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  • Duan, S. P., Wang, C., Liu, W. W. and He, Z. H. (2021). Characteristics of magnetic dipolarizations in the vicinity of the substorm onset region observed by THEMIS. Earth Planet. Phys., 5(3), 239–250. DOI: 10.26464/epp2021031
    Citation: Duan, S. P., Wang, C., Liu, W. W. and He, Z. H. (2021). Characteristics of magnetic dipolarizations in the vicinity of the substorm onset region observed by THEMIS. Earth Planet. Phys., 5(3), 239–250. DOI: 10.26464/epp2021031
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Characteristics of magnetic dipolarizations in the vicinity of the substorm onset region observed by THEMIS

  • With conjunction observations of electromagnetic fields and plasma from Time History of Events and Macroscale Interactions during Substorm (THEMIS) in the near-Earth magnetotail, we investigate the spatial and temporal properties of substorm dipolarizations in the near-Earth plasma sheet (NEPS) during a substorm at 03:23 UT on 12 February 2008. Substorm dipolarizations with different features are detected by three near-Earth THEMIS probes (THA (P5), THD (P3) and THE (P4)) in the magnetotail. In the current sheet with a large plasma beta value (β > 2, where β is the ratio of the plasma thermal pressure to the magnetic pressure), the dipolarization within the substorm onset region, (−10.4, 2.8, −2.6)RE_gsm, has a large initial magnetic field elevation angle, θ > 60°, θ = arctan (Bz/(Bx2+By2)1/2), and is accompanied by energetic ion (tens to hundred keV) dispersionless injection detected by THD (P3). This substorm onset dipolarization is characterized by Bx and By components around 0 nT with significant fluctuations. The Bz component increases sharply and its subsequent magnitude approaches the total magnetic field, Bt. The maximum value of the elevation angle approaches 85° during the later substorm expansion phase. In the NEPS with β ~ 1, the dipolarization outside the substorm onset region is characterized by a magnetic elevation angle with a small beginning value of θ < 45° and following multi-step enhancements during the substorm expansion phase. The maximum value of the elevation angle approaches to 70° during the later substorm expansion phase. Our observation results indicate that characteristics of dipolarization with a large beginning elevation angle within the substorm onset region provide a new indicator to identify substorm onset location.
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