JpGU-AGU Joint Meeting 2020

Presentation information

[E] Oral

P (Space and Planetary Sciences ) » P-EM Solar-Terrestrial Sciences, Space Electromagnetism & Space Environment

[P-EM13] Dynamics of Magnetosphere and Ionosphere

convener:Aoi Nakamizo(Applied Electromagnetic Research Institute, National Institute of Information and Communications Technology), Mitsunori Ozaki(Faculty of Electrical and Computer Engineering, Institute of Science and Engineering, Kanazawa University), Akiko Fujimoto(Kyushu Institute of Technology), Yuka Sato(Nippon Institute of Technology)

[PEM13-28] Differences in Near-Earth Magnetotail Evolution Between Pseudosubstorms and Substorms

*Yukinaga Miyashita1, Kento Fukui2, Shinobu Machida2, Yoshizumi Miyoshi2, Akimasa Ieda2, Toshi Nishimura3, Vassilis Angelopoulos4 (1.Korea Astronomy and Space Science Institute, 2.Institute for Space-Earth Environmental Research, Nagoya University, 3.Boston University, 4.University of California, Los Angeles)

Keywords:substorm, pseudosubstorm, pseudobreakup, magnetotail, ballooning instability, THEMIS

Pseudosubstorms (pseudobreakups) are similar to substorms during the early stage of auroral development but differ in the later stage. That is, pseudosubstorms are not accompanied by poleward expansion, while substorms are. To understand what causes this difference, we statistically studied temporal and spatial development of the near-Earth magnetotail at X=-7 to -11 Re around pseudosubstorm and substorm onsets, based on THEMIS data. We find that near-Earth reconnection occurs before onset for both pseudosubstorms and substorms, but the earthward flow generated by reconnection is slower for pseudosubstorms than for substorms. Dipolarization, together with magnetic field fluctuations, occurs at X=-8 Re for both cases, but it is weaker at other distances for pseudosubstorms than for substorms. This result suggests that the current disruption related to dipolarization does not expand tailward and hence auroral poleward expansion does not occur for pseudosubstorms. Furthermore, the total pressure is larger at X=-8 to -11 Re for several minutes before onset for substorms than for pseudosubstorms. The total pressure gradient increases more largely after onset for substorms than for pseudosubstorms. We suggest that these differences are important factors for determining whether ballooning instability causing current disruption grows in a wide area, that is, whether the initial action develops into a substorm or subsides as a pseudosubstorm.