The nonthermal continuum radiation (NTC) beaming angle is computed over the entire Van Allen Probes A mission when the spacecraft was in the dawn sector. The conditions in the dawn sector are favorable for the wave vector to lie near/in the spacecraft’s spin plan allowing a favorable estimate of the beaming angle, and the dawn sector is also advantageous in that previous studies show NTC occurrence to peak in this sector. We found that scatter plots, over the entire mission, of beaming angle versus magnetic latitude form a distinct inverted V pattern, with the apex at/near the magnetic equator. This pattern was sharpest for frequencies (f) ≲ 100 kHz. Using the NTC beaming formula from LMCT, we show that such an inverted V pattern is expected due to the large variation in the plasmapause location over the entire mission. The theoretical derived pattern qualitatively reproduces the observed pattern but not quantitatively. The lack of quantitative agreement is discussed and is attributed to several factors, one factor is off centered emissions from the radio window. The qualitative agreement strongly supports LMCT as being the dominant mechanism generating NTC for f ≲ 100 kHz. For f ≳ 100 kHz the inverted V pattern becomes less distinct, and strong near equatorial beaming is observed. After considering contamination of our selections by left-handed polarized AKR, our study suggests that besides LMCT another unidentified NTC generation mechanism becomes important for f ≳ 100 kHz.

The backflow plume from an electric thruster can lead to the accumulation of electrostatic charge on the spacecraft, leading to a negative charge. Interactions between the plume and solar wind can further influence the charge distribution, resulting in variations in spacecraft potential and interference with sensitive instruments. A 3D Particle-In-Cell (PIC) simulation tool within the Spacecraft Plasma Interaction Software (SPIS) is used to compute spacecraft charging effects from 0.067 to 1 Astronomical unit (AU). The study examines the dynamic behaviour of ambient electrons and ions, thruster electrons, and CEX-ions, as well as photoemission and secondary electrons, and solar photon flux impact on the spacecraft potential. The main finding is the demonstration that the high dominance of CEX-ions and thruster electrons helps to achieve a low and stable negative potential ranging from -2 to -6 V from 0.067 AU to 1 AU when the thruster is on, as opposed to the varying range of -5 to +9 V with the thruster off. Other findings are that the elimination of photoelectrons or secondary electrons has a comparatively greater impact on spacecraft potential when the thruster is off, as opposed to when the thruster is on. Both CEX-ions and thruster electrons significantly contribute to the mitigation and regulation of spacecraft potential towards a less negative potential in situations where photoemission or secondary electrons are absent or relatively unimportant.

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.