QUASI-STEADY COROTATING STRUCTURE OF GEOMAGNETIC DISTURBANCE DURING SOLAR MINIMUM FROM 13TH THROUGH 20TH SOLAR CYCLE

The corotating variation of geomagnetic index Chas been studied by the digital filter, superposedepoch and harmonic analysis methods covering the long-time series of data from the 13th through the 20th solar cycles. The main results obtained show that during solar minima the corotating variation has quite steady sturcture of distribution in the Carrington rotation, for which the phase of the second harmonic remains nearly the same in each of the even or odd cycles, and reverses from one to another cycle. Inferred from the seasonal trend of the distribution, it has been interestingly noted that each of the two main peaks maintains the same magnetic polarity during the even cycles, therefore it is likely that their source region located in the northern and southern solar hamispheres resectivey for the left and right peaks. Also, the location of the peak drifts against the solar rotation just like the earth’s main magnetic field. The implication of the above important results would be that the stable hi