Transpolar arcs (TPAs) are often cusp-aligned. Especially when multiple TPAs appear simultaneously, they join at the auroral signature of the cusp. Here we investigate the dayside connection point of TPAs using Defense Meteorological Satellite Program measurements and identify three cases where the tip of the TPA ends in a localized brightening. One is a typical cusp spot with a TPA attached. The cusp appears just poleward of the oval with a near circular shape. In the second case, multiple cusp spots are observed over a 3 MLT wide region, each connected to a TPA. In the third case, the brightening at the tip of a TPA is identified as high-latitude dayside aurora (HiLDA). Cusp aurora appears between the HiLDA and the duskside oval. Plasma flows and particle characteristics indicate a lobe origin of the HiLDA. Our results indicate a more complicated connection between TPAs and dayside aurora than previously anticipated.

Context. We investigated the response of the Venusian atmospheric ion escape under the effect of interplanetary coronal mass ejections (ICMEs) using the Latmos Hybrid Simulation (LatHyS). Aims. In particular, we focused on the influence of extreme ICME dynamic pressures and temperatures, with the temperature being a parameter that has not been extensively studied in the past. Methods. Simulations were performed for two different dynamic pressures and three different temperatures. For the case of the dynamic pressure simulations, a density and a velocity enhancement event were studied separately. The H+ and O+ ion escape was then examined and compared for different escape channels. Results. In both dynamic pressure enhancement cases, we find that there is no clear dependence of the O+ ion escape on the dynamic pressure, which is consistent with observations. On the other hand, the temperature of the incoming solar wind positively influences the H+ and O+ ion escape. This is attributed in part to the enhanced gyroradius of the particles, which allows them to penetrate deeper into the planet’s atmosphere.

Mutual impedance experiments are in situ plasma diagnostic techniques for the identification of the plasma density and the electron temperature. Different versions of mutual impedance instruments were included in past and present space missions (e.g., Rosetta, BepiColombo, JUICE and Comet Interceptor). New versions are currently being devised to fit the strong mass, volume and power constraints on nanosatellite platforms for future multi-point space missions. In this study, our goal is to define and validate two new instrumental modes (i.e., chirp and multi-spectral modes) to improve the time resolution of the experiment with respect to typical mutual impedance instrumental modes (i.e., frequency sweep). Higher time resolution measurements are expected to simplify the integration of mutual impedance experiments onboard nanosatellite platforms by facilitating antenna sharing between different experiments. The investigation is performed both (a) numerically, using a 1D-1V electrostatic full kinetic Vlasov-Poisson model and, (b) experimentally, with laboratory tests using a vacuum chamber and a plasma source. From a plasma diagnostic point of view, we find that both the chirp and multi-spectral modes provide measurements identical to the (reference) frequency sweep mode. From an instrumental point of view, multi-spectral measurements are faster than frequency sweep measurements but they require larger amounts of onboard computing resources (i.e., larger power consumption). Chirp measurements, instead, outperform frequency sweep measurements both in terms of measurement duration (20 times faster) and onboard processor usage (20% less).

Multiple transpolar arcs appearing simultaneously in the polar cap have gained much interest in recent years. By analyzing Defense Meteorological Satellite Program Special Sensor Ultraviolet Spectrographic Imagers data, we report for the first time, that less than half of the multiple arc events occur simultaneously in both hemispheres. In 60% of the cases, multiple arcs appear in only one hemisphere. There is a clear difference in interplanetary magnetic field (IMF) conditions for those two groups. Conjugate multiple arcs appear on average during stronger northward IMF and smaller IMF clock angles than non-conjugate multiple arcs. Only non-conjugate multiple arcs show a dependence on IMF B-X. They form in the northern (southern) hemisphere during negative (positive) B-X. An IMF B-X induced interhemispheric asymmetry in the magnetospheric field line topology might explain why multiple arcs appear sometimes in only one hemisphere.