| Popis: |
Long-term changes of the 27 day variation of the geomagnetic disturbances were investigated to study the solar cycle dependence of the solar wind stream pattern. Harmonic analysis was performed for each declining portion from solar cycle 11 to 21. The following results were obtained. (1) The amplitude of the first harmonic component exhibits the semiannual enhancement in the declining portion of the even cycles. (2) The second harmonic component exhibits quasi-constancy in the phase in the declining portion of the solar cycle 12, 16 and 20 but not in the solar cycle 14 and 18. (3) In the odd cycles, there is no systematic feature in the first and second components. (4) In some of the even cycles, the yearly set of the 27 day pattern reconstructed with the first and second harmonic components reveals the existence of two large stream regions in the heliographic latitude, one of which is in the Northern Hemisphere and the other is in the Southern Hemisphere. These two regions do not always have the distance of about 180° in the heliographic longitude. |
