4:45 PM - 5:00 PM
[PEM11-06] Revisiting the energy conversion process of Birkeland current generation
Keywords:Birkeland Current, Magnetosphere-Ionosphere Coupling, Energy Conversion
As shown by Vasyliunas [1970], the magnetospheric diamagnetic current has a finite divergece when it crosses the region with a finite B gradient and connects to the Field-Aligned Current (FAC). A pressure gradient force, the origin of the diamagnetic current in a force balance to the Ampere force, never twists plasma flow. While for the development of magnetic shear, which corresponds to FAC, combination of Ampere’s law , Faraday’s induction law and MHD Ohm’s law require the gradient of plasma vortex along B-field. In other words, for the existence of a quasi-steady FAC in the MHD scheme, the plasma vorticity along the B-field is inevitably required.
Of course, for the development of plasma vorticity, we need a dynamical process that twists the plasma. What is the dynamical process that twists the plasma as FACs are generated due to the divergence of the diamagnetic current? A conventional answer to this question is a mode conversion between the compressional mode and the Alfven mode when the diamagnetic current is growing (in inductive process). However, in principle, the magnetosphere-ionosphere coupling system forms a dissipative structure in the open solar-terrestrial system. Therefore, even in a macroscopic quasi-steady system, the constant conversion from the thermal energy to the magnetic energy and the internal mode conversion from magnetic compression to the magnetic shear should continuously take place. In this sense, we need to revisit the dynamical process of FAC. In this presentation, we will discuss what is the dynamical process and what is the quasi-steady state of FACs in a dissipative structure of the open magnetosphere-ionosphere system.
Of course, for the development of plasma vorticity, we need a dynamical process that twists the plasma. What is the dynamical process that twists the plasma as FACs are generated due to the divergence of the diamagnetic current? A conventional answer to this question is a mode conversion between the compressional mode and the Alfven mode when the diamagnetic current is growing (in inductive process). However, in principle, the magnetosphere-ionosphere coupling system forms a dissipative structure in the open solar-terrestrial system. Therefore, even in a macroscopic quasi-steady system, the constant conversion from the thermal energy to the magnetic energy and the internal mode conversion from magnetic compression to the magnetic shear should continuously take place. In this sense, we need to revisit the dynamical process of FAC. In this presentation, we will discuss what is the dynamical process and what is the quasi-steady state of FACs in a dissipative structure of the open magnetosphere-ionosphere system.