First multispacecraft ion measurements in and near the Earth’s magnetosphere with the identical Cluster ion spectrometry (CIS) experiment

TLDR

Magnetospheric physics studies the dynamics of the magnetopause, cusp, and boundary layers and their interactions with the solar wind. The paper presents first results of the CIS instruments, demonstrating their high performance and capabilities. The Cluster Ion Spectrometry experiment on the four Cluster spacecraft measures full 3‑D ion distributions of H⁺, He⁺, He²⁺, and O⁺ from thermal energies to ~40 keV/e using two analyzers—CODIF for mass‑to‑charge composition and HIA for high‑resolution angular measurements—each with dual sensitivities to extend dynamic range. The instruments captured high‑quality data across the central plasma sheet, magnetopause, magnetosheath, solar wind, cusp, and auroral regions, demonstrating the value.

Abstract

Abstract. On board the four Cluster spacecraft, the Cluster Ion Spectrometry (CIS) experiment measures the full, three-dimensional ion distribution of the major magnetospheric ions (H+, He+, He++, and O+) from the thermal energies to about 40 keV/e. The experiment consists of two different instruments: a COmposition and DIstribution Function analyser (CIS1/CODIF), giving the mass per charge composition with medium (22.5°) angular resolution, and a Hot Ion Analyser (CIS2/HIA), which does not offer mass resolution but has a better angular resolution (5.6°) that is adequate for ion beam and solar wind measurements. Each analyser has two different sensitivities in order to increase the dynamic range. First tests of the instruments (commissioning activities) were achieved from early September 2000 to mid January 2001, and the operation phase began on 1 February 2001. In this paper, first results of the CIS instruments are presented showing the high level performances and capabilities of the instruments. Good examples of data were obtained in the central plasma sheet, magnetopause crossings, magnetosheath, solar wind and cusp measurements. Observations in the auroral regions could also be obtained with the Cluster spacecraft at radial distances of 4–6 Earth radii. These results show the tremendous interest of multispacecraft measurements with identical instruments and open a new area in magnetospheric and solar wind-magnetosphere interaction physics.Key words. Magnetospheric physics (magnetopause, cusp and boundary layers; magnetopheric configuration and dynamics; solar wind - magnetosphere interactions)