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

1961 ◽  
Vol 263 (1312) ◽  
pp. 127-135 ◽  
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.

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

1961 ◽  
Vol 263 (1312) ◽  
pp. 101-117 ◽  
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.

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

1961 ◽  
Vol 263 (1312) ◽  
pp. 118-126 ◽  
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.

Semidiurnal Anisotropy of Galactic Cosmic Ray Intensity

1971 ◽  
Vol 49 (1) ◽  
pp. 34-48 ◽  
Author(s):  
G. Subramanian
Keyword(s):  
Energy Spectrum ◽  
Counting Rate ◽  
Interplanetary Space ◽  
Cosmic Ray ◽  
Cosmic Ray Intensity ◽  
The Earth ◽  
Positive Exponent ◽  
Semidiurnal Variation ◽  
Using Data ◽  
Galactic Cosmic Ray

The semidiurnal variation of galactic cosmic ray intensity is investigated using data from mainly high counting rate neutron and meson monitors during 1964–1968. It is shown that in order to explain the observed semidiurnal variation it is necessary that an anisotropy of cosmic ray intensity be present in interplanetary space. The energy spectrum and the asymptotic latitude dependence of the anisotropy are then determined. The energy spectrum has a positive exponent close to + 1 for the power law in energy. The strength of the anisotropy decreases more rapidly than cosλ with increasing asymptotic latitude λ, both cos2λ and cos3λ being acceptable. The distribution of cosmic ray intensity in the range of heliolatitudes ± 7.25° at the orbit of the earth, obtained using data from the Ottawa neutron monitor, does not support the explanation of the semidiurnal variation based on the models of Subramanian and Sarabhai or Lietti and Quenby.

scholarly journals 39. The anisotropy of primary cosmic radiation and the electromagnetic state in interplanetary space

1958 ◽  
Vol 6 ◽  
pp. 377-385
Author(s):  
V. Sarabhai ◽  
N. W. Nerurkar ◽  
S. P. Duggal ◽  
T. S. G. Sastry
Keyword(s):  
Experimental Data ◽  
Cosmic Rays ◽  
Cosmic Radiation ◽  
Interplanetary Space ◽  
Daily Variation ◽  
Cosmic Ray ◽  
The Sun ◽  
Cosmic Ray Intensity ◽  
Daily Variations ◽  
Primary Cosmic Radiation

Study of the anisotropy of cosmic rays from the measurement of the daily variation of meson intensity has demonstrated that there are significant day-today changes in the anisotropy of the radiation. New experimental data pertaining to these changes and their solar and terrestrial relationships are discussed.An interpretation of these changes of anisotropy in terms of the modulation of cosmic rays by streams of matter emitted by the sun is given. In particular, an explanation for the existence of the recently discovered types of daily variations exhibiting day and night maxima respectively, can be found by an extension of some ideas of Alfvén, Nagashima, and Davies. An integrated attempt is made to interpret the known features of the variation of cosmic ray intensity in conformity with ideas developed above.

scholarly journals Galactic Anisotropy of Cosmic Ray Intensity Observed by an Air Shower Experiment

2006 ◽  
Vol 23 (3) ◽  
pp. 129-134
Author(s):  
Mahmud Bahmanabadi ◽  
Mehdi Khakian Ghomi ◽  
Farzaneh Sheidaei ◽  
Jalal Samimi
Keyword(s):  
Daily Variation ◽  
Cosmic Ray ◽  
Cosmic Ray Intensity ◽  
Extensive Air Shower ◽  
Air Shower ◽  
The Earth ◽  
The Galaxy ◽  
Unidirectional Anisotropy ◽  
Galactic Cosmic Ray ◽  
Shower Array

AbstractWe have monitored multi-TeV cosmic rays by a small air shower array in Tehran (35°43′ N, 51°20′ E, 1200 m = 890 g cm−2). More than 1.1 × 106 extensive air shower events were recorded. These observations enabled us to analyse sidereal variation of the galactic cosmic ray intensity. The observed sidereal daily variation is compared to the expected variation which includes the Compton–Getting effect due to the motion of the earth in the Galaxy. In addition to the Compton–Getting effect, an anisotropy has been observed which is due to a unidirectional anisotropy of cosmic ray flow along the Galactic arms.

THE ONSET TIMES OF FORBUSH-TYPE COSMIC RAY INTENSITY DECREASES

1959 ◽  
Vol 37 (9) ◽  
pp. 970-982 ◽  
Author(s):  
A. G. Fenton ◽  
K. G. McCracken ◽  
D. C. Rose ◽  
B. G. Wilson
Keyword(s):  
Daily Variation ◽  
Cosmic Ray ◽  
Consistent Pattern ◽  
Maximum Sensitivity ◽  
Geomagnetic Disturbances ◽  
Cosmic Ray Intensity ◽  
Early Stages ◽  
The Earth ◽  
Directional Anisotropy ◽  
Quiet Day

The onset times of a number of Forbush-type decreases observed at four widely spaced stations are compared, and it is shown that appreciable differences occur. The stations selected were Hobart, Mawson, Ottawa, and Sulphur Mountain. It was found that a consistent pattern is obtained for the events studied when the onset times are plotted as a function of the direction of maximum sensitivity of the recorders relative to the earth-sun line. This is interpreted as being due to a directional anisotropy that exists in the mechanism producing the decreases, at least in the early stages. The depression occurs first for particles arriving from directions between 30° and 120° west of the earth–sun line. The relation between these observations and geomagnetic disturbances and the quiet-day daily variation is discussed.

Anisotropy of transient variations of cosmic-ray intensity

1968 ◽  
Vol 46 (10) ◽  
pp. S871-S874
Author(s):  
Masami Wada ◽  
Hiroo Komori
Keyword(s):  
Angular Distribution ◽  
Interplanetary Space ◽  
Principal Direction ◽  
Cosmic Ray ◽  
Distribution Functions ◽  
Present Calculation ◽  
Cosmic Ray Intensity ◽  
The Earth ◽  
Rotation Of The Earth ◽  
Transient Variations

The angular distribution of the anisotropy of cosmic rays in interplanetary space is generally assumed to follow a cosine function. In the case of the daily variation, the source direction lies essentially in the equatorial plane. In the present calculation, the following three points were taken into account: (1) the latitude of the principal direction, (2) the angular distribution functions, and (3) the increases in flux of cosmic-ray particles. The response functions, the asymptotic directions, and the variation spectra are also involved in the calculation. Because of the rotation of the earth with respect to the source direction, which is fixed at the 12-h meridian, the daily variations are obtained. The variations include higher harmonics if the angular distribution is other than a simple cosine function.Comparing the calculated curves with observed data, the anisotropy in the space outside the geomagnetic field can be estimated with parameters such as the source direction in latitude and longitude, the half-width of the angular distribution, and the amplitude and exponent of the variation spectrum, which are all time-dependent. An increase which occurred on 24 March 1966 was analyzed.

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

1968 ◽  
Vol 46 (10) ◽  
pp. S801-S804 ◽  
Author(s):  
A. Hashim ◽  
T. Thambyahpillai ◽  
D. M. Thomson ◽  
T. Mathews
Keyword(s):  
Diurnal Variation ◽  
Large Amplitude ◽  
Solar Minimum ◽  
Daily Variation ◽  
Cosmic Ray ◽  
Local Source ◽  
Equatorial Station ◽  
East And West ◽  
Set Up ◽  
East West

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.

Anisotropy in cosmic-ray intensity associated with Forbush decreases

1968 ◽  
Vol 46 (10) ◽  
pp. S854-S858 ◽  
Author(s):  
T. Mathews ◽  
J. B. Mercer ◽  
D. Venkatesan
Keyword(s):  
Daily Variation ◽  
Forbush Decrease ◽  
Cosmic Ray ◽  
Turbulent Plasma ◽  
The Sun ◽  
The West ◽  
Cosmic Ray Intensity ◽  
Rate Of Development ◽  
The Earth ◽  
Scattering Centers

A study of the Forbush decrease of 23 September 1966 shows that the predecrease anisotropy developed from a direction 85° to the west of the sun–earth line. The rate of development of the anisotropy suggests that the "turbulent" plasma producing the Forbush decrease occupied a volume of diameter ≈0.2–0.3 AU. If the plasma clouds away from the earth produced the anisotropy at the earth, then it is reasonable to attribute a part of the highly variable daily variation in cosmic-ray intensity to such distant scattering centers.

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