Cluster Status Report - May 2004
Recent Science highlights are the first measurements of the currents in the magnetotail. One of the precursor processes to reconnection is the thinning of the current sheet in the centre of the tail. Recently, Cluster made the first measurements of the current in the tail using the coulometer or Ampere's law technique using the four spacecraft. It was shown that the maximum intensity of the current was 140 nAm-2 or about 30 times its usual value. The estimated profile of the dawn-to-dusk current density along the Z direction shows that the half thickness of the tail current sheet was about 300 km. When the thickness of the current sheet becomes this thin (less than the ion inertia scale length) the ion motions are no longer governed by the magnetic field and cannot be described as a fluid, while the electrons can be still behave as a fluid. As a result, it is believed that the dawn ward motion of the electrons carries the current.
Cluster is the ideal tool to study the dynamic of the magnetosphere and its changes induced by changing conditions at the Sun and in the solar wind. A recent study at the border of the magnetosphere, in the polar cusp, has shown that the polar cusp moved back and forth three times due to changes in the direction of the solar wind. This can be understood if we compare the Earth's magnetosphere as a windsock that is moving as the wind direction changes. The solar wind flow direction is usually not taken into account in studies of dynamics of the magnetosphere and this study shows that it can sometimes be an important factor.
JSOC is coordinating 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. Interferences between the Japanese Servis 1 mission and Cluster 3 were not observed up to now.
User access to the nationally funded Cluster Science Data System (CSDS) is increasing steadily. The average download by individual users over the last four months was 5.8 Gbytes/month.
The preparation for the archiving of the Cluster data (CAA) is progressing well. The CAA team consists of a project manager, a technical manager, two software engineers; the last software engineer will join the team in June. In addition an instrument engineers/scientist will be working at each of the ten European PI institutes for the data preparation. The milestone for the end of this year is to archive the data from the first year of operations (2001).