Solar rotation signatures in cosmic dust data measured by the Wind spacecraft

Through serendipitous measurements with its plasma wave antennas, the Wind spacecraft recorded more than one hundred thousand impacts of cosmic dust particles onto the spacecraft body. Frequency analysis of the time series of impact data reveals signatures of the solar rotation.

These solar rotation signatures are transient in time. Case studies of time periods with particularly long-lasting corotating interaction regions (CIRs) yield stronger solar rotation signatures in the dust data than case studies of time periods with short-duration CIRs or few CIRs. This indicates that CIRs are a likely cause of the solar rotation signatures, possibly in combination with the alternating sector structure of the solar wind.

One physical mechanism that can cause the solar rotation signature, besides temporary changes of the spacecraft's floating potential that may influence the signal, is a local depletion of dust particles when a CIR passes by the spacecraft. A similar mechanism has been proposed to occur during coronal mass ejections (CMEs) and has been observed in close vicinity to the Sun with Parker Solar Probe. A statistical depletion analysis of the Wind cosmic dust impact data finds that both CMEs and CIRs with strong magnetic fields can locally deplete dust. This effect is strongest for small particles in CMEs.