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An instrumented sounding rocket launched from Wallops Island Virginia has flown through a midlatitude spread F (MSF) event in conjunction with simultaneous ionosonde, HF radar, and 244 MHz scintillation observations from the ground. The in situ measurements include the electric field, horizontal neutral wind, and plasma density within the spread F region. The ground‐based HF radar measurements of wave signatures in the bottomside F region ledge reveal the presence of waves propagating to the north and northwest prior to and during the spreading event. The periods of these bottomside waves range from 16 to 60 min, and they are shown to be associated with a strong tropical storm located ∼2000 km southeast of the launch site. Enhancements in the auroral current system occur about an hour before the MSF first appears, but none of the observed waves can be attributed to this source. The new phase‐sensitive ionosonde system operated at Wallops Island during the experiment confirms the long‐standing hypothesis that this particular spread F event arises from multipath echoes distributed over a wide field of view in the bottomside F region. Evidence of vertically displaced plasma that could produce such multipath echoes is observed in the rocket data at and above the F region peak over spatial scales smaller than the wavelengths observed on the bottomside ledge by the HF radar, but similar to the range separation given by the high resolution ionosonde echoes when the scale lengths of the structures are interpreted in magnetic coordinates. No significant plasma density structures smaller than a few kilometers are observed in the rocket data, and no unusual scintillation is observed along a path coincident with the rocket trajectory.

The Turbulent Oxygen Mixing Experiment (TOMEX), which was carried out at White Sands Missile Range in New Mexico on 26 October 2000, included a rocketborne trimethyl aluminum (TMA) chemical tracer experiment. The subsequent TMA trails provided detailed information about the horizontal neutral wind, turbulence, and diffusivity properties of the atmosphere between approximately 85 and 140 km altitude. Measurements with the University of Illinois Na wind/temperature lidar located at the Starfire Optical Range, NM, provided a detailed time history of the stability properties between 85 and 105-km altitude, including high-resolution wind and temperature measurements prior to and during the chemical tracer measurements. The diffusivities estimated from the trail expansion rates have values consistent with the values expected for molecular diffusion above 110-km altitude and values that are larger than those for molecular diffusion at most altitudes below. Below 103 km, both regions of dynamic and convective instability were found, and the diffusivities are strongly controlled by the instabilities. The unstable regions are well mixed, but the intermediate regions, in some cases, have very small eddy energy dissipation rates. The nearly instantaneous measurements also suggest that eddy diffusion is still important in the height range between 103 km, the nominal turbopause height, and 110 km.

The Turbulent Oxygen Mixing Experiment (TOMEX) was designed to measure the atmospheric response to the existence of unstable layers as determined by wind and temperature measurements from 80 to 105 km. TOMEX combined Na lidar measurements, from Starfire Optical Range in Albuquerque, New Mexico, with a launch of a payload from White Sands Missile Range, located between 100 and 150 km south of Starfire. The payload included a trimethyl aluminum chemical release to measure winds and diffusion, a 5-channel ionization gauge to measure neutral density fluctuations at high vertical resolution, and a 3-channel photometer experiment to measure atomic oxygen related airglow. The rocket was launched when the lidar data indicated the presence of convectively and dynamically unstable regions between 80 and 100 km altitude. For several hours prior to the launch, there had existed a large amplitude atmospheric gravity wave or tide which brought the background atmosphere into being nearly convectively unstable over the 85 to 95 km region. In addition a large overturning in Na density, possibly due to a convective roll, existed at altitudes around 100 km. This type of instability had not been previously seen and identified in this altitude region. The TOMEX payload measured the existence of Kelvin-Helmholz billows, enhanced neutral density fluctuations, enhanced energy dissipation, and well-mixed regions. These features were associated with convectively unstable regions, dynamically unstable regions, convective rolls, and the presence of this large wave. The unstable regions were persistent and covered large vertical (and horizontal regions) of the atmosphere. The atmospheric mixing and energy dissipation appeared to be largely determined by the presence and nature of these instabilities.

On October 26, 2000, a Black Brant V sounding rocket carrying a chemical tracer release was launched from the rocket range at White Sands, New Mexico, as part of the Turbulent Oxygen Mixing Experiment (TOMEX). The releases occurred approximately 150 km from the location of the Starfire Optical Range where the University of Illinois sodium lidar was operated to measure winds and temperatures in the mesosphere and lower thermosphere. The geometry for the experiment was such that the lidar beam was able to intersect the release point for the chemical tracer trail on the upleg part of the flight near an altitude of 95 km. In all, a total of five lidar beam directions were used to sample the region from approximately 85 to 105-km altitude in the vicinity of the releases. Combining the lidar Doppler velocity data from the various beam directions made it possible to produce profiles of vector horizontal winds that could be compared directly with the winds obtained from the triangulation of the chemical tracer trails.