RELATIONSHIP
Wolfgang STORM-SUBSTORM Baumjohann
Max-Planck-Institut fiir extraterrestrische Phy sik Postbox 1603, D-85740 Garching, Germany fax: [phone], email: bj @mpe-garching.mpg.de
ABSTRACT
It is well-known that some substorms are associated with strong particle injection into the Earth's ring current, while others are not. The former type of substorms occurs during magnetic storm episodes. However, recently it was found that most of the typical substorm tail signatures are also strongly influenced by magnetic storm activity. The magnetic field dipolarization in the near-Earth tail is much more pronounced for substorms which occur during the main phase of magnetic storms than for nonstorm substorms. Moreover, only for storm-time substorms the lobe magnetic pressure decreases during the expansion phase. Hence, the classic signatures of reconnection at a near-Earth neutral line are associated with storm-time rather than non-storm substorms. A possible explanation for the different signatures of storm-time and non-storm substorms may lie in the more prolonged intervals of southward IMF, and thus longer-lasting dayside reconnection, during magnetic storm intervals. The long duration of the southward IMF and the associated rapid recurrence of several substorms can also explain the higher temperature of the storm-time plasma sheet. Both effects taken together, i.e., the stronger dipolarization and thus stronger earthward transport of more energetic particles during storm-time substorms, lead to a more effective injection of more energetic particles into the ring current and may, hence, explain the storm-time decrease of the Dst index.
Dst, nT
0 -200 27 28 29 30 August 1978 31
Figure 1. Interplanetary magnetic B, component and AE and Dst indices during a magnetic storm (on 28 August) and a subsequent interval of large-amplitude interplanetary Alfvknic fluctuations (after Ref. 1). However, the Earth's magnetotail behaves ...
Baumjohan_Storm-Substorm_ICS3