spase://CNES/NumericalData/CDPP-AMDA/Cluster/Cluster2/PEACE/clust2-pea-mom

The CAA Moments data are electron density, velocity vector, pressure tensor and heat flux vector. The vectors and tensors are provided in GSE coordinates. Velocity and temperature are also provided as components perpendicular and parallel to the magnetic field. The magnetic field data is taken from CSDS FGM PP data, at present. In a possible future release we would ideally use CAA FGM data, but it is considered unlikely that there will be major differences except in very weak field regions. Furthermore : * T_perp and T_para are determined by projecting the pressure tensor along the magnetic field and dividing by the density and by Boltzmanns constant. T_perp is the average of the two perpendicular components. * v_para = (v.b) b and v_perp = v - (v.b) b. where v is the velocity vector and b is the magnetic field unit vector. These data are produced on the ground using 3-D data and thus are available at time resolutions which are limited by the rate at which 3-D data can be transmitted. The data source used to generate the mome nts is always the best available resolution 3-D data; this means mainly 3DR data but in the case 3DX or 3DXP are available these are used instead for the MOMENTS production (see Mode_DataOrigin_HEEA/LEEA). Choices on the best way to combine data from the two sensors can be made in the moments production software; in the first release the moments are made using LEEA data in the energy overlap region. In some situations, use of both sensors together may be a better choice, for example in case s where the distribution changes during a spin as the method can resolve time aliasing errors. If resources allow, the Moments product at CAA may be updated to take advantage of this possibility. The advantage of these ground - calculated moments is that the best available calibration data is used, a correction can be made for the spacecraft potential measurements (collected by the EFW experiment), and spacecraft electrons can be properly removed. The current release has been generated automatically using default values to control the approach to potential correction and photoelectron removal, and has not been systematically human - validated, so some errors may exist. Specifically, the spacecraft potential, Vsc, is set to be 1 V greater than the measured probe - spacecraft potential provided by the electric field experiment (EFW) and the lower energy cutoff for the moments integration is set to reject the energy bin containing the EFW potential and the one above that (which in practice may also contain counts due to spacecraft electrons). Sometimes cold electrons are present which can appear in the same energy bin as the spacecraft photoelectrons, therefore both the cold electrons and spacecraft photoelectrons are removed resulting in underestimated electron densities. Recent work by the EFW team suggests a more accurate determination of from would be a term that increases linearly above ~10 V (Cully et al., 2007) but this has not yet been implemented in our CAA moments generation code.