ACE News #3: 10/27/97

Early Data from EPAM, the ACE Electron, Proton and Alpha Monitor



EPAM, the electron, proton, and alpha monitor, was turned on Saturday, August 29, 1997. EPAM provides full unit sphere coverage of ions and electrons in the very rich environment that covers the transition from interplanetary dominated phenomena at low energies to solar events at higher energies. EPAM has five apertures spaced at different angles from the ACE spin axis. Four magnetic and foil apertures (LEMS/LEFS) measure ions (0.04 <= Ei <= 5.0 MeV) and electrons (40 <= Ee <= 325 keV) and a composition aperture (CA) determines atomic species (~0.3 <= E <= 5.0 MeV/nuc) from H to Fe.

The figure above shows a representative group of EPAM channels that highlight some of the capabilities of the instrument. Each curve shows 30 minute averaged count rates covering 12 days from September 15 through 26, 1997. The top panel shows ion rates, (49 <= Ei <= 59) keV, at 120° from the ACE spin axis. It contains a small, long-duration, solar/interplanetary event that lasts from day 261 through day 266. The event is punctuated by a number of approximately hour-long bursts of ions escaping upstream from the magnetosphere, labeled "MS." Nearly one hundred magnetospheric events have been observed within the first 30 days of the mission. The second panel shows 0.58-1.1 MeV ions and their very different time profile at these higher energies. The third panel shows alpha particles (0.42 - 1.3 MeV/nuc). The complex nature of this event can be seen by comparing the time profiles of the protons and alphas. The early portion of the event, days 261 - 264, is rich in heavy nuclei. The fourth and fifth panels show ~ 0.50 - 2.0 MeV/nuc CNO and 0.28 - 0.88 MeV/nuc Fe nuclei. In fact, the Fe group is nearly as plentiful as the CNO group in the early portion of the event. The bottom panel shows the triple solar electron events (46 - 55 keV) from the increasingly active Sun in late September.

EPAM was developed by the Johns Hopkins Applied Physics Laboratory.
.....contributed by Dr. Robert Gold, JHU/APL.


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Last modified 23 October 1997, mrt
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