Origins of plasmaspheric hiss

Plasmaspheric hiss is an electromagnetic wave emission responsible for electron loss from the radiation belts, particularly in the slot region (2 < L < 3). There are two leading theories for the origin of plasmaspheric hiss: in situ amplification of wave turbulence in space and lightning-generated whistlers. Here we analyze CRRES wave data together with the global distribution of lightning to test both theories. Using the entire CRRES wave database, we split the data into seven frequency bands between 0.1 and 5 kHz and examine the ionospheric mapping of the wave intensities in the slot region as a function of season, magnetospheric location, and magnetic activity. The wave intensities peak in the frequency range 0.2-0.5 kHz and become progressively smaller at higher frequencies. The wave intensities at low frequencies, f < 1 kHz, are independent of lightning flash rate, are stronger on the dayside, and peak during the equinoxes. In contrast, the wave intensities at high frequencies, f > 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.