Direct‐driven mechanism for geomagnetic storms

Abstract

We have obtained the injection function for the part of the storm‐time depression which is related to the cross‐tail current and corresponding currents on the magnetopause. This injection function is QTC=−κU/S, where U is the electric potential difference between the dawn and dusk sides of the magnetosphere, S is the equatorial cross‐section of the stable trapping region, and κ is a coefficient varying from 0.5 to 1.5 depending on the state of the magnetosphere and solar wind pressure. The injection function QTC appeared to be close to the observed one for the Dst‐variation.

Ionospheric and boundary contributions to the Dessler-Parker-Sckopke formula for <i>Dst</i>

“…The contribution to b(0) given by Eq. (48) is similar in form and value to previous estimates derived from various models of magnetotail currents (Alexeev et al, 1996;Arykov and Maltsev, 1996) or from empirical arguments Maltsev, 1998, 2000;Turner et al, 2000;Ohtani et al, 2001). As derived here, however, it does not depend on specific assumptions about current systems and is not affected by controversies (e.g.…”

Reinterpreting the Burton‐McPherron‐Russell equation for predicting Dst

“…From a fit to observations, Burton et al [1975] determine Q as the function Q ′ given by with F the function defined by where α and the (small and mostly unimportant) offset cE 0 are constants. Their values as estimated most recently by McPherron and O'Brien [2001] are α = −4.65 nT hr −1 (mV m −1 ) −1 , cE 0 = 0.05 mV m −1 , given in commonly used units; only rarely [ Siscoe and Crooker , 1974; Arykov and Maltsev , 1996] is it pointed out that α is actually an inverse length, the value given above corresponding to (121 R E ) −1 . The rectifying function F ( x ) is the simplest mathematical representation of the dependence on the angle θ between the interplanetary magnetic field and the Earth's dipole moment; other, essentially equivalent representations, involving more complicated but smooth functions of θ, have been proposed (cf.…”

Phase shift (time) between storm-time maximum negative excursions of geomagnetic disturbance index Dst and interplanetary Bz

“…Burton et al (1975) proposed a solar wind pressuredependent correction formula to remove the contribution of magnetopause currents to D st . Thirdly, Arykov and Maltsev (1996) pointed out that tail currents can dominate D st development during storms. For some moderate storms, Turner (2000) and Turner et al (2000) showed that the magnetotail currents accounted for $25% of D st and suggested that this contribution should be estimated for strong storms.…”