On March 27, 1996 the POLAR ultraviolet imager that can provide global images of the auroral lights remotely from space was turned on. Thus the first conjunction event that utilized the full power of the ISTP era took place. Auroras that extended over 5 degrees in latitude and as wide as 3 local time zones were observed to light up above the polar skies. (figure 1, clock-dial inserts). As the WIND spacecraft (named after the Solar Wind that it routinely monitors) was zipping by Earth towards its closest approach to the planet, it passed from the vicinity of the GEOTAIL satellite (named after the Earth's magnetic-tail that it routinely measures). The correlation between the POLAR auroral images and the space plasma acceleration was astounding. Previous studies had failed to produce a tight agreement between auroral phenomena and magnetotail acceleration attributed to conversion of Sun's electrodynamic energy to particle energy. POLAR's ability to routinely and globally monitor the auroral emissions and the ideal formation of the other ISTP satellites allowed correlations of the energy transport at a fraction-of-a-minute accuracy.
As in every case of observing old phenomena with new, more powerful tools, surprise was not absent from this ISTP conjunction: The close proximity of the satellites, a mere 4 Re (1 Re=Earth's radius, or 6400 km), would have every scientist believe that the the two spacecraft's local measurements of the energy and flux circulation through the magnetospheric system would exhibit only small differences. To their surprise, the energy conversion and flux transport processes were much more localized than expected. The measured plasmas at the two spacecraft were so different that the net transport measured at GEOTAIL was almost twice the one measured at WIND (bottom of figure). Apparently the process of solar energy conversion to particle speed at the nightside magnetosphere, although driven by global changes, operates on short spatial scales. Future investigations are expected to focus on the detailed particle correlations between different spacecraft at many different scale sizes in order to determine the important scale size for transport, and the microstructure of the energy conversion process.
A GRL paper on this event has been submitted to the special issue on ISTP. A postscript version of the submitted text can be obtained by shift-clik on the word submitted.ps. The figures and the interactions with the co-authors can be viewed at: POLAR-GEOTAIL-WIND 960327 conjunction substorms.