IN-SITU OBSERVATIONS OF BIFURCATION OF EQUATORIAL IONOSPHERIC PLASMA DEPLETIONS

Vector electric field measurements from the San Marco D satellite are utilized to investigate the bifurcation of ionospheric plasma depletio ns (sometimes called ''bubbles'') associated with nightside equatorial spread F. These depletions are identified by enhanced upward ExB conv ection in depleted plasma density channels in the nighttime equatorial ionosphere. The in situ determination of the bifurcation process is b ased on de electric field measurements of the bipolar variation in the zonal flow, westward and eastward, as the eastbound satellite crosses isolated signatures of updrafting plasma depletion regions. We also p resent data in which more complicated regions of zonal velocity variat ions appear as the possible result of multiple bifurcations of updraft ing equatorial plasma bubbles.