A three-dimensional time-dependent model was used to study the ionization and plasma expansion characteristics of barium clouds in the ionosphere. Neutral gas clouds with a total mass of 1 kg were released with a spherical Gaussian density distribution and the subsequent photoionization by solar UV radiation and ion cloud expansion were modeled. The results from three simulations are presented: a cloud without a directional velocity; a cloud with an initial velocity of 5 km/s across the B field; and a cloud with initial velocity components of 2 km/s both along and across the B field. For the cloud without a directional velocity, the ionization occurs in a spherical volume. The resulting Ba+ cloud expands along the B field and the Ba+ density distribution gradually becomes ellipsodial from the inner to the outer parts of the Ba+ cloud. The electrostatic snowplow effect associated with the expanding Ba+ cloud creates a hole in the O+ background at the center of the Ba+ cloud and creates two O+ density bumps on the two sides of the Ba+ cloud. For the neutral gas release with an initial velocity across the B field, the resulting Ba+ cloud has a cometlike density distribution at early times.

Eventually, because of the expansion along the B field, the Ba+ cloud becomes sheetlike. Again, there are two O+ density enhanced regions and one O+ density depletion region in the background ionosphere. For these two cases, although there are O+ density depletions, there are no electron density (total plasma) depletions. When the neutral gas cloud has initial velocity components both along and across the B field, the situation is quite different. The resulting Ba+ cloud has a complicated density distribution. The BA+ snowplow effect creates an O+ density hole on one side and an O+ density bump on the other side of the expanding Ba+ cloud. There is a net plasma depletion on the side opposite to the Ba+ cloud motion along the B field. ¿American Geophysical Union 1992