Statistical characteristics of bursty bulk flow events

TLDR

The study aims to investigate the one‑to‑one correspondence between bursty bulk flow events and substorm phases, and to quantify BBFs’ contribution to total transport during substorms. The authors analyze AMPTE/IRM and ISEE‑2 satellite data using a common methodology to characterize the statistical properties of BBFs in the inner plasma sheet. BBFs correlate positively with the AE index, are most frequent earthward near midnight and far from Earth, become increasingly tailward with distance, and account for 60‑100% of earthward mass, energy, and magnetic flux transport, making them the primary transport mechanism in the inner plasma sheet.

Abstract

Using a common methodology to analyze data from the AMPTE/IRM and ISEE 2 satellites we report on the statistical properties of bursty bulk flow events (BBFs) in the inner plasma sheet (IPS). A positive correlation between BBFs and the AE index suggests that BBFs are predominantly geomagnetically active time phenomena. Earthward BBFs are more frequent close to midnight and away from Earth, up to a distance of ∼19 R E . Tailward BBFs are very infrequent in the IRM data set and somewhat less infrequent in the ISEE 2 data set in the region of the satellites' spatial overlap, possibly due to the more active conditions prevailing during the ISEE 2 mission in that region. However, in both data sets the ratio of tailward to earthward BBFs increases with distance from Earth; more than 20% of all BBFs are anti‐sunward tailward of X = −19 R E in the ISEE 2 data set. BBFs are responsible for 60‐100% of the measured earthward transport of mass, energy and magnetic flux past the satellite in the regions of maximum occurrence rate, even though they last approximately 10‐15% of the IPS observation time there. Thus BBFs represent the primary transport mechanism at those regions. The one‐to‐one correspondence between BBFs and substorm phase, as well as the relative contribution of BBFs to the total transport observed during substorms are questions that await further investigation based on multi instrument studies of individual events.