~ Pergamon Journal of Atmospheric and Terrestrial Physics, Vol. 58, No. 16, pp. 1895-1901, 1996 Copyright © 1996 Elsevier Science Ltd Printed in Great Britain. All rights reserved 0021-9169(95)00181-6 0021~169/96 $15.00+0.00 Simulation of the initial evolution of the CRRES G-9 barium release in the ionosphere S. N. Zaitsev, G. P. Milinevsky and A. M. Evtushevsky Space Physics Laboratory, Physics Department, Kiev University, Kiev, Ukraine (Received in final form 31 August 1995; accepted I September 1995) Abstract--The optical peculiarities of the initial ion cloud dynamics in the CRRES G-9 Caribbean barium release are studied. Comparison of simulation results and optical data of 'skidding' of the ion barium cloud observed by low-light-level TV-images indicates good agreement. The simulation is based on a modified 2D electrostatic code. The background electric field and a model of the inhomogeneous ionization of the neutral cloud were included. The fragmentation of the back of the cloud during the ion 'skidding' process is explained by the results of the simulation. Copyright © 1996 Elsevier Science Ltd INTRODUCTION The purpose of this paper is the simulation and analy- sis of the CRRES (;-9 barium cloud evolution based on the optical data obtained from the research vessel 'Professor Zubov' (Milinevsky et al., 1994). The simu- lation presented explains the filamentation that occurs behind the ion cloud. The fine-scale structure of the ion cloud was observed from the vessel located such that the release point was close to the magnetic zenith. We use the 2D motion model of an artificial plasma cloud in an inhomogeneous ionosphere for the initial evolution (t < 3 s). In contrast to the model used by Huba et al. (1992), the inhomogeneous ionization process and the background ionospheric electric field have been considered. EXPERIMENTALRESULTS In the CRRES Caribbean G-9 release, the barium ion cloud was stopped several kilometers from the release point, along the satellite trajectory. A so-called 'skidding' effect wa,~ observed in the release (Huba et al., 1992). The formation of the field-aligned barium ion jet at the end of the skidding distance was observed from the research vessel (Fig. 1). We call this 'the main ion jet'. The main ion jet is several times brighter than other parts of the ion cloud. In contrast to the results of Huba et al. (1992), the two distinct ion filaments were observed in the gap between the release point and the main ion jet position. The main ion jet is of 3 km width and the jet axis is located at a distance of 18 km from the release point. Two other ion filaments, of 1 km width, are placed at 10 and 15 km from the release point. The main ion jet was observed for 20 min of the G- 9 release records. The ion filament formed at 15 km distance was registered close to the main ion jet for 10 min. The position measurements of the fine-scale structure within the skidding distance were made using the images obtained in the first 22 s after the release. SIMULATION MODEL A simulation of the 'skidding' process was made which included the background electric field and an inhomogeneous ionization model that were not dis- cussed by Huba et al. (1992) or in other previous simulations. The geometry of the simulation model is shown in Fig. 2. The neutral barium cloud moves from the Tfi vn /x Fig. 2. Geometry of the simulation model. D ,7 1895