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The Condor equatorial electrojet campaign: radar results

Document Type

Article

Journal/Book Title/Conference

Journal of Geophysical Research

Volume

92

Publisher

American Geophysical Union

Publication Date

1987

First Page

13561

Abstract

A review of the experimental and theoretical background to the Condor equatorial electrojet campaign is followed by the presentation and discussion of VHF radar interferometer and HF radar backscatter data taken concurrently with two rocket in situ experiments reported in companion papers (Pfaff et al., this issue (a, b). Both experiments were conducted in strongly driven periods with the on-line radar interferometer displaying signatures of what has been interpreted in earlier radar work (Kudeki et al., 1982) as kilometer scale gradient drift waves. Low-frequency density fluctuations detected by in situ rocket sensors confirm the earlier interpretation. VHF radar/rocket data comparisons also indicate the existence of a turbulent layer in the upper portion of the daytime electrojet at about 108 km altitude driven purely by the two-stream instability. Nonlinear mode coupling of linearly growing two-stream waves to linearly damped 3-m vertical modes could account for the radar echoes scattered from this layer, which showed no indication of large-scale gradient drift waves. Nonlinear mode coupling may therefore compete with the wave-induced anomalous diffusion mechanism proposed recently by Sudan (1983) for the saturation of directly excited two-stream waves. Nighttime radar data show a bifurcated layer with the two parts having comparable echo strength but oppositely directed zonal drift velocities. The lower layer shows narrow backscatter spectra; the upper layer is characterized by kilometer scale waves and vertically propagating type 1 waves. The charateristics of the topside large-scale waves show clear consistency with the predictions of nonlocal gradient drift instability theories. The observed sheared flow could be due to neutral winds or a reversal of the vertical polarization fields. Lack of concurrent in situ polarization field or density profile measurements, unfortunately, prevents us from determining the actual cause unambiguously.

https://doi.org/10.1029/JA092iA12p13561

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