Plasma turbulence and coherent structures in the polar cap observed by the ICI-2 sounding rocket

Abstract

The electron density data from the ICI-2 sounding rocket experiment in the high-latitude F region ionosphere are analyzed using the higher-order spectra and higher-order statistics. Two regions of enhanced fluctuations are chosen for detailed analysis: the trailing edge of a polar cap patch and an electron density enhancement associated with particle precipitation. While these two regions exhibit similar power spectra, our analysis reveals that their internal structures are significantly different. The structures on the edge of the polar cap patch are likely due to nonlinear wave interactions since this region is characterized by intermittency and significant coherent mode coupling. The plasma enhancement subjected to precipitation, however, exhibits stronger random characteristics with uncorrelated phases of density fluctuations. These results suggest that particle precipitation plays a fundamental role in ionospheric plasma structuring creating turbulent-like structures. We discuss the physical mechanisms that cause plasma structuring as well as the possible processes for the low-frequency part of the spectrum in terms of plasma instabilities.