Wave heating and acceleration of solar wind ions by cyclotron resonance

Abstract. Alfvén waves and ion-cyclotron absorption of high-frequency waves are frequently brought into models devoted to coronal heating and fast solar-wind acceleration. Signatures of ion-cyclotron resonance have already been observed in situ in the solar wind and in the upper corona. In the lower corona, one can use the line profiles to infer the ion temperatures. But the value of the so-called "non-thermal" (or "unresolved") velocity, potentially related to the amplitude of Alfvén waves propagating in the corona, is critical in firmly identifying ion-cyclotron preferential heating. In a previous paper, we proposed a method to constrain both the Alfvén wave amplitude and the preferential heating, above a polar coronal hole observed with the SUMER/SOHO spectrometer. Taking into account the effect of instrumental stray light before analysing the line profiles, we ruled out any direct evidence of damping of the Alfvén waves and showed that ions with the lowest charge-to-mass ratios were preferentially heated. We re-analyse these data here to correct the derived non-thermal velocity, and we discuss the consequences on the main results. We also include a measure of the Fe VIII 1442.56 Å line width (second order), thus extending the charge-to-mass ratio domain towards ions more likely to experience cyclotron resonance.

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Drivers of the solar wind: then and now

Philosophical Transactions of The Royal Society A Mathematical Physical and Engineering Sciences ◽

10.1098/rsta.2005.1713 ◽

2005 ◽

Vol 364 (1839) ◽

pp. 505-527 ◽

Cited By ~ 24

Author(s):

Joseph V Hollweg

Keyword(s):

Solar Wind ◽

Pressure Gradient ◽

Cyclotron Resonance ◽

Coronal Holes ◽

Ion Cyclotron Resonance ◽

The Sun ◽

Principal Mechanism ◽

Fast Wind ◽

Ion Cyclotron ◽

Spacecraft Data

Early spacecraft data in the 1960s revealed solar wind properties, which could not be well explained by models in which the electron pressure gradient was the principal accelerating force. The Alfvén waves discovered around 1970 were thought for a while to provide additional energy and momentum, but they ultimately failed to explain the rapid acceleration of the fast wind close to the Sun. By the late 1970s, various data were suggesting the importance of the ion-cyclotron resonance far from the Sun. This notion was soon applied to the acceleration region close to the Sun. The models, which resulted, suggested that the fast wind could be driven mainly by the proton pressure gradient. Since the mid-1990s, Solar and Heliospheric Observatory has provided remarkable data, which have verified some of the predictions of these theories, and given impetus to studies of the ion-cyclotron resonance as the principal mechanism for heating the coronal holes, and ultimately driving the fast wind. After a historical review, we discuss the basic ideas behind current research, emphasizing the particle kinetics. We discuss remaining problems, especially the source of the ion-cyclotron resonant waves.

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Wave–particle resonance condition test for ion-kinetic waves in the solar wind

Annales Geophysicae ◽

10.5194/angeo-34-393-2016 ◽

2016 ◽

Vol 34 (4) ◽

pp. 393-398 ◽

Cited By ~ 2

Author(s):

Y. Narita ◽

E. Marsch ◽

C. Perschke ◽

K.-H. Glassmeier ◽

U. Motschmann ◽

...

Keyword(s):

Solar Wind ◽

Cyclotron Resonance ◽

Electron Cyclotron Resonance ◽

Resonance Condition ◽

Electron Cyclotron ◽

Astronomical Unit ◽

Field Fluctuations ◽

Particle Resonance ◽

The Magnetic Field ◽

Thermal Speed

Abstract. Conditions for the Landau and cyclotron resonances are tested for 543 waves (identified as local peaks in the energy spectra) in the magnetic field fluctuations of the solar wind measured by the Cluster spacecraft on a tetrahedral scale of 100 km. The resonance parameters are evaluated using the frequencies in the plasma rest frame, the parallel components of the wavevectors, the ion cyclotron frequency, and the ion thermal speed. The observed waves show a character of the sideband waves associated with the ion Bernstein mode, and are in a weak agreement with the fundamental electron cyclotron resonance in spite of the ion-kinetic scales. The electron cyclotron resonance is likely taking place in solar wind turbulence near 1 AU (astronomical unit).

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