About this Research Topic
Plasmas are ubiquitous in nature, surround our local geospace environment and permeate the universe. Single-point space missions have described many properties of near-Earth and heliospheric plasmas as measured both in situ and remotely. However, a full description of our plasma environment requires three-dimensional measurements.
Cluster was the first such mission, and until data began to flow from the Magnetospheric Multiscale Mission (MMS), it was the only mission designed to describe the three-dimensional structure of plasma phenomena in geospace. To achieve this, Cluster consists of four identical spacecraft flying in a tetrahedral configuration, thereby making it possible to distinguish between spatial and temporal variations.
Cluster data have been used to investigate properties of magnetic reconnection in the Earth's environment, leading in particular to a significant progress in understanding the microphysics of magnetic reconnection, especially where reconnection occurs, and revealing the subsequent both adiabatic and non-adiabatic particle energization. Using Cluster datasets also contributed to determine currents and vorticity (computed as the curl of the magnetic and velocity fields, respectively) in various regions of geospace, and the turbulence correlation scales in the solar wind and Earth's plasmasheet.
In particular, it has been possible to describe for the first time the three-dimensional properties of the inertial range of interplanetary turbulence at ion scales, and, using high-resolution magnetic field data, to study turbulence at electron scales at which the plasma dissipates, discontinuities form and intermittency manifests itself. Thanks to plasma high-resolution data, detailed properties of the electron velocity distribution functions in solar wind have been explored, providing signatures that serve as a proxy for the structure of the magnetic and electric fields.
Cluster has made it clear that multiple spacecraft missions coupled with high time resolution instruments, can be performed down to the smallest scale lengths. Consequently, NASA launched a new mission in 2015, the Magnetospheric Multiscale Mission. It consists of four identical spacecraft that uses Earth's magnetosphere as a laboratory to study the microphysics of magnetic reconnection with unprecedented resolution. The three-dimensional and time-varying physical phenomena studied by Cluster, can thus now be explored on much smaller spatial and temporal scales. Indeed, MMS sensors are measuring, e.g., particle velocity distribution functions, as well as electric and magnetic fields, with milliseconds time resolution, enabling the identification of small scales (1-10 km) and rapidly moving structures (10-100 km/s).
The scope of the Research Topic "Improving the Understanding of Kinetic Processes in Solar Wind and Magnetosphere: From CLUSTER to MMS" is to highlight the role of these two missions in augmenting our knowledge of many plasma processes that occur in the plasma universe. In particular, the authors are welcome to describe how the understanding of a plasma process has evolved and/or improved
from the first Cluster observations to the current MMS high-resolution measurements.
Image credits: NASA/Goddard/Conceptual Image Lab
Keywords: Solar wind, magnetosphere, space missions, kinetic processes, data analysis
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