Compressional wave events in the dawn plasma sheet observed by Interball-1

O Verkhoglyadova,A Agapitov,V Ivchenko,Yu Yermolaev,A Andrushchenko,S Romanov

doi:10.1007/s00585-999-1145-7

O Verkhoglyadova, A Agapitov + Show 4 more

Open Access

https://doi.org/10.1007/s00585-999-1145-7

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Abstract

Abstract. Compressional waves with periods greater than 2 min (about 10-30 min) at low geomagnetic latitudes, namely compressional Pc5 waves, are studied. The data set obtained with magnetometer MIF-M and plasma analyzer instrument CORALL on board the Interball-1 are analyzed. Measurements performed in October 1995 and October 1996 in the dawn plasma sheet at -30 RE ≤ XGSM and |ZGSM| ≤ 10 RE are considered. Anti-phase variations of magnetic field and ion plasma pressures are analyzed by searching for morphological similarities in the two time series. It is found that longitudinal and transverse magnetic field variations with respect to the background magnetic field are of the same order of magnitude. Plasma velocities are processed for each time period of the local dissimilarity in the pressure time series. Velocity disturbances occur mainly transversely to the local field line. The data reveal the rotation of the velocity vector. Because of the field line curvature, there is no fixed position of the rotational plane in the space. These vortices are localized in the regions of anti-phase variations of the magnetic field and plasma pressures, and the vortical flows are associated with the compressional Pc5 wave process. A theoretical model is proposed to explain the main features of the nonlinear wave processes. Our main goal is to study coupling of drift Alfven wave and magnetosonic wave in a warm inhomogeneous plasma. A vortex is the partial solution of the set of the equations when the compression is neglected. A compression effect gives rise to a nonlinear soliton-like solution.Key words. Magnetosphere physics (magnetotail) · Space plasma physics (kinetic and MHD theory; non-linear phenomena)

Highlights

Concurrent variations of the magnetic ®eld pressure and plasma thermal pressure with periods greater than 2 min at low geomagnetic latitudes, namely compressional Pc5 waves, have been variously studied based on the data set obtained with OGO 5 (Kokubun et al, 1977), ATS 6 (Su et al, 1977), ATS 1 (Bar®eld and McPerron, 1978), GOES 2, 3 (Bar®eld and Lin, 1983), GEOS 2 (Walker et al, 1982) and AMPTE (Bauer et al, 1995)
It should be noted that the measurements performed at the geostationary orbit with two satellites GOES 2, 3 (Takahashi et al, 1985) and four satellites (Takahashi et al, 1987) revealed the standing structure of the compressional Pc5 wave along the geomagnetic ®eld line (Takahashi, 1988; Takahashi et al, 1990)
It should be noted that these vortices are localized in the regions of anti-phase variations of the magnetic ®eld and plasma pressures

Summary

Introduction

Concurrent variations of the magnetic ®eld pressure and plasma thermal pressure with periods greater than 2 min (about 10±30 min) at low geomagnetic latitudes, namely compressional Pc5 waves, have been variously studied based on the data set obtained with OGO 5 (Kokubun et al, 1977), ATS 6 (Su et al, 1977), ATS 1 (Bar®eld and McPerron, 1978), GOES 2, 3 (Bar®eld and Lin, 1983), GEOS 2 (Walker et al, 1982) and AMPTE (Bauer et al, 1995). To study properties of compressional wave events in the dawn plasma sheet, the authors provided an analysis of plasma and magnetic ®eld measurements in the middle tail of the Earth magnetosphere for selected time intervals. Simulation results are arguments in favour of connection of background magnetic ®eld enhancement with the ring current disturbances during active geomagnetic periods Such a discrepancy between the model and mean experimental values may be explained by the crude evaluation of the time delay. It should be noted that these vortices are localized in the regions of anti-phase variations of the magnetic ®eld and plasma pressures To support this statement we note that the vortices and compressional wave events are detected at the same time intervals To support this statement we note that the vortices and compressional wave events are detected at the same time intervals (compare Figs. 2 and 8)

October 1996

Conclusions