In situ measurements of winds, electric fields and electron densities at the onset of equatorial spread-F

The results of barium-strontium(Ba-Sr) releases and Langmuir probe measurements at the onset time of equatorial spread- F by two RH-560 rockets launched from SHAR on 16 February 1982 are discussed. Winds and electric fields are measured by Ba-Sr blob releases at heights of 139, 182, 225 and 294 km. The horizontal winds reveal the presence of vertical shears in both the zonal and meridional components located around 150 and 160 km, with minimum shear strengths of 1.7 and 1.9 m s ^-1 km ^-1. respectively. The largest zonal wind observed was 112±3 m s^-1 at 225 km. Significant magnitudes (10-40 m s ^-1) of vertical winds were also measured at altitudes of 182, 225 and 294 km, which are below the altitude of the F-layer. Electron density irregularities were also observed in a localized height region at 240-300 km by a Langmuir probe flown by the second RH-560 rocket. The causative mechanisms of the observed density irregularities are discussed and comparison between the various possible destabilizing mechanisms are made.