Morphology of the magnetospheric barium release

Abstract

The magnetospheric barium release experiment of September 21, 1971, was observed by a high‐performance image intensifier television camera system from Kitt Peak National Observatory, Tucson, Arizona. The system produced high‐resolution video recordings of the dynamic morphology of the barium ion cloud. The system was calibrated for absolute sensitivity, thus enabling the reconstruction of the barium density profiles in the cloud. The ionized plasma expands along the field line with the velocity somewhat greater than the neutral expansion velocity. Perpendicular to the magnetic field line, the expansion of the cloud is limited by the forces exerted by the earth's magnetic field. Thus, the cloud takes up a field‐aligned filamentary structure. As early as 30 sec after release, two major filaments could be distinguished. Two minutes after release, the cloud already consisted of at least 8 or 10 filamentary striationlike structures. These are formed in the low‐density expanded part of the cloud. These striations and the diffuse parts of the cloud move in a direction perpendicular to the magnetic field with a velocity different from that of the main dense core of the cloud. This differential velocity moves the lower‐density parts away from the main core. These lower‐density parts appear to be highly structured in the form of fieldaligned striations. During the first 8 min after release, the high‐density main core part erodes to a very narrow strip, which is about 12 km wide. This width of the central core is less than the diameter of the gyro‐orbit of the initial velocity barium ions in the ambient magnetic field. The rapid fragmentation of the cloud to such narrow forms has interesting implications for the stability of dense magnetospheric plasma clouds.

The Cameo Barium Releases: E∥ fields over the polar cap

“…(1) at I min after a release at 31,000 km Mende [1973] observed Ba + expanding slightly beyond the neutral cloud, suggesting a slight but detectable acceleration, and (2) Haerendel et al [1971] reported that sensitive TV images showed ions at 1150 km after 750 s following a 930 km middle latitude sounding rocket release even though film records did not show the high velocity tail in the initial distribution which would be required for this observation. It was speculated that a high velocity tail in the ion distribution might result from the pulling action of the photoelectrons that were produced with excess energy.…”

TheL= 6.6 Oosik Barium Plasma Injection Experiment and magnetic storm of March 7, 1972

“…Called striation development, the process has been ascribed by most authors to the gradient E x B instability [Linson and Workman, 1970;Vi51k and Haerendel, 1971], which is related to the differential motion of the barium ions with respect to the neutral wind. Striations also have been observed to develop in barium thermite releases at very high altitudes in the magnetosphere, where there is no neutral atmosphere [l•61k and Mende, 1973]. In these cases, the early striations are thought to arise from a Rayleigh-Taylor instability during the deceleration phase of the expansion of the ion cloud [Haerendel and L'•t, 1970;Pilipp, 1971 ].…”

Transverse motion of high‐speed barium clouds in the ionosphere

“…One interestng problem that requires further investigation is the dynamics of a high speed plasma cloud moving transverse to the ambient geomagnetic field. Experimentally this phenomenon has been studied using shaped charge barium releases (Wescott et al, 1980;Simons et al, 1980;Koons and Pongratz, 1981) and rocket barium releases (Mende, 1973;Brence et al, 1973;Heppner et al, 1981), and will be a major part of the scientific studies for the upcoming CRRES mission (Combined Release and Radiation Effects Satellite) sponsored by NASA and the Air Force. It should be noted that the high speed releases to date have been relatively small (barium vapor less than 1 kg) compared to those planned for the CRRES mission (up to 10 kg of barium vapor).…”