Cluster Status Report - January 2009
02 Feb 2009 14:23
The tilt of Cluster 3 (45° with respect to Cluster 4) has been successfully performed in May 2008. This allowed the 3D electric field to be measured for the first time by combining both spacecraft measurements. Preliminary results show the successful measurement of parallel electric fields in the auroral zone. The tilt also improved significantly the localization of the sources of radio waves in the magnetosphere.
Cluster constellation phasing manoeuvres have been completed as of early August. The constellation has been targeted at the neutral sheet with C1, C2, C3 separated by 10 000 km and C3, C4 separated by 3000 km. A slight acceleration of the degradation of the solar array has been observed since March-April due to the orbit’s lower perigee altitude (below 10 000 km) and the longer time spent by the spacecraft in the Earth’s radiation belts.
A long eclipse season ran from 17 September till 10 October. Among all 4 spacecraft there was a total of 12 nominal eclipses (all payload off), 6 "Decoder only" eclipses (C1, C3 and C4) and 5 complete power downs (C1). Everything went according to plan and all spacecraft could be recovered after the eclipses.
The Cluster Active Archive (CAA) continues to distribute data to the user community. The CAA has currently 713 registered users with an average of 20 new users every month. From April 2008 to September 2008 the averaged data download rate was 300 GB per month.
The 16th Cluster workshop took place on 23-26 September 2008 in New Hampshire, USA. It was the first workshop combined with the NASA THEMIS mission. THEMIS is a five-spacecraft mission to study plasma physics and in particular the phenomenon generating magnetospheric substorms. The THEMIS spacecraft are in an equatorial orbit while Cluster is in a polar one, making them fully complementary. New results on the generation of substorms were presented, privileging magnetic reconnection as trigger mechanism. More data are however needed to confirm this scenario.
A recent paper, by Darrouzet et al., was published in Annales Geophysicae on a statistical analysis of plasmaspheric plumes in the inner magnetosphere. This study utilises the WHISPER wave sounder onboard Cluster and provided information on the occurrence rate of the plume as a function of magnetospheric indices, providing information on size, extent and density variation. This work is important for inner magnetospheric physics. Plasmaspheric plumes are thought to affect the reconnection rate at the dayside magnetosphere, and hence the transfer of solar wind plasma into the magnetosphere.