Abstract. During the MaCWAVE winter campaign in January 2003, layers of enhanced echo power known as PMWE (Polar Mesosphere Winter Echoes) were detected by the ESRAD 52 MHz radar on several occasions. The cause of these echoes is unclear and here we use observations by meteorological and sounding rockets and by lidar to test whether neutral turbulence or aerosol layers might be responsible. PMWE were detected within 30 min of meteorological rocket soundings (falling spheres) on 5 separate days. The observations from the meteorological rockets show that, in most cases, conditions likely to be associated with neutral atmospheric turbulence are not observed at the heights of the PMWE. Observations by instrumented sounding rockets confirm low levels of turbulence and indicate considerable small-scale structure in charge density profiles. Comparison of falling sphere and lidar data, on the other hand, show that any contribution of aerosol scatter to the lidar signal at PMWE heights is less than the detection threshold of about 10%.
Abstract. The electrical structure of NLC/PMSE regions was investigated by different rocket-borne in situ probe techniques as part of the DROPPS program. Gerdien condenser measurements of very small mobility values suggest concentrations of positively charged aerosols/dust comparable to the density of more mobile positive ions at PMSE/NLC altitudes. Relative electron density values and associated large-and small-scale vertical structure measured by DC Langmuir probes revealed very deep (by a factor of 50) biteouts in PMSE/NLC regions. These biteouts were seen during strong and weak NLC conditions when PMSEs were either present or absent.
[1] Results from a sounding rocket experiment launched on September 19, 2004 from Kwajalein Atoll, Marshall Islands are reported. A large modulation of the temperature profile in the upper mesosphere was observed with a local maximum at 92 km, 40 K warmer than 2 km below. The temperature gradient between 92 and 102 km was nearadiabatic, suggesting strong mixing. Turbulence was observed in the lower part of the mixed layer, as evidenced by neutral and plasma density fluctuations on both the upleg and downleg portions of the flight. The plasma density gradient was less steep in the mixed region. The turbulent energy dissipation rate was found to be 170 mW/kg. The thermal structure can be described as an upper mesospheric inversion layer, possibly caused by enhanced wave breaking or turbulent heat transport.
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.
While we have conducted previous rocket investigations of NLC/PMSE ion properties, the DROPPS payloads provided the first opportunity to fly a complete complement of our probe systems for simultaneously evaluating the region's electrical structure as well as the presence of charged aerosols.
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