Abstract
Arecibo ISR observations and VHF coherent backscatter data collected with a radar situated in southern Puerto Rico are examined to understand the causes of quasi-periodic variations in VHF returns from lower E-region heights (∼93 km). It is found that Bragg scale density irregularities causing the observed VHF backscatter are formed and propagated horizontally in a density perturbation field localized at the upper boundary of a tidal ion layer. The density perturbation has a 7 km horizontal wavelength, propagates in southwest direction, and it is not aligned with the geomagnetic field. Thus the production mechanism of the observed density perturbation cannot be the gradient-drift instability often invoked to account for the generation of mid-latitude sporadic E radar echoes. Nevertheless, secondary gradient-drift instability operating on the gradients of the southwest propagating perturbation remains the most likely cause of Bragg scale electron density waves responsible for the VHF returns.
Original language | English (US) |
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Pages (from-to) | L14805 1-4 |
Journal | Geophysical Research Letters |
Volume | 31 |
Issue number | 14 |
DOIs | |
State | Published - Jul 28 2004 |
ASJC Scopus subject areas
- Geophysics
- General Earth and Planetary Sciences