The Turbopause experiment: atmospheric stability and turbulent structure spanning the turbopause altitude

Abstract

Abstract. Very few sequences of high resolution wind and temperature measurements in the lower thermosphere are available in the literature, which makes it difficult to verify the simulation results of models that would provide better understanding of the complex dynamics of the region. To address this problem the Turbopause experiment used four rockets launched over a period of approximately two hours from Poker Flat Research Range, Alaska (64 • N, 147 • W) on the night of 17-18 February 2009. All four rocket payloads released trimethyl aluminum trails for neutral wind and turbulence measurements, and two of the rockets carried ionization gauges and fixed-bias Langmuir probes measuring neutral and electron densities, small-scale fluctuations and neutral temperatures. Two lidars monitored temperature structure and sodium densities. The observations were made under quiet geomagnetic conditions and show persistence in the wind magnitudes and shears throughout the observing period while being modulated by inertia-gravity waves. High resolution temperature profiles show the winter polar mesosphere and lower thermosphere in a state of relatively low stability with several quasi-adiabatic layers between 74 and 103 km. Temperature and wind data were combined to calculate Richardson number profiles. Evidence for turbulence comes from simultaneous observations of density fluctuations and downward transport of sodium in a mixed layer near 75 km; the observation of turbulent fluctuations and energy dissipation from 87-90 km; and fast and irregular trail expansion at 90-93 km, and especially between 95 to 103 km. The regions of turbulent trails agree well with regions of quasi-adiabatic temperature gradients. Above Correspondence to: G. A. Lehmacher (glehmac@clemson.edu) 103 km, trail diffusion was mainly laminar; however, unusual features and vortices in the trail diffusion were observed up to 118 km that have not been as prevalent or as clearly evident in earlier trail releases.

Observation of electron biteout regions below sporadic E layers at polar latitudes

“…The main purpose of the experiment was to study the transition from strong mixing and turbulence to more laminar behavior as visible in chemical trail releases. Results of the wind, temperature, and turbulence measurements were reported by Lehmacher et al (2011), and a mixing event in the mesosphere observed in the sodium layer was studied by Collins et al (2011).…”

“…The blue and red rocket profiles are shifted in time and scaled to match the electron densities (see also Fig. 2 in Lehmacher et al, 2011). Background densities are 8 × 10 9 m −3 and layer peak densities are 3 to 4 × 10 10 m −3 , which is low compared to many other Es measurements.…”

“…The zonal wind nodes descend at a rate of −1.3(±0.3) km h −1 , characteristic for long-period gravity waves. Based on the hodographs, Lehmacher et al (2011) identified two major wave motions with periods of 12 and 8 h and vertical wavelengths of 30 and 10 km, respectively.…”

“…Notice the close agreement of the background current for the two flights in the upper D region and lower E region. The smallscale fluctuations attributed to mesospheric neutral turbulence were discussed in Lehmacher et al (2011).…”

“…The detection of neutral and charged meteoric smoke or dust particles in the mesosphere has become a very active field, and different rocket techniques have been deployed (e.g., Havnes et al, 1996;Croskey et al, 2004;Rapp et al, 2005;Lynch et al, 2005;Knappmiller et al, 2008). Mathews (1987) discusses the possibility of electron attachment to dust particles from meteor ablation.…”