Simultaneous conjugate ground-satellite ULF pulsation measurements at the middle latitudes

Abstract

Abstract. The spectra of three series of simultaneous ground (Budkov Observatory) and satellite (Freja) ULF measurements have been processed. The following features were studied in the FFT spectra, power-spectra and cross-spectra of the six-minute samples, recorded during quasi-conjugate approaches of Freja to the local Budkov magnetic field line: (a) the Doppler frequency shift (about 1mHz and less) in the predominant and some particular spectral components on Freja; (b) the amplitude relations between the ground and satellite (ratios 0.3 to 0.8); (c) phase shifts between particular signal components on the spacecraft above the ionosphere (in the azimuthal y-direction on Freja) and on the ground (in the meridional x-direction at Budkov) have been estimated (phase lags on the ground ≤ 0.9rad) and (d) also dynamical characteristics of the fundamental wave modes in the (x,y)-plane, perpendicular to the magnetic field line, have been estimated for the predominant spectral components, considering standing oscillation along the field line. Azimuthal wave numbers were about 2.0, propagating northwest at ~400km/s.