The solar and geophysical data in the period from January 1st, 1971 to January 18th, 1977 are devided into 442 intervals, each containing 5 consecutive days. The 195 intervals before September 1st, 1973 were difined as "declining phase" and the following 247 intervals as "minimum phase". Each interval can be characterized as geomagnetic disturbed "D" or calm "N" according to the. beginning of geomagnetic storm.On the other hand, we try to define by computer the disturbed days on the base of solar or geophysical features in association with the geomagnetic storms in the first two third of number of intervals (refered to as "learning period") in both declining and minimum phase in order to determine certain threshold values necessary for this method. Then we use this method to identify the "D" and "N" intervals in the remaining one third of number of intervals (refered to as "test period").The main results as follows:(1) In the declining phase the comprehensive flare index (CFI) of importance equal 6 or more, the radio bursts of Type IVwith duration 10 min, or more and the interplanetary magnetic field (IMP) sector boundary passage through Earth are most likely associated with geomagnetic storm.(2)In the minimum phase the solar active source exhibiting 27-day reoccurring tendency (i.e.. the high speed stream from the coronal hole) and the IMFsector boundary passage through Earth are most likely the cause of geomagnetic disturbances.(3)The recognition efficiency is 73-82% in the learning period and 73-80% in the test period with error < 30% in both eases.We also have made experiments of orthogonal design with a member of groups of threshold values and test of significance. The resulting confidence limit in this method is greater than 97.5%.
DownLoad: