Dependence of ELF emissions on the location of the plasmapause

ELF emissions at 1.3 kHz are observed at altitudes below 1500 km by a receiver on board spacecraft OV3 3. Correlations of the emissions with local time, magnetic latitude, and the planetary magnetic index Kp show that they have the same characteristic dependence with these parameters as has chorus observed by other satellites. The altitude dependence of the magnetic field intensity agrees with that predicted for a wave propagating completely trapped on a tube of force without attenuation. In a few instances, simultaneous measurements of electromagnetic field intensities, wave propagation direction, and electron density were available to show that the emissions were propagating in the whistler mode. The most interesting feature of the emissions is their dependence on the position of the plasmapause. For high Kp, the probability of occurrence increases as the plasmapause moves to a lower L value. The peak intensity of the emission occurs near the plasmapause