Lockwood (2001) reconstructed the coronal flux for the last 500 years using a similar linear relation between the flux and the concentration of cosmogenic 10 Be isotopes in polar ice. Here we show that the applied linear relations are oversimplified and lead to unphysical results on long time scales. In particular, the cosmic ray intensity reconstructed by Lockwood (2001) for the last 130 years has a steep trend which is considerably larger than the trend estimated from observations during the last 65 years. Accordingly, the reconstructed cosmic ray intensity reaches or even exceeds the local interstellar cosmic ray flux around 1900. We argue that these unphysical results obtained when using linear relations are due to the oversimplified approach which does not take into account the complex and essentially nonlinear nature of long-term cosmic ray modulation in the heliosphere. We also compare the long-term cosmic ray intensity based on a linear treatment with the reconstruction based on a recent physical model which predicts a considerably lower cosmic ray intensity around 1900.Key words. Interplanetary physics (cosmic rays; heliopause and solar wind termination) – Geomagnetism and paleomagnetism (time variations, secular and long-term)

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Time variations of directional cosmic ray intensity at low latitudes - III. Interpretation of solar daily variation and changes of east-west asymmetry

Proceedings of the Royal Society of London Series A - Mathematical and Physical Sciences ◽

10.1098/rspa.1961.0151 ◽

1961 ◽

Vol 263 (1312) ◽

pp. 127-135 ◽

Cited By ~ 1

Keyword(s):

Energy Spectrum ◽

Interplanetary Space ◽

Daily Variation ◽

Cosmic Ray ◽

Local Source ◽

Cosmic Ray Intensity ◽

The Earth ◽

Low Latitudes ◽

Time Variations ◽

East West

The daily variation of cosmic ray intensity at low latitudes can under certain conditions be associated with an anisotropy of primary radiation. During 1957-8, this anisotropy had an energy spectrum of variation of the form aϵ -0.8±0.3 and corresponded to a source situated at an angle of 112 ± 10° to the left of the earth-sun line. The daily variation which can be associated with a local source situated along the earth-sun line has an energy spectrum of variation of the form aϵ 0 . Increases in east-west asymmetry and the associated daily variation for east and west directions can be explained by the acceleration of cosmic ray particles crossing beams of solar plasma in the neighbourhood of the earth. For beams of width 5 x 10 12 cm with a frozen magnetic field of the order of 10 -4 G, a radial velocity of about 1.5 x 108 cm/s is required. The process is possible only if the ejection of beams takes place in rarefied regions of inter planetary space which extend radially over active solar regions. An explanation of Forbush, type decreases observed at great distances from the earth requires similar limitation on the plasma density and conductivity of regions of interplanetary space. The decrease of east-west asymmetry associated with world-wide decreases of intensity and with SC magnetic storms is consistent with a screening of the low-energy cosmic ray particles due to magnetic fields in plasma clouds.

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A Medium Rigidity Muon Experiment for the South Pole Station

Publications of the Astronomical Society of Australia ◽

10.1017/s1323358000026631 ◽

1985 ◽

Vol 6 (1) ◽

pp. 48-52 ◽

Cited By ~ 3

Author(s):

M. L. Duldig ◽

R. M. Jacklyn ◽

M. A. Pomerantz

Keyword(s):

Cosmic Ray ◽

Optimization Techniques ◽

University Of Delaware ◽

South Pole ◽

Medium Energy ◽

Cosmic Ray Intensity ◽

Novel Approach ◽

Time Variations ◽

Telescope System ◽

The U.S

AbstractA proposal for a medium rigidity muon telescope system to be installed at the U.S. South Pole Station for observations of time variations of cosmic ray intensity is at present being prepared by Professor Pomerantz, Director of the Bartol Research Foundation, University of Delaware and Drs Jacklyn and Duldig of the Cosmic Ray Section, Antarctic Division, Department of Science. A novel approach to medium energy cosmic ray observations viewing in equatorial to mid-latitude directions is described. The absorber depth required for the proposed 50-1000 GV rigidity range would be achieved by locating the telescope system at a depth of approximately 7 metres water equivalent (MWE) in the ice and viewing at high zenith angles. Optimization techniques used in the telescope design are presented together with the unique advantages of the location. Justification for the experiment and comparison with important observatories in this rigidity range are also discussed.

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