Evolution and dissipation of imbedded rotational discontinuities and Alfvén waves in nonuniform plasma and the resultant proton heating
Abstract
We show that nonuniform Alfvén speed gradients across field lines generally arise from the evolution of Alfvén waves. The evolution of a group of nonlinear Alfvén waves with the same sign of parallel wavenumber generate small-amplitude pressure-balanced structures (PBSs) which cause the speed variations. This always causes refraction. In most cases, the Alfvén waves also couple to magnetosonic waves and acquire a weak compressional component and can undergo resonant absorption or transfer, wherein wave energy can propagate across field lines. At large amplitudes the waves also generate imbedded rotational discontinuities (RDs). Some of these RDs can be dissipated owing to resonant transfer. This process could partly contribute to the observed decrease of solar wind RDs with increasing distance from the Sun. Resonant transfer also triggers a cascade due to steepening, which leads to sustained proton heating. The cascade produces oblique and large wavenumber waves which travel in different directions and have associated compressions. Protons interact with these by pitch angle scattering. They gain energy from second-order Fermi acceleration and from Landau and transit time damping. Oblique waves are inferred to be present in the dissipation range of Alfvénic fluctuations at 1 AU. We argue that the process of proton heating should proceed similarly to simulation results. We also propose a role for the wave imbedded RD in coronal heating through its formation in the chromosphere and its likely dissolution in the corona where wave amplitudes are very small.
- Publication:
-
Journal of Geophysical Research
- Pub Date:
- April 2001
- DOI:
- 10.1029/2000JA000268
- Bibcode:
- 2001JGR...106.5661V
- Keywords:
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- Interplanetary Physics: Discontinuities;
- Interplanetary Physics: MHD waves and turbulence;
- Space Plasma Physics: Discontinuities;
- Space Plasma Physics: Wave/particle interactions