East/west directional measurements of the cosmic-ray solar daily variation at an equatorial station

Two large scintillator telescopes of cubical geometry, tilted at an angle of 45° to the vertical, were set up pointing in the east and west directions at the equatorial station Makerere. Data from these telescopes are available from July 1964 onwards. During the initial year of observation the solar diurnal variation in both telescopes, after pressure correction, had an amplitude of about 0.2%, but the absence of any appreciable phase difference between the east and west directions suggests that in the intermediate range of rigidities (say 50–150 GV) there was no appreciable primary anisotropy during the last solar minimum. This conclusion is in agreement with that drawn from similar measurements made at Chacaltaya. The large amplitude of the Makerere diurnal variation, however, suggests that there is a substantial "local" source of the diurnal variation which is significantly different from that observed at Chacaltaya. The possible origin of this "local" source is briefly discussed.

Download Full-text

Time variations of directional cosmic ray intensity at low latitude - II. Time variations of east-west asymmetry

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

10.1098/rspa.1961.0150 ◽

1961 ◽

Vol 263 (1312) ◽

pp. 118-126 ◽

Cited By ~ 2

Keyword(s):

Geomagnetic Storms ◽

Daily Variation ◽

Cosmic Ray ◽

Middle Latitude ◽

Geomagnetic Disturbance ◽

Equatorial Station ◽

Cosmic Ray Intensity ◽

Primary Cosmic Radiation ◽

Time Variations ◽

East West

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.

Download Full-text

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.

Download Full-text

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.

Download Full-text

PERIODICAL FLUCTUATION STUDIES OF COSMIC-RAY DIURNAL VARIATIONS DURING THE QUIET-SUN PERIOD 1962–64

Canadian Journal of Physics ◽

10.1139/p67-220 ◽

1967 ◽

Vol 45 (8) ◽

pp. 2733-2748 ◽

Cited By ~ 1

Author(s):

Masahiro Kodama

Keyword(s):

Diurnal Variation ◽

Solar Minimum ◽

Counting Rate ◽

Solar Rotation ◽

Rotation Period ◽

Cosmic Ray ◽

Diurnal Variations ◽

Statistical Studies ◽

Periodic Fluctuations ◽

Recurrence Tendency

Statistical studies of periodic fluctuations of the cosmic-ray diurnal variation have been performed, using neutron and meson component data obtained by the high-counting-rate cosmic-ray monitors at Deep River. The data cover an interval from May 1962 to October 1964, a period of descending solar activity ending near the solar minimum. It is shown that a 27-day recurrence tendency of the amplitude of the diurnal variation occasionally appears as well as shorter recurrent variations, ranging from one-half to one-sixth of the solar rotation period. The correlations of these fluctuations with some typical solar and terrestrial indices are examined in order to search for possible origins of the shorter recurrent variations. A possible connection with the Kp index exists.

Download Full-text

Variation with solar cycle of the diurnal variation of cosmic rays underground

Canadian Journal of Physics ◽

10.1139/p68-351 ◽

1968 ◽

Vol 46 (10) ◽

pp. S784-S787 ◽

Cited By ~ 14

Author(s):

Victor H. Regener ◽

Derek B. Swinson

Keyword(s):

New Mexico ◽

Diurnal Variation ◽

Solar Minimum ◽

Solar Maximum ◽

Cosmic Ray ◽

Local Solar Time ◽

The North ◽

Primary Particles ◽

Cosmic Ray Flux ◽

Diurnal Maximum

The cosmic-ray diurnal variation has been observed with scintillator telescopes at a depth of 40 m.w.e. at Chacaltaya, Bolivia, since the last solar maximum, and at the same depth near Albuquerque, New Mexico, since the last solar minimum. During the solar maximum from 1958 to 1960 the amplitude of the diurnal variation was 0.3% for the Chacaltaya telescopes, but at solar minimum early in 1965 it was as low as 0.05%. Since that time, the amplitude has been steadily increasing, and it is now between 0.1% and 0.2% at both the Bolivia and the New Mexico stations.The telescopes measure the cosmic-ray flux from the north, south, east, and west directions, as well as from the vertical; and the various observed times of the diurnal maximum for these directions confirm the extraterrestrial nature of the anisotropy. The maximum occurs at approximately 15 h local solar time in the vertical telescopes. A study of the asymptotic directions of these telescopes for differing primary energies, and of the behavior of the phases of the diurnal variation at the two stations, gives indications of the energies of the primary particles responsible for the diurnal variation. The results are compared with the models of Axford and of Ahluwalia and Dessler.

Download Full-text

The Upper Limiting Primary Rigidity of the Cosmic Ray Solar Anisotropy

Australian Journal of Physics ◽

10.1071/ph650451 ◽

1965 ◽

Vol 18 (5) ◽

pp. 451 ◽

Cited By ~ 7

Author(s):

RM Jacklyn ◽

JE Humble

Keyword(s):

Diurnal Variation ◽

Sea Level ◽

Free Space ◽

Daily Variation ◽

Cosmic Ray ◽

Neutron Monitors ◽

Annual Average ◽

Average Value

A method of determining the upper limiting rigidity of the solar diurnal variation of the cosmic ray primaries in free space is described. It involves a comparision of the response to the anisotropy of neutron monitors at sea level and of meson telescopes underground. Making use of the model for the free-space first harmonic proposed by Radio, McCracken, and Venkatesan, the annual average value for the upper limiting rigidity (Ru) in 1958 is estimated to have been 95 GV with an error of estimate of about 10-20 GV. Changes in the observed annual mean daily variation between 1958 and 1962 indicate that Ru may have decreased by about 20-40 GV over this period, but a more refined analysis is needed to confirm this.

Download Full-text

Directional measurements of the cosmic-ray daily variation at a vertical depth of 60 m.w.e. in London

Canadian Journal of Physics ◽

10.1139/p68-352 ◽

1968 ◽

Vol 46 (10) ◽

pp. S788-S793 ◽

Cited By ~ 7

Author(s):

D. S. Peacock ◽

J. C. Dutt ◽

T. Thambyahpillai

Keyword(s):

Solar Minimum ◽

Daily Variation ◽

Vertical Direction ◽

Cosmic Ray ◽

The Sun ◽

Statistical Accuracy ◽

Daily Variations ◽

The Earth ◽

Cosmic Ray Flux ◽

Very High

Semicubical telescopes pointing in the vertical direction and inclined cubical telescopes pointing in the east and north directions have been employed to measure the cosmic-ray daily variation at an underground site in London. Although the statistical accuracy of the measured daily variations is not very high, there are strong indications that during 1965, which was the year of maximum cosmic-ray flux associated with the last solar minimum, tire upper limiting rigidity of the corotation anisotropy (with time of maximum at 1800 h) was reduced to such low values that a Compton–Getting effect due to the motion of the earth around the sun became observable. Also, the atmospheric contribution to the measured solar daily variations appears to be very small. There is no evidence for an enhancement of the observable sidereal daily variation associated with the lowering of the upper limiting rigidity of the corotation anisotropy.

Download Full-text

41. The solar daily variation of the cosmic ray intensity

Symposium - International Astronomical Union ◽

10.1017/s0074180900237972 ◽

1958 ◽

Vol 6 ◽

pp. 392-403

Author(s):

H. Elliot ◽

P. Rothwell

Keyword(s):

Magnetic Field ◽

Cosmic Rays ◽

Daily Variation ◽

Cosmic Ray ◽

Earth’S Magnetic Field ◽

Cosmic Ray Intensity ◽

Primary Particles ◽

Earth's Magnetic Field ◽

East And West ◽

Solar Daily Variation

Some recent measurements of the solar daily variation for cosmic rays incident from the east and west directions at 45° to the vertical in London are described. The results do not agree with those to be expected if the variation was due to a non-isotropic flux of primary particles entering the earth's magnetic field. This result is discussed in relation to other evidence and it is concluded that the daily variation is probably due to a modulation of the primary cosmic ray intensity in the earth's magnetic field.

Download Full-text