Diurnal Variations in the Power Spectrum and Polarization of Telluric Currents at Conjugate Points, L = 2·6

Abstract

The power spectrum of telluric currents, at the sub-auroral latitude where L = 2�6, shows a pronounced diurnal variation. The variation is contributed mainly by a strong peak at about 40 s, which shows a large cyclic fluctuation in amplitude and also a tendency to shift in frequency. The amplitude is larger and the period somewhat shorter during the day-time. The 40-s peak is also subject to appreciable random fluctuation in period. The spectrum shows shorter periods (7-14 s), and longer periods (several hundred seconds) in addition to the 40-s peak. There is a general shift to slightly longer periods at the time of auroral onset. The spectra are compared with those obtained at other latitudes. A period of about 40 s appears to have a wide distribution in latitude. It can be followed from mid latitudes to latitudes in the auroral zone and polewards of the auroral zone. The ignificant variation with geomagnetic latitude seems to be the relative amount of power associated ith anyone period rather than in the period itself. The observations are not readily econciled with theoretical estimates of magnetospheric oscillation in the transverse and compressional modes.