Physics
Scientific paper
Dec 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufmsm52a..08p&link_type=abstract
American Geophysical Union, Fall Meeting 2009, abstract #SM52A-08
Physics
[2700] Magnetospheric Physics
Scientific paper
Magnetospheric substorms have long been the focus of magnetospheric physics. The main unsolved issue is the triggering process of the substorm expansion onset. Despite many studies in the last three decades, the chronological relationship between magnetotail reconnection, auroral break-up and near-Earth dipolarization remains a controversial question. The coordinated Cluster-Double Star measurements and the THEMIS mission were deigned to resolve the controversy with observations of the substorm onset time history by employing multiple satellites and ground-based all-sky aurora imagers and magnetometers. This talk provides a summary of recent case studies of THEMIS and Cluster-Double Star data analyses. The main results are summarized as follows: (1) In some substorm events mid-tail reconnection or its associated earthward flow are measured a few/a couple of minutes ahead of the auroral breakup and near-Earth dipolarization (‘outside-in’). After the expansion phase onset, dipolarization progresses tailward (‘inside-out’). It is likely that ‘outside-in’ and ‘inside-out’ successively proceed during a typical substorm and are responsible for initiation and evolution of substorm expansion phase, respectively. (2) Reconnection initiates substorm onset through two steps: the initial onset of pseudobreakups and the major onset of the expansion phase. The initial onset is related to plasma sheet reconnection of closed field lines, while the major onset is followed by tail lobe reconnection of open field lines. Tail lobe reconnection supports most energy released in substorms; without it the activities remain as pseudobreakups or small substorms. (3) In some substorms there is evidence that ‘inside-out’ seems to be related to tailward retreat of reconnection. (4) Substorm intensity is determined eventually by the energy/magnetic flux stored the tail lobe and released in through tail lobe reconnection.
Cao Xinwu
Chu Xiaoyong
Fu Siqi
Mishin V. V.
Pu Zhang
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