P. J. Christiansen

Banded electron cyclotron harmonic instability-a first comparison of theory and experiment

A study, which is the first of its kind, uses information derived from simultaneously measured wave spectra and particle distributions as the input to a theoretical linear instability model of an electrostatic cyclotron harmonic wave event recorded on GEOS-1. The presence of a hot loss cone component of the particle distribution is established experimentally, and the model accounts reasonably for the observed frequencies and relative strengths of the (n+1/2)fc and upper hybrid emission features.

GEOS-1 observations of electrostatic waves, and their relationship with plasma parameters

In this paper we describe and discuss the occurrence of natural wave emissions detected by GEOS-1 at frequencies above the electron gyrofrequency. The bulk of the data presented comes from the first six months of satellite operation and thus concerns mainly dayside phenomena. The paper is arranged as follows:After some general remarks, a classification of the wave phenomena is developed in Section 2, and experimental evidence and morphological information relevant to this classification are contained in Section 3. Section 4 includes some preliminary comments on nightside observations. The results are discussed in Section 5, where it is argued that they can be understood as manifestations of electron cyclotron harmonic (Bernstein) wave emission in a plasma parameter range which has only very recently received any theoretical examinations. This theme is further developed in a comparison paper (Ronnmark et al., 1978).

AMPTE-UKS observations of current sheets in the solar wind

Abstract Active current sheets or diamagnetic cavities in the solar wind have been observed both by the AMPTE-UKS spacecraft on a number of occasions, and independently from ISEE by Thomsen et al /1/. Preliminary results from one of these UKS observations have been discussed recently by Schwartz et al /2/. In this paper we consider these phenomena in more detail. Results are presented for the position of five events. High resolution plasma data and plasma wave activity associated with these current sheets are examined.

Electrostatic emissions studied in high resolution

Specific examples are presented for two types of electrostatic emission which have been studied on GEOS 1 and GEOS 2 with high spectral and fast temporal resolution. 1. (A) In the mid-morning hours (6 – 9 LT) the strongest electrostatic emissions are often observed as bursts lasting from less than a second to several hours. Simultaneously rapid changes are observed in the warm electron distribution and at ELF (15 – 450 Hz) only on the large electric antenna. High spectral resolution (Δf ∼ 11 Hz) shows that these emissions near the plasma frequency (∼ 30 KHz) sometimes display spectral features whose separation in frequency is equal to the frequency of the electrostatic ELF emission in the region of the lower hybrid frequency. 2. (B)Around local midnight following a substrom rapid step like changes occur in the intensity of electromagnetic ELF emission. Simultaneously the normal structured electrostatic (n + 12 fce emission features are replaced by an intense broad spectrum. Relations between these variations and auroral pulsations Observed at the foot of the field line are presented.

E.S. wave morphology near the geostationary orbit

A general morphology of magnetospheric electrostatic emissions at and within the geostationary orbit has been derived from the combined data sets produced by the European Space Agency Satellites GEOS1 (2–8RE) and GEOS2 (Geostationary at 6.6 RE). The occurence of emission type is related to local plasma parameters. After earlier results from GEOS1 had shown the geomagnetic equator to be the site of the most intense electron cyclotron harmonic mode (ECH) emissions at n + 12fce GEOS2 was manoevered on several occasions through the model geomagnetic equator (15° E geographic at the geostationary orbit). At low Kp the strong emissions are confined to ± 1° of the geomagnetic equator and are a factor of one hundred more powerful than waves at only 2 – 3° off the equator. Increasing Kp appears to enlarge the average latitudinal confinement (relative to the model field equator) and may result from distortions of the minimum field equator away from its quiescent location. The latitutde of the most-intense average emission moves to the south in summer and to the north in winter with increasing Kp. A comparison of GEOS1 data with GEOS2 data points to the fact that these equatorially confined emissions are limited in geomagnetic L and LT to regions where the ratio of cold upper hybrid fuH to electron gyro-frequency fce lies approximately in the range 4 – 10 corresponding to a region a few RE in radial extent just outside the plasmapause at most local times.

Low frequency waves seen during the AMPTE barium release

Abstract The AMPTE barium ion release in the solar wind at 1232 UT on 27 December 1984 produced strong electric component plasma wave noise at frequencies below 3.9 kHz (amongst other emissions) which was detected at both the AMPTE-UKS and AMPTE-IRM spacecraft. In the region outside the magnetic cavity, this noise appears to be correlated with electron heating and changes sin the magnetic field. This paper compares data from the two spacecraft at high temporal resolution in order to identify the waves and the associated processes.

Electron Cyclotron Waves in the Earth’s Magnetosphere

Observations of electrostatic waves in the Earth’s magnetosphere which exhibited complex frequency banding related to harmonics of the electron gyrofrequency (“3/2 fce emissions”) were first reported by Kennel et al (1). The authors also pointed out that, given the large amplitudes often attained by the waves (≳ 1 mV/m), electrons would be rapidly diffused in velocity space and the resulting precipitated fluxes could provide a significant contribution to the diffuse component of auroral precipitation.