Nighttime High-Latitude Observations of Two-Stream Irregularities and Sporadic-E During the VortEx Sounding Rocket Campaign

The Vorticity Experiment (VortEx) sounding rocket mission consisted of two campaigns from Andøya Space Center, with the science objective of correlating vorticity in both horizontal and vertical motions in the lower thermosphere‐mesosphere region, near the terrestrial turbopause. The first campaign (VortEx‐1) took place on 23 March 2023 while the second campaign (VortEx‐2) was conducted on 10 November 2024. The launch for each campaign consisted of an instrumented Terrier Improved Orion rocket aimed at measuring the plasma and neutral characteristics of the lower thermosphere along with another Black Brant IX rocket to disperse chemical tracer trails and obtain neutral wind in the lower thermosphere. In this paper, we primarily focus on the nighttime irregularities observed by the Langmuir probes on VortEx‐1 and VortEx‐2 in the vicinity of plasma enhancements in the E‐region during disturbed geomagnetic conditions. Electric field measurements along with plasma density spectrograms from the VortEx‐2 instrumented payload indicate that the two‐stream instability was likely the mechanism that produced the smaller‐scale features over tens of meters scales associated with a moderate electric field of 24 mV/m in the southwest direction during upleg, but the instabilities were not prominent during downleg when the electric field magnitude is lower. The two‐stream instability is also the likely mechanism for the irregularities observed with VortEx‐1. A zonal wind shear and an associated Sporadic‐E layer were observed during VortEx‐1 from the rocket and EISCAT measurements. The observations indicate dynamic changes in the high‐latitude ionosphere across spatial and temporal differences.