Studies of high latitude mesospheric turbulence by radar and rocket 2: measurements of small scale turbulence

Abstract

Measurements of mesospheric small scale turbulence and associated larger scale wave structures were obtained during equinox by rocket probes flown in coordination with the nearby Poker Flat MST Radar. One rocket series (29 March 1985) included a parachute-borne, electrostatic probe for measuring relative fluctuations in positive ion density, while the other salvo (1 April 1985) included a fixed bias nose tip probe to measure electron current and associated small scale density irregularities. The measured small scale plasma density variations are indicative of neutral air motions. A − 5 3 value for the spectral index, characteristic of turbulence in the inertial subrange, was generally observed for plasma density fluctuations in the region of strong MST radar returns. A comparison of the variance calculated from the power density spectra of the nose tip probe's current with the MST radar's S/N ratio demonstrated consistent measurements of electron density fluctuations. Also, both measurements indicated the presence of saturating waves. The occurrence of 1–3 km wavelike perturbations, superposed on a larger wave (~7 km) in the wind velocity field, was identified by the MST radar. Consistency between MST radar, meteorological and probe measurements of the wave structures is observed in the region where turbulence was detected. The 1–3 km waves are believed to be more important in the transport of energy and momentum and also in the production of turbulence in the lower mesosphere.