UCSD Iterative Tomography Analyses Applied to STEREO HI Observations

The STEREO spacecraft provide heliospheric imaging systems particularly designed to maximize the scientific return of heliospheric Thomson-scattering brightness data from a non-Earth perspective. To aid in this analysis we have adapted the UCSD iterative tomography analyses for use with STEREO Heliospheric Imager observations to provide plasma densities of the inner heliosphere. These analyses show all manner of solar wind features with unprecedented precision- resolutions of a few degrees in latitude and longitude, solar distances of a few hundredths of an AU, and temporal cadences of about one hour in regions viewed by these instruments. Included in these are Stream Interaction Regions (SIRs) and Interplanetary Coronal Mass Ejections (ICMEs). These structures include shocked plasma density enhancements in front of SIRs and ICMEs, enhanced density in SIRs and in slow ICME sheath regions. They also show plasma voids in regions behind SIRs and ICMEs. In this analysis we look carefully at the shape and evolution of several plasma voids behind ICMEs as they evolve outward from close to the solar surface until they reach 1 AU where they are measured in situ.