During the Twin Rockets to Investigate Cusp Electrodynamics (TRICE-2) High-Flyer rocket’s passage through the cusp the high frequency (HF) radio wave receiver observed three intervals of banded Upper-Hybrid (UH) waves. The bands begin at the UH frequency ($\sim$1.2–1.3 MHz), descending to as low as 1.1 MHz, with amplitudes of hundreds of mV/m. The spacing of the bands are $\sim$4.5–6 kHz and the number of bands ranges from three to ten. Simultaneously, the very low frequency (VLF) radio wave receiver observed Lower-Hybrid (LH) waves with amplitudes ranging from 1–10 mV/m and frequencies of 4.5-6 kHz. Slight variations of the spacings of the bands in the UH waves were closely correlated with variations in the LH peak frequencies. Two possible wave-wave interactions are explored to explain this phenomenon: decay of an UH wave into a lower frequency UH wave and a LH wave, and coalescence of independent UH waves and LH waves that spawn UH waves. Using a dispersion relation calculator with electron and ion distribution functions based off those observed by the particle instruments suggests that UH waves, and to a lesser degree LH waves, can be excited by linear instabilities. Kinematic analysis of the waves dispersion relations and the wave matching conditions show that wave-wave interactions linking UH and LH modes are possible through either decay or coalescence. This analysis along with comparisons of the energy densities of the waves, and the ratio of their occupation numbers suggest that the decay process is more likely than coalescence.

The High-Bandwidth Auroral Rocket (HIBAR) was launched from Poker Flat, Alaska on January 28, 2003 at 07:50 UT towards an apogee of 382 km in the night-side aurora. The flight was unique in having three high-frequency (HF) receivers using multiple antennas parallel and perpendicular to the ambient magnetic field, as well as very low frequency (VLF) receivers using antennas perpendicular to the magnetic field. These receivers observed five short-lived Langmuir wave bursts lasting from 0.1–0.2 s, consisting of a thin plasma line with frequencies in the range of 2470–2610 kHz that had an associated diffuse feature occurring 5–10 kHz above the plasma line. Both of these waves occurred slightly above the local plasma frequency with amplitudes between 1–100 μV/m. The ratio of the parallel to perpendicular components of the plasma line and diffuse feature were used to determine the angle of propagation of these waves with respect to the background magnetic field. These angles were compared to the theoretical Z-infinity angle that these waves would resonate at, and found to be comparable. The VLF receiver detected auroral hiss at frequencies between 5–10 kHz throughout the flight from 100–560 s, a frequency matching the difference between the plasma line and the diffuse feature. A dispersion solver and associated frequency- and wavevector-matching conditions were employed to determine if the diffuse features could be generated by a nonlinear wave-wave interaction of the plasma line with the lower frequency auroral hiss waves. The results show that this interpretation is plausible.

Auroral whistler mode radio emissions called saucers are of fundamental interest because they require an unusually stationary emission process in the dynamic auroral environment, and it is a mystery how that can happen in this or similar conditions elsewhere in geospace. The Cusp Alfven and Plasma Electrodynamics Rocket (CAPER-2), launched into the polar cusp and obtained the first rocket measurements of a large-scale, multiple-armed dayside saucers, similar to those recently observed by the the DEMETER satellite, with the addition of in situ particle measurements and simultaneous conjugate ground-based measurements. For 300 s prior to cusp entry, CAPER-2 detected ~15 truncated saucer arms lasting 5–50 s. Directional analysis using waveforms, combined with ground-based data, suggests that these originate within the cusp. Ray-tracing analysis indicates source altitudes ~2500 km. On-board particle instruments show dispersed electron bursts in the cusp, presumed Alfvenically accelerated, corresponding to approximately the same source heights as the saucers.