Passage of the solar current disk and major geomagnetic storms

Abstract

It is shown that major geomagnetic storms (¦Dst¦ > 100γ) tend to develop at about the time of the passage of the solar current sheet or disk at the location of the Earth, provided this passage is associated with (1) a large impulsive increase of the IMF magnitude B, (2) a negative value of the IMF angle Θ (Theta), and (3) an increasing solar wind speed. The passage occurs in association with the 27-day rotation of the warped current disk or a temporal up-down movement of the latter. The period in which ∂¦Dst¦/∂t< 0 during major storms coincides approximately with the period when the solar windmagnetosphere energy coupling function ɛ becomes ≳1019 erg s−1. These conclusions do not depend on the phase of the sunspot cycle.