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The ultra-low-frequency (ULF) geomagnetic pulsations observed at two nearly conjugate mid-latitude sites are examined to study their spatial structure and polarization, and learn about the role of ionospheric conductivity in forming their ground signatures. The data of 1999–2002 from Antarctica and New England (L of 2.4) are compared with the numerical results obtained in a simple plane model of ULF wave propagation through the ionosphere and atmosphere. The multi-layered model environment includes an anisotropic and parametrically time-dependent ionosphere, a uniform magnetosphere and a conducting Earth, all placed in a tilted geomagnetic field. The measured diurnal and seasonal variations in the orientation angle of the polarization ellipse are interpreted as effects of hydromagnetic wave propagation through the ionosphere and conversion to an electromagnetic field below. Essentially, the phase, amplitude and polarization of ULF waves observed at the ground are controlled by the wave''s spatial structure in the magnetosphere and ionospheric transverse conductivities. The differences shown by the characteristics of simultaneous pulsations in conjugate areas arise mainly from different local ionospheric conditions, while the source waves of the pulsations are common to both sites. [Copyright &y& Elsevier]

Abstract: Results of HF diagnostics of traveling ionospheric disturbances (TIDs) over the Antarctic Peninsula are presented that have been obtained in the frequency-and-angular sounding technique developed at the Institute of Radio Astronomy, National Academy of Sciences of Ukraine (Kharkov, Ukraine). A specially designed HF transmitter was deployed at the Polish Antarctic station Henryk Arctowski to radiate probe signals. Variations in trajectory parameters (angles of arrival and Doppler frequency shifts) of the probe signals used for recovering TID characteristics were recorded at the Ukrainian Antarctic station Akademik Vernadsky with a compact-size three-channel coherent receiver based on the Doppler interferometry technique. The propagation path length was approximately 440km. Round-the-clock measurements were performed between 31 January and 16 March, 2004 at frequencies 5 to 7MHz, depending on the ionospheric conditions. The total time of observations was about 1000h. Results of preliminary processing of the measured data are reported. Characteristic parameters of the disturbances are presented and possible sources of their generation are discussed. [Copyright &y& Elsevier]