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MEPI Energetic Particle Fluxes (36-Sec) from Wide Angle Particle Spectromtr(WAPS)


Availability: Archived at NSSDC, accessible from elsewhere

Time span: 1977-11-09 to 1979-09-10


These experimenter-supplied data from the Medium Energy Particles Instrument (MEPI) on ISEE-1 consist of 3-dimensional distributions of energetic particle fluxes from the Wide Angle Particle Spectrometer (WAPS) for the period 10Nov77 to 08Sep79. The data are written in VAX binary form. Ion and electron fluxes are provided, organized by spin, sector, and energy channel. A complete 3-D measurement in 8 (16 in high bit rate mode) logarithmically spaced energy channels of ion fluxes from 24 keV to 2 MeV and electron fluxes from 22.5 keV to 1.2 MeV is made in 96 (192 in high bit rate mode) directions every 36 seconds. Resolution at the sector level of 3/8 second at low bit rate (3/16 second at high bit rate) can be inferred. The data files also contain header information (scan begin time, spacecraft GSE and GSM coordinates, scan direction, bit rate mode, etc.), magnetometer data, and a spin/sector pitch angle matrix. Fluxes are given in (cm^2-sec-ster-keV)^-1. The energy passbands and other channel attributes given in the accompanying documentation. The magnetometer data included here have not been processed as thoroughly nor corrected as completely for the effects of spacecraft spin as those provided by the magnetometer experiment Principal Investigator. The raw MEPI data have been converted to geophysical units for the convenience of the user assuming that ion counts are dominated by protons. This assumption has been proven to be well-supported from experience; however, the fluxes can be converted back into counts using the proton characteristic energy limits of each channel, and new fluxes calculated based on known or assumed compositional make-up of the plasma. The data quality is generally good. During certain intervals, the operation of another on-board instrument resulted in anomalously high count rates in the low energy ion and electron channels. This is readily recognizable by indicated fluxes that are above a specified value (higher than any recorded naturally in the instrument lifetime) in the lowest energy ion channel. A subroutine to recognize this and flag the data is provided. The MEPI instrument performed flawlessly from launch until September 8, 1979, when a component failure rendered it inoperable.

Data are available online at

Alternate Names

  • MEPI/WAPS 3-D Distr. Func. (36-S)


  • Space Physics: Magnetospheric Studies
  • Space Physics: Heliospheric Studies


  • 77-102A-09H

Additional Information



Questions and comments about this data collection can be directed to: Dr. H. Kent Hills



NameRoleOriginal AffiliationE-mail
Dr. Donald J. WilliamsData ProviderApplied Physics
Mr. Robert M. CandeyGeneral ContactNASA Goddard Space Flight
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