Study of the 27-day variations of the galactic cosmic ray intensity and anisotropy

We demonstrate that the general features of the radial and azimuthal components of the anisotropy of galactic cosmic rays can be studied by the harmonic analysis method using data from an individual neutron monitor with cut off rigidity <5GV. In particular, we study the characteristics of the 27-day (solar rotation period) variations of the galactic cosmic ray intensity and anisotropy, solar wind velocity, interplanetary magnetic field strength and sunspot number. The amplitudes of the 27-day variations of the galactic cosmic ray anisotropy are greater, and the phases more clearly established, in A>0 polarity periods than in A<0 polarity periods at times of minimum solar activity. The phases of the 27-day variations of the galactic cosmic rays intensity and anisotropy are opposite with respect to the similar changes of the solar wind velocity in A>0 polarity periods. No significant dependence of the amplitude of the 27-day variation of the galactic cosmic ray anisotropy on the tilt angle of the heliospheric neutral sheet is found. Daily epicyclegrams obtained by Chree’s method show that the 27-day variations of the galactic cosmic ray anisotropy during A>0 polarity periods follow elliptical paths with the major axes oriented approximately along the interplanetary magnetic field. The paths are more irregular during A<0 polarity periods.

...We confirm that the experimental data of neutron monitors are in a good agreement with the theoretical results when the heliolongitudinal asymmetry of the solar wind velocity is included in the model describing the 27-day variations of the GCR intensity and anisotropy [4], [5]...
...The dependence of the amplitudes of the 27-day variations of the GCR intensity and anisotropy on the A>0 and the A<0 polarity periods we explained owing to the existence of the heliolongitudinal asymmetry of the solar wind velocity [4], [5]...
...The scattered distributions of the phases of the 27-day variations of the GCR intensity and anisotropy (Fig. 3b) for A<0 polarity period are one of the general motivations that the amplitudes of the 27-day variations of GCR intensity and anisotropy are greater in A>0 polarity period than in the A<0 polarity period [1], [2], [5]...
...Analysis of the Chree diagrams for the long period data (1975-2004) of the solar wind velocity show that for different intervals in the considered period there is appearing the synchronized quasi-periodic (~ 27 days) recurrence owing to existence of the long-lived active heliolongitudes [5]...
...10ab. For comparison in Fig. 11ab are presented the changes of the amplitudes of the 27-day variations of the GCR intensity and anisotropy calculated based on the solutions of the Parker’s equation when the heliolongitudinal asymmetry of the solar wind velocity is taken into account [5]...

Keywords (6)

Study of the 27-day variations of the galactic cosmic ray intensity and anisotropy,10.1016/j.asr.2007.06.001,Advances in Space Research,M. V. Alania,A

Citation Context (1)

R. Modzelewska, et al. On the 27-day variations of the galactic cosmic rays intensity and ani...

References (8)

27Day variations of galactic cosmic rays and changes of solar and geomagnetic activities (Citations: 8)

Magnetospheric effects in cosmic rays during the unique magnetic storm on November 2003 (Citations: 14)

Recurrence Phenomena in Small Cosmic-Ray Bursts (Citations: 6)

The Effect of a Fisk-Type Heliospheric Magnetic Field on Cosmic-Ray Modulation (Citations: 18)

Geomagnetic time-relationships (Citations: 2)

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