Wynne Calvert

Kilometric continuum detected by Geotail

A new kind of terrestrial continuum that appears to be generated inside the Earths plasmasphere has been detected by the Geotail satellite at an orbital distance of 10 to 30 RE in the dayside and evening sectors of the magnetosphere. This previously undetected emission, which will be called “kilometric continuum,” is found to consist of slowly drifting narrowband signals at a frequency of 100 to 800 kHz, corresponding to the plasma frequency inside the plasmasphere at an altitude extending down to only a few thousand kilometers in the topside equatorial region of the Earths ionosphere. Unlike normal continuum, kilometric continuum is found to occur only near the magnetic equator, where it appears to be unrelated to magnetic activity and is emitted within a well-defined beam within only ∼10° of the magnetic equator.

Ion cyclotron bands in VLF saucers

Abstract In the wideband VLF data obtained by the polar orbiting DE -1 satellite over the polar night ion trough region of the upper ionosphere, conspicuous frequency-band structures are found to occur both in absorption and emission, particularly associating with VLF saucers. These proton cyclotron harmonic bands are sometimes observable up to the 10th harmonic. The attenuation bands, which appear in both the magnetic and electric data from DE -1, presumably indicate that the ions of atomic hydrogen from the polar ionosphere are accelerated by the ac electric fields of VLF waves oscillating normal to the static magnetic field, analogous to a cyclotron accelerator. The observed frequencies of the cyclotron harmonics are generally somewhat higher than the local cyclotron frequencies computed from the onboard magnetometer data, suggesting that the acceleration is taking place in the layer below the satellite at a geocentric distance of less than about 1.5 Earth radii. This example indicates the existence of upward propagating hiss at those altitudes inside the auroral zone. On the other hand, the frequency shifts of the emission bands are found to be space and time dependent, with the harmonic frequencies inside the V-shaped saucers being somewhat higher than those outside. These frequency shifts are attributed to a combination of two different types of Doppler shift, one due to the orbital motion of the satellite and the other due to the upward motion of the medium at the emission source. This indicates the existence of an upward plasma flow at the source, with a velocity of the order of 20 km s −1 inside the saucer. The amount of this frequency shift decreases with increasing harmonic order, indicating a higher phase velocity for the electrostatic waves of higher harmonic order.