Abstract
AbstractWe review the range of applications and use of the curlometer, initially developed to analyze Cluster multi‐spacecraft magnetic field data; but more recently adapted to other arrays of spacecraft flying in formation, such as MMS small‐scale, 4‐spacecraft configurations; THEMIS close constellations of 3–5 spacecraft, and Swarm 2–3 spacecraft configurations. Although magnetic gradients require knowledge of spacecraft separations and the magnetic field, the structure of the electric current density (for example, its relative spatial scale), and any temporal evolution, limits measurement accuracy. Nevertheless, in many magnetospheric regions the curlometer is reliable (within certain limits), particularly under conditions of time stationarity, or with supporting information on morphology (for example, when the geometry of the large scale structure is expected). A number of large‐scale regions have been covered, such as: the cross‐tail current sheet, ring current, the current layer at the magnetopause and field‐aligned currents. Transient and smaller scale current structures (e.g., reconnected flux tube or dipolarisation fronts) and energy transfer processes. The method is able to provide estimates of single components of the vector current density, even if there are only two or three satellites flying in formation, within the current region, as can be the case when there is a highly irregular spacecraft configuration. The computation of magnetic field gradients and topology in general includes magnetic rotation analysis and various least squares approaches, as well as the curlometer, and indeed the added inclusion of plasma measurements and the extension to larger arrays of spacecraft have recently been considered.
Highlights
The successful launches of the four Cluster II spacecraft (Escoubet et al, 2001), which began full science operations in eccentric polar orbits in February 2001, heralded a step change in the exploration and analysis of the Earth's magnetosphere, magnetosheath and near-Earth upstream regions
Cluster multi-spacecraft magnetic field data; but more recently adapted to other arrays of spacecraft flying in formation, such as Magnetospheric Multi-Scale (MMS) small-scale, 4-spacecraft configurations; THEMIS close constellations of 3–5 spacecraft, and Swarm 2–3 spacecraft configurations
For the first time 3-D structure and temporal evolution could be probed and partly separated through an evolving spatial array, which allows spatial gradients of key quantities to be analyzed. Such analysis was long anticipated with a number of early designs of methods for Cluster data: an ISSI working team producing the first book on collected multi-spacecraft analysis techniques in 1998 (Paschmann & Daly, 1998)
Summary
The successful launches of the four Cluster II spacecraft (Escoubet et al, 2001), which began full science operations in eccentric polar orbits in February 2001, heralded a step change in the exploration and analysis of the Earth's magnetosphere, magnetosheath and near-Earth upstream (solar wind) regions. For the first time 3-D structure and temporal evolution could be probed and partly separated through an evolving spatial array, which allows spatial gradients (in particular) of key quantities to be analyzed Such analysis was long anticipated with a number of early designs of methods for Cluster data: an ISSI working team producing the first book on collected multi-spacecraft analysis techniques in 1998 (Paschmann & Daly, 1998). The Magnetospheric Multi-Scale (MMS) mission is notable since it follows Cluster in maintaining a close configuration for much of its orbit (Burch, Moore, et al, 2016), but on much smaller separation scales (a few km), while THEMIS has achieved a 3-spacecraft configuration (of the magnetospheric spacecraft) in its extended operations (Angelopoulos, 2008) and Swarm achieved 2 and 3 spacecraft formations at low Earth orbit (LEO) polar altitudes (Friis-Christensen et al, 2008) on meso-scales (∼100 km)
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