1. 27-Day Variations Of The Galactic Cosmic Ray Intensity And Anisotropy In Different Solar Magnetic Cycles (1964-2004) M.V. Alania, A. Gil, K. Iskra, R. Modzelewska

2. Abstract We study the 27-day variations of the GCR anisotropy and intensity, solar wind velocity and interplanetary magnetic field strength for different solar magnetic cycles. We find that the average amplitudes of the 27-day variation of the GCR anisotropy for the minima epochs of solar activity are larger in the solar positive polarity period than in the negative polarity period being in a good correlation with the similar changes of the amplitudes of the 27-day variation of the GCR intensity versus the solar magnetic cycles. The amplitudes of the 27-day variations of the anisotropy, SW velocity and IMF do not depend on the TA of the HNS for different the qA>0 and the qA<0 periods of solar magnetic cycle as it was found before for the amplitudes of the 27-day variation of the GCR intensity.

3. Introduction The 27-day variation of the GCR anisotropy, has been studied less intensively up to present. It is partly connected with the complexity of the reliable revealing of the 27-day recurrence of the anisotropy by means of diurnal variation of GCR; diurnal variations have low values (<0.3%) and their phases are undergoing to the significant dispersion during the Sun’s rotation period. Earlier, Dorman and Shatashvili using the Chree’s analysis method have shown that a duration of the 27-day variation of GCR anisotropy is not less than the duration of the 27- day variation of the GCR intensity. Alania showed that the duration of the 27- day variation of the GCR anisotropy is definitely larger and exists when the 27- day variation of the GCR intensity is absent. The comprehensible 27-day variation of the GCR anisotropy was revealed for the minimum epoch of solar activity 1965 when the valuable 27-day recurrence of the major parameters of solar activity and SW were absent.

4. It was assumed that the 27-day recurrence of GCR anisotropy observed in 1965 could be related with the drift of GCR in the well established 27-day recurrence of the sector structure of the interplanetary magnetic field (IMF). Any investigation of the feature of the 27-day recurrence of GCR anisotropy versus the solar magnetic field polarity has not carried out up to present. The purpose of this paper is to study the feature of the 27-day recurrence of GCR anisotropy and its relation with the changes of GCR intensity in different the qA>0 and the qA<0 periods of solar magnetic cycle and with the tilt angles (TA) of the HNS.

5. Experimental data & methods To study the temporal changes of the amplitudes of the 27-day variations of the GCR anisotropy and intensity versus the TA of the HNS were used the experimental data of neutron monitors. The radial and the tangential components of the solar daily variations of GCR intensity were calculated by means of hourly data of neutron monitors using the harmonic analyses method taking into account an influence of the Earth magnetic field. Then, using again the harmonic analyses method (the period equals 27 days) we obtain

6. The average values of the amplitudes of the 27-day variation of the GCR anisotropy A27 A[%]1964-661975-771986-881996-98 Kiel 0.0345±0.00150.0487±0.00150.0175±0.0010 0.0500±0.0010 Rome 0.0384±0.00110.0587±0.00120.0016±0.0006 0.0604±0.0008 Moscow 0.0226±0.00160.0542±0.00150.0140±0.0006 0.0527±0.0009 Apatity 0.0148±0.00130.0659±0.00140.0133±0.0007 0.0355±0.0010 Table 1

7. The average values of the amplitudes of the 27-day variation of the GCR anisotropy K – Kiel, M – Moscow, R – Rome, A - Apatity

8. Changes of the A27A and A27I versus the time The converted to the heliosphere average amplitudes of the A27I (squares) and A27A (triangles) obtained by Kiel and Rome neutron monitors data for the qA>0 (1975-78 and 1995-98) and the qA<0 (1964-67 and 1985-88) periods Gil et al., 2005

9. The distributions of the amplitudes of the 27-day variation of the GCR intensity for Kiel nm versus the TA The distributions of the amplitudes of the 27-day variation of the GCR intensity for Kiel neutron monitor data versus the tilt angles (for different periods of solar magnetic cycle) for the 1976-2004 A27I = (0.007  0.051)  + 0.555  0.002 A27I = (0.009  0.073)  + 0.449  0.002

10. The distributions of the amplitudes of the 27-day variation of the GCR intensity for Kiel nm versus the tilt angles The distributions of the amplitudes of the 27-day variation of the GCR intensity for Kiel neutron monitor data versus the tilt angles (tilt angles are 0-15 0 (a), 16-75 0 (b)) for the 1976-2004 A27I = (-0.007  0.076)  + 0.578  0.008 A27I = (0.005  0.080)  + 0.728  0.002

11. The distributions of the amplitudes of the 27-day variation of the GCR anisotropy for Kiel nm versus the tilt angles The distributions of the amplitudes of the 27-day variation of the GCR anisotropy for Kiel neutron monitor data versus the tilt angles (for different periods of solar magnetic cycle) for the 1976-2004 A27A = (0.000  0.010)  + 0.166  0.001 A27A = (0.001  0.012)  + 0.090  0.001

12. The distributions of the amplitudes of the 27-day variation of the GCR anisotropy versus the TA The distributions of the amplitudes of the 27-day variation of the GCR anisotropy for Kiel neutron monitor data versus the tilt angles (tilt angles are 0-15 0 (a), 16-75 0 (b)) for the 1976-2004 A27A = (0.001  0.020 )  + 0.131  0.002 A27A = (0.000  0.014)  + 0.152  0.000

13. The distributions of the amplitudes of the 27-day variation of the IMF versus the tilt angles A27B = (0.001  0.057)  + 0.936  0.001 The distributions of the amplitudes of the 27-day variation of the IMF data versus the tilt angles for the 1976-2004

14. The distributions of the amplitudes of the 27-day variation of the SW velocity versus the tilt angles A27SW = (-0.123  3.223 )  + 65.503  0.085 The distributions of the amplitudes of the 27-day variation of the SW velocity data versus the tilt angles for the 1976-2004

15. A r, A  Temporal changes of the annual radial component of the anisotropy (bold-faced bars on the abscissa show time intervals of the global magnetic field reversals) Temporal changes of the annual tangential component of the GCR anisotropy

16. Changes of the GCR anisotropy versus the direction of the regular IMF Changes of the GCR anisotropy versus the direction of the regular IMF in different sectors ( '+' corresponds to the IMF lines directed from the north hemisphere, '  ' vise-versa direction)

17. Changes of the GCR anisotropy versus the direction of the regular IMF Changes of the GCR anisotropy versus the direction of the regular IMF in different epochs of SA. ( '+' corresponds to the IMF lines directed from the north hemisphere, '  ' corresponds to the vise-versa direction)

18. Harmonic diagram of the average anisotropies of GCR for the periods of different periods of solar magnetic cycle Harmonic diagram of the average anisotropies of GCR for the periods of qA>0 and qA<0. On the axes are presented radial and heliolongitudinal components of anisotropy in %.

19. Drifts

20. Drifts 2 Duldig, 2000

21. Conclusions The amplitudes of the 27-day variations of the GCR anisotropy, IMF’s strength and SW velocity do not depend on the tilt angles of the HNS for the period of 1976-2004. The amplitudes of the 27-day variation of the GCR anisotropy are considerably larger in the minima and near minima epoch for the qA>0 periods than for the qA<0 periods of solar magnetic cycle. These conclusions are in a good agreement with the similar changes of the amplitudes of the 27-day variation of the GCR intensity.