Ionospheric Irregularities in the Cusp Ionosphere: In situ Observations by NorSat-1 Satellite

Ionospheric irregularities can greatly influence the trans-ionospheric signals due to the scintillation effect, and thus they can affect the satellite-based communication and navigation systems. Due to their practical space weather impacts, it is of great interest to study plasma irregularities and their generation mechanisms. However, our understanding of plasma structuring mechanisms at high latitudes is still not complete partially due to insufficient in situ data at high-resolution. The first Norwegian scientific satellite, NorSat-1, provides a good opportunity to enhance our understanding of the multi-scale features of ionospheric irregularities. Norsat-1 is a polar orbiting microsatellite at $\sim$600 km altitude. NorSat-1 carries the multi-needle Langmuir probe (m-NLP) system, which is capable of collecting currents from four different voltages at a rate up to 1 kHz. The electron density can be derived from the collected currents. Here we present a case study using the m-NLP instrument to characterize small-scale ionospheric plasma structures. NorSat-1 crossed the cusp ionosphere in a noon-midnight orbit. With the support from ground and space-based auroral images, we see that the cusp ionosphere is a region with mesoscale (40-80 km) electron density enhancements that are likely due to pulsed electron precipitations. The density enhancements are associated with significant small-scale irregularities.