Minimum variance free wave identification: Application to Cluster electric field data in the magnetosheath

Abstract

The electric field measurements provided by the EFW instrument on board Cluster spacecraft are used to identify the mode of plasma waves observed in the magnetosheath. Previous identifications of magnetosheath wave modes have involved either the use of dimensionless transport ratios (DR) calculated using magnetic field and plasma parameters or the use of magnetic field measurements together with a Minimum Variance (MV) analysis. However, by utilising simultaneous four point measurements it is possible to identify the observed wave dispersion without having to resort to the use of either the calculations of DR or MV. It is, therefore, possible to identify the mode of the observed waves using measurements of any parameter (electric field, density etc.). In the present paper low frequency waves observed in the electric field by Cluster spacecraft travelling through the magnetosheath are studied. The wave dispersion relation obtained from the data indicates that observed waves are mirror waves.