The variation of interplanetary parameters at Earth orbit has previously been studied by superposedepoch analysis of the spacecraft data obtained during solar cycle 20. It was shown that the magnetosonic speed possesses a quasi‐steady, but slightly drifting, distribution in Carrington longitude during all phases of solar cycle 20. Other magnetic parameters such as the Alfvénic speed and ratios of magnetic and total pressure to the kinetic energy density also reflect this same organization in Carrington longitude in both the maximum and minimum years. We extend the study of the quasi‐steady corotating solar‐terrestrial variation to include the long‐time series of geomagnetic index C9 data covering solar cycles 13–20. Using the superposed‐epoch method in conjunction with digital filter and harmonic analysis, we find that during solar minima the corotating variation has a quite steady structure of distribution in the Carrington rotation, with the phase of the second harmonic remaining nearly the same in each of the even or odd cycles and shifting a large angle, probably reversing, from one to the next. Analysis of seasonal trends of the distribution suggests each of the two main peaks maintains the same magnetic polarity during the even cycles, and it is likely that their source regions are located in the northern and southern solar hemispheres, respectively, for the first and second peaks within each rotation. In addition, the locations of the peaks in the even cycle minima show only a small systematic drift in heliospheric longitude (about 6 Carrington days, net) from 1913 to 1974. The implication is that the stable high‐speed solar wind streams originate from a deeply rooted configuration of the general solar magnetic field which persists for at least four solar cycles.
The geomagnetic effects of the total solar eclipse in Mohe area and the partial eclipse occurred on March 9, 1997 in China are analyzed in this paper. The geomagnetic effects of the eclipse widely distributed in China are obtained, which show H component decreases obviously and is symmetric along the latitude with a center near 33°N during the eclipse time. These results of solar eclipse geomagnetic effects are the newest in recent years obtained in the largest area in China.
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