WAVE-VECTOR OBSERVATIONS OF THE 2-STREAM INSTABILITY IN THE DAYTIME EQUATORIAL ELECTROJET

Detailed measurements of electric field wavevectors of the Farley-Bune man two-stream instability in the daytime equatorial electrojet were g athered on a sounding rocket flown from Alcantara, Brazil. Primary two -stream waves were detected in the altitude region of 104 - 108 km, wh ere the current density and polarization electric field maximized and where intense 3 m vertical echoes were observed by a 50 MHz backscatte r radar. The in-situ measured wave components are predominantly orient ed in the horizontal, zonal direction. Spaced receivers reveal wavelen gths of 11-14 m with phase velocities of about 370 m/s at the peak wav e power near 106.5 km. These velocities are constant from 1-15 m, indi cative of dispersionless flow. Although the neutral wind was not measu red, the in-situ phase velocity appears to be below that predicted by linear theory.