2017 ARTEMIS SCIENCE NUGGETS
The magnetotail plasma sheet configuration: ARTEMIS as the most distant point in the magnetotail spacecraft constellation
by Anton Artemyev
UCLA EPSS/IGPP
Introduction
The plasma sheet, a region filled by hot rarefied and weakly magnetized plasma, occupies the center region of the Earth's magnetotail and serves as a reservoir of energetic particles for injections into the inner magnetosphere. Dynamical properties of this region are controlled by spatial distributions of plasma density and temperature. Until recently, plasma density and temperature gradient statistics in the Earth's magnetotail have been collected for different distances independently, and so far there has been no conjugated probing of the plasma sheet configuration below and above ∼30 Earth radii (RE) downtail.
Observations
Data from spacecraft constellations operating in the magnetotail during the last few years has allowed us to investigate the plasma sheet's configuration along the entire magnetotail up to lunar distance. We collected a dataset of conjugated observations from the THEMIS spacecraft around r ∼10 RE, the Geotail spacecraft around r ∼25 RE, and the ARTEMIS spacecraft around r∼55 RE. Using this dataset, we investigated plasma temperature and density gradients along and across (along the tangential magnetic field Bx) the magnetotail. Plasma temperature statistics collected with these measurements demonstrate the critical role played by temperature gradients in balancing the magnetotail at all distances.
|
| Figure 1. Schematic view of spacecraft constellation operating within the magnetotail. Top-right panels shows distributions of plasma density and temperature collected within simultaneous measurements of THEMIS (~12RE), Geotail (~25RE), and ARTEMIS (~55RE) spacecraft. |
Conclusion
By using near-simultaneous observations of plasma sheet profiles at various distances along the magnetotail from several spacecraft, we were able to determine the 2-D distribution of plasma density and temperature. Using these 2D profiles ni(Bx), Ti(Bx) measured at different radial distances, we estimate the ratio of magnetic field energy at the current sheet boundary to plasma thermal energy near the neutral plane. This study clearly shows that the plasma temperature change along and across the magnetotail contributes to the pressure balance more significantly than the plasma density change.
References
Artemyev, A. V., V. Angelopoulos, H. Hietala, A. Runov, and I. Shinohara (2017), Ion density and temperature profiles along (XGSM) and across (ZGSM) the magnetotail as observed by THEMIS, Geotail, and ARTEMIS, J. Geophys. Res., 122, 1590–1599, doi:10.1002/2016JA023710.Biographical Note
Anton Artemyev is an Assistant Researcher in space physics at the University of California, Los Angeles. His investigations are focused on magnetotail current sheet structure and dynamics.
Please send comments/suggestions to
Emmanuel Masongsong / emasongsong @ igpp.ucla.edu