December 1, 1970 to April 28, 1972 - ARPA Project SECEDE
Contractor: University of Alaska, Geophysical Institute.
Amount of Contract: $283,849.00
Striations develop within large (12-352 kg releases) barium ion clouds in a two-stage process. First the clouds split into sheets commencing at the trailing edge of the cloud. Then distortions or pinching effects within the individual sheets cause the formation of field-aligned raylike structures. In the clouds observed, the individual sheets were 200 m to 1000 m in thickness and were spaced 700 m to 2000 m apart. Quasi-sinusoidal waviness or spatially periodic thickenings exhibited a wavelength typically 700 m to 1000 m.When rod-like structures appeared, these were typically-200 im to 400 m. in diameter and were spaced along the pre-existing sheet at 700 m to 1000 m on centers. 
October 15, 1972 - Rocket energy beams create artificial aurora
An accelerator intended to send electron beams upward along an L=1.24 magnetic field line was flown from a rocket launched from Kauai, Hawaii, on October 15, 1972. Though the intent was to produce several hundred observable auroral streaks in the southern hemisphere, imaging instruments operated there aboard jet aircraft detected only a single aurora. 
November 1972 - ARPA Project SECEDE II barium cloud releases
The general goals of the Secede barium release program have been geared to the development of a practical technique by which plasma interaction with the ionosphere could be experimentally studied and suitable theories of such interactions developed therefrom. The Secede experimental program has, for the most part, consisted of two coordinated aspects, that of radio frequency radar measurements and that of optical measurements. In studying barium cloud phenomenology and morphological development, optics has provided the key means of observing and recording the physical history of the release. In addition to providing photographic, radiometric, and spectrographic records after the fact, optical coverage can be displayed in real time for purposes of tracking the cloud(s) as well as for identifying morphological changes. 
May 14, 1973 - NASA Skylab launch knocks out radio communication over Atlantic Ocean
Routine Faraday rotation observations of the VHF signal from the geostationary satellite ATS 3 made at Sagamore Hill (Massachusetts) revealed that an unusually large and rapid decay in the ionospheric total electron content (TEC) occurred near 1240 EST on May 14, 1973. The disturbance appeared as a dramatic ‘bite‐out’ of substantial magnitude (≥50%) and duration (of the order of hours) in the expected diurnal TEC curve for that day. Observations from other sites revealed that a ‘hole’ in the ionospheric F region was created over a region approximately 1000 km in radius. The onset of the TEC disturbance occurred within 10 min of the launch of NASA's Skylab workshop by a Saturn 5 rocket. As the rocket moved at F region heights, the burning second‐stage engines passed within 150 km of the Sagamore Hill ray path to ATS 3. A detailed analysis of the aeronomic reactions initiated by the constituents of the exhaust field revealed that the F2 region plasma experienced a devastating loss process as the plume expanded. The specific mechanism involved was the rapid ion‐atom interchange reactions between the ionospheric O+ and the hydrogen and water vapor molecules in the plume, followed by dissociative recombination of the molecular ions. Model calculations of the diffusion of the plume in the ionosphere and its effect upon continuity equation calculations for TEC showed an excellent agreement with the observed onset and magnitude of the effect. The phenomenon has interesting astrophysical and geophysical implications. 
November 4, 1974 - High-explosive shaped Barium charges pound ionosphere
Barium ions are well suited for tracing out magnetic field lines, because they resonantly scatter sunlight in several visible wavelengths and because ions are constrained to spiral about magnetic field lines while traveling freely parallel to the field. By use of high explosive shaped charges with hollow conical liners of barium metal, detonated above 500‐km altitude, jets of barium plasma with a range of initial velocity of 8 to 20 km/sec have been created. 
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