Cooperatives Roles of Dynamics and Topology in Generating the Magnetosphere‐Ionosphere Disturbances: Case of the Theta Aurora. Issue 12 (5th December 2018)

• Record Type: Journal Article
• Authors: Tanaka, T.; Obara, T.; Watanabe, M.; Fujita, S.; Ebihara, Y.; Kataoka, R.; Den, M.
• Is Part Of: Journal of geophysical research. Volume 123:Issue 12(2018)
• Page Start: 9991
• Page End: 10, 008
• Publication Date: 2018-12-05
• Subjects: theta aurora -- separatrix -- null -- separator -- separator reconnection -- convection; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2018JA025514
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: To understand the magnetosphere‐ionosphere (M‐I) disturbances, it is necessary to know the change in the null‐separator structure along with the development of convection. The present paper explains this proposition by taking the case of the theta aurora that occurs after the switch of interplanetary magnetic field By and reveals auroral development inside the polar cap. The interplanetary magnetic field change is followed by the reformation of the null‐separator structure to cause a convection transient and a successive deformation of separatrices inside the magnetosphere, where separatrices separate the space into different volumes that include different types of magnetic field lines, and intersections of separatrices form separators that connect nulls. By the reconnection on the separator, energy inflow occurs from the solar wind to the magnetosphere. Convection driven by this energy transports nulls. In the case of theta aurora, two new nulls on the dayside coexist with two old nulls carried toward the tail by convection. Each set of nulls generates two open‐closed boundaries (separatrices) bounded by separators. Thus, open‐closed boundaries are divide into four parts. Separatrices generated by different sets partially become side by side near the nightside stem limes. The theta aurora is generated at the area corresponding to the low‐latitude side with respect to both of two boundaries. Thus, the occurrence of the theta aurora is a natural consequence of a transition in the null‐separator structure. The present example indicates that the global structure of the magnetosphere is almost decided from the skeleton of nulls. Key Points: The theta aurora is simply the ionospheric projection of the reformation process of the null‐separator structure after a switch of IMF By The theta aurora appears between two separatrices formed on both sides of the stem lines connecting nightside nulls and the ionosphere Magnetospheric disturbances are generated under the cooperation of dynamical and topological deformations of the system