Observations and model comparisons of early‐time expansion characteristics of a satellite‐Borne barium‐lithium release at F‐region altitudes

We describe the very‐early‐time expansion processes (≈0 ‐ 3 s) of the CRRES G‐9 Ba⁺/Li⁺ cloud release, as manifested by thermal‐ and photo‐ionization mechanisms, by coupling to the background ionosphere, and by differential acceleration of multi‐ion constituents. In our data analysis we present the very first “in situ” evidence of electrostatic snowplow effects in an expanding plasma cloud, with arguments that these effects are the result of ambipolar fields and that kinetic effects of ion‐neutral collisions have little influence in the G‐9 scenario. In addition to the electrostatic snowplow process, the results show mass‐dependent effects on the expansion of ion and neutral constituents in the cloud. These effects are manifested in the observation that the Li⁺ ions “outpace” the heavier Ba⁺ in the expansion process, and take on forerunner characteristics at the cloud's leading edge.