A quantitative model for cyclotron wave-particle interactions at the plasmapause (original) (raw)
Related papers
Journal of Atmospheric and Solar-terrestrial Physics, 2001
It has generally been assumed in the past that the plasmapause is a preferred region for the generation and propagation of electromagnetic ion cyclotron (EMIC) waves in the Earth's magnetosphere. One assumption invoked the overlap of the expanding cold plasmapause with the inner edge of the hot ring current during storm recovery to provide favourable conditions for EMIC instability. The plasmapause was also expected to provide a convenient gradient for guiding the waves from equatorial sources to higher latitudes. The paper commences from a historic perspective and reviews the development of the ideas from the 1960s that relate the source of EMIC waves to the plasmapause. CRRES spacecraft observations of EMIC wave events over L = 3:5-8 and associated plasmapause locations indicate that the plasmapause is a region of wave generation and propagation, with signiÿcant wave power seen in the plasmatrough, but is not necessarily the preferred region. Other results show that wave occurrence predominates in the afternoon and increases with radial distance and a He + slot is seen in the data. These agree with earlier AMPTE-CCE results from Anderson et al. (J. Geophys. Res. 97 (1992) 3075, 3089). New results from CRRES show all wave polarisations (left-hand, linear, and right-hand) are seen within 8 • of the equator whereas linear predominates over 20-30 • latitude. Waves are observed in background plasma densities of 4-300 cm −3 . Wave frequencies above the He + cyclotron frequency are concentrated outside the plasmapause in lower density regions of 2-30 cm −3 .
Journal of Geophysical Research, 2007
1] It is shown that intense ion cyclotron turbulence can be induced in the near-Earth space by shaped release of neutral gas of materials such as lithium, cesium, etc. Release of 1 ton of neutral lithium gas in the Earth's equatorial plane at L = 2 can introduce about 30 GJ of energy which can be used to excite waves around the lithium ion cyclotron harmonics that readily evolves into the turbulent state. The energy is obtained by converting the orbital kinetic energy of the neutral lithium atoms into free energy for the electromagnetic waves through photoionization and creation of a ring distribution in the lithium ion velocity perpendicular to the ambient magnetic field. This distribution function is highly unstable and can spontaneously trigger large amplitude shear Alfven waves near lithium cyclotron harmonics with unique nonlinear properties. These waves lead to pitch angle scattering of the trapped electrons in a broad energy band.
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, 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.
A case study of electron precipitation fluxes due to plasmaspheric hiss
Journal of Geophysical Research: Space Physics, 2015
We find that during a large geomagnetic storm in October 2011 the trapped fluxes of >30, >100, and >300 keV outer radiation belt electrons were enhanced at L = 3-4 during the storm main phase. A gradual decay of the trapped fluxes was observed over the following 5-7 days, even though no significant precipitation fluxes could be observed in the Polar Orbiting Environmental Satellite (POES) electron precipitation detectors. We use the Antarctic-Arctic Radiation-belt (Dynamic) Deposition-VLF Atmospheric Research Konsortium receiver network to investigate the characteristics of the electron precipitation throughout the storm period. Weak electron precipitation was observed on the dayside for 5-7 days, consistent with being driven by plasmaspheric hiss. Using a previously published plasmaspheric hiss-induced electron energy e-folding spectrum of E 0 = 365 keV, the observed radio wave perturbation levels at L = 3-4 were found to be caused by >30 keV electron precipitation with flux~100 el cm À2 s À1 sr À1. The low levels of precipitation explain the lack of response of the POES telescopes to the flux, because of the effect of the POES lower sensitivity limit and ability to measure weak diffusion-driven precipitation. The detection of dayside, inner plasmasphere electron precipitation during the recovery phase of the storm is consistent with plasmaspheric hiss wave-particle interactions and shows that the waves can be a significant influence on the evolution of the outer radiation belt trapped flux that resides inside the plasmapause. The influence of plasmaspheric hiss on electron precipitation in the L = 3-4 region has been assessed using pitch angle diffusion codes with wave power distributions based on satellite observations [see Meredith et al., HARDMAN ET AL.
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.
2002
We analyze the 2000-2001 years' data on relativistic electrons from our instruments installed on EXPRESS-A (geosynchronous orbit; Ee=0.8-6 MeV) and MOLNIYA-3 (apogee=40000 km, perigee=500 km, i=65 degrees; Ee=0.8-5.5 MeV) along with other correlated measurements: GOES series (Ee>2 MeV), geomagnetic indices (Dst, AE) and interplanetary parameters (solar wind, IMF). The goal is to investigate the first time found cases of the increased relativistic electron fluxes at the inner L shells observed in a storm while at the geosynchronous distances the- flux remains lower than its pre-storm level. Typically these cases occur after an abrupt reorientation of Bz from south to north at the very beginning of a storm recovery phase, during the periods of northward Bz and correspondingly low substorm activity. In the discussed periods, low intensity of relativistic electrons at the geosynchronous orbit is seen even though a very high-speed solar wind is observed. The opposite examples of storms with the increased electron intensity at the geosynchronous distances occurred during a period of low-speed solar wind are shown. In these cases high-level substorm activity and Bz-fluctuations were observed on the recovery phase. The mechanisms responsible for the electron acceleration in the inner and outer L-shells are discussed. We also use the formula which binds a storm-time maximum Dst-amplitude with an L-coordinate of the peak of storm-injected relativistic electrons for the sake of possible predicting the ring- current plasma-pressure distribution and the westward electrojet position in a storm.