UCLA

Plasmoids have been observed over a broad distance along Earth's magnetotail, from X= -30 RE to -200 RE (X points positively sunward along the sun-Earth line). As described in the near-Earth-neutral-line (NENL) substorm model, reconnection at the NENL causes a plasmoid to be formed and ejected tailward. Because distant-tail (X<-100 RE) plasmoids are correlated one-to-one with large, isolated substorms, they are reliable remote signatures of substorms. Such a correlation, however, does not exist between mid-tail (-100 RE < X <-30 RE) plasmoids and substorms. Also, as indicated in recent studies, magnetic reconnection may be quite localized rather than extending across the entire magnetotail in the dawn-dusk direction. Hence, plasmoid formation and evolution are not well explained by the two-dimensional NENL substorm model. In this dissertation, I will reconcile these seemingly inconsistent observations and describe the formation and expulsion of plasmoids from a three-dimensional perspective using multi-point observations of mid-tail plasmoids and other reconnection-generated structures (dipolarization fronts and anti-dipolarization fronts).

To understand the formation and expulsion of plasmoids in three dimensions, I investigate the following unresolved questions: What are the three-dimensional configurations of plasmoids in the near-Earth region, the mid-tail, and the distant-tail? Is local lobe reconnection required for plasmoid ejection? How does a plasmoid that originates near Earth evolve while propagating tailward? My results reveal that a mid-tail plasmoid is typically localized and its azimuthal extent increases with increasing substorm intensity. Local lobe reconnection is not always necessary for plasmoid ejection, and thus a plasmoid can grow due to continuous reconnections on closed field lines. Reconnection produced not only plasmoids, but also anti-dipolarization front (ADF), which shares similar observed properties with plasmoids but represents an interface between the reconnected hot outflow and the ambient plasma sheet plasma. In this dissertation, I present a case study suggesting that an ADF could evolve into a plasmoid.