Equatorially trapped plasmas, and the equatorial noise, were one of the most prominent features of the SCATHA observations.
Here is the work done with Dynamics Explorer 1 - Plasma Observations, the Density Minimum, and my one theory paper.
A recent article reports on Cluster observations of equatorial noise.
And my favorite paper, and the only one with any real theory - " Comparison Between Liouville’s Theorem And Observed Latitudinal Distribution Of Trapped Ions In The Plasmapause Region". Had to use data from SCATHA and DE-1 to get the complete story.
funny note - Khazanov & Miller, from Michigan, had seen the work presented at a conference, then apparently rushed off and submitted a theory paper to GRL. They wanted to get prior claim to the idea, I suppose. Of course, Lewis Scott's thesis preceded the GRL article by about 2 years, so it's pretty clear who stole whose idea.
One other note - I worked on this paper while back in Huntsville for a summer program (ASEE). The short version is here. I would not mention that except for the exceptional work by Mike Pangia, which apparently never got published anywhere else. Mike showed that the non-Maxwellian distributions we were seeing, better modeled, apparently, as kappa distributions, could be derived from first order thermodynamic principles. The Kappa Distribution as a Variational solution for an Infinite Plasma A really important piece of work, that never got much further exposure.