In Situ Measurements of Small-Scale Structures in Neutrals and Charged Aerosols

Abstract

The ECOMA sounding rocket program began in 2006 and involved the launching of six instrumented rockets for studying properties of mesospheric aerosols and related phenomena from the north-Norwegian Andøya Rocket Range (69°N; 16°E). Among other things, the ECOMA payloads carried the CONE instrument and the ECOMA particle detector to measure densities of neutral air and charged aerosols, respectively. These measurements were done with very high spatial resolution and precision which allows us to study small-scale structures in those species at spatial scales down to one meter. While small-scale fluctuations in the plasma may originate from either electrodynamics or neutral dynamical processes, neutral density fluctuations are a unique tracer for turbulent velocity fluctuations. Such measurements can be used to derive the spectral content of the turbulence field from which, in turn, the turbulent energy dissipation rate can be reliably derived. Accompanying ground based measurements by VHF radar that, in particular, continuously monitor polar mesosphere summer echoes (PMSE), allow us to investigate connection between those phenomena and small-scale structures in charged aerosols. Simultaneous measurements of the densities of neutral air and charged aerosols make it possible to derive Schmidt numbers with a high spatial resolution. Our measurements show that the charged aerosols inside and between the PMSE layers are highly structured down to spatial scales of a few meters. The Schmidt numbers derived for the charged aerosols fall within the range from ~6 to ~4500 which implies particle radii from ~ 1 to ~ 26 nm.