Abstrakt
The foreshock is a region filled with a turbulent plasma located upstream the Earth's bow shock where interplanetary magnetic field (IMF) lines are connected to the bow shock surface. In this region, ultra-low frequency (ULF) waves are generated due to the interaction of the solar wind plasma with particles reflected from the bow shock back into the solar wind.
It is assumed that excited waves grow and they are convected through the solar wind/foreshock, thus the inner spacecraft (close to the bow shock) would observe larger wave amplitudes than the outer (far from the bow shock) spacecraft. The paper presents an analysis of excited ULF fluctuations observed simultaneously by two closely separated ARTEMIS spacecraft on the lunar orbit under a nearly radial IMF.
We found ULF fluctuations (in the plasma rest frame) that can be characterized as a mixture of transverse and compressional modes with different properties at both locations. Moreover, we identified both growing and damped waves at the inner spacecraft.