Cluster Status Report - February 2003
A short deployment of the two faulty wire booms on EFW (electric field sensor) did not cure the problem. The PI team is now working on a change of the on-board software which should restore the high-time resolution measurements. All other instruments are working well.
Science highlights
- The polar cusp, which are "windows" in the Earth's magnetic field where the plasma from the solar wind can enter directly, has been observed in great detail. A stagnant region, characterized by an isotropic plasma population, has been observed at the entry of the cusp. More detailed studies and more examples will be analysed to see if this region exists all the time or only during particular solar wind conditions.
- Solitons are magnetic "holes", where the magnetic field decreases to about 20% of its original value and the plasma density increases by a factor 2.5. They are short pulses of around 10s. The solitons are believed to be produced by electromagnetic waves and are observed in most regions of the Earth's environment. Cluster, with four spacecraft, could observe that the solitons are moving at around 250 km/s and have a size of about 2000 km. These results have been accepted for publication in Phys. Rev. Letters.
- The magnetotail is the part of the Earth's magnetic field opposite to the Sun. It is elongated over very large distances (more than 10 times the distance to the moon) due to the solar wind flow. At its centre, this elongation forms a current sheet. With the four spacecraft surrounding the current sheet, Cluster has confirmed that it can sometimes be split into two current sheets. In addition, instead of being flat, the current sheet see waves propagating over it at speed around 200 km/s.
- Cluster has observed ultra-low-frequency (ULF) waves around the bow shock region where the solar wind is decelerated to a sub-sonic speed. Electromagnetic waves are very important in this region since they are believed to play a key role in the deceleration of the solar wind. Four spacecraft timing techniques on magnetic field measurements were used to determine the wave properties, like the direction of propagation. It was shown that the four spacecraft technique gives good results for all type of waves while the single spacecraft technique, very frequently used in the past, is limited to the circularly polarized waves. Therefore all type of waves can now be fully studied with four spacecraft.
Operations and Archiving
The JSOC is successfully co-ordinating the scientific operations including the US instrument with DSN. ESOC performed successfully the spacecraft operations and delivered 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 3.9 Gbytes/month. A new version of the CSDS web interface as been delivered by the Joint Science Operation Centre (JSOC) to the data centres in November 2002.