Cluster Status Report - April 2003
The decrease in the power output from the solar array in 2002 was only 4 W as compared to 2001 which was 17 W. As we are moving away from Solar max, we have encountered fewer solar storms. At this rate there should be no problem in reaching the end of the mission (end December 2005). Short eclipses (less than one hour) were passed successfully in March.
The spacecraft-2 CIS telemetry, that has been used by PEACE (low energy electrons) since last year, is now being shared with RAPID (high energy electrons and ions). The on-board tables were changed to define one mode with PEACE priority (5 orbits out of 6) and another with RAPID priority (1 out of 6).
Science highlights
Cluster observed magnetic reconnection in the polar cusp. The polar cusp is the region above the pole where particles from the solar wind enter directly into the magnetosphere and reach the Earths atmosphere. The reconnection process accelerates ions which then can produce a bright spot in the aurora. The NASA IMAGE spacecraft was recording the proton aurora at the same time and detected a bright spot. This is the first time that we have observed the reconnection process at high altitude and its direct effect on the ionosphere. These results will be published in Geophysical Research Letters and in fact have been proposed as the cover of the journal.
Magnetic reconnection was also observed in the magnetotail, the region of the Earths magnetic field opposite the Sun. With the four spacecraft surrounding the reconnection region, Cluster could detect the so-called "Hall" currents expected when ions are decoupled from electrons. In addition very strong electric fields were observed near the reconnection site which could explain the acceleration of plasma usually observed.
Surface waves were observed on the dawn flanks of the magnetosphere. 25 crossings of the waves were observed during 1.5 hours. The shape and motion of the waves could be fully characterized by the four Cluster spacecraft: speed 65 km/s and dimension 22000 km (3.4 Earth radii). These waves do not seem to agree with "Kelvin-Helmoltz" processes usually expected to produce them.
Two Cluster workshops were organized in March 2003. The first one at ISSI (Bern, CH) on "Magnetospheric Boundaries and Turbulence: Cluster Results". Three working groups on Foreshock and Magnetosheath, Bow Shock and Magnetopause/Cusp will meet twice a year and publish a book at the end of 2004. The second workshop on the magnetotail was organised in conjunction with the Cluster SWT in Graz (A). Five topics were discussed (current sheet structure, reconnection, current disruption, bursty bulk flow and plasmasheet/lobe structure). For each topic old events (2001) and new events (2002) were presented. Main highlights were new measurements in the reconnection region (e.g. Hall currents, electron energy dispersion, strong electric fields) and a case study of a geomagnetic substorm where we have a very good conjunction with Cluster, Geotail and Polar aligned on the Sun-Earth line.
Operations and Archiving
JSOC is co-ordinating successfully the scientific operations, including the US instrument, with DSN. ESOC is performing successfully the spacecraft operations and is delivering the data to the Cluster community as expected.
User access to the nationally funded Cluster Science Data System (CSDS) is increasing every month. The average download by scientific users over the last three months was 6.5 Gbytes/month.
The set-up of the Cluster Active Archive (CAA) has started after the approval from SPC in February. A design archiving team has been formed with members from ESA, external members involved in archiving and a PI representative. This team meets every two months to prepare the design of the system. Regular reporting and exchange with the Cluster PIs is done at the SWT. The system design review will take place in October 2003.