Plasmaspheric hiss is an electromagnetic wave emission responsible for electron loss from the radiation belts, particularly in the slot region (2 2 kHz, increase with flash rate, are stronger on the nightside, and peak during the boreal summer. The wave intensities increase with magnetic activity for all frequencies on the dayside but are independent of magnetic activity on the nightside. The data suggest that in situ amplification of wave turbulence in space is the main source of wave power below 1 kHz, whereas wave power above 2 kHz is more related to lightning-generated whistlers. The results suggest that natural plasma turbulence should dominate the loss of relativistic (approximately MeV) electrons in the slot region 2 < L < 3.