No abstract

Broadband electric field fluctuations with typical amplitudes of 10–20 mV/m peak‐to‐peak and frequencies from 0 Hz to 3 kHz (BB‐ELF) were observed coincident with a region of ≤200 eV transverse H+ acceleration (TAI) near the poleward edge of the pre‐midnight aurora. The coherence and phase velocity of the electric fields were measured using a interferometric antenna array over the frequency range of ≈ 100 Hz to 3 kHz. These electric field fluctuations were found to have the following characteristics: 1) incoherence perpendicular to the geomagnetic field, 2) coherence parallel to the the geomagnetic field, 3) parallel phase velocity (ω/k∥) of 30–35 km/s upwards, 4) 0 < |k∥/k⟂| < 0.22. We show that these properties are compatible with the emission being electrostatic H+ cyclotron (EHC) waves. We also discuss possible generation mechanisms for the waves, and their relationship to the TAI.

Abstract. High temporal resolution electron detectors aboard the PHAZE II rocket flight have shown that the energy-dispersed, field-aligned bursts (FABs) are time coincident with pitch angle-dispersed electrons having energies at the maximum voltage of the inverted-V potential. This modulation of the energetic inverted-V electrons is superimposed upon an energy-diffused background resulting in a peak-to-valley ratio of -2 for the pitch angle-dispersed electrons. Since the characteristic energy of the FABs, the order of an eV, is considerably less than that of the plasma sheet electrons (the order of a keV) presumably falling through the inverted-V potential to create the discrete aurora, the modulation mechanism has to be independent of the electron temperature. The mechanism must accelerate the cold electrons over a range of energies from the inverted-V energy down to a few tens of eV. It must do this at the same time it is creating a population of hot, pitch angle-dispersed electrons at the inverted-V energy. Both the energy dispersion of the FABs and the pitch angle dispersion of the inverted-V electrons can be used to determine a source height assuming both populations start from the same source region at the same time. These calculations give source heights between 3500 and 5300 km for various events and disagreement between the two methods the order of 20%, which is within the rather substantial error limits of both calculations. A simple mechanism of providing a common start time for both populations of electrons would be a turning on/off of a spatially limited (vertically), inverted-V potential. The energy-dispersed FABs can be reconstructed at rocket altitudes if one assumes that cold electrons are accelerated to an energy determined by how much of the inverted-V potential they fall through when it is turned on. Similarly, the pitch angle-dispersed, inverted-V electrons can be modeled at rocket altitudes if one assumes that the plasma sheet electrons falling through the entire potential drop all start to do so at the same time when the potential is turned on. The FABs seem to fluctuate at either -10 Hz or near 100 Hz. An important constraint of the on/off mechanism is whether cold electrons (1 eV) can fill the inverted-V volume during the off cycle. The maximum vertical height of the 10 kV potential region for the 10 Hz events would be the order of 100 and 10 km for the 100 Hz events. To get 10 kV, these heights require parallel electric fields of 0.1 and 1 V/m respectively for the 10 and 100 Hz events assuming that the filling is along B from below the inverted-V potential. Alternative mechanisms are also discussed in the light of the data presented. IntroductionIt is generally accepted that there is parallel electric field acceleration of auroral electrons occurring at altitudes the order of 1 R E. The FAST spacecraft at altitudes of -4000 km is either below or within an upward directed electric field region responsible for the acceleration of the electrons producing the discrete aurora within the upw...

Two argon ion generators were operated during a sounding rocket flight from Sondre Stromfjord, Greenland, on February 10, 1985. The ion generators were flown to investigate ion beam dynamics and beam effects on the ionosphere. The other major purpose of the flight was investigation of auroral electrodynamics as the rocket passed over auroral arcs. One generator emitted an ion beam perpendicular to the magnetic field and the other a beam parallel to the field. The ion generators were on a subpayload that was separated from the main payload early in the flight. Ion detectors, an electric field meter and wave receivers were carried on the main payload to provide diagnostic measurements during the ion beam operations. Seventeen operations of the generators were observed over a 480‐s interval before the rocket reentered the atmosphere. There was evidence of heating of the ionosphere around the subpayload during each ion beam emission. Ions of energy 100 to 200 eV, the ion beam energy range, were observed at the main payload during the first seven operations of each generator, with payload separation distances up to 800 m, reaching the main payload from directions appropriate for beam ions. In addition, there were also ions reaching the detectors during beam operations, with higher and lower energies and different directions than those expected from the beam ions. Waves were observed during most of the first seven operations of each beam. Hydrogen, helium and oxygen cyclotron harmonics were observed in some of the perpendicular‐beam operations. Waves were weak or absent during the first and third parallel‐beam operations at separation distances near 80 and 320 m. In general the waves generated by the parallel beam were weaker than those generated by the perpendicular beam. The parallel beam waves were line emissions, some at approximate multiples of the hydrogen cyclotron frequency, between 5 and 7 kHz, near the lower hybrid frequency. During the fourth perpendicular gun operation, with separation distance 380 m and near peak altitude, absorption lines, separated by the hydrogen cyclotron frequency, were observed in the auroral hiss band.

No abstract