МГД ВИХРИ В КОРОНЕ СОЛНЦА

Centre for Fusion, Space & Astrophysics

МГД ВИХРИ В КОРОНЕ СОЛНЦА

Седьмая Ежегодная Конференция «Физика плазмы в солнечной системе» 6 - 10 февраля 2012 г., ИКИ РАН )



Development of KH waves on the upper ejecta flank region. Snapshots are taken every 12 s.

The (projected) propagation velocity of the “perturbations” is about half the ejecta front speed, Vejecta.



Kelvin-Helmholtz instability:


• Typical size: 10 Mm, developed in about 30 s.• The increment is 0.05-0.03 s−1.• Miura (1984): the increment is 0.1VejectaΔL.• Sound speed: 504 km s−1 at 11 MK.• Alfven speed < 918 km s−1 – quite possible.• As the fastest growing KH modes is known to

occur at wavelength approximately 6–12 ΔL, we deduce that ΔL≈ 2-3 Mm



Analogy: CME and magnetosphere



Standing kink modes:


Vortex shedding is an unsteady flow that takes place in special flow velocities (according to the size and shape of the cylindrical body). In this flow, vortices are created at the back of the body and detach periodically from either side of the body.





MHD numerical simulations





In low-beta MHD, the Strouhal number is about 0.2 for a very broad range of parameters



Conclusions:•Generation of Alfvenic vortices by KHI is observed in the solar corona for the first time with SDO/AIA.

•Alfvenic vortices are essentially compressible: contain spiral-armed perturbations of the magnetic field strength and plasma mass density up to 50–60% of the background values.

•For a broad range of parameters of low-beta plasmas, the Strouhal number is 0.15–0.25.

•The findings have important implications for the kinematics of CME (aerodynamic drag force) and transport coefficients (macroscopic turbulence).

МГД ВИХРИ В КОРОНЕ СОЛНЦА

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