Dependence of the near‐Earth magnetotail magnetic field on storm and substorm activities

Abstract

Considering these points along with the results obtained for the lobe magnetic field, we discuss the changes in the large-scale distribution of the neutral sheet current during the course of major substorms: During the expansion onset of substorms, the neutral sheet current increases in the near-Earth magnetotail and decreases in the midmagnetotail: The neutral sheet current subsequently decreases in both the near-Earth and middistant tail regions during the recovery phase of substorms, where the current reduction is particularly evident near R = 6 R•. It is also suggested that not only in the near-Earth magnetotail but in the midmagnetotail the cross-tail current is significantly enhanced during intense storms.

Mercury's cross‐tail current sheet: Structure, X‐line location and stress balance

“…Our statistical analyses of the MESSENGER data show that B lobe decreases with increasing with an exponent of ~ 3.1. At Earth, this exponent ranges from ~ 0.9 to 2.7 [ Nakai et al ., ], which is lower than our Mercury results. This suggests that magnetotail flaring should cease comparatively closer to Mercury than is the case at Earth.…”

Substorm-associated large-scale magnetic field changes in the magnetotail: a prerequisite for "magnetotail deflation" events

“…This view appears to be rather reasonable, since the critical intensity of the cross-tail current must change considerably, depending on the outer and inner physical conditions. Nakai et al (1999) suggested that the magnetic field magnitude near X =∼20 R E in the neutral sheet region increases with a decrease in Dst and/or an increase in the solar wind dynamic pressure. Since a small B z value in the neutral sheet region is one of the necessary conditions for triggering the tearing mode instability (e.g.…”

“…If the magnetopause closure current decreases in association with the reduction of the tail current during deflation events, the contributions from these two current systems are expected to compensate each other. Furthermore, on the basis of their statistical study, Nakai et al (1997Nakai et al ( , 1999 argued that the partial ring current is enhanced in association with the occurrence of substorms. If this is the case, the contribution from the enhanced partial ring current can weaken the effect of the reducing tail current.…”

“…Nakai et al, 1999). Thus, we must eliminate the effect of these quantities from the lobe field intensity to search for an internal condition for triggering unloading processes.…”

“…One of the difficulties in finding the critical condition for deflation events is attributed to the fact that they seem to occur regardless of the lobe magnetic field intensity, as shown in the later section. During the last decade the statistical behavior of the lobe magnetic field has been studied (Nakai et al, 1991(Nakai et al, , 1999Nakai and Kamide, 1994;Fairfield and Jones, 1996;Ostapenko and Maltsev, 2000). They showed that the magnitude of the lobe magnetic field depends primarily on the solar wind pressure and geomagnetic activity represented by the Dst index.…”