DE‐1 observations of lower hybrid waves excited by VLF whistler mode waves

Abstract

Recent satellite data show high amplitude lower hybrid (LH) waves excited by electromagnetic (EM) whistler mode waves throughout magnetospheric regions where small scale magnetic‐field‐aligned plasma density irregularities exist. One important consequence in the auroral acceleration region is the heating of suprathermal ions by the excited LH waves. To evaluate such heating it is necessary to know the wavelength (λ) range of the waves, information not previously available since most past observations were made with long (l ≥ 75; l=antenna length) electric dipole antennas which have very poor response for λ < l. New observations using the short 9 m electric dipole antenna on the DE‐1 spacecraft show that LH waves with λ ≤ 10 m are excited by EM input waves from ground‐based VLF transmitters. Sequential observations on the short (9 m) and long (200 m) dipole antennas show that the long antenna generally has no measurable response to LH waves with λ ≤ 26 m. Since most previous correlative observations of LH waves and ion conics in the low altitude auroral acceleration region have involved long electric antennas, it is suggested that the intensity of the LH waves in this region may have been seriously underestimated.