[P-EM15] Dynamics of Magnetosphere and Ionosphere

[PEM15-03] Dynamic Evolution of Bursty Bulk Flows (BBFs) Revealed by Two-way Coupled MHD-PIC Model and Multi-instrument Observations

*Shasha Zou¹、Xiantong Wang¹、Zihan Wang²、Weijie Sun³、Yuxi Chen¹、Gábor Tóth¹ (1.University of Michigan, Ann Arbor、2.University of Texas, Arlington、3.University of California, Berkeley)

キーワード：magnetotail, substorm, particle heating and acceleration, magnetosphere-ionosphere coupling

The dynamics of Bursty Bulk Flows (BBFs) is an outstanding magnetosphere-ionosphere coupling problem associated with sudden magnetic field topology reconfiguration and explosive current formation, particle acceleration, and energy release in the magnetosphere, and is believed to be playing a central role in geomagnetic disturbances, such as substorms. Using a two-way coupled magnetohydrodynamics with embedded kinetic physics model, we perform an event simulation to study electron velocity distribution functions (VDFs) evolution associated with BBFs observed by Magnetospheric Multiscale (MMS) satellite on May 16, 2017. Multiple ground and space-based instruments, such as Poker Flat Incoherent Scatter Radar and magnetometers, are used to reveal the MIT coupling features associated with this BBF event. The simulated BBF macroscopic characteristics and electron VDFs agree well with observations. The VDFs from the BBF tail to its dipolarization front (DF) during its earthward propagation are revealed and they show clear energization and heating. The electron pitch angle distributions (PADs) at the DF are also tracked, which show interesting energy dependent features. Lower energy electrons develop a "two-hump" PAD while the higher energy ones show persist "pancake" distribution. Our study reveals for the first time the evolution of electron VDFs as a BBF moves earthward using a two-way coupled global and kinetic model, and provides valuable contextual understanding for the interpretation of satellite observations.