Electrostatic VLF waves observed in the polar magnetosphere

Abstract

Abstract : Broadband electrostatic emissions are detected by a VLF receiver aboard the satellite OV3-3 (1966-70A). Enhancements of the electric-field intensity in ten bandpass channels at frequencies between 400 Hz and 14.5 kHz are observed when the spacecraft passes over the south polar region at altitudes between 2500 and 4500 km (satellite apogee). The power spectral density of these emissions decreases approximately as the inverse fourth power of the observed frequency. The most interesting feature of these emissions is the range of invariant-magnetic-latitudes (INVL) over which they are observed. The low-latitude limit at which they are detected is typically 72 to 76 degrees INVL in local morning and 68 degrees INVL near midnight. This dependence suggests that these emissions occur on magnetic-field lines along which the polar wind flows. During geomagnetically active periods, electrostatic waves with a high-frequency cutoff between 1.3 and 3.9 kHz are also observed in this altitude range. These emissions occur at latitudes below the low-latitude limit of the polar-electrostatic waves and above the latitude of the plasmapause. (Author)