On cyclotron wave heating and acceleration of solar wind ions in the outer corona

Abstract

Abstract. The preferential heating and acceleration of O +s ions, as observed by Ultraviolet Coronagraph Spectrometer (UVCS) on Solar and HeliosphericObservatory (SOHO) [Kohlet al., 1998] in the solar coronal holes have been interpreted and modeled by invoking wave-particle cyclotron resonance [Cranmer et al., 1999a[Cranmer et al., , 1999b. However, in the model of Cranmer et al. [1999a, 1999b] and in other subsequent models the assumption of a rigid slope of the wave spectrum was made in calculating the wave energy absoftion by the different ion species. In the present paper it is shown that a self-consistent treatment of the wave damping and absorption is necessary and leads to substantially different results. On the basis of quasi-linear theory, the interaction between the ions and the ion-cyclotron waves [Marsch et al., 1982a;Marsch, 1998] is studied. The total energy conservation equation, including the kinetic energy of the resonant particles and the wave energy, is derived and discussed in detail. The spectral evolution equation for cyclotron waves, when being controlled by the wave growth/damping rate and WKB effects, is solved self-consistently together with the full set of anisotropic multifluid equations for the ions including the cyclotron-resonance wave heating and acceleration rates. From the numerical results we reach the following conclusions: (1) It is physically questionable to use a spectrum with a fixed spectral slope near the cyclotron resonance when one calculates the partition of wave energy among the different ionic species and the kinetic degrees of freedom parallel and perpendicular to the magnetic field. This assumption neglects the important effects of wave absorption and the concurrent reshaping of the wave spectrum, and thus leads in the dissipation domain to extremely low amplitudes of the waves and to difficulties in supplying enough energy to balance the wave absorption at the cyclotron resonances. (2) If the spectrum is allowed to evolve self-consistently and concurrently with the particles' heating and acceleration through wave absorption, such a high perpendiculax temperature and corresponding large temperature anisotropy as observed by UVCS do not occur or cannot be maintained. We conclude that the UVCS oxygen ion observations have not yet been explained satisfactorily by the cyclotron-resonance theory.

Ion Heating by a Spectrum of Obliquely Propagating Low-Frequency Alfvén Waves

“…When the amplitude of the waves is sufficiently large, the velocity of the ion stochastic motions has a continuous spectrum of frequencies near the ion cyclotron frequency due to the nonlinear coupling between the ion gyromotion and the Alfvén waves, which leads to ion stochastic motions. Low-frequency Alfvén waves are thought to be pervasive in the solar corona (Belcher et al 1969;Tu & Marsch 2001). The energy of these low-frequency Alfvén waves can be transferred to that of higher frequencies by the perpendicular cascade in incompressible MHD turbulence (see, e.g., Cranmer & van Ballegooijen 2003 and references therein), or by three-wave interactions in compressible MHD turbulence with the existence of fast magnetosonic waves (Chandran 2005).…”

“…Numerous theoretical and experimental papers have been published to investigate resonant heating of ions by Alfvén waves (Isenberg & Hollweg 1983;Cranmer et al 1999;Li et al 1999;Tu & Marsch 2001;Lu et al 2006aLu et al , 2006b). In these works, the cyclotron resonant condition (ω − k || v || = nΩ 0 , where n is an integer, ω and k are the frequencies and wavevectors of the Alfvén waves, respectively.…”

Upward propagating high-frequency Alfvén waves as identified from dynamic wave-like spicules observed by SOT onHinode

“…The models may basically be divided into two kinds. One kind of model assumes high-frequency Alfvén waves with the cyclotron damping mechanism (e.g., Axford et al 1999;Tu & Marsch 2001;He et al 2008). The other kind of model assumes lowfrequency Alfvén waves which are subject to a nonlinear damping mechanism (e.g., Matthaeus et al 1999;Hollweg 2000;Suzuki & Inutsuka 2005;Cranmer et al 2007).…”

Sensitive Test for Ion-Cyclotron Resonant Heating in the Solar Wind

“…Candidate theories that can produce both the observed temperature profiles and non-thermal ion signatures generally build on the dissipation of a given type of fluctuation or small-scale structure in the plasma [12][13][14][15][16]. In these models, different types of waves couple directly to a subset of ions or electrons in phase space resulting in preferential heating of certain species and the observed nonthermal ion properties.…”