Spin-modulated spacecraft floating potential: Observations and effects on electron moments

Using the Three-Dimensional Plasma electron analyzers on the Wind spacecraft, we have analyzed several years of solar wind electron data. We find an anomalous core electron drift of roughly 40 km/s in the sunward xGSEdirection, regardless of the direction of the magnetic field. We interpret this drift as an effect of a spin modulation in the spacecraft floating potential, which can be effectively modeled with the addition of a dipole term to the potential. For typical solar wind conditions, the amplitude of potential modulation is a fraction of a volt. The modulation has negligible effects on the even electron moments (density and temperature) but noticeable effects on the odd moments (bulk velocity and heat flux).