Broadband Enhancements in the Cusp Ionosphere Observed by TRICE-2 Sounding Rockets

Abstract:

On 08 December 2018, the TRICE-2 mission launched twin sounding rockets from the Andoya Space Center into the northern polar cusp with a suite of plasma sensing instruments. The first sounding rocket achieved an altitude of about 1042km while the second flew below the other at around 756km. The plasma wave instruments consisted of 4 antennas measuring DC and very low frequencies (VLF) in the spin-plane of the rocket and an antenna measuring high frequencies (HF) along the spin axis of the rocket. Both sets of antennas found correlated broadband enhancements frequently throughout the flight. These appeared as very sharp (rise and fall time scales of ~ 5ms) and short (~10 ms in duration) vertical stripes in the spectrograms and occurred about once per second on average within active regions of the cusp. In total, over 200 such events have been observed between the two flights. At first believed to be instrumental artifacts, the time series analysis indicates that there is a strong, unipolar shift in all DC components of the electric field, which could be the result of a payload floating potential change, although in many cases density structure was not evident in the HF wave cutoffs. Furthermore, the higher frequency waves (>100 kHz) sometimes show frequency cutoffs and structuring, in some cases, with longer duration than the VLF wave signature. It’s possible that these waves are incident L- or R- mode whistler waves trapped and excited in the ionosphere. Thus, these results further elucidate the highly structured nature of the auroral ionosphere and the fascinating collection of waves that inhabit it.