IMP LEPEDEA Data Made FTP-Accessible

Volume 16, Number 1, March 2000

By Joseph King and Natalia Papitashvili

Over the years Professor Louis Frank and his colleagues at the University of Iowa have flown a series of increasingly sophisticated instruments for the determination of the distribution functions of protons and electrons within the Earth's magnetosphere, especially the Earth's magnetotail. One of this series, called the Low Energy Proton and Electron Differential Energy Analyzer (LEPEDEA), flew on the Interplanetary Monitoring Platform (IMP) 8.

The IMP 8 LEPEDEA determined distribution functions every 2+ minutes by measuring proton and electron fluxes in 15 energy windows between 60 eV and 40 keV (approximately) in each of 16 azimuthal directions about the IMP spin vector. The IMP spin vector is normal to the ecliptic plane, and the IMP spin period is about 23 rpm.

The traditional approach to LEPEDEA data management at the University of Iowa has been to generate daily colored spectrograms from which times of special interest could be identified and then to do scientific analyses from essentially raw data for the times of interest. Unfortunately, such near-raw data were virtually impossible for use away from the University of Iowa. As such, they were never archived at NSSDC, although a set of the spectrograms would be archived.

However, there was some extra IMP project funding available several years ago for preparation of archive-appropriate data products. Led by Dr. Cheryl Huang, the Iowa team created digital distribution function data for time spans jointly selected by Iowa and the IMP project, and sent these data to NSSDC on six 9-track tapes in the early 1990s. The time spans included the 1978-1980 period of the early International Sun-Earth Explorers (ISEE)-IMP overlap, the 1982-1983 period in which ISEE 3 was in the Earth's deep magnetotail, and the 1986 Polar Region Outer Magnetosphere International Study (PROMIS) period. The data cover only the LEPEDEA-optimal magnetotail phase of the IMP orbit (near circular at ~200,000 km).

NSSDC has recently converted these data from binary to ASCII, g-zipped them, and made them FTP-accessible at In addition, NSSDC also created a single (non-zipped) file containing just the electron and ion densities and the ion velocity vectors (GSE X, Y components only) as extracted from the full data records.

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Author:Miranda Beall
Curator:Lori Persichitti
Responsible Official: Dr. Joseph H. King, Code 633
Last Revised: 16 May 2000 [NAB]