Small-Scale (Sub-decameter) Plasma Density Irregularities in the Topside Ionosphere Using High-cadence Plasma Current Measurements on e-POP (Swarm-E)

We have performed a statistical analysis of small-scale (sub-decameter) plasma density irregularities in the topside ionosphere (at 325-1500 km altitude) using the high-cadence (1000 samples/sec) sensor surface current data from the Imaging Rapid-scan Ion Mass Spectrometer (IRM) onboard the Swarm-E / Enhanced Polar Outflow Probe (e-POP). The measured current consists of contributions from the ambient and non-ambient electrons and ions, and it is proportional to and serves as a proxy for the local plasma density. The high-cadence current data are averaged over time intervals up to 0.5 s (to facilitate comparison with previous studies) and the analysis is undertaken separately for the case of positive and negative net currents, respectively. We have developed and validated an algorithm to identify small-scale structures of plasma density depletions and enhancements, by finding local minima (depletions) and maxima (enhancements) in the measured current amplitude in each case.  We will compare and contrast the statistical distributions of small-scale plasma density depletion and enhancement structures down to sub-100 m scale, including their altitude, magnetic latitude, magnetic local time distributions and spectral characteristics.