Cluster recent highlights at dayside boundaries

Abstract:

After more than 16 years in space, the Cluster mission is continuing to deliver groundbreaking results, thanks to its ability to move the four spacecraft with respect to each other, according to the science topic to be studied. The main goal of the Cluster mission, made of four identical spacecraft carrying each 11 complementary instruments, is to study in three dimensions the key plasma processes at work in the main regions of the Earth’s environment: solar wind and bow shock, magnetopause, polar cusps, magnetotail, and auroral zone. During the course of the mission, the relative distance between the four spacecraft has been varied more than 55 times from a few km up to 36000 km to address the various scientific objectives. The smallest distance achieved between two Cluster spacecraft was 3 km in December 2015, about 50 times smaller than planned at the beginning of the mission. The rate of change of separation distances has accelerated in the last few years with the Guest Investigator programme that allowed scientists in the community to propose special science programmes requiring a new spacecraft constellation. We will present recent science highlights obtained such as the evanescence of the bow shock under sub-Alfvénic solar wind, plasma acceleration in Kelvin-Helmholtz waves, magnetic reconnection acceleration at O-lines, new method to find magnetic nulls outside the Cluster tetrahedron, statistical studies of ionospheric outflows and plumes near the magnetopause, multi-altitude measurements of field aligned currents and origin of theta auroras. We will also present the Cluster Science Archive, which was implemented to provide, for the first time for a plasma physics mission, a permanent and public archive of all the high-resolution data from all instruments. Collaboration with other mission such as MMS, THEMIS, Van Allen Probes and Arase (ERG) will also be highlighted.