Some Things We Know about the Coherent Structure of the Solar Wind
Abstract
Two contrasting views of the coherent structure of the solar wind describe the structure as intermittent turbulence versus flux tubes (or some combination thereof). To gauge these two descriptions, some things that are known about the structure are discussed. (For convenience, the flux-tube view will be utilized.) (1) The strong current sheets (directional discontinuities) that comprise the flux-tube walls contain the majority of the Fourier power: the amplitudes of the magnetic-field jumps across the current sheets and the recurrence times of the field jumps determine the amplitude and shape of the Fourier "inertial range". (2) The frequency location of the Fourier breakpoint at the end of the inertial range is determined by the thicknesses of the strong current sheets: it may also be the case that the profile shapes of the current sheets determines the spectral index above the breakpoint. (3) In going from tube to tube one sees a sudden change in magnetic-field-aligned plasma flow within the tubes. (4) The plasma properties (density, specific entropy, beta) change suddenly from tube to tube. (5) The alpha-to-proton helium abundance changes suddenly from tube to tube. (6) The intensity of the electron heat flux differs from tube to tube. (7) The thicknesses of the plasma boundaries are consistent with Bohm or gyro-Bohm diffusion. (8) The plasma "chunk sizes" do not statistically evolve between 0.3 AU and 1 AU, showing no evidence of mixing of the solar-wind plasma by the action of turbulence. (9) The flux tubes are on average "round" but their cross sections are flattened in compression regions and stretched out in rarefaction regions. Some implications of these known things are drawn.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2019
- Bibcode:
- 2019AGUFMSH11B..06B
- Keywords:
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- 2134 Interplanetary magnetic fields;
- INTERPLANETARY PHYSICS;
- 2159 Plasma waves and turbulence;
- INTERPLANETARY PHYSICS;
- 2164 Solar wind plasma;
- INTERPLANETARY PHYSICS;
- 4415 Cascades;
- NONLINEAR GEOPHYSICS