A study of small-scale waves and turbulence in the mesosphere using simultaneous in situ observations of neutral gas and plasma fluctuations

Abstract

During the DYANA campaign a series of new sounding rocket payloads named TURBO were flown to study the fine scale structure of the mesosphere and lower ionosphere/thermosphere. The payloads were instrumented for in situ simultaneous measurements of neutral, ion and electron density fluctuations with an accuracy of better than 0.1% and a spatial resolution of typically 1 m. This important new feature allows detailed studies of the relation between fluctuations in the ionospheric plasma and the non-ionized air to be performed. Fritts and Thrane [(1990) J. atmos. terr. Phys. 52, 827], in a model study, examined the relationship between ion and neutral density fluctuations in the presence of ion source and sink terms. Their results indicated that the ion/neutral density ratio in the middle atmosphere ranges between an adiabatic and a chemical equilibrium limit, depending on the characteristics of the wave or turbulent motion and the ion production and recombination rates. In the present paper we examine some examples of structures observed with the TURBO instruments and show that both small-scale waves and turbulence can be identified by comparison with the model. The results open a promising line of research which may- give better insight into the small-scale dynamics of the mesosphere