I. Nagano

Electrostatic solitary waves (ESW) in the magnetotail: BEN wave forms observed by GEOTAIL

The authors report on broadband wave features captured by the wave form capture receiver on the GEOTAIL satellite. In the plasma sheet boundary layer, the broadband specta are composed of a series of pulses, which the authors term electrostatic solitary waves. They propose a model to account for these wave events as highly nonlinear instabilities of electron beams.

The Numerical Simulation of VLF Chorus and Discrete Emissions Observed on the Geotail Satellite using a Vlasov Code

The work consdiers VLF chorus elements observed omn the Geotail satellite, which passes the equator at 10 earth radii. We have used a VHS Vlasov simulation code to model these emissions, employing all the ambient plasma data observed on Geotail. Excellent agreement with observation results, with steep risers and slow fallers being reproduced. The results confirm the overall validity of the non linear trapping theory of VLF emissions, and also confirm the efficacity of the Vlasov VHS code.

Relation between electrostatic solitary waves and hot plasma flow in the plasma sheet boundary layer: GEOTAIL observations

The authors present studies which show correlations between plasma ion flow properties in the plasma sheet boundary layer, and the spectral properties of the broadband radiation observed there by GEOTAIL, referred to as electrostatic solitary waves. The width and spacing between the pulses is observed to change on time scales of milliseconds.

Statistical nature of impulsive electric fields associated with fast ion flow in the near-Earth plasma sheet

Statistical characteristics of impulsive electric field (IEFD) associated with fast earthward ion flows in the inner central plasma sheet were studied by using electric field data obtained from the double-probe instrument on board the Geotail satellite. It is shown that the strongest electric field is produced in the region between X AGSM = -15 R E and -9 R E where the fast earthward flow is decelerated. The IEFDs are short-lived with a timescale of ∼2 min on the average, compatible with the timescale of other signatures of substorm fine structures. This strong cross-tail electric field, coincident with the braking of the fast flow and correlated with the magnetic field dipolarization, has important implications for the particle acceleration in the near-Earth plasma sheet.

Collaborative experiments by Akebono satellite, Tromsø ionospheric heater, and European incoherent scatter radar

Joint experiments using the Akebono satellite and the ionospheric heating facility and European incoherent scatter radar near Tromso were carried out in November 1990 and February 1991. In these experiments, Tromso HF transmissions were amplitude modulated at frequencies of 2.5 and 4.0 kHz. Signals radiated from the polar electrojet (PEJ) antenna in the heated ionosphere at these VLF frequencies were detected for five passes out of seven passes of the semipolar orbiting Akebono satellite. A ground-based observation of the VLF radiation from the PEJ was made in the November campaign at Lycksele in Sweden, 554 km south of the heating facility. Measurements of electron density profiles and dc electric fields in the ionosphere were carried out by the EISCAT incoherent scatter radar [Folkestad et al., 1983] located in the vicinity of the ionospheric heater. The results of the experiments are compared with those obtained by ray tracing and full-wave analyses.

Terrestrial 2fp radio source location determined from WIND/GEOTAIL triangulation

We combine simultaneous WIND/GEOTAIL direction-finding analyses of terrestrial 2f p radio emission to provide the first 3-D source location by two spacecraft triangulation. These observations were made when WIND and GEOTAIL were relatively close to the electron foreshock and to each other. For two cases presented the 2f p radio source centroid was stationary and located in the upstream wing of the electron foreshock region some 15 - 50R E from the contact point. In a third case the 2f p source centroid followed the change in orientation of the electron foreshock.

Satellite and ground observations of HIPAS VLF modulation

Joint experiments between the new Japanese satellite EXOS-D (Akebono) and the HIPAS (High Power Active stimulation) facility located at Fairbanks, Alaska were made in 1989. The HF radiation was modulated in amplitude by 2.5 kHz signal. On November 28, 1989, EXOS-D detected the VLF signal at an altitude of 2300 km with an E field of 15 μV/m and a B field of 0.25 pT. The angle between the wave normal and the geomagnetic field was found to be less than 20°. Simultaneous ground observations were made using loop antennas at a distance about 35 km from HIPAS. The 2.5 kHz signal amplitude there at the time of the satellite observation was 1.3 pT. If this wave magnetic field is assumed to be due to an ionospheric AC current of 0.65 A, the signal strength at the satellite is roughly consistent within a factor of 3, which is much better consistency than those observed by James et al. (1984).

Electron density profiles in the ionospheric D-region estimated from MF radio wave absorption

Abstract Electron density measurements in the lower ionosphere were carried out more than 6 times during the period from 1975 to 1992 by using sounding rockets launched at KSC (Kagoshima Space Center in Japan). Low electron densities were estimated from the absorption of the characteristic mode of ground-based radio signals (17.4 kHz and 873 kHz) in the lower ionosphere measured by onboard receivers. Two kind of methods, i.e., VLF mode absorption and MF absorption methods were developed to estimate the D-region electron density by comparing the observed wave intensity with that calculated by a full wave treatment. In this paper, both absorption methods are introduced paying attention to the capability of low electron density measurement. In particular the S-310-18 rocket experiment is discussed in detail, in which the D-region electron density profile derived from the altitude variation of MF radio wave intensity is presented. Finally the lower ionospheric electron density profiles so far measured by those method at mid-latitude in Japan are compared with those of the IRI-95 model.

Wave form analysis of the continuum radiation observed by GEOTAIL

The Plasma Wave Instrument (PWI) onboard the GEOTAIL spacecraft has frequently observed Continuum Radiation (CR) throughout the geomagnetic tail region, including the Magnetosheath (MS), the Lobe, the Plasma Sheet Boundary Layer (PSBL), and the Plasma Sheet (PS). In addition to the usual Escaping CR (from 10 kHz to 30 kHz) and the Trapped CR (from about 5 kHz to 10 kHz), CR with the frequency structure extending down to 1 kHz (the local plasma frequency) has often been observed in the Lobe region. Waveforms of the electric field in the frequency range less than 4 kHz, which is acquired by Wave Form Capture in the PWI, are used to analyze in detail the frequency-time structure of such low-frequency CR near the lower cutoff. Two distinct cutoff frequencies modulated by the antenna spinning indicates that the CR in the Lobe region propagates both in the O mode and in the X mode almost perpendicular to the earthward geomagnetic field line. The CR in the Lobe region, especially in the vicinity of the PSBL, is sometimes accompanied by intense electrostatic electron-cyclotron-harmonic (ECH) (n + 1/2) waves. These suggest that such a low-frequency CR in the distant tail region is most likely to be generated from the ECH waves near the PSBL, and trapped within the Lobe between the PSBL and the MS.

Low Frequency plasma wave Analyzer (LFA) onboard the PLANET-B spacecraft

The Low Frequency plasma wave Analyzer, LFA, on board the PLANET-B spacecraft has been developed to measure the Martian plasma waves. Two orthogonal electric dipole wire antennas, 50 m tip-to-tip, in the spacecraft spin plane are used to measure plasma waves, dc electric fields, and the spacecraft potential relative to the ambient plasma. The LFA has capability to measure the wave spectrum in the band from 10 Hz to 32 kHz, and to capture the signal waveform in the band from dc to 32 kHz by using a 4 MByte memory. The LFA scientific objectives are to explore the following: (1) Macroscopic plasma environment and boundaries from the solar wind to the ionosphere, (2) Microscopic plasma phenomena induced by the interaction between the solar wind and the Martian atmosphere and the moon Phobos, (3) Generation and propagation of electromagnetic waves, (4) Plasma densities and waves in the nightside ionosphere and tail, and (5) Comparison of Martian plasma waves with those of other planets such as non-magnetized Venus and magnetized Earth.