Abstract
Abstract. The high-speed stream following the corotating interaction regions (CIRs) was analyzed. As a result of the analysis, it is found that the geomagnetic field is continuously disturbed in the high-speed stream in question. The geomagnetic disturbances with long duration recurred several rotations between December 1993 and June 1994. These disturbances were associated with a large recurrent coronal hole expanding from the south pole of the Sun. High-speed solar wind from this coronal hole was observed by the IMP-8 satellite during this period. However, the observed intensities of the geomagnetic disturbances were different for each recurrent period. This is explained by the seasonal effect. The disturbed geomagnetic condition continued in the high-speed stream after the passage of the CIRs. The long duration of these disturbances can be explained by the continuous energy input into the Earth's magnetosphere from the high-speed regions following the CIRs. This kind of long-duration geomagnetic disturbance in association with coronal holes has been observed in the declining phase of other solar cycles. The relation between the coronal-hole area and the maximum solar-wind velocity is not good for the well-developed large coronal hole analyzed here.
Highlights
Some geomagnetic disturbances recur with about a 27day period during several solar rotations. Bartels (1934) gave the name M-regions to the solar sources of these recurrent geomagnetic disturbances
It is generally accepted that these 27-day recurrent geomagnetic disturbances are associated with corotating interaction regions (CIRs) formed between the high-speed solar wind emanating from coronal holes and the preceding slow solar wind
Between December 1993 and June 1994 (Bartels rotation number 2910±2916), long-duration geomagnetic disturbances recurred several rotations associated with a large negative-polarity coronal hole extending from the south pole of the Sun [P
Summary
Some geomagnetic disturbances recur with about a 27day period during several solar rotations. Bartels (1934) gave the name M-regions to the solar sources of these recurrent geomagnetic disturbances. It is generally accepted that these 27-day recurrent geomagnetic disturbances are associated with corotating interaction regions (CIRs) formed between the high-speed solar wind emanating from coronal holes and the preceding slow solar wind. This is based on the results of several spacecraft observations (Neupert and Pizzo, 1974; Timothy et al, 1975; Nolte et al, 1976; Bohlin and Sheeley, 1978; Broussard et al, 1978; Sheeley et al, 1976). The relation between this index and solar-wind parameters is explained physically (Feldstein, 1992, and references therein). Burton et al (1975) noted that there is an empirical relationship between the Dst index and solarwind parameters [e.g., velocity (V), the north-south component of the IMF (Bz), and mass density (q); the solar-wind electric ®eld (VBz) and the dynamic pressure (q V 2/2)]
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