Solar, Interplanetary and Terrestrial Features Associated with Periods of Prolonged Positive and Negative Dst Index
1989 Volume 41 Issue 12 Pages 1001-1023
Details
1989 Volume 41 Issue 12 Pages 1001-1023
From a survey of the published final values of the geomagnetic index Dst for the period 1958-1972, we found long time intervals of over 25-30 days, during which this index remained consistently positive (Dst+) or negative (Dst-). A study is made of relevant parameters on the ground, in the magnetosphere, in the solar wind and on the Sun to seek out systematic features associated with the two conditions. In order to eliminate factors arising from seasonal and solar cycle variations, we selected pairs of Dst+ and Dst- which involve successive months of the same year, or the same month of two successive years.
Three parameters which show a systematic difference between Dst+ and Dst- intervals are found to be 1) the state of solar photospheric magnetic fields 2) the flux density of solar MeV protons measured in the magnetosphere and 3) the southward component of the interplanetary magnetic field. While the effect of the last on geomagnetic activity has been well-discussed in the literature, it is suggested that the correlations of the first two to the conditions of Dst+ and Dst- demand a careful scrutiny of the solar-terrestrial relationship.
