Generation of hiss beyond plasmapause by magnetosonic waves (original) (raw)
Related papers
Plasmaspheric hiss observations in the evening and afternoon quadrants
Journal of Geophysical Research, 1975
An instrument to detect the magnetic components of ELF signals propagating in the magnetosphere was carried on Explorer 45. Over 600 hours of observations in the inner magnetosphere near the equatorial plane have been examined. These observations were obtained in late 1971 and the first half of 1972 when the satellite apogee was in the evening and alternoon quadrants. The strongest rfiost persistent signals were plasmaspheric hiss from a few hundred to a few thousand hertz. Broad band signals of 25 m'y were common. Frequently, the hiss terminated abruptly during a satellite pass near and inside the boundary of the plasmasphere. Hiss boundaries were observed usually beyond L = 4 in quiet times, Kp = 0 to 1+, but were frequently beyond apogee near L = 5. During disturbed times, Kp > 4+, hiss boundaries remained near L = 5 from 1600 to 1900 LT but were below L = 4 from 2000 to 2400 LT. The magnetic index best correlated with the hiss boundary near midnight was Dst, the ring current index. The boundary location near midnight ranged from L = 2.5 for Dst =-160 • to L = 5.5 for Dst: 0. The peak intensity of hiss during an orbit occurred most frequently in the alternoon about I RE inside the hiss boundary. The most intense hiss was observed in the recovery phase of magnetic storms at the inner edge of the ring current. The source of the hiss appears to be the outer plasmasphere. Generation of hiss through cyclotron resonance with energetic electrons is the probable source for most of the hiss. Ring current protons, forming a peak in the proton flux between 10 and 100 keV, may be a source for some of the hiss.
Plasmaspheric Hiss: Coherent and Intense
Journal of Geophysical Research: Space Physics, 2018
Intense~300-Hz to 1.0-kHz plasmaspheric hiss was studied using Polar plasma wave data. It is found that the waves are coherent in all local time sectors with the wave coherency occurring in approximately three-to five-wave cycle packets. The plasmaspheric hiss in the dawn and local noon time sector are found to be substorm (AE*) and storm (SYM-H*) dependent. The local noon sector is also solar wind pressure dependent. It is suggested that coherent chorus monochromatic subelements enter the plasmasphere (as previously suggested by ray tracing models) to explain these plasmaspheric hiss features. The presence of intense, coherent plasmaspheric hiss in the local dusk and local midnight time sectors is surprising and more difficult to explain. For the dusk sector waves, either local in situ plasmaspheric wave generation or propagation from the dayside plasmasphere is possible. There is little evidence to support substorm generation of the midnight sector plasmaspheric hiss found in this study. One possible explanation is propagation from the local noon sector. The combination of high wave intensity and coherency at all local times strengthens the suggestion that the electron slot is formed during substorm intervals instead of during geomagnetic quiet (by incoherent waves). Plasmaspheric hiss is found to propagate at all angles relative to the ambient magnetic field, θ kB. Circular, elliptical, and linear polarized plasmaspheric hiss have been detected. No obvious, strong relationship between the wave polarization and θ kB was found. This information of hiss properties should be useful in modeling wave-particle interactions within the plasmasphere. Plain Language Summary Plasmaspheric hiss is found to be coherent (at all local times). The coherency occurs in packets of~3 to 5 cycles. For the dawn and noon local time sectors, a scenario of substorm and solar wind pressure generation of outer zone chorus with further propagation into the plasmasphere is supported by the data analysis results. The predominant wave polarization of hiss is found to be elliptical, with some minor presence of circular and linear polarizations. This is in general agreement with theoretical expectations.The presence of intense, coherent plasmaspheric hiss strongly supports the new hypothesis that the electron slot is formed during substorms rather than geomagnetic quiet periods. The loss of relativistic E~1MeV electrons for the inner magnetosphere (L > 6) may be due to wave-particle interactions with coherent plasmaspheric hiss.
Journal of Geophysical Research, 1994
Protons that are convected into the inner magnetosphere in response to enhanced magnetic activity can resonate with ducted plasmaspheric hiss •n the outer plas. masphe.re via .an anomalous Doppler-shifted_cyclotron resonance. Plasmaspheric hiss is a right-nana.-polarizea electromagnelac emission that is observed to fill the plasmasphere on a routine basis. When plasmasphbric hiss is confined within field-aligned ducts or ghided along densi.t3(gradients, wave normal angles remain largely below 45 ø. This allows resonant interaclaons wi•h •ons at typical ring current and radiationbelt energies to takeplace. Such field-aligned ducts have been Observed bofh within the plasmasphere (Kozyra et al., •987a; Koons, 1989) and in regions outside of the plasmasphere (Chan andHolzer, 1976). Wave intensities are estimated using statistical •nformafion from studies of detached plasma regions (Chan et al., 1974). D•ffusion coefficients are presented for a range of L shells and proton energies for a fixed wave distribution. Harmonic resonances in the range n = _+100 are considered in order to include interactions between hiss at 100 Hz to 2 kHz frequ_enc•es, and protons in the energy range between-10 keV and 1. _000 keV.. Diffusion timescales are estimated to be of the order oftens of days and comparable to or snorter than lifetimes for Coulomb decay and charge exchange losses over most of the energy and spatial ranges of interest. 1. Introduction Low-altitude satellite observations of locally mirroring and precipitating ions have documented a characteristic region of anisotropic proton precipitation on field lines that map to the outer plasmasphere [S•raas et al., 1977; Lundblad and S•raas, 1978]. The proton precipitation is anisotropic in the sense that the loss cone is not filled; therefore the diffusion of protons into the loss cone is slow relative to their bounce period. Interestingly enough, when coincident observations of ground-based 630-nm emission and proton precipitation are available, pronounced peaks in the locally mirroring, highenergy (>100 keV) protons, within this anisotropic precipitation zone, often occur on field lines that map to stable auroral red (SAR) arcs in the midlatitude ionosphere. These peaks in the locally mirroring protons are indicative of enhanced pitch angle scattering and are believed to reflect increased wave activity at high altitudes on SAR arc field lines. Lundblad and S•raas [1978] interpreted this correlation between enhanced proton pitch angle scattering and SAR arc emissions as support for the ion cyclotron wave damping theory of SAR arc formation [Cornwall et al., 1971]. According to this theory, the anisotropic ring current proton distribution, with perpendicular temperature greater than parallel temperature, is unstable to the production of electromagnetic ion cyclotron waves with frequencies below the ion gyrofrequency in the outer plasmasphere. The outer plasmasphere is a favored region for the wave growth because Copyright 1994 by the American Geophysic• Union. P•per number 93JA01532. 0148-0227/94/93JA 4)1532505.00 resonant proton energies are lowered, in this region of high thermal plasma density, to values of the order of ring current energies. Ring current protons, in resonance with ion cyclotron waves, may be scattered into the atmospheric loss cone and precipitated. The maximum amplification of these waves occurs near the equatorial plane (minimum B values) for ion cyclotron wave normal vectors aligned with the magnetic field direction. During the Course of propagation in a magnetic mirror geometry, the wave-normal angle of the ion cyclotron wave becomes oblique. At these oblique wave-normal angles, significant Landau damping to the thermal electrons can occur; effectively, transferring energy from the energetic ring current protons to the thermal electrons using the ion cyclotron waves as a mediary. Some proton precipitation is expected to occur on field lines associated with the ion cyclotron waves due to enhanced pitch angle scattering but is not involved in the production of the 630-nm emission associated with the ARarc.TheenergytransferredtothethermalelectronsintheouterplasmasphereisresponsiblefortheAR arc. The energy transferred to the thermal electrons in the outer plasmasphere is responsible for the ARarc.TheenergytransferredtothethermalelectronsintheouterplasmasphereisresponsiblefortheAR arc formation process. This energy is transported down field lines to the subauroral ionosphere. The increased heat input into the thermal electrons results in a region of elevated electron temperatures. Electrons in the high energy tail of the MaxwellJan distribution at F region heights excite oxygen atoms to the 1D state during collisions [Cole, 1965]. At high altitudes (z > 400 km), where collisions are rare, excited oxygen atoms radiatively relax with the emission of a photon at 630 nm, producing a stable auroral red ($AR) arc. Spectral purity is maintained because there are very few electrons with enough energy (E > 4.2 eV) to excite oxygen to the 1 $ state. The de-excitation of the iS state produces a photon at 557.7nm wavelength. The ratio of red to green line emissions in a typical $AR arc is >> 1 [cf. Rees and Robie, 1975].
Journal of Geophysical Research, 2006
1] We analyze wave and particle data from the CRRES satellite to determine the variability of plasmaspheric hiss (0.1 < f < 2 kHz) with respect to substorm activity as measured by AE*, defined as the maximum value of the AE index in the previous 3 hours. The study is relevant to modeling the acceleration and loss of relativistic electrons during storms and understanding the origin of the waves. The plasmaspheric hiss amplitudes depend on spatial location and susbtorm activity, with the largest waves being observed during high levels of substorm activity. Our survey of the global distribution of hiss indicates a strong day-night asymmetry with two distinct latitudinal zones of peak wave activity primarily on the dayside. Equatorial hiss (jl m j < 15°) is strongest during active conditions (AE* > 500 nT), with an average amplitude of 40 ± 1 pT observed in the region 2 < L < 4 from 0600 to 2100 MLT. Midlatitude (jl m j > 15°) hiss is strongest during active conditions with an average amplitude of 47 ± 2 pT in the region 2 < L < 4 from 0800 to 1800 MLT but extending out beyond L = 6 from 1200 to 1500 MLT. Equatorial hiss at 600 Hz has minimum cyclotron resonant energies ranging from 20keVatL=6to20 keV at L = 6 to 20keVatL=6to1 MeV at L = 2, whereas midlatitude hiss at 600 Hz has minimum resonant energies ranging from 50keVatL=6to50 keV at L = 6 to 50keVatL=6to2 MeV at L = 2. The enhanced equatorial and midlatitude hiss emissions are associated with electron flux enhancements in the energy range of tens to hundreds of keV, suggesting that these electrons are the most likely source of plasmaspheric hiss. The enhanced levels of plasmaspheric hiss during substorm activity will lead to increased pitch-angle scattering of energetic electrons and may play an important role in relativistic electron dynamics during storms.
1997
An attempt is made to con®rm the generation mechanism of plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite in the equatorial region both at small and large wave normal angles by calculating their magnetic ®eld intensities in terms of incoherent Cerenkov radiation mechanism and cyclotron resonance instability mechanism, using appropriate and suitable plasma parameters. The ELF intensities calculated by Cerenkov radiation mechanism, being 4 to 5 orders of magnitude lower than the observed intensities, rule out the possibility of their generation by this mechanism. On the other hand, the intensities calculated under electron cyclotron resonance instability mechanism are found to be large enough to account for both the observed intensity and propagation losses and hence to con®rm that plasmaspheric ELF hiss emissions observed aboard GEOS-1 satellite both at small and large wave normal angles were originally generated in the equatorial region by this mechanism just near the inner edge of the plasmapause. The dierence in the observed intensities of two types of the emissions has been attributed to the propagation eect rather than the generation efect.
ELF hiss generation at lower edge of inner radiation belt
An attempt has been made to investigate the possibility of generation of ELF hiss emissions (a few hundred Hz < f < 3 kHz) at the lower edge of inner radiation belt (L = 1.2) by calculating their equatorial magnetic field intensities in terms of incoherent and coherent Cerenkov radiation mechanisms. The results indicate that ELF hiss emissions can not be generated by incoherent Cerenkov radiation mechanism at this location, because the intensities calculated in terms of this mechanism are found to be much lower than the observed intensities. The intensities calculated in terms of coherent Cerenkov radiation mechanism, being several orders of magnitude higher than the observed ones, indicate that the conditions are propitious for the generation of ELF hiss emissions (other than the plasmaspheric hiss) having large wave normal angles at the lower edge of inner radiation belt (L = 1.2) through partially coherent Cerenkov radiation mechanism. This is not, however, true in the case of plasmaspheric hiss (f < 1 kHz), which is thought to be originated in the vicinity of the plasmapause through electroncyclotron resonance instability mechanism and reaching the lower L-shells after several magnetospheric reflections from there.
Excitation of helium cyclotron harmonic waves during quiet magnetic conditions
Journal of Geophysical Research, 1998
A general approach to the generation of ion cyclotron harmonic waves observed on board the Akebono satellite in the deep plasmasphere is presented. It is shown that during quiet magnetic conditions the development of the hydrodynamic cyclotron instability with growth rate ,-/oc n•/2 where ni is the number density of the hot heavy ions, is suppressed by the field-aligned inhomogeneity of the dipole magnetic field. The instability is, in this case, controlled by the weak resonant interaction of the waves and the trapped particles with growth rate-/oc ni. The waves are generated by a kinetic instability involving hot helium ions with a ring-like distribution. Such ions are present in the magnetosphere during quiet magnetic conditions. A simple analytical model of this instability accounting for the inhomogeneity of the ambient magnetic field is used. It is shown that the ULF wave observations during quiet times on board the Akebono satellite are in a reasonable agreement with the present theoretical approach.
1992
In the present paper, some possible parametric decay instabilities of fast magnetosonic waves (FMSW) near the second harmonic of ion cyclotron frequency have been considered in oneion species hydrogen plasmas. The decay channels of FMSW include an ion Bernstein wave as a high-frequency decay wave and a low-frequency decay wave either as an ion-acoustic wave or kinetic Alfvin wave. Applications have been pointed out to the ASDEX [Plasma Phys. Controlled Fusion 28, 235 ( 1986)] and ACT-l [Rev. Sci. Instrum. 53,4 ( 1982)] toroidal devices where parametric decay instabilities of FMSW near the second harmonic of ion cyclotron frequency have been observed in the scrape-off layer and near the edge plasma. It has been shown that the growth rate is sufficiently high at the edge and may thus contribute to the energy deposition to the edge plasma. A comparison between various decay processes has been discussed for different toroidal devices. Applications have also been pointed out to Earth's magnetospheric plasmas where some magnetic fluctuations have been observed. 79
Broadband Electrostatic Noise in the Magnetotail: Its Relation to Plasma Sheet Dynamics
Journal of Geophysical Research, 1985
Intense broadband electrostatic at the magnetopause [Gurnett et al., 1979]. noise is often observed in the magnetotail when Essentially identical wave phenomena have been the fast tailward flow and the southward polarity detected also in the Jovian magnetosphere [Barbosa of the magnetic field indicate the progress of et al., 1981]. reconnection. We compare features of the noise The nature of the broadband electrostatic noise with simultaneous observations of the magnetic is not yet understood. Although the electrostatic field, plasma and energetic electrons. The noise ion-cyclotron instability and the lower-hybridintensity seems to maximize when the plasma drift instability have been suggested as possible density minimizes and the energetic electron flux generation mechanisms [Gurnett et al., 1979; and rises in a spikelike fasion, appreciably later papers cited therein], there is a wide gap between than the onset of the fast tailward flow associat-the frequency of the unstable waves and the highed with the southward magnetic polarity. Spectral frequency end of the observed spectrum. It is characteristics of the noise suggest that in its even questionable if the noise can be attributed-high frequency (f>fg) part at least the noise does to one of the normal modes of plasma waves because not belong to normal modes of plasma waves. the duration of the burst can be as short as < 8 Several possibilities are considered for what this ms. Hence Anderson et al. [1982] have been led to noise might be, including quasi-thermal noise in suggest that the noise (which they called the non-Maxwellian plasma, artificial noise "spikes") has the characteristics of small scale generated by spacecraft interaction with the plasma potential irregularities convecting past medium, or electrostatic noise with wavelengths the antenna. less than a Debye length. This brief report analyzes the enhancements of the broadband electrostatic noise that occurred in et al.: Brief Report 4459 ß • /•