HIGH-LATITUDE HP DOPPLER OBSERVATIONS OF ULF WAVES - I - WAVES WITH LARGE SPATIAL SCALE SIZES

A quantitative study of observations of the ionospheric signatures of magnetospheric ultra low frequency (ULF) waves by a high-latitude (geo graphic: 69.6 degrees N 19.2 degrees E) high-frequency Doppler sounder has been undertaken. The signatures, which are clearly correlated wit h pulsations in ground magnetometer data, exhibit periods in the range 100-400 s and have azimuthal wave numbers in the range 3-8, They are interpreted here as local field line resonances, Phase information pro vided by O- and X-mode Doppler data support the view that these are as sociated with field line resonances having large azimuthal scale sizes . The relative phases and amplitudes of the signatures in the Doppler and ground magnetometer data are compared with a model for the generat ion of Doppler signatures from incident ULF waves. The outcome suggest s that the dominant mechanism involved in producing the Doppler signat ure is the vertical component of an E x B bulk motion of the local pla sma caused by the electric field perturbation of the ULF wave.