Data from the magnetometers track the passage of Cluster's four spacecraft through the plasma sheet
Copyright: ESA 2001 (Data courtesy of Professor Andri Balogh, Imperial College London)
The top graph is an overview, showing fluctuations in the magnetic field between 06:00 UT (07:00 CET) and 16:30 UT (17:30 CET). Note the sudden drop in solar energy (blue line) between 13:30 UT and 15:15 UT, when spacecraft 2 (Salsa) entered the Earths shadow and went into eclipse.
The lower graph zooms in on the time period 09:30 UT (10:30 CET) to 12:30 UT (13:30 CET), before the spacecraft entered the Earths shadow.
On this occasion, the Cluster quartet crossed the plasma sheet before entering the eclipse. Data from all four spacecraft (available to 12:00 UT about 3.5 hours before the eclipse started) show the dropouts in the magnetic field characteristic of the complex structure of the plasma sheet and the strong electrical currents that flow in it.
It can be clearly seen that Cluster crossed these structures from the way the magnetic field data from the four instruments track each other, except for some significant differences with spacecraft 3 (Samba), which was flying a little south of the other three at the time.
When the eclipse came, Cluster was already in the southern 'suburbs' of the central plasma sheet, as can be seen from the strength of the magnetic field from spacecraft 2, the only spacecraft which was scheduled to return magnetic field data at that time. The smaller disturbances at the time of the eclipse are almost certainly parts of the tail plasma sheet and not due to lack of sunlight at the time.
(Data courtesy of Professor Andri Balogh, Imperial College London)