Formation of Alfvén Wave Ducts by Magnetotail Flow Bursts. Issue 9 (26th September 2022)

• Record Type: Journal Article
• Authors: Yang, Ziyi; Zhang, Binzheng; Lotko, William; Sorathia, Kareem A.; Pham, Kevin; Luan, Xiaoli; Dou, Xiankang; Lei, Jiuhou
• Is Part Of: Journal of geophysical research. Volume 127:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-26
• Subjects: Alfvén wave ducts -- magnetosphere -- Alfvénic Poynting flux; Magnetospheric physics -- Periodicals; Space environment -- Periodicals; Cosmic physics -- Periodicals; Planets -- Atmospheres -- Periodicals; Heliosphere (Astrophysics) -- Periodicals; Geophysics -- Periodicals; 523.01
• DOI: 10.1029/2022JA030841
• Languages: English
• ISSNs: 2169-9380

Abstract

Abstract: Geomagnetic activity in Earth's outer magnetosphere stimulates intense and sometimes explosive flows of electromagnetic power propagating earthward as Alfvén waves. Observations show that among its various magnetospheric sources, Alfvénic Poynting flux from the magnetotail reaches the ionosphere with the greatest intensity. Dayside fluxes are statistically weaker though more persistent. Flankside fluxes are weakest. We show using global magnetohydrodynamic simulations that these distributions can be attributed to the formation (or not) of meridionally narrow, relatively uniform, low Alfvén conductance channels that efficiently transmit Alfvénic power to the near‐Earth space. These Alfvén ducts form naturally at the heads of flow bursts in the magnetotail but not in flankside flux tubes, where the transmission of Alfvénic power is strongly attenuated by reflections at large conductance gradients along the propagation path. The results elucidate the underlying physics that control efficient transmission of electromagnetic power from the magnetotail to low altitude to power Alfvénic aurora. Plain Language Summary: Geomagnetic activities usually produce Alfvén waves in Earth's outer magnetosphere. In simplest form, an Alfvén wave behaves as a wave on a transmission line with magnetic field lines serving as the lines. Injections of Alfvénic power into Earth's ionosphere cause spectacular dynamic aurora. In this study, we present the discovery of a new phenomenon revealed in global geospace simulations—formation of Alfvén wave ducts. Their occurrence explains the efficient transmission of electromagnetic power from Earth's magnetotail to its ionosphere and atmosphere to produce dynamic aurora as observed in the past. More importantly, this study serves as a new foundation of powering terrestrial (and outer planetary) aurora with global magnetic field, from the view of large‐scale electromagnetic wave energy transmission. Key Points: We discovered a new phenomenon revealed in global geospace simulations—formation of Alfvén wave ducts The suggested Alfvén ducts promote low‐loss transmission of equatorial Alfvénic power to the near‐Earth space Alfvén ducts elegantly explain the different propagation efficiencies of Alfvénic power in the magnetosphere