Variations in the GCR Flux Associated with Heliospheric Transient Structures Near the August 20, 2006 Forbush Decrease

On August 20, 2006 a Forbush decrease observed at Polar in the Earth's magnetosphere was also seen at the INTEGRAL spacecraft outside the magnetosphere during a very active time in the solar wind. Data from Polar HIST and from INTEGRAL's Ge detector saturation rate (GEDSAT), which measures the GCR background with a threshold of ~200 MeV, show similar, short-period GCR variations in and around the Forbush decrease. The solar wind magnetic field and plasma conditions during this time reveals three interplanetary shocks present in the days leading up to and including the Forbush decrease. The first two shocks are driven by interplanetary coronal mass ejections (ICMEs) and the last one by a high-speed stream. However, the solar wind following these shocks and during the Forbush decrease is not particularly geoeffective. The Forbush decrease, which begins at ~1200 UT on August 20, 2006 is the largest intensity change during this active time, but there are many others on a variety of timescales. Looking at more than 14 consecutive hours of INTEGRAL and Polar data on August 21, 2006 shows great similarities in the time history of the measurements made aboard the two satellites coupled with differences that must be due to GCR variability on a scale size of the order or less than their separation distance. Despite the spacecraft separation of over 25 Re, many of the larger intensity fluctuations remain identical at both satellites. Autocorrelation and power spectral analyses have shown these are not ar-n processes and that these fluctuations are statistically significant. Such analyses can be done with high confidence because both detectors aboard Polar and INTEGRAL have large geometric factors that generate high count rates on the order of 1000 particles per spin, ensuring rigorous, statistically significant samples.