Electromagnetic waves near the proton cyclotron frequency: Stereo observations
- Department of Astronomy, University of Maryland, College Park, MD 20742 (United States)
- Institute of Geophysics and Planetary Physics, University of California, Los Angeles, CA 90095 (United States)
- Space Science Laboratory, University of California, Berkeley, CA 94720 (United States)
- Max-Planck-Institut für Extraterrestrische Physik, D-85741 Garching (Germany)
- Solana Scientific Inc., Solana Beach, CA 92075 (United States)
- Institute for the Study of Earth, Oceans, and Space, University of New Hampshire, Durham, NH 03824 (United States)
- Heliophysics Science Division, NASA Goddard Space Flight Center, MD 20771 (United States)
Transverse, near-circularly polarized, parallel-propagating electromagnetic waves around the proton cyclotron frequency were found sporadically in the solar wind throughout the inner heliosphere. They could play an important role in heating and accelerating the solar wind. These low-frequency waves (LFWs) are intermittent but often occur in prolonged bursts lasting over 10 minutes, named 'LFW storms'. Through a comprehensive survey of them from Solar Terrestrial Relations Observatory A using dynamic spectral wave analysis, we have identified 241 LFW storms in 2008, present 0.9% of the time. They are left-hand (LH) or right-hand (RH) polarized in the spacecraft frame with similar characteristics, probably due to Doppler shift of the same type of waves or waves of intrinsically different polarities. In rare cases, the opposite polarities are observed closely in time or even simultaneously. Having ruled out interplanetary coronal mass ejections, shocks, energetic particles, comets, planets, and interstellar ions as LFW sources, we discuss the remaining generation scenarios: LH ion cyclotron instability driven by greater perpendicular temperature than parallel temperature or by ring-beam distribution, and RH ion fire hose instability driven by inverse temperature anisotropy or by cool ion beams. The investigation of solar wind conditions is compromised by the bias of the one-dimensional Maxwellian fit used for plasma data calibration. However, the LFW storms are preferentially detected in rarefaction regions following fast winds and when the magnetic field is radial. This preference may be related to the ion cyclotron anisotropy instability in fast wind and the minimum in damping along the radial field.
- OSTI ID:
- 22356933
- Journal Information:
- Astrophysical Journal, Vol. 786, Issue 2; Other Information: Country of input: International Atomic Energy Agency (IAEA); ISSN 0004-637X
- Country of Publication:
- United States
- Language:
- English
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