Criteria of interplanetary parameters causing intense magnetic storms ( Dst < −100 nT)

Abstract

Ten intense magnetic storms ( D st < −100 nT) occurred during the 500 days from 16 August 1978 to 28 December 1979. From our analysis of ISEE-3 field and plasma data, it is found that the interplanetary causes of these storms are long-duration, large and negative (< −10 nT) IMF B Z events, associated with interplanetary duskward-electric fields >5 mV m −1, that last for intervals >3 h. Because we find a one-to-one relationship between these interplanetary events and intense storms, we suggest that these criteria can, in the future, be used as predictors of intense storms by an interplanetary monitor such as ISEE-3. These B z events are found to occur in association with large amplitudes of the IMF (magnitude 13–30 nT) within 2 days after the onset of either high-speed solar wind streams or of solar wind density enhancement events, giving important clues to their interplanetary origin. Some obvious possibilities will be discussed. The close proximity of the B z events and magnetic storms to the onset of high speed streams or density enhancement events is in sharp contrast to interplanetary Alfven waves and HILDCAA events previously reported by the authors (Tsurutani and Gonzalez, 1986, Planet. Space Sci. 35, 405) and thus the two interplanetary features and corresponding geomagnetic responses can be thought of as being complementary in nature. An examination of opposite polarity (northward) B z events with the same criteria ( B z > 10 nT, with dawn ward-electric fields >5 mV m −1, that last for intervals >3 h) shows that their occurrence is similar both in number as well as in their relationship to interplanetary disturbances, and that they lead to low levels of geomagnetic activity. Although 90% of the events were associated with high-speed streams and interplanetary shocks, the amplitude of the storms had little dependence on the strength of the shocks.