Analysis of DC electric fields and ELF band waves observed by SS-520-2 sounding rocket in the polar region

SS-520-2 sounding rocket was launched from Norway on Dec. 4, 2000. We developed EFD (Electric Field Detector) onboard SS-520-2 rocket, and observed DC electric fields and ELF band waves (0-50Hz). According to the DC electric fields analysis, we confirmed the existence of DC electric fields. The amplitudes of these DC electric fields are up to 50mV/m, and their directions are almost south-west. Especially, strong DC electric fields are observed during the rocket decreasing period. During all the observation time, on the other hand, no clear ELF waves are observed in EFD data. In the EFD data analysis, spiky pulses are observed in the almost all EFD data. These pulses are synchronizing with the rocket spin frequency 1.5Hz. These are generated due to the photo electron emission, called photo electron pulses. The amplitudes of the photo electron pulses are expected to be related to the local plasma environment, e.g. electron density and temperatures. Though their amplitudes are in inverse proportion to the altitudes of the rocket, however, we cannot find a clear relation between the distribution of the amplitudes of the photo electron pulses and those of the electron densities, especially in the F region of the ionosphere (500-300km in the altitude) where the electron density increase suddenly. According to the previous study about photoelectron pulses observed by Akebono satellite, the photoelectron pulses are related to the direction of the ambient magnetic field rather than that of the Sun. We investigated the angles between the direction of wire antenna, when photo electron pulses are observed, and that of the Earth's magnetic field, with making use of the MGF data. As a result, we confirmed that the photo electron pulses are observed when the wire antenna become almost parallel to the Earth's magnetic field. This indicates that the photo electron pulses observed by SS-520-2 rocket are also related to the direction of the ambient magnetic field rather than that of the Sun, as previously indicated with using the data of Akebono satellite. We are going to make a statistical study of the amplitudes and duration periods of photo electron pulses and their relation to the Earth's magnetic fields in detail.