[P-EM10] Dynamics of Magnetosphere and Ionosphere

[PEM10-14] Simultaneous Occurrence of Substorm and Pseudosubstorm

*Yukinaga Miyashita^1,2, Madeeha Talha^1,2,3 (1.Korea Astronomy and Space Science Institute, 2.Korea National University of Science and Technology, 3.Pakistan Space and Upper Atmosphere Research Commission)

Keywords:substorm, pseudobreakup, pseudosubstorm, auroral onset arc, magnetotail, THEMIS

Our previous studies showed that the auroral onset arc associated with a substorm develops in three steps. After initial auroral brightening, the onset arc extends azimuthally while its weak wavelike structure gradually grows. The onset arc then enhances further and its wavelike structure also grows more rapidly. Finally, poleward expansion begins. On the other hand, the pseudobreakup (pseudosubstorm) is similar to the early stage of the substorm onset arc development but subsides without proceeding to poleward expansion. Pseudobreakups often occur separately before a substorm, but the separate occurrence does not necessarily seem to be the case. Here, using Time History of Events and Macroscale Interactions during Substorms (THEMIS) data, we show substorm events in which a substorm auroral onset arc and a pseudobreakup arc appeared and developed simultaneously. While a substorm onset arc is developing, an auroral arc very similar to a pseudobreakup also appears and develops for some substorm events. We interpret this arc as a pseudobreakup arc. The pseudobreakup arc appeared either just equatorward or just poleward of the substorm onset arc. Such events are not rare, that is, they occurred for 20% of our selected substorm events. We will discuss the magnetotail processes associated with simultaneous substorm and pseudobreakup events.