Cooperative studies of ionospheric-driven theory and observation data analysis for the solution of auroral breakup

2014 Fiscal Year Final Research Report

• Project/Area Number: 25887050
• Research Category: Grant-in-Aid for Research Activity Start-up
• Allocation Type: Single-year Grants
• Research Field: Space and upper atmospheric physics
• Research Institution: National Institute of Polar Research
• Principal Investigator: HIRAKI Yasutaka 国立極地研究所, 研究教育系, 特任研究員 (80514843)
• Project Period (FY): 2013-08-30 – 2015-03-31
• Keywords: オーロラ / アルヴェン波 / オーロラ渦列 / 電離圏アルヴェン共鳴 / ハイブリッドアルヴェン共鳴 / 磁気圏-電離圏結合

Outline of Final Research Achievements

In this study, we developed a simulation code to correctly pursue the nonlinear evolution of shear Alfven waves that move throughout the magnetic flux tube in the auroral region. First, we performed a nonlinear simulation where an arc-like structure in the field-aligned current is initially provided. We demonstrated that, when the convection electric field exceeds a critical value (~25 mV/m), a convection-driven instability of shear Alfven wave occurs. We found that an initially placed arc splits, intensifies, and rapidly deforms into a vortex street. Secondly, we performed a nonlinear simulation considering ionospheric and magnetospheric cavities of Alfven velocity. Various nonlinear features were found: i) trapping of the ionospheric Alfven resonant modes facilitates deformation of field-aligned current structures, and ii) hybrid Aldven resonant modes grow to cause strong flow shear instability around the magnetic equator.

Free Research Field

プラズマ物理学