Physics
Scientific paper
May 2001
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001agusm..sa61a08r&link_type=abstract
American Geophysical Union, Spring Meeting 2001, abstract #SA61A-08
Physics
0654 Plasmas, 0689 Wave Propagation (4275), 2439 Ionospheric Irregularities, 2443 Midlatitude Ionosphere, 2471 Plasma Waves And Instabilities
Scientific paper
Common volume observations with the Cornell University Portable Radar Interferometer (CUPRI) coherent scatter radar and the Arecibo Observatory incoherent scatter radar (AO-ISR) obtained during the NASA El Coquí campaign of 1992, are used to study the causes of coherent radar backscatter at mid-latitudes. The common volume data reveal that coherent scatter echoes are obtained from sporadic E (Es) layers that exhibit little or no gravity wave altitude modulation and possess high densities and sharp gradients. The echoes are associated with larger than typical F-region south-perpendicular electric fields. The echoes appear to come from the linearly unstable side of the Es layers even though the usual local linear theory is invalid at mid-latitudes. Non-local shorting effects along magnetic field lines play a crucial role at mid-latitudes, and we have developed a theory that takes this into account. The unstable eigen modes are a sum of plane waves with k vectors varying vertically about pure perpendicular propagation by a few degrees (allowing for the spatial localization of the modes on the top or bottom of the layer). The k vectors are also approximately aligned with the E x B drift. While both density and potential modes peak in amplitude on the unstable side of the layer, the density mode peaks closer to the maximum of the layer than does the potential mode. The separation and shape of the modes is determined by the profile of the vertical scale length, Lz = Ne / (d)/(dz) Ne; convergent growing solutions are found when the scale length profile exhibits a deep local minimum (steep gradient). We used a narrow Gaussian layer superimposed on a constant background density. Perhaps surprisingly, the constant background is essential for the numerical calculations. It can be small but not zero.
Farley Donald T.
Rosado-Román José M.
Seyler Charles E.
Swartz Wesley E.
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