Cross-Energy Couplings from Magnetosonic Waves to Electromagnetic Ion Cyclotron Waves through Cold Ion Heating inside the Plasmasphere (original) (raw)
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Journal of Geophysical Research: Space Physics, 2013
1] A cold electron heating event associated with electromagnetic ion cyclotron (EMIC) waves is observed and modeled. The observational data of particles and waves are collected by the Thermal Emission Imaging System spacecraft at magnetic local time 17.0-17.2. During this event, intense He + band EMIC waves with the peak frequency 0.25 Hz are excited, corresponding to the observed phase space density (PSD) of distinct anisotropic ions. Meanwhile, substantial enhancements in energy flux of cold (1-10 eV) electrons are observed in the same period. The energy flux of electrons below 10 eV is increased by several to tens of times. We use a sum of kappa distribution components to fit the observed ion PSD and then calculate the wave growth rate driven by the anisotropic hot protons. The calculated result is in good agreement with the in situ observation. Then, we investigate whether the excited EMIC waves can transfer energy to cold electrons by Landau resonant absorption and yield electron heating. Using the typical Maxwellian distribution for cold electrons, we evaluate the wave damping rates resulted from the cold electrons in gyroresonance with EMIC waves. The simulating results show that the strong wave growth region in the He + band induced by anisotropic ions corresponds to the strong wave damping region driven by cold electrons. Moreover, cold electrons can be heated efficiently at large wave normal angles. The current results provide a direct observational evidence for EMIC-driven cold electron heating-a potential mechanism responsible for stable auroral red arc.
Nonlinear interaction of ion-cyclotron waves with fast protons in the magnetosphere
sta of1 lnv the magnetoýphe]e Se1 wit еп€ tiol ter ým of1 tha nat, mai the Tht ord finc whC flec rот .ра B(z and vaI 1. INTB,oDUCTIoN 1Ъе conseqrrenceý of t}e feaonant int€ ractlona Ьеhrееп waveв and parH,cleB in а plaвma confhed Ьу а magnetic fteld аrе регtiпепt to tЪе physicB of laboratory plaBmаs and plaBmaB in sрасе, as can Ье shоvrп Ьу Bimply cltiпg thе rQgеатсh оп instabilities in adiabatic confinement вуst€ mя,i the тевеаrсh оп cyclotTon heating (вее Ref. 2 Bnd the Цtвrаtчrе cited tbeTe), tlв elfoЁ to int€ rpret the паfirrаl and maJr-made vlf апd цlf гаdiаtiоп iп the magпеtоярhеrэ,8rа Bnd the рrоьlеm of int€ Ipr€ ting the fine ýtпrсtчrе of the вроrаФс воlдт radio еmlsвiоп.5 Tlmofeevz hаs studied in detail the попliпеаr tnteraction of сirсчlаrlу polarized waveB with сhаrgеd раrtlсlеs 1п cormectlon with the theoly of the сусlоtrоп heating of рlаsmав 1п magBetic conflnement sуst€ mý. Under cyclotron-heating condftions, the саsе of цовt intereBt 1в kпча << О (k rr iB the longttudinal wave пчmЬоr, апd v1, and Qс аr€ tb thеrmаl and cyclotron velocities of Фе раrticles of thе соrrевропФпg BlBcieB), and this is tЪе саsе dealt wtth 1п Ref. 2. In the рrФlеm of the interaction of cyclotron wачеs with fast раrfi,сlеs in Фе mцпеtоврhеrе, lt Ь песеssаry to trest the саве of large DoppleT BhlftB Вцч9 -Qg, пrhете vq is фе characteriýtic velocity of the faBt particles). Тhis сirсчmstапсе rафсаllу сhапgеg the пдfurе of the рrоЬlеm. Until rэсепtlу, this latter саве hаs been analyzed аввчmirц that the characterlstic tlmeB т of the рrосеsýеs чпdеr сопsldеrаff,оп (8ее the фsсчýslоп belщI for mоrе detatls) ýatbfy the сопфtiоп т << ,Q6{, whеr€ Qь is t}e сhаrасtеrlstiс bounce frequency of the partlcles between the magnetlc mirrоrs. Мчсh rроrk has Ьееп carried out чпdеr thls aBsumption (вее Ref. б and the litеrаtчrе cited there). For ýpical magnetospheric condltions, фе inequality , .. O5t соrrеsропds to rаthег large wave amplltudes (оr growth rаtеs).
Theory and observation of electromagnetic ion cyclotron triggered emissions in the magnetosphere
Journal of Geophysical Research, 2010
1] We develop a nonlinear wave growth theory of electromagnetic ion cyclotron (EMIC) triggered emissions observed in the inner magnetosphere. We first derive the basic wave equations from Maxwell's equations and the momentum equations for the electrons and ions. We then obtain equations that describe the nonlinear dynamics of resonant protons interacting with an EMIC wave. The frequency sweep rate of the wave plays an important role in forming the resonant current that controls the wave growth. Assuming an optimum condition for the maximum growth rate as an absolute instability at the magnetic equator and a self-sustaining growth condition for the wave propagating from the magnetic equator, we obtain a set of ordinary differential equations that describe the nonlinear evolution of a rising tone emission generated at the magnetic equator. Using the physical parameters inferred from the wave, particle, and magnetic field data measured by the Cluster spacecraft, we determine the dispersion relation for the EMIC waves. Integrating the differential equations numerically, we obtain a solution for the time variation of the amplitude and frequency of a rising tone emission at the equator. Assuming saturation of the wave amplitude, as is found in the observations, we find good agreement between the numerical solutions and the wave spectrum of the EMIC triggered emissions.
Journal of Geophysical Research: Space Physics, 2013
1] Understanding excitation of electromagnetic ion cyclotron (EMIC) waves remains a considerable scientific challenge in the magnetospheric physics. Here we adopt correlated data from the Thermal Emission Imaging System (THEMIS) spacecraft under low (K p = 1 + ) and medium (K p = 4) geomagnetic activities to investigate the favorable conditions for the excitation of EMIC waves. We utilize a sum of bi-Maxwellian components and kappa components to fit the observed ion (6-25 keV) distributions collected by the electrostatic analyzer (ESA) onboard the THEMIS spacecraft. We show that the kappa distribution models better and more smoothly with the observations. Then we evaluate the local growth rate and path-integrated gain of EMIC waves by bi-Maxwellian and kappa distributions, respectively. We demonstrate that the path-integrated wave gain simulated from the kappa distribution is consistent with observations, with intensities 24 dB in H + band and 33 dB in He + band. However, bi-Maxwellian distribution tends to overestimate the wave growth rate and path-integrated gain, with intensities 49 dB in H + band and 48 dB in He + band. Moreover, compared to the He + band, a higher proton anisotropy is needed to excite the H + band waves. The current study presents a further observational support for the understanding of EMIC wave instability under different geomagnetic conditions and suggests that the kappa-type distributions representative of the power law spectra are probably ubiquitous in space plasmas.
Energization of ionospheric ions by electrostatic hydrogen cyclotron waves
Geophysical Research Letters, 1981
Interactions between ionospheric ions and a monochromatic electrostatic hydrogen cyclotron wave were studied numerically for conditions corresponding to the auroral plasma. Strong heating of the minority ions He+, He++, and 0+ were observed. The fraction of the initial ion population which underwent heating was found to strongly depend on the mass, charge, and initial temperature of the ion species.
Generation of proton aurora by magnetosonic waves
Scientific Reports, 2014
Earth's proton aurora occurs over a broad MLT region and is produced by the precipitation of low-energy (2-10 keV) plasmasheet protons. Proton precipitation can alter chemical compositions of the atmosphere, linking solar activity with global climate variability. Previous studies proposed that electromagnetic ion cyclotron waves can resonate with protons, producing proton scattering precipitation. A long-outstanding question still remains whether there is another mechanism responsible for the proton aurora. Here, by performing satellite data analysis and diffusion equation calculations, we show that fast magnetosonic waves can produce trapped proton scattering that yields proton aurora. This provides a new insight into the mechanism of proton aurora. Furthermore, a ray-tracing study demonstrates that magnetosonic wave propagates over a broad MLT region, consistent with the global distribution of proton aurora. E arth's proton aurora is formed when charged protons precipitate into the atmosphere loss cone, within a few degrees at the equator, and subsequently collide with the neutral atmosphere at low altitudes 1 . Proton aurora can provide important information for understanding magnetosphere-ionosphere interaction by supplementing the direct imaging of the magnetosphere 2 . Since charged protons are easily trapped inside the Earth's magnetic field due to a minimum magnetic field existing at the equator, such proton precipitation requires a scattering mechanism to break the first adiabatic invariant. In the basically collisionless and tenuous magnetosphere, interactions between protons and plasma waves can induce such non-adiabatic scattering. One important plasma wave, electromagnetic ion cyclotron (EMIC) wave can interact with protons and efficiently scatter protons into the atmosphere 3-6 . However, strong EMIC waves are present primarily along the plasma plume in the duskside 7-9 and on the dayside in the outer magnetosphere L . 6 10-12 . This appears to be difficult for EMIC wave alone to explain the broad MLT distribution of proton auroral emission from the morning sector to the dusk sector associated with the precipitating protons at lower L-shells. Hence, the fundamental and long-outstanding problem as to what mechanism is primarily responsible for proton auroral emission still remains unresolved. Another important wave, fast magnetosonic (MS) wave, also named equatorial noise 13 , can resonate with protons, potentially leading to rapid pitch angle scattering of protons. Furthermore, MS waves can propagate eastward (later MLT) or westward (earlier MLT) over a broad region of MLT 14-16 . However, it has not been possible so far to determine whether MS wave is indeed another generating mechanism of the proton aurora, because simultaneous observations concerning MS wave activity, proton pitch distribution and proton auroral emissions are challenging due to extremely difficult observational conditions. Fortunately, such simultaneous observations were serendipitously found in the unique events on September 16, 2003, to identify such mechanism.
Heating and cooling of protons by turbulence-driven ion cyclotron waves in the fast solar wind
Journal of Geophysical Research, 1999
The effects of parallel propagating nondispersive ion cyclotron waves on the solar wind plasma are investigated in an attempt to reproduce the observed proton temperature anisotropy, namely, Tpñ >> Tpl ] in the inner corona and Tpñ < Tpl I at 1 AU. Low-frequency Alfv•n waves are assumed to carry most of the energy needed to accelerate and heat the fast solar wind. The model calculations presented here assume that nonlinear cascade processes, at the Kolmogorov and Kraichnan dissipation rates, transport energy from low-frequency Alfv•n waves to the ion cyclotron resonant range. The energy is then picked up by the plasma through the resonant cyclotron interaction. While the resonant interaction determines how the heat is distributed between the parallel and perpendicular degrees of freedom, the level of turbulence determines the net dissipation. Ion cyclotron waves are found to produce a significant temperature anisotropy starting in the inner corona, and to limit the growth of the temperature anisotropy in interplanetary space. In addition, this mechanism heats or cools protons in the direction parallel to the magnetic field. While cooling in the parallel direction is dominant, heating in the parallel direction occurs when Tpñ >> Tpl |. The waves provide the mechanism for the extraction of energy from the parallel direction to feed into the perpendicular direction. In our models, both Kolmogorov and Kraichnan dissipation rates yield Tp_t_ >> Tpl I in the corona, in agreement with inferences from recent ultraviolet coronal measurements, and predict temperatures at 1 AU which match in situ observations. The models also reproduce the inferred rapid acceleration of the fast solar wind in the inner corona and flow speeds and particle fluxes measured at 1 AU. Since this mechanism does not provide direct energy to the electrons, and the electron-proton coupling is not sufficient to heat the electrons to temperatures at or above 10 ½ K, this model yields electron temperatures which are much cooler than those currently inferred from observations. 1. Introduction Recent measurements of the inner corona by the Ultraviolet Coronagraph Spectrometer (UVCS) [Kohlet al., 1995] on board SOHO have provided the first evidence for the existence of a temperature anisotropy of protons and heavy ions in polar coronal holes within 5 Rs of the solar surface. Measurements of the resonantly scattered Lyman c• spectral line, from which Copyright 1999 by the American Geophysical Union. Paper number 1998JA900126. 0148-0227/99/1998J A900126509.00 information on the protons is derived [see Allen et al., 1998], and of spectral lines from other heavy ions, such as 0 +5 , have shown that the spread of their velocity distribution in the direction perpendicular to the magnetic field, or effective temperature, Tñ, is much larger than that in the parallel direction, or Tll [Kohlet al., 1998; Liet al., 1998]. For protons, the inferred ratio Tpñ/Tpt I reaches a maximum of about 4 below 5 Rs. Earlier in situ Helios observations of the fast solar wind in the ecliptic plane yielded an average ratio of 1.7 at 0.3 AU, decreasing to 0.8 at I AU [Marsch et al., 1982a]. Clearly, the development of a temperature anisotropy in the inner corona and its persistence into interplan-2521 2522 LI ET AL.' HEATING AND COOLING OF PROTONS IN THE FAST SOLAR WIND etary space have important implications for the mechanisms responsible for coronal heating and solar wind acceleration. Attempts to include the proton temperature anisotropy in solar wind models were made earlier by Leer and Axford [1972] and more recently by Sandbeek and Leer [1994] and Hu et al. [1997]. In these studies an ad hoc heating function was used. While the Leer and Axford [1972] and $andbeek and Leer [1994] studies reproduced conditions typical of the slow solar wind, the work by Hu et al. [1997] tried to match the characteristics of the fast solar wind. One of the original results of the Hu et al. [1997] study was the finding that the inclusion of a proton temperature anisotropy in the models requires that either the protons be highly anisotropic in the inner corona or that a mechanism, in addition to adiabatic expansion, must exist to cool protons in the direction parallel to the magnetic field. Hu et al. [1997] also noted that the heating due to Alfv•n wave dissipation was not sufficient to account for the observed proton temperature at I AU. Numerical simulations of magnetized plasmas showed that ion cyclotron waves not only heat ions in the direction perpendicular to the magnetic field but, interestingly enough, also cool them in the parallel direction when the wave frequency is lower than the ion cyclotron frequency [Busnardo-Neto et al., 1976]. Arunasalam [1976] proved that indeed this phenomenon could be accounted for by the quasi-linear theory of ion-cyclotronresonant interaction in the resonant limit. The process basically involves the transfer of energy from the parallel to the perpendicular motions when the energy in the waves is below the energy available at the ion cyclotron resonance frequency. Since low-frequency Alfv•n waves axe commonly observed in the solar wind [Smith et al., 1995; Belcher and Davis, 1971] and are the low-frequency manifestation of ion cyclotron waves, they provide an attractive mechanism for the development of the temperature anistropy. Power spectra of magnetic field fluctuations in the solar wind, most likely of Alfv•nic nature, are typically of the form PB c• k-v, where k is the wavenumber and • the spectral index. Since observa
Journal of Geophysical Research, 2007
1] The further development of a self-consistent theoretical model of interacting ring current ions and electromagnetic ion cyclotron waves is presented. In order to adequately take into account wave propagation and refraction in a multi-ion magnetosphere, we explicitly include the ray tracing equations in our previous self-consistent model and use the general form of the wave kinetic equation. This is a major new feature of the present model and, to the best of our knowledge, the ray tracing equations for the first time are explicitly employed on a global magnetospheric scale in order to self-consistently simulate the spatial, temporal, and spectral evolution of the ring current and of electromagnetic ion cyclotron waves. To demonstrate the effects of EMIC wave propagation and refraction on the wave energy distribution and evolution, we simulate the May 1998 storm. The main findings of our simulation can be summarized as follows. First, owing to the density gradient at the plasmapause, the net wave refraction is suppressed, and He + -mode grows preferably at the plasmapause. This result is in total agreement with previous ray tracing studies and is very clearly found in presented B field spectrograms. Second, comparison of global wave distributions with the results from another ring current model reveals that this new model provides more intense and more highly plasmapause-organized wave distributions during the May 1998 storm period. Finally, it is found that He + -mode energy distributions are not Gaussian distributions and most important that wave energy can occupy not only the region of generation, i.e., the region of small wave normal angles, but all wave normal angles, including those to near 90°. The latter is extremely crucial for energy transfer to thermal plasmaspheric electrons by resonant Landau damping and subsequent downward heat transport and excitation of stable auroral red arcs.
Journal of Atmospheric and Solar-Terrestrial Physics, 2015
Behaviors of the integrated wave gain of electromagnetic ion cyclotron (EMIC) waves in the H + -He + plasma of the inner magnetosphere is investigated. The integrated wave gain is obtained by integration of a temporal local growth rate along a geomagnetic field line. The local growth rate is determined by the method of generalized on the case of a bi-ion plasma. The concentration of the cold plasma is obtained on a basis of an empirical model of the plasmasphere and trough by . The energetic proton flux in the equatorial inner magnetosphere is set by the empirical model of , which refers to the conditions of low geomagnetic activity. The coefficients of EMIC wave reflection from the conjugated ionosphere are calculated using the International Reference Ionosphere (IRI) model. It is shown that the integrated wave gain of the EMIC waves increases with L -shell increasing and peaks around 14-20 MLT. In the afternoon sector the integrated wave gain reaches maximum in the cold plasma of higher density. Here the EMIC waves with the frequency below the equatorial He + gyrofrequency will be generated. The main findings of our study are in agreement with the basic experimental results on the EMIC wave occurrence in the equatorial middle magnetosphere known from satellite observations.
Simulation of electromagnetic ion cyclotron triggered emissions in the Earth's inner magnetosphere
Journal of Geophysical Research, 2011
1] In a recent observation by the Cluster spacecraft, emissions triggered by electromagnetic ion cyclotron (EMIC) waves were discovered in the inner magnetosphere. We perform hybrid simulations to reproduce the EMIC triggered emissions. We develop a self-consistent one-dimensional hybrid code with a cylindrical geometry of the background magnetic field. We assume a parabolic magnetic field to model the dipole magnetic field in the equatorial region of the inner magnetosphere. Triggering EMIC waves are driven by a left-handed polarized external current assumed at the magnetic equator in the simulation model. Cold proton, helium, and oxygen ions, which form branches of the dispersion relation of the EMIC waves, are uniformly distributed in the simulation space. Energetic protons with a loss cone distribution function are also assumed as resonant particles. We reproduce rising tone emissions in the simulation space, finding a good agreement with the nonlinear wave growth theory. In the energetic proton velocity distribution we find formation of a proton hole, which is assumed in the nonlinear wave growth theory. A substantial amount of the energetic protons are scattered into the loss cone, while some of the resonant protons are accelerated to higher pitch angles, forming a pancake velocity distribution.