ELECTRON-DENSITY FLUCTUATIONS IN THE EQUATORIAL MESOSPHERE - NEUTRAL TURBULENCE OR PLASMA INSTABILITIES

Electron density fluctuations were measured with rocket borne nose-tip probes launched on August 19, 1994 at 12:08 LT and August 24, 1994 at 10:39 LT from Alcantara, Brazil (2.3 degrees S, 44.4 degrees W) durin g the MALTED/Guara campaign. The spectral analysis of the fluctuations shows evidence for neutral turbulence in the region of 85 to 90 km fo r both flights. Falling spheres launched 44 and 13 minutes prior to th e main payloads indicate superadiabatic lapse rates in this height reg ion. Also for the two flights, the electron density fluctuations betwe en 90 and 110 km are dominated by the equatorial electrojet which has been observed simultaneously by the 50-MHz CUPRI VHF radar. The in sit u data show significant plasma irregularities associated with the elec trojet at altitudes well below those that return detectable radar echo es, and where they can interfere with the fluctuations attributed to n eutral turbulence.