Structures of Density and Velocity Fluctuations in the Auroral Oval and Their Impact on Communication and Radar Systems

摘要

A new class of ionospheric irregularities in the auroral oval associated with large structured plasma flows has been recently isolated with radar and satellite in-situ measurements. These density irregularities have large power spectral densities (psd) at short scale lengths (approx. hundreds to tens of meters). The paper characterizes the density and velocity spectra in such regions and discusses their impact on scintillation observations and radar performance. The structured plasma flows may occur in association with large (approx. 10 micro A per sq m) or small (approx. 1 micro A per sq m) field aligned currents. The velocity spectra have fairly shallow power spectral indices (approx. -1.5) in regions of large field aligned currents and are steep (approx. -3) in regions of small current flows. The density spectra, on the other hand, can be described by a power law index approx. -2 in both the large and small field aligned current regions. The temporal structure of scintillations will thus be dictated not only by the scattering strength but also by the large flow velocities encountered in the auroral oval. The density structures with large psd at short scale lengths are expected to introduce considerable ionospheric clutter in HF radar systems. The effect of E-region conductivity in modifying small-scale (<1 km) F-region structure and its implication for communication and radar systems is discussed. (rh)