Noise induced on an electric antenna and its effective length in solar wind: Application to CLUSTER observations

Two problems related to the performance of an electric antenna in the solar wind are addressed. Namely, the noise induced on the antenna and its effective length at the close vicinity of the plasma resonance. The antenna is a double sphere dipole on the Cluster spacecraft and data are obtained from the WBD instrument. The noise data are interpreted to estimate the plasma parameters. In case the antenna is receiving regular signals, including quasi-harmonic signals coming from a distant source either of natural or artificial origin, it is its effective length that determines the voltage on antenna terminals. We show that the effective length grows by more than one order of magnitude for waves at the local plasma frequency propagating downstream to the receiver.