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Ann. Geophys., 25, 1311-1322, 2007
www.ann-geophys.net/25/1311/2007/
© European Geosciences Union 2007
Wavelength dependence of the linear growth rate of the Es layer instability
R. B. Cosgrove
Center for Geospace Studies, SRI International, Menlo Park, California, USA
Abstract. It has recently been shown, by
computation of the linear growth rate, that midlatitude
sporadic-E (Es) layers are subject to a large scale
electrodynamic instability. This instability is a logical
candidate to explain certain frontal structuring events, and
polarization electric fields, which have been observed in Es
layers by ionosondes, by coherent scatter radars, and by rockets.
However, the original growth rate derivation assumed an infinitely
thin Es layer, and therefore did not address the short
wavelength cutoff. Also, the same derivation ignored the effects
of F region loading, which is a significant wavelength dependent
effect. Herein is given a generalized derivation that remedies
both these short comings, and thereby allows a computation of the
wavelength dependence of the linear growth rate, as well as
computations of various threshold conditions. The wavelength
dependence of the linear growth rate is compared with observed
periodicities, and the role of the zeroth order meridional wind is
explored. A three-dimensional paper model is used to explain the
instability geometry, which has been defined formally in previous
works.
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