BALLOON MEASUREMENTS ABOVE THE SOUTH-POLE - STUDY OF IONOSPHERIC TRANSMISSION OF ULF WAVES

We report here an experimental study of the Hughes and Southwood model of the transmission of electromagnetic signals from the ionosphere/magnetosphere to the lower atmosphere. The electric field data were obtained from one of eight high-latitude balloon payloads launched above the south geographic pole during the South Pole Balloon Campaign in the 1985-1986 austral summer. The magnetic field data are from the South Pole magnetometer. The balloon payloads were instrumented with double-probe electric field detectors and bremsstrahlung X ray detectors. One of the events from flight 7 (January 8, 1986, at 1500-1800 UT (1130-1430 MLT)) had an amplitude in the range of 10-20 mV/m and a period of several minutes. In the magnetosphere, the wave was probably an Alfven mode. The wave event was superimposed on background fluctuations that can be attributed to turbulence. The results agree with the predictions of the model in that the best coherence is observed between parallel components of E versus B. The results disagree with the predictions of the model in two respects. First, we find a frequency structure not predicted by the model, and second, we find intervals where the electric and magnetic field polarizations are of opposite handedness. The first discrepancy was modeled by taking account of the measured electrostatic turbulence. The second problem remains a puzzle.