Structure and Composition Measurements in Equatorial Ionospheric Bubbles

R. Narcisi

Jan 1980 · Air Force Geophysics Laboratory, Air Force Systems Command, United States Air Force

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Two multi-instrumented Terrier Malemute rockets including ion mass spectrometers were launched from Kwajalein on the nights of 17 and 23 July 1979 during equatorial Spread F events. Detailed ionospheric structure and composition measurements were made between about 100 and 590 km. The first flight penetrated six areas of 'bite-outs' spread over the range 265 to 560 km on upleg as well as several more depletions on downleg. The strongest irregularities, up to 90 percent depletion, occurred at the altitudes of 265 to 285 km just above the F region ledge at 250 km. There was no evidence of enhanced bottomside tracer ions (NO(+), O2(+) or meteoric ions) in any of the holes, which were composed mostly of O(+) and smaller amounts of N(+). From the composition signatures, the source of the bubbles appeared to be near the F region ledge. Within the higher altitude holes, the N(+)/O(+) ratios were smaller than the adjacent ionosphere ratios, indicating not only that the source regions were near the ledge, but also that the bubbles had initiated earlier when the ledge was at higher altitudes. While O(+) and N(+) exhibited strong fluctuations, NO(+) and O2(+) had fairly smooth profiles with scale heights similar to N2 and O2 respectively, demonstrating steady-state conditions and a stable neutral atmosphere with an exospheric temperature of about 1100K. This suggests that neutral atmospheric turbulence is not a major source of the ionospheric irregularities. Time periods for ion-chemical processes to achieve the observed composition are discussed in terms of bubble formation times and rise velocities.