On the estimation of the current density in space plasmas: Multi- versus single-point techniques. (June 2017)

• Record Type: Journal Article
• Authors: Perri, Silvia; Valentini, Francesco; Sorriso-Valvo, Luca; Reda, Antonio; Malara, Francesco
• Is Part Of: Planetary and space science. Volume 140(2017)
• Page Start: 6
• Page End: 10
• Publication Date: 2017-06
• Subjects: Multi-spacecraft technique -- Electric current vector -- Space plasmas; Space sciences -- Periodicals; Atmosphere, Upper -- Periodicals; Sciences spatiales -- Périodiques; Haute atmosphère -- Périodiques; 523
• DOI: 10.1016/j.pss.2017.03.008
• Languages: English
• ISSNs: 0032-0633

Abstract

Abstract: Thanks to multi-spacecraft mission, it has recently been possible to directly estimate the current density in space plasmas, by using magnetic field time series from four satellites flying in a quasi perfect tetrahedron configuration. The technique developed, commonly called "curlometer" permits a good estimation of the current density when the magnetic field time series vary linearly in space. This approximation is generally valid for small spacecraft separation. The recent space missions Cluster and Magnetospheric Multiscale (MMS) have provided high resolution measurements with inter-spacecraft separation up to 100 km and 10 km, respectively. The former scale corresponds to the proton gyroradius/ion skin depth in "typical" solar wind conditions, while the latter to sub-proton scale. However, some works have highlighted an underestimation of the current density via the curlometer technique with respect to the current computed directly from the velocity distribution functions, measured at sub-proton scales resolution with MMS. In this paper we explore the limit of the curlometer technique studying synthetic data sets associated to a cluster of four artificial satellites allowed to fly in a static turbulent field, spanning a wide range of relative separation. This study tries to address the relative importance of measuring plasma moments at very high resolution from a single spacecraft with respect to the multi-spacecraft missions in the current density evaluation. Abstract : Highlights: Curlometer has been tested in a synthetic magnetic turbulence model. Close to discontinuities, inter-spacecraft separations of sub-electron scales give a good estimation of the current density. Indirect evidence that the use of high-resolution single spacecraft plasma data would better estimate the current density.