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We present a study of the spectral characteristics of protons in the Earth's plasma sheet for various geomagnetic disturbance levels. The study is based on about 5400 h of data combined from the Cluster RAPID and CIS instruments obtained during the tail season (July-October). The overall proton spectral shape is generally that of a κ distribution, that is, resembling a Maxwellian at lower energies which smoothly merges into a power-law tail at higher energies. The actual spectral long-term slope depends on various magnetospheric driver parameters, but is on average around 3.5-4. During disturbed conditions, such as geomagnetic storm or substorm periods, a shift in the characteristic energy is observed. For two individual storms, we also found a hardening of the spectra. Unlike the electron spectra, we do not see any significant local time dependence in the spectral slope, but we find higher average ion fluxes in the dusk side. We also do not find any direct response in the energy spectra to changes in the interplanetary magnetic field or solar wind dynamic pressure. This suggests that energization of the ions are mainly due to internal processes in the plasma sheet. [ABSTRACT FROM AUTHOR]

We present the first electron and ion moment maps (density, velocity and temperature) of the martian plasma environment, using data from the ELS and IMA sensors of the ASPERA-3 experiment onboard Mars Express. Moments are calculated by integration and by Gaussian fits to the phase space distribution. The methods of calculation and the calibration parameters relevant for the calculation are described in detail in the first part of the paper. The estimation of ionospheric electron densities assumes that the thermal electron temperature can be determined by the instrument – despite a cut-off by a negative spacecraft potential. The spacecraft potential is estimated by the location of photoelectron peaks in the energy spectrum. For the magnetosheath we separate the low energy part of the electron spectrum – presumably spacecraft photo electrons and the high energy part. For ions, we present maps for solar wind protons and alpha particles. Protons with energies below 500 eV which may play an important role in the ionosphere are not measured by the instrument. As well the low speed solar wind protons are not sampled very well. The maps reveal all the boundaries of the Mars-solar wind interaction and give a good qualitative description of the plasma behavior at the different interaction regions. [ABSTRACT FROM AUTHOR]