In situ observations of small scale neutral and plasma dynamics in the mesosphere / lower thermosphere at 79° N.

From June 29 to July 7 2003, the German-Norwegian ROMA/SVALRAK campaign (ROMA = Rocket borne Observations in the Middle Atmosphere) took place at the SVALRAK rocket range, Ny-Ålesund (79^°N, 11^°E; Spitsbergen). The main scientific aim of this campaign was to study polar mesosphere summer echoes (PMSE) and mesospheric turbulence. During this campaign a total of three instrumented sounding rockets was launched. In addition, ground based observations with a VHF radar and a potassium lidar at Longyearbyen complemented the in situ measurements. All three sounding rockets were equipped with the CONE (= COmbined sensor for Neutrals and Electrons) instrument to measure small scale structure of neutral air and electron density, and neutral temperature. The PIP (= Positive Ion Probe) instrument was used to measure small scale structure of the positive ion density. Furthermore, two cold plasma probes (CPP) were used to measure electron temperature, and a particle detector was employed to detect signatures of charged aerosols. During the first launch, an electric field experiment was also incorporated, while during the other two launches, Faraday rotation experiments yielded absolute electron number densities. During all three rocket flights a PMSE was observed by the VHF radar, whereas the potassium lidar detected a noctilucent cloud (NLC) only during the second launch. Signatures of the charged particles forming the PMSE and NLC layers were recorded by the onboard particle detectors. During the first launch neutral air density fluctuations indicating turbulence in the altitude region from ∼ 74 km up to ∼ 90 km were detected by the CONE instrument. In addition, CONE recorded very strong and high frequency neutral density fluctuations between altitudes of 90 km up to the apogee of ∼ 106 km. Clearly, these fluctuations are of non-turbulent origin. Strong positive ion and electron density fluctuations were also detected in the same altitude region (∼ 90 -106 km). These plasma fluctuations are typical for plasma instabilities such as the gradient drift or Farley-Buneman instability. However, to our knowledge observations of fluctuations in the neutral gas in conjunction with plasma instabilities have never been recorded before.