STEREO A HI Observations Now Provide Near Real Time High-Resolution 3-D Density Reconstructions of the Inner Heliosphere

The STEREO spacecraft Heliospheric Imagers (HIs) were designed to view the region between Sun and Earth and thereby maximize the scientific return of heliospheric Thomson-scattering brightness data from a non-Earth perspective along the Sun-Earth line. We have recently adapted the UCSD Solar Mass Ejection Imager (SMEI) iterative tomography analyses for use with STEREO HI data to provide 3-D reconstructed plasma densities of the inner heliosphere in the region viewed by these instruments. Now, as STEREO A approaches the Earth, this provides an unprecedented ability to reconstruct densities in that portion of the inner heliosphere Earthward of the Sun, and allows an ahead-of-time prediction of plasma density properties at high resolution in this region. Because we are using HI data with a long temporal base removed, both Stream Interaction Regions (SIRs) and Interplanetary Coronal Mass Ejections (ICMEs) are among the phenomena that can be diagnosed in the analyses. Here we show this near real time system operation that, albeit limited by the fact the latency of the current STEREO HI scientific image data is three to five days, provides imagery of the plasma density and its measurement at various locations throughout the inner heliospheric region viewed. The reconstructions are updated every six hours, which is well within the time limit needed to forecast the arrival of the fastest heliospheric structures at Earth. This system benchmarks computing needs for high-resolution 3-D reconstruction analyses of this type, and prototypes the forecasting capability for future similar spacecraft heliospheric imager instruments operated with a shorter data latency.