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The characteristics of a polarized radio wave detected by an antenna onboard a spacecraft depend on the relative positions of the transmitting source and the spacecraft, the orientation of the satellite antenna with respect to the wave propagation direction, the electric field of the incident wave, and the properties of the medium traversed by the wave. Precise knowledge of the radio wave propagation direction and the receiver antenna orientation is needed for resolving the received signal properties. In this work, the focus is on the coordinated experiments between the Radio Receiver Instrument (RRI) on Swarm-E and the Natural Resources Canada Ottawa transmitter (45.4°N, 75.6°W). Three experiments, in which the RRI boresight was along the ram (13 December 2017), nadir (20 December 2017) and slew-to-target (21 December 2017) directions were selected for detailed investigations and comparisons. The deviation of the RRI boresight direction from the propagation direction of the wave vector was up to 10° in the slewed pass and varied between 0° and 180° in the two other passes. The effects of the antenna pointing direction were pronounced in the observed powers on each dipole and affected the observed (apparent) polarization characteristics. The observations were not sufficient for describing the polarization state of the original signal during one third of the RRI-ram experiment when only one dipole was receiving the signal with optimal geometry. The methods developed lay the foundation for mitigating the attitude effects to determine the true polarization characteristics of the radio wave. [ABSTRACT FROM AUTHOR]

The artificial low frequency (LF) signals recorded at topside ionosphere from DEMETER satellite were analyzed in this paper, and the typical diurnal and seasonal variations were illustrated around 162 kHz in electric field spectra. The larger power spectrum density (PSD) values in electric field at local nighttime and in winter season all demonstrate the correlation feature of lower plasma content to higher penetration of LF waves into ionosphere. Around Wenchuan earthquake, the comparison of signal-noise-ratio (SNR) values in electric field with each half month during January to May in 2008 and the same half month in May from 2005 to 2007 revealed their lowest values and small covering area around the preparation region of Wenchuan earthquake in 2008. Combined with other researches in VLF radio waves and geochemical observations from satellite, the interaction of ion accumulation and upward movement from gas-water release at surface might be a key factor to disturb the ionospheric plasma density, and then possibly leading to the decrease of low energy penetration of LF radio waves from the artificial transmitted source at ground. [ABSTRACT FROM AUTHOR]

Abstract: Based upon the most efficient electron acceleration near the midplane of 3D non-neutral driven reconnecting current sheet (RCS) and the electrostatic wave excitation by the drift Maxwellian distribution of electrons in Vlasov simulation, we assume that the electrostatic waves mainly propagate opposite to the reconnecting electric field and investigated how these waves affect the electron acceleration. The main results are: (1) when the electron’s velocity equals to the phase speed of the waves, they will be trapped and have the different accelerating characteristics from the untrapped electrons through solving the momentum equations of electrons analytically; (2) the test particle simulations further prove that the number of the energetic electrons decreases with the increasing intensity of unstable waves, and the distribution of the energetic electrons takes on the double power-law. [Copyright &y& Elsevier]