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Ann. Geophys., 24, 1387-1400, 2006
www.ann-geophys.net/24/1387/2006/
© European Geosciences Union 2006
Rocket and radar investigation of background electrodynamics and bottom-type scattering layers at the onset of equatorial spread F
D. L. Hysell1, M. F. Larsen2, C. M. Swenson3, A. Barjatya3, T. F. Wheeler4, T. W. Bullett5, M. F. Sarango6, R. F. Woodman6, J. L. Chau6, and D. Sponseller7
1Earth and Atmospheric Science, Cornell University, Ithaca, New York, USA
2Physics and Astronomy, Clemson University, Clemson, South Carolina, USA
3Electrical and Computer Engineering, Utah State University, Logan, Utah, USA
4Electrical Engineering, Pennsylvania State University, University Park, Pennsylvania, USA
5Space Vehicles Directorate, Air Force Research Laboratory, Hanscom AFB, Massachusetts, USA
6Jicamarca Radio Observatory, Instituto Geofísico del Perú, Lima, Peru
7Kwajalein Range Services LLC., ALTAIR Radar, United States Army Kwajalein Atoll – Reagan Test Site, Republic of the Marshall Islands, USA
Abstract. Sounding rocket experiments were conducted during the NASA EQUIS II
campaign on Kwajalein Atoll designed to elucidate the electrodynamics
and layer structure of the postsunset equatorial F region
ionosphere prior to the onset of equatorial spread F
(ESF). Experiments took place on 7 and 15 August 2004, each comprised
of the launch of an instrumented and two chemical release sounding
rockets. The instrumented rockets measured plasma number density,
vector electric fields, and other parameters to an apogee of about
450 km. The chemical release rockets deployed trails of trimethyl aluminum
(TMA) which yielded wind profile measurements. The Altair radar was
used to monitor coherent and incoherent scatter in UHF and VHF bands.
Electron density profiles were also measured with rocket beacons and
an ionosonde. Strong plasma shear flow was evident in both
experiments. Bottom-type scattering layers were observed mainly in the
valley region, below the shear nodes, in westward-drifting plasma
strata. The layers were likely produced by wind-driven interchange
instabilities as proposed by
Kudeki and Bhattacharyya (1999). In both experiments, the layers were patchy and
distributed periodically in space. Their horizontal structure was
similar to that of the large-scale plasma depletions that formed later
at higher altitude during ESF conditions. We argue that the
bottom-type layers were modulated by the same large-scale waves that
seeded the ESF. A scenario where the large-scale waves were themselves
produced by collisional shear instabilities is described.
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