Simultaneous Multi‐Point In Situ Plasma Density Measurements of a Mid‐Latitude Sporadic E Layer

Abstract

We present the first spatially distributed, simultaneous multipoint in situ observations of a mid‐latitude sporadic E layer obtained from the Sporadic E Electrodynamics Demonstration (SpEED Demon) sounding rocket mission that launched from Wallops Flight Facility on 24 August 2022. The SpEED Demon rocket deployed four ejectable dropsondes that measured relative ion density along their trajectories. Data processing techniques for these payloads are discussed, and the collected data from within a ∼100 km altitude nighttime sporadic E layer are presented. Several small‐scale irregularities with peak wavelengths of 20–40 m and power spectral density slopes between −2.6 and −4.3 were detected by all four dropsondes. We suggest that these irregularities were associated with wind‐driven gradient drift instabilities. A double‐peaked density structure was observed during the downleg portion of the flight trajectory. Based on climatological plausibility, in situ data, ionosonde measurements, and comparison with simulated density profiles, we find that this structure appears to be consistent with ion density modulations caused by Kelvin‐Helmholtz billows in the neutral atmosphere. However, given the absence of neutral wind and electric field measurements, this mechanism cannot be confirmed with certainty; instead, we demonstrate the Kelvin‐Helmholtz modulation provides a plausible explanation of the observed structure within the sporadic E.