This project will use data from the THEMIS spacecraft and the GLD360 global lightning detection network to determine the extent to which plasmaspheric hiss is generated by lightning. In addition, observations from the DEMETER satellite will be used to determine to what extent the plasmaspheric hiss resembles magnetospheric chorus emissions. This data will be used to examine the hypothesis that chorus is a major source of plasmaspheric hiss. The project will also use a 10-year data set of gournd-based chorus from Palmer Station, Antarctica to examine the role of magnetospheric chorus waves on the phase-space density of energentic electrons in Earth's radiation belts.
The research is related to the Geospace Environment Modeling program focus group on the radiation belts and magnetospheric waves. It has societal benefits because of the importance of understanding the radiation belts where high energy particles can damage spacecraft. The project also has education and training benefits because it funds a postdoctoral scholar.
The first part of this research was concerned with determining whether ground measurements of electromagnetic waves which originate in space (so-called "plasmaspheric hiss") could be used as a substitute for in situ (spacecraft-based) measurements of those waves. This is an important question because ground stations are orders of magnitude less expensive to build and operate when compared to satellites. We determined that, although ground and in situ observations of hiss are correlated under certain circumstances, they are not correlated in general. We do not believe that observations of hiss from a single ground station are adequate to replace in situ measurements at this time. The second part of this research was focused on using solar wind data (currently measured by one or more spacecraft, with minimal temporal gaps in coverage) and geomagnetic indices (measured by ground receivers on the Earth with no temporal gaps in coverage) to model the amplitude of two types of electromagnetic emissions that are naturally generated in the Earth's magnetosphere: "chorus" and "hiss." These emissions play a significant role in the dynamics of the Earth's radiation belts, a region of trapped energetic particles which, under certain conditions, can pose a significant hazard to satellites and astronauts. Thus, accurate modeling of chorus and hiss is a prerequisite for accurate modeling of radiation dynamics. In this research, we constructed empirical statistical models of equatorial chorus and hiss measurements from the THEMIS spacecraft from 2008--2011. We were then able to run these models for any time when solar wind data and geomagnetic index data was available. By simulated a geomagnetic storm using our models, we were able to show, for the first time, the global dynamic evolution of these emissions during storms.
