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A numerical solution of the dispersion equation for electromagnetic waves in a hot magnetized collisionless plasma has shown that, in a current-free ionospheric plasma, the distortion of the electron distribution function reproducing the downward flow of a thermal electron component and the compensating upward flow of the suprathermal electrons, which are responsible for the resulting heat flux, can destabilize quasi-electrostatic ion sound waves. The numerical analysis, performed with ion densities and electron temperature taken from the data recorded by the Interkosmos-24 (IK-24, Aktivny) satellite, is compared with a VLF spectrum registered at the same time on board. This spectrum shows a wide frequency band emission below the local ion plasma frequency. The direction of the electron heat flux inherent to the assumed model of VLF emission generation is discussed

We present the results of a case study of quasi-periodic (QP) ELF/VLF hiss emissions detected on board the Freja and Magion5 satellites. Detailed analysis of available QP events revealed certain specific features of their dynamic spectra, which have not been reported earlier. In particular, we found an event with an increase in the frequency drift rate during the generation of a single element of QP emission, and an event with alteration of QP elements having different frequency drift rates. Another event demonstrates the possible relationship between QP hiss emissions and discrete VLF emissions. Properties of QP events are compared with parameters of energetic electrons and cold plasma, and other available data. Possible scenarios for the formation of these emissions are discussed on the basis of self-consistent simulations of the cyclotron instability, employing the information obtained experimentally. It is shown that the generation regime of self-sustained pulsations can explain consistently our data set. We show that our numerical model is capable of explaining the mentioned specific features of the dynamic spectrum of QP emissions. Comparison of the modeling results with experimental data yields an estimate for the parameters not measured directly. Key words. Magnetospheric physics (plasma waves and instabilities; energetic particles, precipitating; energetic particles, trapped)

The noise bands at lower hybrid resonance (LHR) frequency at a satellite position have already been observed and described. Observations onboard the MAGION 5 satellite revealed oblique noise bands above the local LHR frequency. Examples of such oblique bands, both in review (large time-scale) spectrograms, and in detailed (small time-scale) spectrograms are presented. Based on ray-tracing simulations, an explanation of these oblique bands is suggested. We show that they are formed due to the separation of nonducted whistler mode waves of different frequencies propagating near the so-called resonance cone. The influence of plasmaspheric disturbances upon these emissions is also discussed. We suggest that oblique noise bands are mainly formed under quiet conditions, when indistinct plasmapause is situated at higher L shells.

We present the patterns of high frequency energetic electron (~ 20 to ~ 300 keV) pulsations in middle latitudes, in subauroral and auroral regions, based on low altitude nearly polar orbiting satellite (Intercosmos-24, project ACTIVE) measurements. Two detectors with different orientations allowed the fluxes within and outside the loss cone to be compared. The trapped electrons do not exhibit the strong pulsations observed within the bounce loss cone. The pitch angle diffusion coefficient changes significantly on time scales comparable to or even shorter than the bounce period of electrons. The same is valid for changes of precipitating electron energy spectra. There are indications that both pitch angle and energy diffusion are in operation. VLF emissions at f < 3.5 kHz with a complicated structure are observed simultaneously with the electron pulsations, but there is no clear correlation between waves and particles. If the characteristics of the electron pulsations and VLF emissions are of a temporal character, they are qualitatively consistent with the models of nonlinear wave particle interactions, or with the concept of a flowing cyclotron maser. However, the pulsations may originate from fine spatial structure. Variability of the precipitation flux implies short time and/or small scale changes of ionization at altitudes down to 70 km.

International audience; We present two examples of INTERBALL-1 data near both the high and low-latitude tail magnetopause (MP) under disturbed conditions. For the high-latitude case, MAGION-4 data determine the scales of the MP current sheets which are in the order of 100–500 km for the main ones, 50–200 km for Flux Transfer Events (FTEs) and a few km for the fine structures and ULF turbulence. The MP speed was 15–30 km/s. The energetic protons in the magnetosheath (MSH) provide evidence of reconnection upstream of the spacecraft (S/C). The tailward flows grow for the northward MSH magnetic field when the reconnection site is believed to be shifted tailward of the cusp. The inner boundary layer (BL) after the disturbance consists of tailward and earthward flowing plasma of MSH origin and cold mantle plasma flowing tailward The earthward flow is evidence of reconnection tailward of the S/C, which is regarded as a specific feature of the disturbed conditions. Local production of a plasma-sheet-like plasma at high latitudes is argued based on the inner BL plasma characteristics. The following features are observed in both cases: (a) FTEs for both northward and southward MSH fields; (b) waves in the current sheet vicinities over ten mV/m and 15 nT peak-to-peak; (c) electron fluxes with scales down to a few km with extra heating especially parallel to the magnetic field; (d) outer turbulent boundary layers with a deflected magnetic field; (e) ions with time-energy dispersion-like features and deflected ion fluxes. In the downstream dawn region at the transition between the low-latitude boundary layer and the plasma sheet (LLBL/PS), multiple MP encounters are observed. In the LLBL parallel electron intensifications correlate with ULF magnetic fluctuations.

VLF broadband measurements, RF diagnostic, electron density, and temperature measurements from the MAGION-3 satellite were used to study changes in the outer ionosphere during the intense, SSC associated magnetic storm on May 9, 1992. The MAGION-3 satellite as a part of the APEX Project was at this time in the midnight sector at altitudes between 1000 and 2000 km. Signatures of electron temperature peaks, whistler cut-offs, occurrence of different types of emissions, as well as pronounced equatorward edges of the plasma trough allowed us to estimate the equatorial plasmapause position. The inner plasmasphere shrank to values lower than L=2 during the main phase of this storm. The plasmapause position determined from the top-side ionosphere examination agrees well with in situ equatorial studies, except for during large and rapid changes in geomagnetic activity. The position, movement, and shape of the main ionospheric trough, and the waves occurring in this area, particularly the enhancement of broad band emission inside the plasmasphere during the recovery phase of a substorm, permit us to build a clearer view of the topside ionosphere during strong disturbances.

Strong fluctuations (SF) of energetic electrons within the local loss cone (LC) from high resolution data on Active, a low altitude, high inclination satellite, are reviewed. The pitch angle diffusion rate of electrons at L > 4 is rapidly changing by one order up to the isotropic pitch angle distribution, corresponding to strong diffusion. The duration of the spikes to nearly strong diffusion limit is increasing with latitude. The statistical study shows the maximum occurrence of fluctuations within LC is in the noon sector and at latitudes 65 – 70°. Strong geomagnetic activity increases the probability of SF occurrence. One of the possible mechanisms consistent with the observations is the nonlinear precipitation oscillator (Davidson 1986; Davidson and Chiu, 1991).

Parameters of thermal plasma measured within the scope of the ACTIVE Project in the interval containing the magnetic storm with SSC on March 20, 1990, were analyzed to study the response to this storm in the outer ionosphere. VLF broadband measurements and data on energetic ion and electron fluxes in the range of 17.7 – 277 keV were also available. Measurements at altitudes above 2000 km in the morning sector allow us to estimate the depth to which the plasmasphere has been affected by increased convection. Measurements in the evening sector provide the possibility to judge whether an inner plasmapause exists and whether a plasmaspheric bulge has formed.

Spectral broadening of signals from a ground-based VLF transmitter was observed onboard the Magion-3 sub-satellite during electron beam injection from the lntercosmos-25 (APEX) satellite. Broadening of the order of 300–500 Hz was apparently correlated with the 2 s-periodic sequence of the electron gun pulses which were modulated in amplitude with frequencies 30.5 < fm < 31,250 Hz. No effects were found for those electron gun pulses with fm = 62.5, 125 and 250 kHz. The observations were made in the middle latitude ionosphere at altitudes between 1175 and 1580 km; the distance between satellite and sub-satellite was about 250 km. The electron gun current and the energy of electrons were 100 mA and 10 keV, respectively, and the duration of the elementary pulse of current was 2 μs. The data are interpreted in terms of the scattering of whistler mode waves into quasi-electrostatic waves by periodic small-scale plasma inhomogeneities or ELF plasma turbulence created by the pulsemodulated electron beam in the ionosphere.

Special types of VLF signals, which follow whistlers and spherics and have an anomalous dispersion near the lower hybrid resonance (LHR) frequency, have been observed on the low-altitude Intercosmos satellites. These signals have been named LHR whistlers and LHR spherics, respectively. A mechanism is suggested for the formation of their spectra, based on the peculiarities of quasi-resonance wave propagation at frequencies near the LHR frequencies. It is shown that the large dispersion observed may be accounted for by a significant increase in the propagation time of the wave as its frequency approaches the maximum in the LHR frequency profile.

International audience; We present the results of a case study of quasi-periodic (QP) ELF/VLF hiss emissions detected on board the Freja and Magion 5 satellites. Detailed analysis of available QP events revealed certain specific features of their dynamic spectra, which have not been reported earlier. In particular, we found an event with an increase in the frequency drift rate during the generation of a single element of QP emission, and an event with alteration of QP elements having different frequency drift rates. Another event demonstrates the possible relationship between QP hiss emissions and discrete VLF emissions. Properties of QP events are compared with parameters of energetic electrons and cold plasma, and other available data. Possible scenarios for the formation of these emissions are discussed on the basis of self-consistent simulations of the cyclotron instability, employing the information obtained experimentally. It is shown that the generation regime of self-sustained pulsations can explain consistently our data set. We show that our numerical model is capable of explaining the mentioned specific features of the dynamic spectrum of QP emissions. Comparison of the modeling results with experimental data yields an estimate for the parameters not measured directly. Key words. Magnetospheric physics (plasma waves and instabilities; energetic particles, precipitating; energetic particles, trapped)

We present a detailed study of chorus emissions in the magnetosphere detected on board Magion 5, when the satellite was not far from the magnetic equator. We determine the frequency sweep rate of more than 8500 electromagnetic VLF chorus elements. These results are compared with the backward wave oscillator (BWO) regime of chorus generation. Comparison of the frequency sweep rate with the BWO model shows: (i) There is a correlation between the frequency sweep rates and the chorus amplitudes. The frequency sweep rate increases with chorus amplitude, in accordance with expectations from the BWO model; (ii) The chorus growth rate, estimated from the frequency sweep rate, is in accord with that inferred from the BWO generation mechanism; (iii) The BWO regime of chorus generation ensures the observed decrease in the frequency sweep rate of the chorus elements with increasing L-shell.Key words. Magnetospheric physics (VLF emissions, energetic particles) – Space plasma physics (wave-particle interactions)

Щuроmныŭ хо¶rt; чaсmоmы нuжне о uбрu¶rt;но о резонaнсa (НГР) во внещнеŭ uоносфере сре¶rt;нuх щuроm, коmорыŭ можно оnре¶rt;елumь uз щuрокоnолосных ОНЧ uзмеренuŭ сnуmнuков, чувсmвumельно оmрaжaеm возмущенносmь внуmреннеŭ мa нumосферы. Нa nрuмере мa нumноŭ бурu с внезanным нaчaлом 1-о о anнеля 1976 . nокaзывaеmся возможносmь uсnользовaнuя щuроmно о хо¶rt;a чaсmоmы НГР ¶rt;ля оnре¶rt;еленuя nоложенuя сре¶rt;нещuроmных nровaлов ле кuх uонов u элекmронноŭ коценmрaцuu, a косвенно maкже ¶rt;ля нaблю¶rt;енuя воссmaновленuя nлaзмaсферы nосле возмущенuя.

Шuрокоnолосные ОНЧ нaблю¶rt;енuя сnуmнuкa Инmеркосмос 19 в nерuо¶rt; ноябрь 1979 — мaрm 1980 былu обрaбоmaны с mочкu зренuя nоявленuя сu нaлов нaземных nере¶rt;amчuков нaвu aцuонноŭ сuсmемы Оме a. Окaзывaеmся, чmо в облaсmu nере¶rt;amчuкa Ал¶rt;рa (L=5) нaблю¶rt;aюmся нa¶rt; uоносфероŭ сu нaлы очень чaсmо, nреuмущесmвенно в ночное время, u в nрохож¶rt;енuях сnуmнuкa нa рaссmоянuu ¶rt;о 500 км оm верmuкaлu, nрохо¶rt;ящеŭ nере¶rt;amчuком. Вuсключumельных случaях сu нaлы можно нaблю¶rt;amь ¶rt;aже нa рaссmоянuях больще 2000 км. Только в 10-mu nроценmaх случaев нaблю¶rt;aлось зa сu нaлом, nрохо¶rt;ящuм через uоносферу, эхо с зanоз¶rt;aнuем оm 2,3 ¶rt;о 3,6 с. Покaзывaеmся, чmо нauболее верояmным мехaнuзмом uх вознкновенuя являеmся кaнaлuзuровaнное нaсnросmрaненuе в ¶rt;aкmaх в¶rt;оль сuловых лuнuŭ мa нumно о nоля (вблuзu L=3) aнaло uчно вознuкновенuю ¶rt;вускaчковых свuсmов. В мa нumосоnряженноŭ облaсmu к nере¶rt;amчuку, рaбоmaющему в южном nолущaрuu нa осmрове Лa реюнuон (L=1,35), нaблю¶rt;aлuсь сu нaлы в uнmервaле 1,5