H. Q. Feng

Low‐frequency electromagnetic cyclotron waves in and around magnetic clouds: STEREO observations during 2007–2013

Wave activities in the solar wind are an important topic and magnetic clouds (MCs) are a common phenomenon in interplanetary space, though waves activities associated with MCs have not been well documented. Based on a survey of 120 MCs observed by STEREO spacecraft during the years 2007–2013, this work studies electromagnetic cyclotron waves (ECWs) near the proton cyclotron frequency in and around MCs. For total 7807 ECW events, 24% of them occurred in the regions within MCs while 76% occurred in the regions around MCs. Statistics indicate that ECWs around MCs have higher frequencies, wider bandwidths, and stronger powers relative to the waves in MCs. More ECWs, on the other hand, tend to be related to a plasma with higher temperature, lower density, and larger velocity. In particular, it is found that there exist positive power law correlations between plasma betas and the wave frequencies, bandwidths, and powers. The results imply that the plasma beta should play an important role in determining the properties of ECWs, which is consistent with previous theory studies and the recent simulation results.

The critical intensity of Alfvén waves for electron-cyclotron maser to favor the O-mode emission

The presence of Alfven waves (AWs) has been found to significantly affect electron-cyclotron maser (ECM), which is a powerful emission mechanism in astrophysical plasmas. A conventional ECM driven by power-law electrons with a lower-energy cutoff generally prefers X-mode emission to O-mode. In particular, the ECM possibly favors O-mode because it is dependent on the relative intensity of the present AWs, ξ=Bw2/B02, where Bw and B0 are the field strength of AWs and the ambient magnetic field, respectively. This paper, for the first time, quantitatively investigates the critical relative intensity of AWs, above which the ECM becomes to favor the O-mode emission. It is found that the critical intensity depends on velocity distribution function features of energetic electrons, as well as on ambient plasma parameters. In principle, the critical intensity is in the order of ξ ∼ 10−2 for power-law electrons with a lower energy cutoff, when the fundamental wave in X-mode is suppressed. Moreover, the incorporation...

CYCLOTRON MASER EMISSION FROM POWER-LAW ELECTRONS WITH STRONG PITCH-ANGLE ANISOTROPY

Energetic electrons with power-law spectrum are most commonly observed in astrophysics. This paper investigates electron cyclotron maser emission (ECME) from the power-law electrons, in which strong pitch-angle anisotropy is emphasized. The electron distribution function proposed in this paper can describe various types of pitch-angle anisotropy. Results show that the emission properties of ECME, including radiation growth, propagation, and frequency properties, depend considerably on the types of electron pitch-angle anisotropy, and different wave modes show different dependences on the pitch angle of electrons. In particular, the maximum growth rate of X2 mode rapidly decreases with respect to the electron pitch-angle cosine

The effect of electron holes on cyclotron maser emission driven by horseshoe distributions

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The effect of electron beams on cyclotron maser emission excited by lower-energy cutoffs

at which the electron distribution peaks, while the growth rates for other modes (X1, O1, O2) initially increase before decreasing as

Nature of Turbulence, Dissipation, and Heating in Space Plasmas: from Alfvén Waves to Kinetic Alfvén Waves

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Time-dependent Occurrence Rate of Electromagnetic Cyclotron Waves in the Solar Wind: Evidence for the Effect of Alpha Particles?

increases. Moreover, the O mode as well as the X mode can be the fastest growth mode, in terms of not only the plasma parameter but also the type of electron pitch-angle distribution. This result presents a significant extension of the recent researches on ECME driven by the lower-energy cutoff of power-law electrons, in which the X mode is generally the fastest growth mode.

Statistical Study of Low-Frequency Electromagnetic Cyclotron Waves in the Solar Wind at 1 AU: LOW-FREQUENCY ECWS IN THE SOLAR WIND

This Brief Communication presents a quantitative investigation for the effect of electron holes on electron-cyclotron maser (ECM) driven by horseshoe distributions. The investigation is based on an integrated distribution function for the horseshoe distributions with electron holes. Results show that the presence of electron holes can significantly enhance the ECM growth rate by 2–3 times in a very narrow waveband. The present study suggests that these electron holes probably are responsible for some fine structures of radiations, such as narrowband events in auroral kilometric radiation and solar microwave spikes.

Observations on the Magnetic Disconnections of a Magnetic Cloud from the Sun through Magnetic Reconnection

Electron-cyclotron maser (ECM) is one of the most important emission mechanisms in astrophysics and can be excited efficiently by lower-energy cutoffs of power-law electrons. These non-thermal electrons probably propagate as a directed collimated beam along ambient magnetic fields. This paper investigates the ECM, in which the effect of electron beams is emphasized. Results show the dependence of emission properties of the ECM on the beam feature. The maximum growth rate of the extraordinary mode (X2) rapidly decreases as the beam momentum increases, while the growth rate of the ordinary mode (O1) changes slightly. In particular, the ordinary mode can overcome the extraordinary mode and becomes the fastest growth mode once the beam momentum is large enough. This research presents an extension of the conventional studies on ECM driven by lower-energy cutoffs and may be helpful to understand better the emission process of solar type I radio bursts, which are dominated by the ordinary mode emission.

Observations of a Small Interplanetary Magnetic Flux Rope Opening by Interchange Reconnection

The nature of turbulence, dissipation, and heating in plasma media has been an attractive and challenge problem in space physics as well as in basic plasma physics. A wide continuous spectrum of Alfvenic turbulence from large MHD-scale Alfven waves (AWs) in the inertial turbulence regime to small kinetic-scale kinetic AWs (KAWs) in the dissipation turbulence regime is a typical paradigm of plasma turbulence. The incorporation of current remote observations of AWs in the solar atmosphere, in situ satellite measurements of Alfvenic turbulence in the solar wind, and experimental investigations of KAWs on large plasma devices in laboratory provides a chance synthetically to study the physics nature of plasma turbulence, dissipation, and heating. A session entitled “Nature of Turbulence, Dissipation, and Heating in Space Plasmas: From Alfven Waves to Kinetic Alfven Waves” was held as a part of the twelfth Asia Oceania Geosciences Society Annual Meeting, which took place in Singapore between 2 and 7 August 2015. This special section is organized based on the session.