Electron acceleration by megahertz waves during OEDIPUS C

Abstract

Observations of Electric Field Distributions in the Ionospheric Plasma ‐ A Unique Strategy (OEDIPUS C) was a tethered mother‐son experiment that was launched northward from the Poker Flat rocket range at 0638 UT on November 7, 1995, across a sequence of auroral structures. During the flight's upleg the magnetically aligned tether was deployed to a separation of ∼1.2 km and then cut at both ends. The forward payload contained a 50‐kHz to 8‐MHz stepped‐frequency transmitter. Receivers were carried on both forward and aft payloads. The transmitter swept through the frequency range every 0.5 s. During each of the 3‐ms steps the transmitter emitted only for the first 0.3 ms. The scientific complement also included multiangular electrostatic analyzers on both payloads that were sensitive to fluxes of electrons with energies from 20 eV to 20 keV. The durations of sampling and frequency steps were matched. During the flight the electron gyrofrequency was approximately twice the plasma frequency. When the transmitter swept through the local gyrofrequency, the particle detectors on both payloads detected sounder‐accelerated electrons (SAEs) independent of the energy steps being sampled. In addition, SAEs were detected at the aft payload out to separations of several hundred meters for wave emissions at harmonics of the electron gyrofrequency as well as in the upper hybrid and whistler bands. As the vehicle separation increased, significant time differences developed between the wave‐emission pulses and the onsets/durations of SAE detections. The data indicate that electrons were heated through strong wave‐particle interactions. However, a simple resonant‐interaction explanation appears inadequate. We outline requirements for any models purporting to explain OEDIPUS C measurements.