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.

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.

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.

scholarly journals Prediction of galactic cosmic ray intensity variation for a few (up to 10-12) years ahead on the basis of convection-diffusion and drift model

2005 ◽  
Vol 23 (9) ◽  
pp. 3003-3007 ◽  
Author(s):  
L. I. Dorman
Keyword(s):  
Interplanetary Space ◽  
Intensity Variation ◽  
Cosmic Ray ◽  
Particle Energy ◽  
Cosmic Ray Intensity ◽  
Convection Diffusion ◽  
Drift Model ◽  
Galactic Cosmic Ray ◽  
Near Future

Abstract. We determine the dimension of the Heliosphere (modulation region), radial diffusion coefficient and other parameters of convection-diffusion and drift mechanisms of cosmic ray (CR) long-term variation, depending on particle energy, the level of solar activity (SA) and general solar magnetic field. This important information we obtain on the basis of CR and SA data in the past, taking into account the theory of convection-diffusion and drift global modulation of galactic CR in the Heliosphere. By using these results and the predictions which are regularly published elsewhere of expected SA variation in the near future and prediction of next future SA cycle, we may make a prediction of the expected in the near future long-term cosmic ray intensity variation. We show that by this method we may make a prediction of the expected in the near future (up to 10-12 years, and may be more, in dependence for what period can be made definite prediction of SA) galactic cosmic ray intensity variation in the interplanetary space on different distances from the Sun, in the Earth's magnetosphere, and in the atmosphere at different altitudes and latitudes.

scholarly journals On the heliolatitudinal variation of the galactic cosmic-ray intensity. Comparison with Ulysses measurements

2003 ◽  
Vol 21 (6) ◽  
pp. 1341-1345 ◽  
Author(s):  
G. Exarhos ◽  
X. Moussas
Keyword(s):  
Solar Wind ◽  
Cosmic Rays ◽  
Interplanetary Space ◽  
Cosmic Ray ◽  
Solar Wind Plasma ◽  
Simple Method ◽  
Cosmic Ray Intensity ◽  
Interplanetary Physics ◽  
Diffusion Convection ◽  
Galactic Cosmic Ray

Abstract. We study the dependence of cosmic rays with heliolatitude using a simple method and compare the results with the actual data from Ulysses and IMP spacecraft. We reproduce the galactic cosmic-ray heliographic latitudinal intensity variations, applying a semi-empirical, 2-D diffusion-convection model for the cosmic-ray transport in the interplanetary space. This model is a modification of our previous 1-D model (Exarhos and Moussas, 2001) and includes not only the radial diffusion of the cosmic-ray particles but also the latitudinal diffusion. Dividing the interplanetary region into "spherical magnetic sectors" (a small heliolatitudinal extension of a spherical magnetized solar wind plasma shell) that travel into the interplanetary space at the solar wind velocity, we calculate the cosmic-ray intensity for different heliographic latitudes as a series of successive intensity drops that all these "spherical magnetic sectors" between the Sun and the heliospheric termination shock cause the unmodulated galactic cosmic-ray intensity. Our results are compared with the Ulysses cosmic-ray measurements obtained during the first pole-to-pole passage from mid-1994 to mid-1995.Key words. Interplanetary physics (cosmic rays; interplanetray magnetic fields; solar wind plasma)

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.

Gradient of galactic cosmic rays normal to the solar equatorial plane

1968 ◽  
Vol 46 (10) ◽  
pp. S981-S984 ◽  
Author(s):  
D. Patel ◽  
V. Sababhai ◽  
G. Subramanian
Keyword(s):  
Magnetic Field ◽  
Energy Spectrum ◽  
Cosmic Rays ◽  
Interplanetary Magnetic Field ◽  
Equatorial Plane ◽  
Cosmic Ray ◽  
Galactic Cosmic Rays ◽  
Cosmic Ray Intensity ◽  
Positive Exponent ◽  
Ray Density

Predictions concerning the anisotropy of galactic cosmic rays due to a gradient of cosmic-ray density perpendicular to the solar equatorial plane have been verified experimentally as follows. (1) The energy spectrum of the variation of the semidiurnal component has a positive exponent. (2) The diurnal and the semidiurnal components are oriented with respect to the interplanetary magnetic field. (3) A deficiency of cosmic-ray intensity, Tmin, is observed along the direction of the interplanetary magnetic field on days when the energy spectrum of the diurnal variation has an exponent different from zero.

A two-way sidereal anisotropy

1968 ◽  
Vol 46 (10) ◽  
pp. S611-S613 ◽  
Author(s):  
K. Nagashima ◽  
H. Ueno ◽  
S. Mori ◽  
S. Sagisaka
Keyword(s):  
Time Variation ◽  
Cosmic Ray ◽  
Sidereal Time ◽  
Cosmic Ray Intensity ◽  
Data Support ◽  
Ion Chambers ◽  
Using Data ◽  
Sidereal Anisotropy

The sidereal time variation is analyzed using data for the ion chambers at Cheltenham and Christchurch for the period 1938–58 and for the meson and neutron components during the IGY. All the results derived from these three kinds of data support the existence of a two-way sidereal anisotropy, suggested by Jacklyn, which has two maxima of the cosmic-ray intensity in the directions of 8 h and 20 h S.T. (sidereal time).

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